July 7, 2015
Daniel R. Moorea, Donny M. Camerab, Jose L. Aretab (this summary) with co-author John A. Hawleybc (original article)
- Faculty of Kinesiology and Physical Education, University of Toronto, Toronto ON, M5S 2W6, Canada.
- Exercise and Nutrition Research Group, Department of Exercise Sciences, Australian Catholic University, Fitzroy, Victoria, Australia.
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK.
The original paper is a part of a Special APNM Issue entitled Nutritional Triggers to Adaptation and Performance.
Endurance exercise can lead to the depletion of carbohydrate stores such as liver and muscle glycogen (the main metabolic fuels during high intensity activity) and often induces compensatory fluid loss through an increased sweat rate as a means to thermoregulate. As such, the importance of refuelling and rehydrating is typically at the forefront of many endurance athletes’ recovery goals. However, endurance exercise is also a major stimulus to remodel skeletal muscle, which results in the breaking down of old and/or damaged muscle proteins and the (re)building of new ones in their place. This remodelling during the hours to days after exercise provides the basis for training adaptations, such as the development of more powerful and/or fatigue-resistant muscles, and ultimately increased performance. Therefore, understanding how nutrition can enhance this remodelling process is fundamental for athletes to achieve their training and performance goals.
The remodelling of skeletal muscle is primarily regulated by the rate at which new muscle proteins are built (i.e. muscle protein synthesis; MPS). By providing the requisite amino acid building blocks, dietary protein is a prime regulator of MPS. This fundamental link between dietary protein intake and the stimulation of MPS is well-acknowledged within resistance-trained populations and is targeted as a strategy to enhance training adaptations such as muscle growth. However, we propose that beyond just building bigger muscles, strategies to enhance MPS through periodized protein intake should be essential for the endurance-trained athlete as well.
General guidelines suggest that the daily protein requirement for endurance athletes may be as much as ~100% greater than the current recommended daily allowance of 0.8g/kg/d for sedentary individuals; most endurance athletes meet this increased requirement provided they eat according to their energy needs. However, beyond just achieving a minimum daily protein intake, contemporary research demonstrates that individual meal protein amount, type, and timing can all influence the magnitude and duration for which MPS is elevated after exercise.
Of critical importance to maximizing post-exercise MPS is the consumption of dietary protein immediately after endurance exercise. Beyond this immediate post-exercise window, the regular consumption of protein-containing meals every 3-4h (up to and including before sleep) helps sustain MPS throughout an entire day. Each of these meals (including the post-exercise period) should target a modest protein intake of 20-25g (or the equivalent of ~0.25g/kg) as this amount has been shown to maximally stimulate MPS yet minimize the irreversible loss of dietary amino acids as a source of fuel, the latter of which occurs with larger protein intakes and ultimately represents an inefficient use of this macronutrient. However, proteins that are rapidly digested and naturally enriched in essential amino acids (especially leucine, a key substrate for and stimulator of MPS) are particularly effective at enhancing post-exercise MPS.
While additional research is required to elucidate what effect an optimal protein ingestion strategy has on functional outcomes in endurance athletes, we argue that the individual who is able to maximize skeletal muscle remodelling (and hence MPS) will be better positioned to recovery from and adapt to the stress of training in order to perform at their best during competition. This ultimately positions dietary protein as a vital, and perhaps underappreciated, component of the endurance athlete’s nutritional armour.
Moore, D.R., Camera, D.M., Areta, J.L., and Hawley, J.A. 2014. Beyond muscle hypertrophy: why dietary protein is important for endurance athletes. Appl. Physiol. Nutr. Metab. 39:987-997. doi: dx.doi.org/10.1139/apnm-2013-0591
If you intend citing any information in this article, please consult the original article and cite that source. This summary was written for the Canadian Society for Exercise Physiology and it has been reviewed by the CSEP Knowledge Translation Committee.