Fig. 5. The average Achilles tendon (AT) length change measured directly using the projected MTJ measurement and the corresponding estimates of series elastic element (SEE) length change during walking (A) and running (B) for downhill (-10%; blue), level (0%; green) and uphill (10%; red) conditions. The AT slack length is estimated from the average length of AT during walking on the level at the average time of toe-off. The estimated aponeurosis length change (which includes the proximal GM tendon) is calculated as the difference between the AT length change (relative to the slack length) and the SEE length change. The shaded areas mark the average stance time across each condition.