A rugby game consists of 2 x 40 minute halves, as play is approximately 80 minutes this would suggest that the oxidative system is dominant during play with very little contribution of anaerobic glycolysis. According to Bompa and Haff (2009) rugby athletes would be working in intensity zone 6 as duration is greater than 30 minutes. However, rugby is a sport that consists of high intensity efforts such as sprinting and tackling and this means that anaerobic contributions to energy begin to increase. These high intensity efforts require glycogen to produce ATP. However, if glycogen stores are limited the body will begin to use fatty acids as an energy source to create ATP through the Krebs cycle. This process takes far longer to create ATP when compared to the glycolytic pathway, therefore this will negatively impact the athletes ability to produce these high intensity efforts. Due to the anaerobic demands the athlete will see a greater drop in muscle glycogen and the only way this can be replenished is through sufficient CHO in the diet (Mujika & Burke, 2010).
A low CHO diet can be defined as consuming less than 26% CHO or less than 130gm/day (Oh & Uppaluri, 2020). When the athlete consumes very little CHO this means there is less glycogen stored in muscles. As high intensity efforts require anaerobic contributions to energy this means glycogen needs to be used as the main fuel source. When there is less glycogen in the muscle this will decrease the amount of work that is able to be performed, decrease training capacity and ultimately lead to decreased performance. Low CHO reduces mTOR and AKT levels, negatively impacting performance. This is because AKT and mTOR are associated with protein synthesis. As a result AMPK is upregulated and this stimulates PGC-1a to cause mitochondrial biogenesis (Palacios et al., 2009). An upregulation of AMPK will lead to performance adaptions that are aerobic dominant meaning anaerobic adaptions will decrease.
If the athlete is undertaking resistance training while also competing in rugby matches the adaptions from the resistance training will be negatively impacted. A decrease in mTOR and AKT activity, associated with protein synthesis, will effect recovery and decrease myofiber size and overall muscle mass which is advantageous in a sport like rugby. Increased mTOR activation will help maintain or increase fat free mass improving body composition. The best time to lose body fat would be during off-season when there are no games and training (Dunford & Doyle, 2008). This is because a restriction of energy intake during in-season or pre-season will negatively impact training and performance. During off-season players are taking a break from the rigors of training and following a suitable diet in a calorie deficit will help the athlete lose body fat. When pre-season begins energy expenditure is increasing so returning to an appropriate diet with protein and CHO should be followed.
References:
Bompa, T.O. and G.G. Haff. Periodization: Theory and Methodology of Training. 5th ed.2009.
Dunford, M., & Doyle, J. (2008). Nutrition for sport and exercise (p. 361). Thomson Wadsworth.
Mujika, I., & Burke, L. M. (2010). Nutrition in team sports. Annals of Nutrition and Metabolism, 57(Suppl. 2), 26-35.
Oh, R., & Uppaluri, K. R. (2020). Low carbohydrate diet. In StatPearls [Internet]. StatPearls Publishing.
Palacios, O., Carmona, J., Michan, S., Chen, K., Manabe, Y., & III, J. et al. (2009). Diet and exercise signals regulate SIRT3 and activate AMPK and PGC-1α in skeletal muscle. Aging, 1(9), 771-783. https://doi.org/10.18632/aging.100075
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