Post Exercise Carbohydrate Consumption and Protein Balance
The effect of post-exercise carbohydrate consumption upon net muscle protein balance – Iain Mactier
It is widely recognised that a comparatively small amount of muscle contractions against a heavy load can increase muscle strength (Koopman et al. 2007). Following exercise however, muscle protein breakdown is stimulated to a greater degree than protein synthesis (Koopman et al. 2007). Although repeated resistive training does increase muscle protein synthesis rate to an extent (Roy et al. 1997; Drummond et al. 2008), it is still necessary to increase the net muscle protein balance if there is to be an improvement in muscle strength (Koopman et al. 2007). Appropriate nutrition following exercise is important if this positive protein balance is to be attained, hence the popularity of dietary supplements amongst those engaged in frequent resistive training (Rankin et al. 2004). This abstract aims to explore the effect of post-exercise carbohydrate consumption upon net muscle protein balance, and identify if its intake is beneficial.
Carbohydrate recovery drinks are a simple way of elevating insulin concentrations (Roy et al. 1997), and there is evidence to suggest insulin may have an effect on protein balance (Roy et al. 1997; Koopman et al. 2007). Roy et al. (1997) studied the effects of insulin on muscle protein breakdown and synthesis rates, and urinary excretion in 8 subjects. In the carbohydrate control group, urinary urea nitrogen levels were significantly reduced from 12.28 ± 1.84 g/g creatinine to 8.60 ± 0.66 g/g creatinine (p = <0.05). This suggests a decrease in muscle protein degradation. Any increases in the rate of muscle protein synthesis were deemed statistically insignificant. Post exercise carbohydrate ingestion does improve net protein balance although it still remains negative (Roy et al. 1997; Koopman et al. 2007).
Rankin et al. (2004) sought to compare the effects of carbohydrate and protein based recovery drinks in 19 untrained male subjects over a 10 week resistance training program. Improvements in muscle strength of 44 ± 4%, (p = 0.001) were observed in all subjects. No significant variation in body weight or fat-free soft tissue mass was demonstrated in either group. It is interesting that protein based recovery drinks, which are widely accepted as an effective method for increasing the anabolic response of muscles to exercise (Koopman et al. 2007, Drummond et al. 2008), did not prove superior to carbohydrate based preparations. Carbohydrate however, if co-ingested with sufficient protein has not been shown to further increase muscle protein synthesis (Koopman and Beelen et al. 2007).
In conclusion, post exercise carbohydrate ingestion does not seem to be required to maximise muscle protein synthesis (Koopman and Beelen et al. 2007). Its consumption may be beneficial to those engaging in resistive training since it can increase net protein balance (Roy et al. 1997; Koopman et al. 2007) through decreasing muscle protein breakdown rates (Roy et al. 1997). This can result in improvements in strength (Rankin et al. 2004), although this area would benefit from further research,
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