ABSTRACT
High technology has entered our diversions and leisure activities. Sports, exercise, and training are no longer just physical activities but include machines and techniques attuned to individual capabilities and needs. This chapter considers several factors related to exercise and training that help in understanding human performance and provides a brief summary of some factors that can act mechanical work in humans. Generally, muscles are able to exert the greatest force when the velocity of muscle contraction is zero. Isometric length-tension relationship of a muscle shows that the maximum force developed by a muscle is exerted at its resting length and decreases to zero at twice its resting length. Energy expenditure of muscles undergoing negative work is about one-sixth that of a muscle doing positive work; so, a leg muscle going uphill produces about twice as much heat as a leg muscle going downhill.
