This article is organised as follows:
- Part 01: Introduction.
- Part 02: Classifications of Resistance Training.
- Part 03: Methods of Resistance Training.
- Part 04: Miscellaneous.
PART ONE: INTRODUCTION
This article provides a brief outline of the classification and methods of resistance exercise.
It will look at how we can classify resistive exercise, outlining some of the considerations and precaution to note. It will then provide a description of the various methods of resistance exercise one can use. Finally it will look at some points to consider when purchasing resistance equipment.
PART TWO: CLASSIFICATION OF RESISTANCE EXERCISE
2.0 How Do We Classify Resistance Exercise?
Resistive exercise can be broadly classified into categories comparing the force generated by a muscle or muscle group relative to an external load.
This external load can be applied by numerous mechanisms such as a machine, a person (manual resistance), a stationary object or body weight.
- Exercises where the internal force generated matches the externally applied load are considered to be isometric exercises.
- In isometric exercise, no joint motion takes place, although muscle activation occurs.
- All other activities are dynamic involving joint motion.
- When the external load:
- Is less than the force generated by the muscle concentric contractions result;
- Whereas when external loads exceed the internally generated force, eccentric contractions are produced.
- Resistance applied at a constant velocity is termed isokinetic.
3.0 Isometric Exercise
Isometric exercise is commonly used to increase muscle performance.
Although no joint movement occurs and technically no work is performed (work = force × distance and distance = 0), isometric exercise is considered functional because it provides a strength base for dynamic exercise and because many postural muscles work primarily in an isometric fashion.
Eccentric muscle contractions require that a concentric or an isometric contraction take place first, pre-setting tension in the muscle. For example, the quadriceps muscles preset tension to stabilise the knee in full extension at initial contact during the gait cycle. This allows a subsequent quadriceps eccentric contraction to decelerate the flexing knee to absorb shock. Therefore, isometric contractions are an essential component of many functional activities.
Isometric exercise is a valuable rehabilitation tool in many situations. It is a foundational exercise and isometric training often precedes dynamic muscle training. Isometric exercise is preferred over dynamic exercise when joint motion is uncomfortable or contraindicated, such as postoperatively or with an unstable joint. Isometric exercise is essential to maintain muscle strength and prevent significant declines during immobilisation.
Isometric exercise is used for purposes other than muscle strength training. Isometric contractions are indicated when muscle re-education is required. One of the benefits of isometric exercise is the ability to perform repetitive submaximal contractions as “reminder” or re-education exercises. In contrast to isometric contractions to maintain strength during periods of immobilisation or times when joint motion is contraindicated, isometric contractions for muscle re-education can be submaximal. Following knee or hip injury or surgery, individuals may have difficulty recruiting and activating the quadriceps muscles; following shoulder surgery or injury, individuals may have difficulty recruiting and activating the rotator cuff musculature. Quadriceps setting and rotator cuff isometric exercises at a low, submaximal level can maintain connective tissue mobility (and at the knee, patellar mobility), and muscle mobility and function. These activities are typically initiated prior to dynamic resistive exercises. This prepares the individual for more advanced dynamic activities. Quadriceps and gluteal sets are also used to enhance circulation throughout the lower extremity during periods of bed rest.
These isometric setting exercises are also a prerequisite for more advanced dynamic exercises, particularly those requiring eccentric muscle contractions. This is a more complex neuromuscular activity than one might think. For example, if one were to catch an object being tossed at them, or to jump down from a given height, the brain must first signal the necessary muscles to preset isometric tension in order to decelerate the object upon catching, or the body upon landing, respectively. One of the significant challenges is teaching an individual how much tension to preset to accomplish a given task. In this case, isometric training at different percentages of maximal activation is useful.
Isometric exercise also functions as a component of dynamic exercise such as when weakness exists at a specific point in the range of motion (ROM). Proprioceptive neuromuscular facilitation (PNF) techniques include isometrics as part of a dynamic programme to enhance stability and strengthen muscles in a weak portion of the range. For example, while performing a diagonal pattern, a therapist may stop and apply an isometric contraction at a weaker portion of the range. Isometric contractions are also an important component of stabilisation programmes. Stabilisation programmes are a progressive series of exercises and activities designed to increase an individual’s ability to dynamically control movement at a joint or series of joints. Stabilisation exercises are an important component of treatment programmes for shoulder, knee, and ankle instability, as well as the basis of treatment for many spinal problems. For example, PNF techniques such as alternating isometrics and rhythmic stabilisation use isometric contractions as the basis for stability training.
This resistive mode is easy to understand and perform correctly, requires no equipment, and can be performed in almost any setting. Isometric exercise is most effective when individuals are in a low state of training, because the benefits of isometric exercise decrease as the state of training increases. Research suggests most gains are made within the first five (5) weeks of the onset of training (Atha, 1981).
3.2 Considerations in Isometric Training
Some factors are important in choosing isometric exercise for rehabilitation. Isometric strength is specific to the joint angle. Studies have demonstrated isometric joint angle specificity, noting that strength gained at one joint angle did not predictably carry over to other joint angles (Muller, 1970). Neuromuscular changes accounted for the joint-angle–dependent effects, and obtaining generalized strength gains required multiple-angle training programmes. Whitley (1967) found significantly increased strength at all joint angles after ten (10) weeks of training at specific joint angles. Others have found this general transfer, although only after training was well advanced (Patterson et al., 2001). In the beginning training phase, the strength gains were transferred only when the muscle was at shorter than resting length.
Like most resistive exercise programmes, dosing the exercise is the most challenging aspect. Dosing for strength differs from dosing for muscle re-education, and this differs from dosing for stabilisation. Isometric exercise for these different therapeutic goals requires a specific approach for each. Dosing for strength training has two important variables:
- Intensity; and
- Range of motion (ROM).
Because of the angle specificity, multiple-angle isometric training is recommended whenever possible. Muscle contraction should be maximal or nearly maximal and should be performed to fatigue. Exercise may be performed at a low frequency. Sample dosage parameters for isometric exercise prescription for strength are as follows:
- Perform isometric contractions every fifteen to twenty (15 to 20) degrees throughout the ROM.
- Hold each contraction approximately six (6) seconds.
- The first few seconds of the first maximum contraction appears to trigger the major training effect.
- After the first few seconds, the ability to maintain a maximal contraction drops off dramatically) (Baechle & Earle, 2000).
- Hold the contraction long enough to fully activate all motor units, and repeat it frequently throughout the day.
- Isometric contractions have their greatest effect near maximal contraction, although this may not be possible in many clinical situations.
Dosing for muscle re-education requires a different prescription. Contraction intensity is submaximal and can vary from very low intensity (<20% maximum voluntary contraction or MVC) to >50% MVC.
Exercise at the lowest intensity immediately after injury or surgery to serve as a reminder how to contract the muscle. Following back surgery, the individual might perform abdominal muscle contractions at a very low level; following a patellar dislocation, an individual might perform low level quadriceps contractions. On the other hand, an individual who needs improved thoracic and cervical posture while at a workstation might perform scapular retraction isometrics at 50% or more of MVC throughout the day.
Because intensity and volume are inversely related, isometric contractions for muscle re-education are performed at a high volume. Activities that are performed for postural awareness may be put “on cue” asking the patient to perform a set of isometrics on cue, such as every time the phone rings, or every time a new email message arrives. Progression of these exercises is to dynamic strengthening, isometrics at a higher percentage of MVC, and/or isometric exercise with external resistance, such as holding a position against elastic resistance.
Isometric dosage for stabilisation is somewhere between strengthening and muscle re-education. Stabilisation exercises are like muscle re-education in that one of the goals is to train the muscles to dynamically maintain a joint or series of join within a small range of postures that are the most optimal for the joint structures. An additional goal is to simultaneously strengthen the muscles required to do this. Thus the dosage is more flexible, and is specific to each individual’s situation.
For stabilisation activities, a common pattern would be initial training for muscle re-education, where the emphasis is on contracting the right muscle group and avoiding the “overflow” phenomenon where the individual globally activates all muscles in the region, for example:
- In the lower extremity, individuals might activate quadriceps, hamstrings, and gluteal muscles while trying to perform a quadriceps set.
- In the core, the individual may activate all abdominal muscles when trying to activate only the deep trunk stabilisers.
Once the correct activation has been achieved, the programme might progress to programme with strengthening emphasis, followed again by a muscle re-education programme to teach the individual to activate just enough motor units to accomplish the functional task safely.
- Use caution when prescribing isometric exercise for individuals with hypertension or known cardiac disease.
- Isometric exercise can produce a pressor response, increasing blood pressure.
- Perform isometric exercise without breath holding or a Valsalva manoeuvre.
- Individuals with hypertension may benefit from simple, repeated contractions held only one to two (1 to 2) seconds.
4.0 Dynamic Exercise
Dynamic resistive exercise can be performed in a variety of modes, postures, and dosages, as well as with a variety of contraction types (i.e. concentric or eccentric).
Dynamic exercise implies joint motion and a shortening or lengthening contraction of the working muscle. Dynamic exercises have been called isotonic exercises in the past and the term is still in common usage today despite the technical shortcomings of the term.
Body weight, elastic bands, free weights, pulleys, manual resistance, and weight machines are a few modes of dynamic resistive exercise. Concentric and eccentric contractions can be used in different combinations depending on the mode of exercise chosen (i.e. most weight machines use concentric and eccentric contraction of the same muscle groups whereas manual resisted exercise can use concentric and/or eccentric contractions of opposing muscle groups).
As with isometric exercise, each type of dynamic exercise has risks and benefits, and the training mode must be matched to the specific needs of the individual. The American College of Sports Medicine (ACSM) recommends that for novice and intermediate training, both free weights and machines be used, whereas the advanced and elite athletes’ emphasis should be primarily with free weights (Kraemer et al., 2002).
Although isokinetic exercise is a type of dynamic exercise, it is often considered in a different category from isotonic exercise. Although isotonic exercise can be performed at a constant velocity, it is performed against a constant load. Isokinetic exercise is performed at a constant velocity with accommodating resistance; that is, the isokinetic device “matches” the resistance applied by the subject.
Specific indications and dosage for each type of dynamic exercise is considered in the next part of the article.
PART THREE: METHODS OF RESISTANCE TRAINING
The specific activities and dosage chosen to improve muscle performance depend on many factors, including the individual’s age and medical condition, muscles involved, activity level, current level of training, goals (i.e., strength, power, and endurance), and cause of decreased muscle performance.
This part of the article describes the activities used to increase muscle performance and their relative risks and benefits.
It is important to match the appropriate training mode to the individual’s goals.
6.0 Manual Resistance
Manual resistance can be applied by a (medical/healthcare/exercise) professional, the individual, or another individual.
It is one of the most longstanding forms of resistance training in the rehabilitation profession, and this is likely due to its ease of application and its versatility.
Manual resistance can be applied at a variety of intensities, speeds, ranges, and contraction types. The speed, intensity, contraction type, and movement pattern can be varied during a given exercise. Several well-known techniques such as PNF are applied predominantly with manual resistance.
Manual resistance can be performed in almost any situation where resistance for rehabilitation is required. However, it becomes challenging in situations requiring high force levels, as in training for fitness, wellness, or sports. Manual resistance is especially effective in a number of situations.
Manual resistance is quite effective when strength varies throughout the ROM. An individual may have a portion of the ROM that is either weak or painful; a therapist/trainer can modulate the resistance more easily with manual techniques than with resistive equipment. A therapist/trainer can also apply specific tactile cues to facilitate recruitment at a weak portion of the ROM. Similarly, manual techniques work well if an individual needs assistance through a portion of the ROM, followed by resistance at other positions. Manual techniques are quite useful when teaching proper movement patterns, as manual assistance/resistance can facilitate proper firing patterns. For example, a PNF technique called rhythmic initiation teaches proper movement patterns prior to the addition of resistance.
Manual resistance is indicated when manual contacts are necessary to ensure the proper muscle activation. For example, in some situations synergists may substitute for the desired primary muscle action. Palpation plus manual contacts and tactile cues can facilitate the proper muscle activation and stabilisation. Manual cues with one hand can facilitate isometric stabilisation contractions while the other hand facilitates and resists a dynamic contraction. PNF techniques are very effective for enhancing specific muscle activation patterns and intensities that can become resisted.
Manual resistance works well when needs a specialised technique such as alternating isometrics or rhythmic stabilisation. These are techniques where agonist and antagonist are alternatively activated within a small ROM and at progressively higher speeds until co-contraction provides stability. The alternating aspect of this activity makes manual techniques the optimal form of resistance. Additionally, when a variety of speeds is necessary, manual resistance offers the flexibility to change rapidly, enhancing motor learning opportunities.
Manual resistance has the benefit of being readily available and does not require specific positioning against gravity to achieve resistance. The amount of resistance can be modified as the exercise session progresses, with decreasing resistance as the individual fatigues. The resistance can be more finely adjusted through the range of motion and with every repetition to ensure maximum resistance through the exercise. A therapist/trainer is able to feel the change in force offered by the individual and can adjust the applied resistance appropriately. That way the individual can obtain the maximum resistance tolerated through the entire exercise set. The therapist’s/trainer’s hand position is also easily modified to change the lever arm and resistance offered. Manual resistance also allows manual contact between the therapist/trainer and individual. For many individuals, this tactile contact provides comfort and increases ease.
Another consideration is the labour intensive nature of manual resistance. Manual resistance requires the time, energy, and physical strength of a therapy provider/trainer. Depending upon the body part being exercised and the relative strengths, manual resistance can be physically taxing. Performing PNF diagonal patterns for the lower extremity can be physically difficult and could potentially result in injury to the therapist/trainer using poor body mechanics. Be sure to use proper body mechanics, maximizing hand positioning, base of support, and lever arms to minimise the stress and risk of injury.
Manual resistance is not practical for many home programmes. Caregiver assistance is required and may place the caregiver at risk of injury. For all but the lightest of manual resistance applications (e.g. hand, wrist, and foot) the resistance is too great and the body mechanics challenging. Few homes have sufficient tables or supports at the right height and firmness to allow the caregiver to use good body mechanics.
Measuring and defining manual resistance is difficult. Therapists, and some trainers, use terms like “minimum,” “moderate,” and “maximal” but these are poorly defined and vary from one person to another. For situations where documentation needs to be precise, verifying the dosage of manual resistance can be difficult.
Techniques for performing manual resistance require attention to the individual’s positioning, therapist/trainer positions, manual contact, grading of resistance, and verbal cues. Attention to these details provides the safest experience for both the individual and therapist/trainer. Consider the following points, essential to manual resistance:
- Make sure that the individual’s clothing allows you to see the muscles or joints associated with the exercise.
- Position the individual so that full excursion of the movement is possible without restrictions.
- Make sure that the individual is comfortable and as stable as necessary as dictated by the exercise goal.
- Position yourself in the plane of the movement, using a wide base of support; shift your weight and step as necessary with the movement to maintain good body mechanics.
- Use as wide a contact area as possible to prevent discomfort at the point of resistance or stabilisation application.
- Using a wide, gentle grip, take the individual’s limb through the exercise ROM to teach them the movement pattern.
- While continuing to move through the range, tell the individual that you will be gradually applying some resistance to the movement.
- Be sure to gradually apply and slowly release the resistance to avoid sudden muscle contractions that might cause injury or pain.
Dosing manual resistance can be challenging due to the inability to quantify the intensity of the exercise. A therapist/trainer is able to document sets and repetitions as well as a nominal description of the amount of resistance (i.e. minimum resistance, maximum resistance). Like all forms of resistance, manual resistance is applied with a specific goal in mind (e.g. strength, endurance, and stabilisation) and the sets, repetitions and relevant rest intervals are derived from the goal.
- The exercise should stop when form fatigue becomes evident.
- Exercises can be varied by speed, muscle contraction type (concentric, eccentric, isometric) ROM, and resistance.
- Manually resisted exercises can be performed in an open chain or a closed chain.
7.0 Pulley System
Many pieces of exercise equipment are based on a pulley system where a weight plate is attached via a cable and pulley to a handle or lever that is controlled by the individual. In a standard pulley system, the cable attaches over a single or double round pulley. In other situations, the pulley or cam itself is elliptical, thereby providing variable resistance as they rotate through the cable’s excursion. These are called variable resistance machines and will be considered in Section 8.0; here we will focus on traditional pulley devices without an elliptical cam.
Most pulley systems consist of a simple cable and pulley attached to a weight stack of variable weight increments (e.g. 2.5, 5, or 10 lb). Most pulley systems are a single stack of weights that are freestanding or attached to a wall. The other end of the pulley typically contains a clip or hook to which a number of different implements can be attached. These attachments may include a straight bar, cuff, handgrips, or various sizes and grips of implements designed to allow a wide range of exercises. Activities such as triceps pulls, biceps curls, latissimus pull-downs, rows, shoulder rotations, presses, leg lifts, and crunches are some of the many activities that can be performed with a pulley. Thus, a pulley is a versatile piece of equipment that allows someone to perform a large variety of activities with a single piece of equipment.
A pulley system is indicated any time resistive exercise through a range of motion is necessary. Pulleys are prescribed after baseline strength is established, as most pulley systems start with a minimum of 2.5 lb of resistance. Few pulley systems provide stabilisation such as chairs or benches. Therefore most exercises require dynamic stabilisation from the individual performing the exercise. Chairs or benches can be set up to provide support or stabilisation for specific exercises. For example, an individual with limited standing tolerance or balance may be safer performing biceps curls seated rather than standing.
The most fundamental disadvantage of this type of system is the constant load provided by the equipment. When performing an exercise through a full ROM, the muscle will be maximally loaded only in the weakest portion of the range. The remaining portion of the ROM will be underloaded, failing to achieve the criteria necessary for strengthening. One technique to accommodate for this shortcoming is to train different portions of the ROM at different intensities. For example, an individual may train through the full range of motion at a lower intensity, then perform an additional set at a higher intensity in the mid-portion of the ROM, where the muscle requires higher resistance to overload.
8.0 Variable Resistance Machines
Resistive exercise machines are commonly found in rehabilitation clinics and health clubs/leisure centres. Most of these machines work in a similar fashion, although some differences exist.
Historically, most weight machines were designed to isolate a specific muscle group such as the quadriceps femoris or biceps brachii. Some equipment trains multiple muscle groups in combination patterns such as a leg press or pull-up/heave machine. Those machines using weight stacks have plates weighing 5 to 20 lb each. The weight stack configuration varies with the specific muscle action trained. A pin placed in the weight stack selects the amount of weight to be lifted. The muscle contraction type is concentric during the lifting phase and eccentric during the lowering phase.
The pulley or cam system is an important component of the weight machine. In contrast to a simple pulley system that provides a constant load through the ROM, a variable resistance machine contains an elliptical cam and pulley system that varies the resistance through the ROM. The kidney-shaped cam is an attempt to account for changes caused by varying length-tension relationships through the ROM. Variable resistance devices provide less resistance at the beginning and end of the ROM, and more resistance midrange.
Other machines use hydraulics to provide variable resistance through the range. Again, the machine is designed to provide more resistance in the mid-ROM, replicating “typical” length-tension ratios. Rather than alternating concentric-eccentric contractions of the same muscle groups, the hydraulic resistance machines typically provide reciprocal concentric contractions of opposing muscle groups (e.g. biceps-triceps).
Weight machines also differ in their adjustability. Lever arms and seat positions should be adjustable for a variety of body sizes. This ensures the ability to align the joint axis with the axis of the machine and prevent injury from poor posture or exercise mechanics. Stops and range-limiting devices should be available and easily adjustable.
An advantage of weight machines over other types of resistance is safety. Individuals are stabilised effectively by the equipment, and the risk of falls or injury resulting from instability is minimised. It takes less time to learn weight machine exercises. After the adjustments are learned, the equipment is relatively easy to use, and novice weight lifters are less intimidated by the equipment. Weight machines are also relatively time-efficient because the machines are already set-up. Only a few simple adjustments are necessary, and the patient is ready to begin. These machines frequently isolate a specific muscle group to be trained, and the variable resistance accommodates for changing length-tension relationships better than other types of resistance.
One of the disadvantages of weight machines is their expense. They typically perform only a single exercise. For example, an expensive machine may train only biceps, whereas this could be done inexpensively with a couple of free weights and a bar. Another disadvantage is that weight increases are restricted to fixed increments (i.e. weight plates) on weight machines. Smaller changes of 1 or 2 lb are not possible on most machines. Despite the many size adjustments on weight machines, they still do not fit everyone. Most also have a fixed, two-dimensional movement pattern. Because the machine guides the individual through the ROM, little proprioception, balance, or coordination is learned from the experience. The stabilisation helps with isolation but limits the individual from learning self-stabilisation. Most machines are designed to perform bilateral exercise. In some cases, performing unilateral exercise is difficult, if not impossible.
9.0 Elastic Resistance
Elastic resistance in the form of elastic bands or tubing has improved greatly from its origins as “dental dam” used in dental since its first appearance. It is relatively inexpensive, easy to use, small and light making it ideal for home and travel use, and can be used in an infinite variety of exercises. However, the trade-off for ease of use is the difficulty in quantifying and dosing an exercise programme. Ongoing research is providing further information on forces generated with elastic resistance (Page & Labbe, 2000; Page, Labbe & Topp, 2000; Patterson et al., 2001; Simoneau et al., 2001).
Elastic resistance is a dynamic exercise but cannot be classified as isotonic or isokinetic. The variability in load through the ROM does not allow it to be classified as isotonic and the variability in speed does not allow classification as isokinetic. It has unique characteristics that require it to be considered independent of other types of resistance. Elastic resistance is often compared with an isotonic pulley system. However, the unique characteristics of elastic do not allow a direct comparison with a pulley system (Page & Ellenbecker, 2003).
Unlike a pulley system which has a fixed load, the resistance provided by an elastic band varies with the thickness of the band and the elongation (Patterson et al., 2001; Thomas, Muller & Busse, 2005; Manor, Topp, & Page, 2006). Any elastic material’s resistance to stretch is proportional to its original cross-sectional area (Page & Ellenbecker, 2003). Therefore, doubling the cross-sectional area by folding (effectively doubling) the elastic doubles the resistance. Additionally, elastic resistance has unique force-elongation characteristics. The force increases as the elastic is stretched from 0% to 250% of its resting length. The percentage of elongation, or change in length of the elastic band, is calculated using the following formula:
Percentage of elongation = [(final length) − (resting length) / (resting length)] × 100
This force development is distinct from the torque created when functionally using elastic bands through a ROM with changing moment arms. Like all elastic materials, the force developed when pulling that material in a linear fashion will increase as the material is lengthened until failure is reached. However, the actual amount of torque developed when using elastic bands through a range of motion (such as shoulder abduction) follows an ascending-descending pattern. That is, the torque increases from 0 to 90 degrees abduction as the moment arm increases, then decreases again as the moment arm decreases as the shoulder approaches 180 degrees.
Elastic bands are indicated any time strengthening by an external resistance is required. Elastic resistance can be used in a clinic or gym under a therapist’s or trainer’s supervision respectively. It also works well for home programmes utilised on conjunction with in-house training/rehabilitation. Because it is light and easily transported, elastic resistance works well for those needing to perform exercise while at work or travelling. Resistive bands can be used for:
- Fitness or wellness training;
- Providing challenges to muscle strength, power, endurance;
- As well as plyometric training, balance, and stabilisation.
They can be integrated into a practice or training session to provide additional activity-specific training. Resistive bands can be used for open chain or closed chain exercise, and core strength and stabilisation. The tubing or bands can be attached to work or exercise equipment to provide functional resistance. It works well for individuals who have limited mobility, as the resistance can be applied in a variety of positions or postures. The resistance variation provides individuals with low physical capacity the opportunity to train and improve strength and function (Tafel et al., 1987; Han, Her & Kim, 2007; Puls & Gribble, 2007).
There are some issues to be considered when prescribing elastic band resistive exercises. First, although there is some data about the amount of resistance with different colours of elastic bands, patient implementation variables render it an inexact quantity. The amount of resistance varies with the elongation, so if the individual grasps the band at a different location, or initiates the exercise at a greater percent elongation, the torque may vary from one session to the next. The individual may not understand why the exercise seems easier one day and harder the next.
While the reproducibility of testing or exercise with elastic bands may be questioned due to issues of cross-sectional area, length and origin/stabilisation, the reliability and validity of elastic band use has been established under controlled conditions. Researchers found a 30-second elastic band elbow flexion test to be significantly correlated with a 30-second elbow flexion test using dumbbells (r = 0.62) and maximal isokinetic testing (r = 0.46). The test-retest reliability was high as well (ICC = 0.89) (Manor, Topp & Page, 2006).
Another consideration is the impact of cyclic loading. Like any other elastic medium, loading the material results in changes such as creep. Additionally, cyclic loading (repeatedly stretching and relaxing the bands or tubing) can result in fatigue to the material. Over time, this fatigue can decrease the performance of the elastic and can eventually lead to failure. Research has shown that elastic bands stretch to 100% elongation for 500 cycles, resulting in a 5% to 12% decrease in force (Simoneau et al., 2001). More importantly, the majority of the change occurred within the first 50 cycles. If patients are performing sets of 30 or more repetitions, the elastic can fatigue quickly. Therefore it is important to replace elastic bands frequently.
Like pulleys, elastic resistance exercises can be performed with or without external stabilisation. If no stabilisation is provided, be sure the individual is performing the exercise without substitution.
Like any resistive exercise, the proper dosage is necessary to ensure achieving training/rehabilitation goals. Dosage is more difficult with elastic resistance because of the number of variables associated with this resistance mode. The length of the band, the percentage elongation, the colour of band, and the origin of the elastic resistance all impact the torque developed.
Elastic resistance typically comes in a variety of colours and each colour provides a different amount of resistance. Research on Thera-Band® elastic bands showed a 20% to 30% increase in force production between colours (Page, Labbe & Topp, 2000). Increases in intensity should be accomplished by moving to the next higher level of resistance rather than doubling the elastic band. Doubling the elastic band will double the resistance, while increasing to the next higher level will provide only a 20% to 30% increase, a more moderate and safer intensity increase.
Another important variable in dosing elastic band exercise is the length of the band or tubing. The band should be elongated to no more than 250% of its original length (Page & Ellenbecker, 2003). To maintain the optimal ascending-descending torque curve, the length of the elastic should be equal to the length of the lever arm. In the case of exercise at the shoulder (i.e. abduction or flexion) the tubing should be equal to the length of the arm. This way the elongation through the full ROM will be twice the length of the lever (a 200% elongation) resulting in an optimal torque curve for the shoulder musculature.
The angle of the origin of the tubing also impacts the torque curve and the subsequent resistance. An angle that is too acute will shift the torque curve to the left, increasing torque earlier in the range of motion. An angle that is too obtuse will shift the torque curve to the right, increasing torque later in the range of motion. This may be desirable in specific training/rehabilitation situations, but in general does not reproduce the torque curve of a normal muscle-joint interaction. The trainer/therapist should be aware of the impact of this angle on torque production. The origin of the elastic should be in the plane of the axis of rotation and in the direction of the desired motion (Page & Ellenbecker, 2003).
Finally, the resistance arm angle should be considered during exercise prescription. The resistance arm angle is the angle produced by the band or tubing and the lever arm. The band and the limb should be aligned to ensure a normal physiological ascending-descending torque curve. If this alignment is incorrect, excessive torque may be produced at end range where the least amount is available. It is recommended that the band or tubing be aligned with the ending lever arm at a resistive arm angle of 15 degrees to 0 degree (Page & Ellenbecker, 2003). For example, in shoulder flexion, the band should be placed under the foot so that in the full 180 degrees overhead position, the band pulls nearly straight down, with the wrist-band angle at <15 degrees. A higher angle would place excessive load on the wrist extensor muscles.
Once the individual is properly positioned and the band or tubing colour (resistance) and length determined, the number of sets and repetitions should be determined. The individual should start with slight tension on the band (approximately 25% elongation) and perform the exercise through the desired ROM. Depending upon the individual’s goals (strength, power, endurance, etc.) an increase or decrease in the band colour might be indicated. Like free weights or weight machines, the resistance and number of repetitions depend upon the goal. For traditional strength or endurance training, repetitions at approximately 6 to 10 RM (repetition maximum) would be appropriate. For those doing power training, the intensity would be greater, with intensity at 90% of a 3 RM (Page & Ellenbecker, 2003).
As with any resistive exercise, substitution, form fatigue and stabilisation are factors to be considered. Do not sacrifice form for additional resistance or repetitions. Training programmes can be designed similar to those with traditional weights. As the individual fatigues, consider performing additional sets at a lower elastic band resistance, just as one might to a decreasing training schedule with free weights.
10.0 Free Weights
Free-weight training is the resistive exercise technique of choice for body builders and power lifters. Free weights and cuff weights are also commonly used in rehabilitation. Free-weight training is usually performed with hand-held weights that range from 0.5 up to 75 or more pounds. Free weights can also be combined on a bar with weight plates. Cuff weights typically range from 0.5 to 25 lb.
Free-weight training allows more discrete increases in resistance, and resistance can differ from one side to the other. For example, reciprocal biceps curls can be performed with 10 lb on the injured side and 15 lb on the uninjured side. Incremental increases of 1 to 2 lb or less are available, allowing a more gradual overload. The free-weight equipment is affordable, and a multitude of exercises can be performed with the same free weights. These exercises can include simple strengthening and endurance activities or power training techniques.
Free weight exercises can be performed in a multitude of different ways that meet the needs of individuals. For example, a variety of positions are available and are not restricted by the design of the machine. Biceps curls can be performed in standing, sitting, supine or even prone. They can be performed symmetrically or reciprocally and the patient may have different weights in each hand.
The exercise can be performed at a variety of different speeds and the working ROM can be altered. Changing the position and/or ROM can alter the relationship with gravity, affecting the working muscle group and contraction type. For example, a hamstring curl performed in standing provides concentric resistance during shortening and eccentric resistance while lengthening, both to the hamstring muscle group. This same exercise performed in prone provides concentric resistance with a decreasing moment arm against gravity until the knee approaches the 90-degree angle. At this position, there is no moment arm against gravity and no significant resistance. Continuing into further flexion produces and eccentric contraction of the quadriceps as they are lengthened while trying to slow the flexing knee. Free weight exercises provide a multitude of possibilities to match the exercise with the individual’s goals.
One of the biggest advantages of free-weight training is the neural component of balance. Compared with the external stabilisation provided by a weight machine, the free weight usually has little external stabilisation. These exercises require postural muscle stabilisation beyond the work required to move the weight. The individual lifting with free weights must understand proper posture and spinal stabilisation to prevent injury to the back. If balance is a rehabilitation goal, free weight exercise may be indicated.
The neural demands of free-weight exercise are a disadvantage for some. It takes longer to learn free-weight exercise, because the free-weight tasks usually are more complex than those with weight machines. Novice lifters may be at greater risk for injury because of poor technique. Spotters are necessary for many of the free-weight lifts, increasing the time required to load and unload bars, free-weight training can be less time efficient. However, for those using smaller hand-held weights, these can be more time efficient than weight machines due to the lack of setup time.
Safety tips for individuals training with free weights include working with a knowledgeable partner who can spot safely. Collars should always be used to lock the weights on the bar and prevent movement of the plates on the bar. Proper form and technique should be acquired before lifting with any weight.
Elastic bands, tubing, and pulleys are used in a similar fashion to free weights. One benefit of bands and pulleys over free weights is the ability to position the individual without regard to gravity. Free weights, resistive bands, and pulleys have the advantage of movement in a variety of three-dimensional patterns without fixed movement patterns. This allows highly specific training that matches individual needs. For example, resisted lunging patterns forward, backward, laterally, or diagonally can be performed with elastic bands, pulleys, or free weights. These movement patterns can be performed in whatever range is necessary for the individual, rather than in ranges dictated by a weight machine.
11.0 Isokinetic Devices
Isokinetic dynamometers are designed to provide maximum resistance through the entire ROM. The resistance provided by these devices is termed “accommodating” because once the preset speed is achieved, the dynamometer “matches” the force applied by the individual. The dynamometer provides a counterforce equal to the force applied by the individual. Therefore the individual can obtain the maximum amount of resistance they can tolerate throughout the ROM. If an individual has pain or weakness in a specific portion of the ROM, the remaining portion can still be fully challenged. Additionally, individuals can train at a variety of speeds.
The first isokinetic dynamometers performed resisted reciprocal concentric contractions at speeds fixed by a medical/healthcare professional. The dynamometer was passive in that the machine was unable to move independently; the individual was required to move the dynamometer arm. Newer isokinetic devices are active computerised training and testing devices that are capable of actively moving the individual’s limb for them. These dynamometers provide reciprocal concentric resistance at fixed speeds, and they provide multi-angle isometric resistance, fixed resistance concentric and eccentric contractions, passive motion, and fixed speed concentric and eccentric contractions. Because these dynamometers now function in a variety of modes that the dynamometers are capable of performing, they have become multipurpose testing and training devices. While many dynamometers are capable of providing isometric and isotonic resistance, most providers still refer to these devices as isokinetic dynamometers, and emphasise the isokinetic capabilities of these devices.
The isokinetic mode is used most frequently for muscle performance testing and training. The dynamometers are capable of testing and training muscle groups around most major joints of the body. Muscles around the shoulder, elbow, forearm, and wrist in the upper extremity and the hip, knee, and ankle in the lower extremity are all readily tested and trained using an isokinetic dynamometer. Adaptive attachments allow training for paediatric individuals, industrial medicine (i.e. lifting and work simulation attachments) and closed chain exercise and testing. Isokinetic testing is frequently performed as an alternative to 1 RM testing due to the computerise capabilities of the devices and safety issues. The dynamometer matches the individual’s force output, thereby minimising the chance of injury that is found when performing 1 RM testing, particularly in the presence of an injury. Tests can be performed in a limited ROM and at a fixed speed to assess muscle strength or endurance. Test results are stored in the computer and can be compared with the results of future tests or to population-based norms.
Isokinetic testing is performed to assess muscle performance against some standard. The standard may be the contralateral side, a population norm or a percentage of the antagonist muscle performance. Testing is performed to assess progress after injury or surgery and to determine readiness to advance the rehabilitation programme or to return to activity. In some situations testing is performed pre-season to provide guidance for the training programme or to provide a baseline measure in the case of a future injury.
Testing is typically performed at two or three different speeds to capture speed-specific muscle impairments. Each dynamometer maker has specific testing protocols and standards to follow to ensure validity and test-retest reliability. The data is captured in a computer file and can be examined and manipulated in a variety of different ways. Several important terms are used to describe isokinetic data results.
- Peak torque is the most common variable measured and is the maximum torque generated regardless of where in the ROM it is achieved.
- Work is the total amount of work performed under the torque curve, regardless of ROM, time, or speed.
- Average power is the amount of work (total work under the curve) performed per time unit (P = W/T).
- Time to peak torque is the amount of time it takes to achieve peak torque and the peak torque angle is the joint angle at which peak torque occurred.
Other important and common comparisons are bilateral comparisons and agonist/antagonist ratios. In bilateral comparisons, one extremity is compared with the other to determine the absolute and/or relative difference from side-to-side. In agonist/antagonist ratios, the opposing muscles groups (e.g. quadriceps and hamstrings) are compared with the antagonist given as a proportion of the agonist (e.g. the hamstrings are 70% of the quadriceps). Normative standards for some agonist/antagonist ratios exist.
Isokinetic training is indicated any time an individual needs muscle activation throughout the ROM. Isokinetics work well when there are fluctuations in torque production due to changes in the length-tension relationships or due to pain or pathology causing signification variation in torque production through the range. Unlike a fixed, constant load the activity. If an individual is unable to continue the exercise, they can simply stop without worrying about dropping a weight. Isokinetic training also works well when a variety of speeds need to be trained. Velocity spectrum training (VSRP, velocity spectrum rehabilitation programme), or training through a variety of speeds, is a commonly-used training regimen. Individuals may start at a slow velocity (e.g. 60 degrees per second) and increase speed by 30 degrees per second up to a maximum velocity (i.e., 300 degrees per second) and then decrease speed incrementally until the starting speed is reached. A variety of training programmes can be designed using this technique. The “slow velocity” VSRP generally ranges from 60 degrees per second to 180 degrees per second and back down, while the “medium velocity” VSRP ranges from 120 degrees per second to 240 degrees per second and the “high velocity” from 180 degrees per second to 300 degrees per second and back down.
The passive mode on an isokinetic dynamometer can be used to train isokinetically as well. The passive mode does precisely what the name implies: it passively moves the limb at a preselected velocity. An individual can use this mode in a variety of different ways. An individual might be instructed to relax and let the machine move and mobilise the joint. Alternatively, an individual might be asked to assist the machine in the direction it is moving (a concentric contraction) or to resist against it (an eccentric contraction). Why choose resisting against the passive movement rather than the active isokinetic or isotonic concentric and eccentric contractions? In the active modes, the patient must still generate enough torque to actively move the dynamometer arm and match the preset speed of the machine. In some cases, such as a postoperative surgery or an acute injury, this amount of force may still exceed the muscle’s capacity. In the passive mode, the machine moves continuously, and the patient can provide resistance at the level and in the appropriate ROM given the current training or injury status.
The major advantage of isokinetic resistive training is its ability to fully activate more muscle fibres for longer periods. Because the machine matches the torque provided by the individual, it “accommodates” their changing abilities throughout the ROM. In contrast, free weights (i.e. fixed resistance training) overload only the weakest portion of the range, but the stronger portion (usually the middle third) is not overloaded. For testing purposes, isokinetic dynamometers allow individuals to be tested at a variety of speeds, potentially identifying deficits at more functional speeds. Compared to a 1 RM strength measure, the isokinetic dynamometer produces a force curve through the ROM rather than a single measure. This allows more detailed evaluation of muscle function characteristics (e.g. time to peak torque, total work performed, etc.).
Isokinetic devices allow training at a variety of speeds. The positive effect of fast-speed training on performance is highlighted with isokinetic training. Training at faster speeds can assist the return to functional activities that require less muscle torque development but faster speeds of contraction. Speeds that more closely match an individual’s function can be chosen to match functional velocities. Higher speeds can decrease joint compression forces in areas such as the patellofemoral joint, decreasing the pain and discomfort often seen with heavy resistance exercises. Although less torque is generated at high speeds, the decrease in pain and more functional speeds may produce better results.
Studies assessing the speed variable favour slow-speed isokinetic training over fast-speed training for the development of strength (Gettman & Ayres, 1978). High muscular tension is necessary for generating strength gains and is achieved when the isokinetic speed is slow enough to allow full recruitment and generation of a high resisting force.
The newer isokinetic dynamometers with computer interface also provides feedback for training purposes. This feedback can take many forms, such as visual when trying to reproduce a torque curve or produce enough force to raise a bar to a preset level. Feedback can be auditory with bells when a preset goal is met. Isokinetics can also provide neuromuscular training by requiring the patient to resist at a specific level that is submaximal, a relatively challenging task. While it may be easy for individuals to push as hard as they can to achieve maximum torque production, it is often harder to regulate torque production at lower levels.
Isokinetic resistive training also has disadvantages. These devices are expensive to purchase and maintain. They require trained personnel for setting up patient/client training programmes, testing, and data interpretation. From a biomechanical perspective, most training is done in a single plane, with a fixed axis at a constant velocity in an open kinetic chain. Testing and training in a single plane improve test reproducibility but do not necessarily carry over to function. We rarely move at a constant velocity in functional activities, although this feature provides for maximal loading through the ROM. Newer isokinetic devices have some closed-chain components, which have the advantage of testing a functional movement pattern but the disadvantage of being unable to tell where the muscle performance impairment lies.
Isokinetic exercise is dosed similarly to other types of quantitative resistive training. Isokinetic devices have the advantage of computerised data reduction which helps to see and manage resistive exercise volume and intensity. The computerised system allows for storage of exercise training programmes which can be programmed and executed with minimal setup. This data can then be tracked over time. Like any resistive exercise programme, the volume of activity must be balanced with intensity and viewed within the context of the individual’s daily activities.
12.0 Body Weight
Body weight can be effectively used as resistance.
Resistive exercises for the lower extremity are the most obvious application of body weight as resistance, due to the high number of functional activities that require the lower extremity muscles to move body weight. Walking, running, sports, stair climbing, and transfers of all sorts are examples of activities requiring the movement of body weight.
Upper extremity exercises using body weight are less common, but several examples exist. Push-ups/press-ups, using the arms to push or pull oneself out of bed, or a chair or sporting activities such as gymnastics are examples of upper extremity weight-bearing activities. Many exercises using body weight as the primary resistance are classified as closed chain exercises.
Closed chain exercises are those activities where the distal segment is fixed on a rigid or semi-rigid surface. Squats, lunges, step-ups, or push-ups/press-ups are considered closed chain exercises. Open chain exercises are those where the distal end is free, as in performing a straight leg raise, resistive knee extension, or biceps curl.
Body weight can be minimized by altering the position of the body (e.g. push-ups/press-ups from the knees rather than the feet), using a harness unweighting system, or using a pool.
An advantage of using body weight as resistance is that it is always available and rarely requires equipment. A disadvantage is that it is difficult to isolate specific muscles that need strengthening, and the multi-joint nature of closed chain exercises lends itself to subtle substitution.
PART FOUR: MISCELLANEOUS
13.0 Points to Consider when Purchasing Resistive Equipment
Before purchasing resistive equipment for home use, the following information should be considered:
- Is the equipment safe? Is it approved by a reputable organisation?
- How easy is the equipment to use? How long will it take to learn how to use it?
- Is the equipment versatile? Can it be used to train a number of different muscle groups?
- Will the equipment suit your needs as your training progresses?
Before purchasing equipment, consider joining a health club for a month or two to see:
- Which equipment you tend to use regularly;
- What features you like about some equipment; and
- What features you dislike or seem to be lacking.
Atha, J. (1981) Strengthening muscle. Exercise and Sport Science Reviews. 9, pp.1-73.
Baechle, T.R. & Earle, R.W. (2000) Essentials of Strength Training and Conditioning. 2nd Ed. Champaign, IL: Human Kinetics.
Gettman, L.R. & Ayres, J. (1978) Aerobic changes through 10 weeks of slow and fast-speed isokinetic training. Medicine and Science in Sports. 10, pp.47.
Han, S.S., Her, J.J. & Kim, Y.J. (2007) Effects of muscle strengthening exercises using a Thera-Band on lower limb function of hemiplegic stroke patients. Taehan Kanho Hakhoe Chi. 37(6), pp.844-854.
Kraemer, W.J., Adams, K., Cararelli, E., et al. (2002) American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Medicine and Science in Sports and Exercise. 34, pp.364-380.
Manor, B., Topp, R. & Page, P. (2006) Validity and reliability of measurements of elbow flexion strength obtained from older adults using elastic bands. Journal of Geriatric Physical Therapy. 29(1), pp.18-21.
Muller, E.A. (1970) Influence of training and of inactivity on muscle strength. Archives of Physical and Medical Rehabilitation. 51, pp.449-462.
Page, P. & Ellenbecker, T.S. (2003) The Scientific and Clinical Application of Elastic Resistance. Champaign, IL: Human Kinetics.
Page, P. & Labbe, A. (2000) Torque characteristics of elastic resistance and weight-and-pulley exercise. [Abstract]. Medicine and Science in Sports and Exercise. 32(5 Suppl), pp.S151.
Page, P., Labbe, A. & Topp, R. (2000) Clinical force production of Thera-Band elastic bands. [Abstract]. Journal of Orthopaedic Sports and Physical Therapy. 30(1), pp.A47-A48.
Patterson, R.M., Jansen, S.W.S., Hogan, H.A., et al. (2001) Material properties of Thera-Band tubing. Physical Therapy. 81(8), pp.1437-1445.
Puls, A. & Gribble, P. (2007) A comparison of two Thera-Band training rehabilitation protocols on postural control. Journal of Sport Rehabilitation. 16(2), pp.75-84.
Simoneau, G.G., Bereda, S.M., Sobush, D.C., et al. (2001) Biomechanics of elastic resistance in therapeutic exercise program. Journal of Orthopaedic Sports and Physical Therapy. 31(1), pp.16-24.
Tafel, J.A., Thacker, J.G., Hagemann JM, et al. (1987) Mechanical performance of exertubing for isotonic hand exercise. Journal of Burn Care Rehabilitation. 8(4), pp.333-335.
Thomas, M., Muller, T. & Busse, M.W. (2005) Quantification of tension in Thera-Band and Cando tubing at different strains and starting lengths. Journal of Sports Medicine and Physical Fitness. 45(2), pp.188-198.
Whitley, J.D. (1967) The influence of static and dynamic training on angular strength performance. Ergonomics. 10, pp.305-310.