Muscle Anabolism

As a consequence of normal physical activity, it is estimated that 1-2% of skeletal muscle tissue is synthesised and broken down on a daily basis (Rasmussen & Phillips, 2003). This biological process is normally in equilibrium and therefore skeletal muscle mass remains relatively constant unless there is a stimulus for change. Resistance exercise is a potent stimulus which causes not only an increase in protein synthesis but also an increase in protein breakdown (Borsheim, Tipton, Wolfe, & Wolfe, 2002). This elevation of both synthesis and breakdown is evidence that significant “remodelling” of muscle protein occurs as a result of resistance-training (Rasmussen & Phillips, 2003). If the resistance training stimulus is maintained over a sufficient period of time, the constant remodelling of muscle protein generally leads to a visible increase in muscle mass, a phenomenon called hypertrophy. This gain in muscular size is attributed to prolonged anabolism, a state in which the rate of muscle protein synthesis is greater than the rate of muscle protein breakdown (Chesley et al., 1992).

In Weightlifting, there is particular interest in hypertrophy as we generally associate larger muscles with increased strength. Therefore we are also interested in the conditions that contribute to and maintain a state of anabolism. Among the most important of these conditions are the appropriateness of nutrition, the quantity and type of physical activity and the influence of the endocrine system (hormones).
In regard to nutrition, muscle protein synthesis requires an availability of amino acids. Any meal containing sufficient protein as a source of amino acids that is consumed within 24 hours of resistance exercise results in a net muscle protein accumulation (Rennie & Tipton, 2000). This is because muscle protein synthesis occurs 1-2 hours into the recovery period postexercise (Booth, Nicholson and Watson, 1982) and remains elevated for up to 24h (Chesley et al, 1992; Biolo et al, 1995).

However, in Weightlifting we have a vested interest in optimising the nutritional status to promote hypertrophy. Furthermore, the tendency for elite Weightlifters to train two sessions per day requires the restoration of worked muscles to occur as quickly as possible. It is conceivable that the increased frequency of training may have a negative effect on anabolism and muscle hypertrophy unless there is adequate recovery (Chesley et al, 1992).  Therefore it is greatly important that due consideration is given to nutrition, not only in composition but also timing, to optimise the availability of amino acids for protein synthesis.

 Factors contributing to Muscle anabolism.
Figure 1: Factors contributing to Muscle anabolism.

There is ample evidence that protein should be consumed together with carbohydrate to promote anabolism (Rennie & Tipton, 2000; Rasmussen & Phillips, 2003). The rationale for the consumption of protein and carbohydrate together is provided by Figure 1.

amino acids play a role in providing energy for metabolism and at rest amino acids may contribute 30% of the body’s need for glucose. Therefore not all amino acids are available for protein synthesis. However, the effect of the carbohydrate ingestion and insulin secretion is that more carbohydrate is used for energy metabolism and less amino acids. Therefore the ingestion of carbohydrate has a protein sparing effect and the overall effect of protein and carbohydrate ingestion on anabolism is larger than if protein is consumed alone (Rennie & Tipton, 2000; Rasmussen & Phillips, 2003). There are various recommendations with regard to the quantities of protein and carbohydrate to be ingested after training. One study found that a bolus of 6g of essential amino acids with 35g of carbohydrate after resistance training increased muscle protein synthesis by 350% (Rasmussen et al., 2000). On the otherhand, a study by Tipton and colleagues (1999) recommended a large amount of amino acids (30g-40g) after exercise for stimulation of muscle protein synthesis.

The optimal time for ingesting food sources of amino acids (i.e. protein) to maximise the effects of protein synthesis has been studied. A study by Tipton and colleagues (2001) provided evidence that the ingestion of amino acid/carbohydrate immediately before or immediately after resistance exercise beneficially effects muscle protein synthesis. However, in this study it was concluded that immediately before was better than immediately after. Other studies support the notion that 1-3 hours after exercise is a key window for the ingestion of amino acid/carbohydrate (Rasmussen et al., 2000; Rasmussen & Phillips, 2003). This nutrition window may be explained by MacDougall and colleagues (1999) that muscle protein synthesis peaks around 2-4 hours after resistance training.

It is also useful to have an understanding of the hormonal response to training. Resistance training stimulates the release of various hormones that have an anabolic effect, particularly Growth Hormone and Testosterone (Kramer et al. 1990; Hansen et al., 2001).  This hormonal response is an aspect of the body’s homeostatic mechanisms that promote adaptation to environmental stimuli and thereby our survival. Furthermore, feeding before and after resistance exercise alters the hormonal response (Kraemer et al. 2006) and increases muscle protein synthesis (Rasmussen and Phillips, 2003).