Although effort is required to bend a joint or flex a muscle, the body is able to recycle much of the energy expended through spring-like tendons and elegantly arranged muscles.

But what they certainly advocated is that just as exercise is good for the body, so fasting is a spiritual exercise, allowing us to flex the muscles of the soul.

The unshod runners' style causes more flex in the foot's springlike arch ankle and knee and engages more foot and calf muscles blunting the impact on the body and making for a more comfortable "ride."