MECHANICAL WORK, ENERGY, AND POWER - Biomechanics and Motor Control of Human Movement - page 172

E lg
t

20 . 5 20 . 0

0 . 0286

−

= = 17 . 5W

balance = 17 . 5 − 17 . 34 = 0 . 16 W

2. Thigh Power Balance

powers = F xh V xh + F yh V yh + M h ω th + F xk V xk + F yk V yk + M k ω th
=− 9 . 4 × 1 . 36 + 102 . 8 × 0 . 27 + 8 . 5 × 3 . 98
− 15 . 1 × 2 . 61 − 14 . 6 × 0 . 37 − 5 . 8 × 3 . 98
= 14 . 97 + 33 . 83 − 44 . 81 − 23 . 08
=− 19 . 09 W

E th
t

47 . 4 47 . 9

0 . 0286

−

= =− 17 . 5W

balance =− 17 . 5 − ( − 19 . 09 ) = 1 . 59 W

3. Summary of Power Flows . The power flows are summarized in
Figure 6.20 as follows: 23.08 W leave the thigh into the knee extensors, and
7.19 W enter the leg from the same extensors. Thus, the knee extensors are
actively transferring 7.19 W from the thigh to the leg and are simultaneously
absorbing 15.89 W.

Figure 6.20 Summary of thigh and leg power flows as calculated in Example 6.5.
There is power transfer from the thigh to the leg at a rate of 7.19 W through the
quadriceps muscles plus passive flow across the knee of 44.81 W.