Nutrient Timing & The Post Exercise Window: A Scientific Review

This literature review aims to recognise nutrient-nutrient interactions and its possible implications in modulating protein synthesis, and hypertrophic responses to intensive type training. The two main nutrients that require specific focus are protein and carbohydrates, as they are generally found in high quantities in meals following post exercise that have been known to initiate the adaptive responses to facilitate muscular repair (Kerstick et al, 2008). This is known as the post exercise window which is associated with nutrient timing where studies have inconclusively demonstrated that changes in body composition, specifically increases in fat free mass can significantly change when combined with hypertrophic and strength training (Ivy and Portman, 2004). Studies have suggested that training in this manner increases glycolysis and protein degradation, resulting in muscular damage. In which the ingested nutrients can respond to in a super-compensatory manner to facilitate adaptation causing improvements in body composition and performance. Researchers have coined this period as the ‘anabolic window of opportunity’ where an expiratory time exists in which to ingest nutrients to fully facilitate adaptation (Candow and Chilibeck, 2004; Hulmi et al, 2010; Kukuljan et al, 2009).
It has been recognised that approximately 80% of ATP generation is derived from glycolysis which is the main method in producing energy during resistance training (Lambert and Flynn, 2002). Evidential findings have suggested that one set at 80% 1 repetition max of an isolation triceps exercise to failure can decrease glycogen stores by 12%, while three sets can decrease stores by 24% in type II muscle fibres, as opposed to type I (MacDougall et al, 1999; Robergs et al, 1991). Moreover, exercising the same muscle groups repeatedly at moderate loads for 6-9 sets has been reported to decrease glycogen stores by 36-39% (Robergs et al, 1991; Roy and Tarnopolsky, 1998). These findings should be considered for strength and power athletes during maximal testing due to the whole body working at maximal capacity, in comparison to an isolated muscle group. In some instances, several attempts could be made at maximal loads/sprints/throws etc throughout the course of a competition or training session. This could highlight weaknesses in an athlete’s training or competition if performing in a slight glycogen depleted state as glycogen mediates intracellular signalling through mTOR, mitogen activated protein kinase, and calcium dependant pathways, therefore mediating adaptation (Goodman et al, 2011). Coincidently, decreased glycogen stores causes the attenuation of S6K1 resulting in impaired muscle hypertrophy through the down regulation of mRNA translation for the genes responsible for this action (Churchley et al, 2007; Dennis et al, 2001).
The second aspect of nutrient timing is to focus on protein ingestion in an attempt to attenuate protein degradation and increase protein synthesis from resistance training (Aragon and Schoenfeld, 2013). Since muscle hypertrophy is the causation of increase myofibrillar protein synthesis compared to proteolysis, decreased muscle protein breakdown is favourable to induce a hypertrophic response (Aragon and Schonfeld, 2013). It has been reported that protein degradation is slightly elevated immediately post training, however a more potent response occurs shortly after (Biolo et al, 1997; Kumar et al, 2009). During fasted state resistance training, increased protein turnover caused protein breakdown to be elevated at 195 minutes post, whilst continuing to rise by approximately 50% at the three hour mark, and remained elevated 24 hours later (Pitkanen et al, 2003; Kumar et al, 2009). These findings can suggest that the timing of post resistance exercise nutrients may be beneficial in attenuating proteolysis to initiate muscle hypertrophy and recovery through providing sufficient amino acids to provide a state of positive protein balance. The ingestion of 45g of whey protein isolate which contains approximately 4g of leucine has been shown to acutely cause hyperaminoacidemia that peaked at approximately 50 minutes post ingestion, and remained elevated for a further two hours (Power et al, 2009). This coincides with findings of proteolysis post resistance training, therefore providing a practical usage for protein ingestion. Hypothesise could be created suggesting that consuming protein or selected amino acids immediately post training could meet the bodies demands by 50 minutes, and continue to induce muscle hypertrophy for a further two hours prior to consuming another protein rich meal.
It has been well established that resistance training increases proteolysis, this acute stimulus causes a twofold increase in muscle breakdown which initiates protein synthesis at an elevated rate (Kumar et al, 2009). In order to facilitate adaptation to the stimulus, amino acid ingestion resulting in hyperaminoacidemia can magnify the protein synthesis response (Biolo et al, 1997; Tipton et al, 1999). Investigative studies have demonstrated this; however findings are not always conclusive. This may be due to the individual response observed from training status, as untrained individuals may produce a greater muscle hypertrophic effect (Adams and Bamman, 2012). Therefore, training status must be taken into account when examining the effects of amino acid ingestion and its ability to improve performance on athletes with a greater than sedentary training status.
Aragon and Schoenfeld (2013) suggest that the reasoning behind such elevated rates of protein synthesis post resistance training is due to the majority of acute studies being performed in a fasted state. Therefore increased rates of proteolysis are observed during the training that provides greater anabolic response post training. However, this does not reflect real world scenarios (unless intermittent fasting) where individuals with the goal of increasing muscle hypertrophy often consume a meal in the time leading up to training. It has been reported that the anabolic effect of a meal can last for approximately 5-6 hours, depending on the rate of postprandial protein metabolism (Layman, 2004), however the increased rate of protein synthesis from only amino acid ingestion lasts for three hours (Bohe et al, 2001). Therefore generalised recommendations can be made when warranting the anabolic post exercise window with regard to nutrient timing. It should also be noted that individual nutritional practices can affect the anabolic response of a particular area of interested with regard to protein synthesis.

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