// Strength nutrition - The pathway of adaptation
by Dr Stephen Bird
Research demonstrates that nutritional supplementation strategies
(termed ‘strength nutrition’) enhance the muscular adaptations to
resistance training by shifting the anabolic/catabolic profile toward a
profile more favourable for muscle growth(1-3) with nutrient intake
suggested to be essential for hypertrophy to occur(4). This article
addresses nutritional supplementation strategies as they relate to
strength and power athletes, specifically focusing on key nutrition
concepts related to strength nutrition, and overview mechanisms that
mediate acute physiological responses to resistance exercise through
the ‘pathway of adaptation’ model.
STRENGTH NUTRITION – KEY NUTRITIONAL CONCEPTS
From a practical standpoint, three important concepts need to be considered when determining the effectiveness of strength nutrition, these being:
1. Nutrient quantity (i.e., how much should be consumed)
2. Nutrient quality (i.e., what kind of nutrients should be consumed)
3. Nutrient timing (i.e., when nutrient intake should occur).
Recently, the practical application of strength nutrition concepts, including liquid carbohydrate (CHO), protein (PRO), both whole foods (milk) and specific PRO fractions (whey and casein), amino acid constituents (essential amino acids [EAA] and branch chain amino acids [BCAA]) and mixed nutrient ingestion (PRO plus CHO) has gained popularity. However, an expansive review by Professor Hawley and colleagues(5) titled Innovations in athletic preparation: Role of substrate availability to modify training adaptation and performance, highlights the central question related to strength nutrition, (i.e., whether acute, transient changes in skeletal muscle protein turnover induced by nutrient manipulation translates into greater gains in lean mass, muscle hypertrophy, and/or exercise performance?).
In order to address this central question, the ‘pathway of adaptation’ model can be brought into play.
PATHWAY OF ADAPTATION MODEL
The pathway of adaptation model as proposed by Professor Volek(6) from the University of Connecticut, provides practical representation of applied nutritional concepts that mediate acute physiological responses to resistance exercise, and the chronic muscular adaptations to training. This model defines the sequence of events deemed responsible for exercise-induced muscle growth and increased strength expression following nutrient ingestion. The interactions of four key steps in the acute response appear to be critical, as this represents the ‘anabolic window’ where strength nutrition maximises the training response (see Diagram 1).
There is growing evidence suggesting a link between key nutrients (CHO, PRO/ AA) and the initiation of key signals responsible for protein synthesis, muscle glycogen resynthesis and attenuation of muscle breakdown following resistance exercise. While much of the research has centred on pre and/or post ingestion, ingestion during the exercise bout is an important consideration for strength and power athletes as this represents a specific time period where nutrient status becomes compromised. CHO ingestion during and/or following resistance exercise has been examined based on two primary outcomes, namely (i) glycogen resynthesis and; (ii) hormonal modification. First, CHO ingestion may reduce muscle glycogen loss associated with an acute bout of resistance exercise, and this may be of importance for athletes involved in multiple daily training bouts(7). Secondly, CHO ingestion may shift the exercise-induced hormonal milieu towards a profile more favourable for anabolism(8). Specifically, it is the response of insulin and cortisol that has received much attention(9) as these hormones have major regulatory roles in CHO metabolism and protein turnover. With regard to PRO/AA supplementation, PRO ingestion before and/or after resistance exercise has an additive effect on protein synthesis(10). Additionally, some research suggests that the addition of PRO/AA to CHO may enhance glycogen storage(11). Amino acids and BCAA (leucine, isoleucine and valine in particular), not only provide substrate for protein synthesis but also result in alteration of enzymatic activity responsible for switching on the molecular machinery that manufactures muscle proteins. Of the BCAAs, leucine seems to be the most potent with regard to these effects(12).
AN INTEGRAL COMPONENT
The apparent additive effects of resistance exercise and nutrient availability has led to more practical approaches for the use of strength nutrition. Factors such as nutrient quantity; nutrient quality; and nutrient timing are key concepts that impact upon the effectiveness of strength nutrition to enhance training responses for strength and power athletes. Strength nutrition appears to be an integral component that can favourably influence the key steps in the pathway of adaptation model, and may further promote adaptations to training. Collectively, research supports the notion that:
1. The magnitude and duration of changes in nutrient status determine the anabolic effects on skeletal muscle
2. Inclusion of PRO with different digestive properties (whey and casein) produces a sustained response over the postprandial period
3. The coordinated function of metabolically connected nutrients (mixed nutrient ingestion) is pivotal in enhancing hormonal responses and enhancing muscular performance.
However, further research is required to examine the influence of other amino acid derivatives, such as creatine, β-Alanine, and β-Hydroxy-β-methylbutyrate (HMB), as their inclusion in strength nutrition protocols may enhance responses in the pathway of adaptation model.
Dr Stephen Bird, PhD CSCS AEP
Stephen is the department head for strength and conditioning for the Indonesian National Olympic Committee for the 2008 Beijing Olympic Games, a position he holds through the School of Human Movement Studies, Charles Sturt University. A former recipient of the AAESS Medal and NSCA Graduate Research Award in the USA, Stephen is a consultant to MUSASHI Performance Nutrition. For more information, visit www.musashi.com.au or e-mail firstname.lastname@example.org
NETWORK •WINTER 2008 • PP57-59