Calf raises are a method of exercising the gastrocnemius, tibialis posterior and soleus muscles of the lower leg. The movement performed is plantar flexion, aka ankle extension.
Improper form while performing this exercise, often produced by leaning forward and keeping the knees extended, produces two important biomechanical problems.
First, the vertical line of force extending from the point of contact of the shoulders with the machine creates a moment arm with the low back similar to the previous example (Lifting & Carrying Objects).
This flexion moment on the low back will again have to be countered by the extensor muscles of the low back.
The second biomechanical consequence of this poor exercise technique is a hyperextension moment at the knee joints.
The line of force passes anterior to the knees creating a backward (posterior)-directed hyperextension moment at the knees.
The human knee reaches the limit of its range of motion (ROM) at 1.0° of hyperextension for men and 1.6° of hyperextension for women.
The ‘locked’ knee in this position which is subjected to a large hyperextension moment will counter this moment primarily with soft tissues such as ligaments that if stretched can potentially result in injury.
Correct biomechanical technique for the standing calf raise includes placing the hips, knees, and ankles in line with the line of force, and keeping a slightly flexed position of the knees throughout the exercise.