Figure 3.
Average dimensionless leg stiffness (Kleg) and vertical stiffness (Kvert) across speed. (a) Non-amputees (bioL) increased Kleg with increasing speed; whereas subjects with a unilateral amputation did not change leg stiffness in their UL. (b) Kleg decreased with increasing speed in the AL of unilateral amputees and bilateral amputees (BL). (c,d) All subjects increased Kvert with increasing speed; however, non-amputees increased vertical stiffness to a greater extent than subjects with an amputation. The linear fit equations for Kleg were bioL: Kleg = 0.93x + 16.64, R2 = 0.192, p < 0.001; UL: Kleg = 0.24x + 18.36, R2 = 0.016, p = 0.385; AL: Kleg = −0.53x + 22.26, R2 = 0.092, p = 0.034; BL: Kleg = −0.60x + 22.28, R2 = 0.182, p = 0.017. The linear fit equations for Kvert were bioL: Kvert = 23.72x − 44.49, R2 = 0.889, p < 0.001; UL: Kvert = 16.00x − 17.00, R2 = 0.740, p < 0.001; AL: Kvert = 19.63x − 22.12, R2 = 0.810, p < 0.001; BL: Kvert = 19.15x − 14.06, R² = 0.583, p < 0.001. Plus symbols with dashed line, bioL; open circles with solid line, AL; filled circles with solid line, UL; crosses with dashed line, BL. (Online version in colour.)