How Physical Activity affect requirement of protein?

Research on protein needs for muscular work had its beginning in 1863 when Von Leiberg postulated that muscle protein was destroyed with each contraction of the muscle. On this basis, he recommended that heavy muscular work required a heavy protein diet. This theory has been amply disproved, yet even today many believe that a protein rich diet will contribute to athletic prowess. Today, we know that muscle contraction does not result in destruction of the muscle. It however, requires energy in the form of ATP, glucose and fatty acids and does result in the breakdown of creatine phosphate to creatine which is then converted to creatinine, a nitrogenous waste product excreted in the urine. As the energy requirement is increased to support the increase in muscular activity, so too is the protein requirement in much the same manner as described above for the effects of temperature. In a number of studies, the athletic performance of subject's could not be directly related to the quantity of protein consumed above that determined to be the requirements, their muscular deficiencies were reduced unless a vigorous training programme was included as a part of the experiment's protocol, Since most of the studies were of short duration and since muscle protein has a relatively long half-life, the lack of any demonstrable effect of protein intake on muscle performance is not surprising.