Research Paper Title
What determines the metabolic cost of human running across a wide range of velocities?
The ‘cost of generating force’ hypothesis proposes that the metabolic rate during running is determined by the rate of muscle force development (1/tc, where tc=contact time) and the volume of active leg muscle.
A previous study assumed a constant recruited muscle volume and reported that the rate of force development alone explained ∼70% of the increase in metabolic rate for human runners across a moderate velocity range (2-4 m s-1).
The researchers hypothesised that over a wider range of velocities, the effective mechanical advantage (EMA) of the lower limb joints would overall decrease, necessitating a greater volume of active muscle recruitment.
Ten high-calibre male human runners ran on a force-measuring treadmill at 8, 10, 12, 14, 16 and 18 km h-1 while the researchers analysed their expired air to determine metabolic rates.
They then measured ground reaction forces and joint kinematics to calculate contact time and estimate active muscle volume.
From 8 to 18 km h-1, metabolic rate increased 131% from 9.28 to 21.44 W kg-1tc decreased from 0.280 s to 0.190 s, and thus the rate of force development (1/tc) increased by 48%.
Ankle EMA decreased by 19.7±11%, knee EMA increased by 11.1±26.9% and hip EMA decreased by 60.8±11.8%.
Estimated active muscle volume per leg increased 52.8% from 1663±152 cm3 to 2550±169 cm3.
Overall, 98% of the increase in metabolic rate across the velocity range was explained by just two factors:
- The rate of generating force; and
- The volume of active leg muscle.
Kipp, S., Grabowski, A.M. & Kram, R. (2018) What determines the metabolic cost of human running across a wide range of velocities? The Journal of Experimental Biology. 221(Pt 18). pii: jeb184218. doi: 10.1242/jeb.184218.