Fig. 10. Representative in vivo work loops for the LG (red; upper panels), pMG (blue; middle panels) and dMG (blue; bottom panels) walking at 0.5 m s^–1 on a level treadmill (left column) and running at 2.0 m s^–1 on an inclined treadmill (right column). The area within each loop represents the net work done by each muscle and muscle region. Arrows indicate the direction of the work loop, such that a counter-clockwise loop indicates net positive work and a clockwise loop indicates net negative work (energy absorption). Note that the amount of positive work increased substantially with an increase in speed and incline for the LG.