Sports Fitness Training

Exercise Intensity

Several early studies indicated that at least with aerobic ­type exercise, the contribution of amino acids to exercise energy production was linearly related to exercise intensity. The branched-chain amino acids (leucine, isoleucine, and valine) are the major ones oxidized and the mechanism responsible is thought to be an exercise intensity-dependent activation of the limiting enzyme (branched-chain oxoacid dehydrogenase activity) in their oxidation pathway.

Exercise Type

Apparently any increased protein need for strength exercise does not involve this exercise intensity mechanism because, despite the intense nature of this type of exercise, amino acid oxidation remains unchanged . Likely, this is a result of the large anaerobic component of strength exercise. Consequently, if body­builders need large amounts of protein it is not to provide auxiliary exercise fuel (carbohydrate provides that) but rather because sufficient amino acids must be available to maximize any increase in muscle synthetic rate produced by the exercise stimulus. Several studies indicate that there may be some truth to this commonly held beliet However, the optimal intake would appear to be 1.5-2.0 g/kg/day. This is an amount far less than what many strength athletes consume on a regular basis. Several possibilities might explain this apparent contradiction. Obviously, the athletes could be incorrect, i.e., they may have been influenced by a powerful placebo effect.

Alternatively, some other constituent in high-protein foods might, in combination with the surplus supply of amino acids, be responsible for a muscle-building effect. Several candidates are possible including creatine, a nitrogen compound found in meat and fish that has been studied recently, Although not all studies report positive effects with creatine supplementation, many demonstrate significant ergogenic effects (10% or more), especially during intense brief efforts. Such exercise-enhancing effects combined with a training program might accelerate further the normal gains observed with strength training indirectly via a super training effect. Moreover, some data exist indicating that creatine has anabolic effects on muscle, which could also playa role. Finally, although associated with a variety of adverse health effects, some compounds (i.e., anabolic steroids) are known to be anabolic 46 and it is possible that the high-protein intakes consumed by some strength athletes are only advantageous when combined with these agents.

Exercise Duration

With exercise duration, energy use from amino acids increases likely due to the decreased availability of carbohydrate as the body’s stores of this important fuel can be depleted in a single exercise bout. A similar response occurs with starvation, i.e., protein can be used for energy once the limited carbohydrate stores are exhausted. This may play some role for strength athletes if training sessions are prolonged.

Training History

In endurance exercise training, it appears that amino acid oxidation both at rest and during exercise increases perhaps due to training-induced changes in branched ­chain oxoacid dehydrogenase activity. Yet, this possibility remains controversial as the data from one study disagree and no obvious explanation to explain the discrepancy is available. The data with strength training are also somewhat unclear. It has been suggested that protein needs of novice bodybuilders might exceed those of more experienced strength trainers. Although this is consistent with the well-known observation of greater gains in muscle growth of novice strength trainers, several other studies indicate protein needs remain at similar levels for more experienced strength athletes. A recent study with acute eccentric exercise demonstrated similar increases in protein synthesis between resistance-trained and untrained subjects but that protein breakdown was greater in the latter This observation may explain why prior eccentric exercise reduces subsequent muscle damage and pain, and because eccentric exercise is part of most training programs this may indicate that the magnitude of increased protein needs induced by strength training could be reduced as one becomes more experienced. However, at this point in time, this question cannot be answered conclusively. More study of the protein needs of novice versus experienced strength trainers is definitely needed.