Personal

The current scientific literature is deficient in data to construct firm nutritional recommendations for sprint and/or power athletes. This notion is further complicated by the fact that the individual goal of a particular sprint athlete will certainly vary from that of a power athlete. Furthermore, even within a group of power athletes there will be considerable variation in individual goals such that each goal may diverge from that of another based on the type of exercises performed during training. For example, a competitive power lifter commonly performs such lifts as barbell squat, bench press and deadlifts, which are performed at maximal loads and require maxi-mal force development for very few repetitions. On the other hand, an Olympic-style weight-lifter com-monly performs exercises requiring a slightly greater skill component, such as snatch, clean, and jerk-style lifts, and which are associated with high muscular power (velocity × mass) production. These funda-mental differences in training styles and goals may require nutritional recommendations that are tai-lored towards each athlete.

Protein requirements

A common characteristic for sprint athletes and power- and weight-lifters is that they all use resist-ance training as either their primary mode of train-ing or as an adjunct to other forms of traintrain-ing. Thus, it is reasonable to extrapolate data from the resistance training literature to make broad recommendations on protein requirements. Certainly, widespread resistance training dogma would suggest that to build

‘serious’ muscle it is imperative to construct one’s dietary macronutrient intake around protein and this notion does have support in the scientific literature (Tarnopolsky et al., 1988, 1992; Lemon et al., 1992). It would seem, however, that any argument for protein requirements for power athletes, especially those residing in the western hemisphere, would be absurd as most are currently consuming well above the recommended levels, nominally 0.8–0.9 g/kg/day (Phillips, 2004; Institute of Medicine, 2005). Contrary to the view of excessive protein requirements for ath-letes, another opinion suggests that if the athlete is currently engaged in a strength-training programme,

it may be that protein requirements, as measured by nitrogen balance, are not elevated but actually reduced to some extent (Phillips, 2006; Phillips et al., 2007). This notion is based on the fact that resistance exercise is fundamentally anabolic (Phillips et al., 1997), and a reasonable hypotheses is that resistance training may actually shift the utilisation of dietary amino acids derived from muscle protein degrada-tion toward MPS. Thus, a greater propordegrada-tion of amino acids, in both the fasted and fed states, are being retained in the largest protein pool, skeletal muscle. Furthermore, it is also important to note that chronic consumption of a high-protein diet (>1.6–1.8 g/kg/day) may actually force the body to adapt and increase the capacity of amino acid catabo-lism, since excess nitrogen is fundamentally toxic in biological systems, which in turn forces the athlete to continue chronic consumption of high protein loads to avoid excessive amino acid catabolism of small amino acid loads. The current daily recommendation for meeting protein requirements for strength train-ing athletes is 1.6–1.7 g protein/kg/day (e.g. about 128–136 g protein for an 80-kg individual) (Rodriguez et al., 2009), approximately twice that of a sedentary individual (0.8 g protein/kg/day). It is clear that this amount of protein can be easily obtained through normal dietary habits and likely does not require supplemental protein sources. However, it is becom-ing increasbecom-ingly evident that one aspect of an athlete’s diet that may require special attention is the type/

amount of protein consumed and the timing of pro-tein ingestion relative to exercise. Detailed informa-tion on these topics can also be found in Chapter 10.

A well-recognised performance advantage for an athlete, where power-to-weight ratio plays an impor-tant role, is the maintenance of a high lean body mass to fat mass ratio, which would be a much sought after goal for 100, 200 and 400 m sprinters. In addition, a high lean body mass to fat mass ratio is especially rel-evant for athletes involved in power lifting and/or Olympic weight-lifting as their competitions are divided by weight classes. Indeed, common acute weight loss strategy among athletes is to restrict food/

fluid intake coupled with dehydration strategies prior to competing. It has been suggested that sport-ing events involvsport-ing high power outputs and absolute strength are less affected by acute weight loss (Fogelholm, 1994) or dehydration (Cheuvront et al., 2006). In addition, many power and sprint athletes

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follow a low-residue diet in the last few days leading up to competition to reduce the volume of the faecal contents of the bowel and thereby produce further weight loss (around 300–800 g) (for further informa-tion on low-residue diets, see Chapter 20). However, during training performance may be compromised when commencing certain training sessions with low glycogen stores and/or in a dehydrated state. It is worth highlighting that high intakes of dietary pro-tein do appear to confer certain advantages during periods of energy restriction (Mettler et al., 2010).

A global finding among studies using higher protein diets is that not only do they result in a greater loss of absolute body weight but a greater amount of that weight loss is accounted for by fat mass, albeit in obese individuals (Parker et al., 2002; Layman et al., 2003, 2005; Noakes et al., 2005). Further, it appears that low-fat dairy is also effective in decreasing fat mass, especially in young women who are relatively low dairy consumers (Josse et al., 2009), which may be related to the interplay between calcium and vita-min D on adipocyte metabolism and inhibition of lipid accretion (Zemel, 2004; Teegarden, 2005).

Effects of protein ingestion on muscle protein synthesis

Pioneering work by Rennie and colleagues demon-strated that feeding a meal doubled the rate at which amino acids are incorporated into muscle proteins (Rennie et al., 1982) and this effect on MPS could be achieved exclusively by the protein component (i.e. amino acids) of food (Bennet et al., 1989).

Protein consumption primarily affects MPS through feeding-induced hyperaminoacidaemia, which in turn provides a favourable gradient for inward amino acid transport into the intracellular free amino acid pool within skeletal muscle (Biolo et al., 1997).

Interestingly after about 2 hours of constant exposure to mixed amino acids (by infusion), rates of MPS returned to basal levels during the 6-hour infusion (Bohe et al., 2001). Similar effects on rates of myofi-brillar and sarcoplasmic protein synthesis has been established after bolus ingestion of 48 g of whey protein (Atherton et al., 2010). It has been suggested that the likely fate of the excess amino acids (those supplied over and above the requirements) is deami-nation whereby their carbon skeletons are used for fuel or stored as fat (Bohe et al., 2001).

Addition of other macronutrients to protein

It is well established that consuming a bolus dose of protein alone after resistance exercise has a potent stimulatory effect on exercise-mediated rates of MPS (Moore et al., 2009b; Tang et al., 2009; Burd et al., 2010c). A common and relevant question is one related to the value of adding other components of a meal to a protein-containing drink. The primary physiological regulator of insulin secretion is blood glucose concentration and co-ingestion of carbohy-drates with dietary protein induces a rapid increase in blood glucose compared with dietary protein alone. There is a great deal of controversy surround-ing the role of insulin in regulatsurround-ing muscle anabolism (Volpi et al., 1996; Fujita & Volpi, 2006; Fujita et al., 2006; Rasmussen et al., 2006; Phillips, 2008; Glynn et al., 2010). We and others have proposed that insulin is necessary, but is merely permissive not stimulatory for rates of MPS (Svanberg et al., 1997; Bohe et al., 2003; Cuthbertson et al., 2005; Greenhaff et al., 2008;

Wilkes et al., 2009). Specifically, only a small amount (∼5 μU/ml) of insulin is necessary to allow a full anabolic response to occur, but any further stimula-tion of MPS is driven by extracellular amino acid availability. However, muscle NPB is determined by two variables, MPS and MPB, so carbohydrate con-sumption and the concomitant increase in circulat-ing insulin may have a significant impact on muscle NPB as it appears that hyperinsulinaemia has a potent inhibitory effect on MPB (Pozefsky et al., 1969; Gelfand & Barrett, 1987; Fryburg et al., 1990).

Therefore, the question that arises is whether co-ingesting carbohydrate with protein during post-exercise recovery can optimise muscle NPB.

Koopman et al. (2007) demonstrated that follow-ing a full body resistance exercise routine, consumfollow-ing repeated feedings of small aliquots of protein and carbohydrate did not further enhance whole-body protein synthesis or mixed MPS as compared to repeated feedings of protein alone. Furthermore, the co-ingestion of carbohydrate with protein did not further inhibit whole-body protein breakdown. More recently, it was reported that the addition of 90 g or 30 g of carbohydrate to a 20-g essential amino acid drink conferred the same effect on LPS and leg pro-tein breakdown (LPB) (Glynn et al., 2010). However, the researchers failed to include a group which

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consumed only essential amino acids, precluding their ability to determine the effects of amino acids alone.

We have recently sought to fill this research gap by feeding 25 g of whey protein or 25 g of whey protein plus an additional 50 g of carbohydrate after resistance exercise (Staples et al., 2010). It was demonstrated that consumption of a maximal stimulating dose of whey protein plus carbohydrate had no further stimulatory and/or inhibitory effect on mixed MPS or MPB compared with 25 g of whey protein alone. This is in line with a recent observations that carbohydrate ingestion even beyond a moderate hyperinsulinaemia (∼30 μU/ml) has no further effect on LPB (Greenhaff et al., 2008). Therefore, the addition of carbohydrates has no further effect, provided a maximal 25-g dose of whey protein is consumed (Moore et al., 2009b), on mixed MPS or MPB. However, it remains to be seen if carbohydrates are beneficial when a less than optimal dose (<20 g) of high-quality protein is consumed during post-exercise recovery. It is worth highlighting, however, that high-volume leg resistance exercise has been demonstrated to induce an approximately 26% decrease in muscle glycogen (Tesch et al., 1986) and other workers have demonstrated a similar effect on muscle glycogen in bicep muscles after three sets, but not one set, of arm curl exercise (MacDougall et al., 1999). This notion, coupled with the fact that carbohydrate feeding can restore muscle glycogen content after resistance exercise, has important performance implications for sprint and power-training athletes (Pascoe et al., 1993).

A relatively under-studied area is the addition of fat to a protein meal and the subsequent effects on rates of MPS. Indeed, evidence points to a thesis that a large transient ‘spike’ in hyperaminoacidaemia immediately after exercise is important in maximis-ing exercise-induced rates of MPS. Therefore, it would seem that slowing the absorption of protein, by adding fat, may impact the anabolic response.

Indeed, Dangin et al. (2001, 2003) provide some support for the concept that consuming other com-ponents of a meal (i.e. carbohydrate and fat) has an impact on digestion kinetics and the associated ami-noacidaemia. Specifically, it was reported that con-suming about 30 g of whey protein alone increased blood leucine concentrations about fourfold (Dangin et al., 2001), whereas in another cohort of young men

consuming about 34 g of whey in combination with about 50 g carbohydrate and about 9 g fat increased blood leucine about threefold (Dangin et al., 2003).

Clearly, more research is needed to draw any definite conclusions as to how mixed meal feeding affects exercise-mediated rates of MPS.

Dietary carbohydrate recommendations Carbohydrate intake to meet training and recovery requirements will largely depend on the number of hours training per day, with current carbohydrate recommendations being in the region of 3–7 g/kg/

day when training for 1–2 hours daily (Rodriguez et al., 2009). It has been reported that both interval sprint sessions and an acute bout of resistance exer-cise can deplete muscle glycogen by about 25–40%

(Tesch et al., 1986; Pascoe et al., 1993; MacDougall et al., 1999), and the extent of depletion would largely be dependent on the external work (calculated as the product of repetitions and load) performed during the exercise bout. It has been suggested that female strength athletes may require slightly less carbohy-drate than their male counterparts (Volek et al., 2006). This thesis was based on the notion that if a female consumed her daily recommended amount of carbohydrates, this amount could be too large a proportion of her total caloric needs (Volek et al., 2006). Regardless, it remains to be established if habitually high carbohydrate intakes are beneficial for strength training athletes. Furthermore, since total energy intake is a function of total macronutri-ent intake, it may be advisable that athletes consume carbohydrates at critically important times (i.e.

immediately after exercise) and subsequently adjust daily carbohydrate intake on total energy need.

Is there any evidence to suggest that performing resistance exercise in the glycogen-depleted state has detrimental effects on muscular performance and subsequent anabolism? The effects of low glycogen levels on power and strength production during exercise are equivocal. Some studies indicate that gly-cogen depletion reduces isometric strength, but not isokinetic strength performance (reviewed in Leveritt et al., 1999). Recently, Creer et al. (2005) sought to examine the effects of commencing an acute bout of resistance exercise in the glycogen-depleted state. It was found that some of the intramuscular signalling proteins (i.e. Erk1/2, P90RSK, mTOR) shown to be involved in ‘turning on’ MPS were not affected by low

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muscle glycogen concentrations; however, an upstream signalling protein, Akt, was only significantly phos-phorylated post exercise when glycogen concentra-tions were not compromised. However, Akt has been reported to be related more to insulin availability rather than directly connected to anabolism (Greenhaff et al., 2008). Therefore, further research is needed to determine the effects of performing resist-ance exercise with low muscle glycogen concentra-tions utilising kinetic measurements (i.e. stable isotope methodology).

11.3 Power-type exercises and muscle