How does exercise affect my protein requirement? part one.

Numerous studies involving both endurance and strength exercise have shown that the current recommended protein intake of 0.75g/kg of body weight/day is inadequate for people who participate in regular exercise or sports.  Additional protein is needed to compensate for the increased breakdown of protein during and immediately after exercise, and to facilitate repair and growth.  Exercise triggers the activation of an enzyme that oxidises key amino acids in the muscle, which then are used as a fuel source.  The greater the exercise intensity and the longer the duration of exercise, the more protein is broken down for fuel.  Your exact protein needs depend on the type, intensity and duration of your training.

Bean, Anita. (2009).  The Complete Guide To Sports Nutrition.  London:  A & C Black Publishers Ltd.