By Clance Laylor
Following an acute bout of resistance exercise, skeletal muscle protein synthesis is elevated (Chesley et al. 1992). At the same time the rate of muscle protein breakdown is also elevated, and as a result, net protein balance remains negative. However, when protein (amino acids) is consumed after resistance exercise, net protein balance becomes positive and over time, muscle mass is increased. Therefore, although resistance exercise is fundamentally anabolic, a net gain in muscle mass is only possible via the interaction with protein containing meals (Phillips et al. 2005). The amount of protein required is actually quite small; the dose necessary to achieve maximal increases in protein synthesis is approximately 20 grams of high quality (complete) protein such as dairy (Moore et al. 2008). Timing of protein ingestion appears to warrant careful consideration as delaying protein ingestion by 2 hours after exercise results in a reduction of the training induced increase in muscle fibre hypertrophy and lean mass in young men compared to immediate protein consumption (Hartman et al. 2007). The type of protein ingested (i.e. plant vs. animal) also appears to be an important factor in determining the magnitude of the response. Different types of protein affect whole body protein anabolism and accretion (Dangin et al. 2003) and thus have the ability to positively affect muscle and strength development during resistance exercise (Phillips 2006). Different types of protein may influence the results from resistance training due to factors such as: rate of absorption, amino acid profile, hormonal response, or favourable effects on antioxidant defense (Cribb 2005). As an example, consumption of fat free milk after resistance exercise has been shown to promote greater lean mass accretion than consumption of soy or carbohydrate in young, male weightlifters (Hartman et al. 2007). Consumption of a high quality protein supplement such as whey acts synergistically with resistance exercise to maximize the protein synthetic response, the long term result being gains in muscle protein mass. Whey protein post-workout is not only convenient, it has a very high concentration of essential amino acids (45-55 g/100 g protein) (Bucci & Unlu 2000) with minimal fat, carbohydrate, and lactose. They are also an abundant source of the branch-chain amino acids, particulary leucine (Bucci & Unlu 2000). Overall, consumption of a high quality protein source (such as dairy) immediately after a bout of resistance exercise is necessary to optimize the training response.
Carbohydrate also plays an important role in post-exercise recovery. Carbohydrate ingestion, via it’s ability to increase insulin levels, attenuates protein breakdown post-exercise, thereby making net protein balance more positive (Tipton & Ferrando). As well, consumption of carbohydrate post-exercise has been shown to increase muscle glycogen stores and enhance the recovery process (see: Hargreaves 2004). Muscle glycogen is an important fuel source for contracting skeletal muscle during periods of prolonged physical activity and its depletion has been implicated as a cause of fatigue. Ingestion of a solution containing both glucose and fructose has been reported to enhance rates of gastric emptying and fluid delivery as well as lower ratings of perceived exertion following moderate intensity exercise (Jeukendrup & Moseley 2008). Overall, ingestion of carbohydrate post-exercise can replenish depleted muscle glycogen stores and improve recovery. Lastly, through its ability to enhance insulin levels, carbohydrate consumption may help attenuate post-exercise muscle protein breakdown, thereby making net protein balance more positive.
References
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