Originally Posted by
Savs
I agree with Rip, PEPCACK and atb5161. Energy can be expended by the lifter even though no work (physics definition) is done. Dare I again raise the question about the eccentric portion of the lift? Related questions: How much work is done and how much energy is spent by the lifter to lower and raise the weight? What is the nature of the stretch reflex?
On the way up, the energy, U1, spent by the lifter can be written
U1 = W + Q1, where W = FD is the work done by the lifter, and Q1 is the heat generated since the human machine isn't perfectly efficient.
On the way down, the energy, U2, spent by the lifter can be written
U2 = - W + Q2, since the weight now does work on the lifter.
The total work done by the lifter going down and up is W - W = 0. The total energy spent, however, is not zero but is equal to U1 + U2 = Q1 + Q2.
Any objections?