Nutritional strategies to maximise recovery following strenuous exercise

Race walkers in competition
Author:  Greg Cox, AIS Senior Sports Dietitian
Issue: Volume 28 Number 4

For an athlete to maximise each and every training session it is important to consider issues that allow an athlete to optimise their recovery between exercise bouts. This is particularly important for athletes who are expected to training more than once a day. Although cold water immersion, contrast water immersion, stretching, compression, and massage are all important components that may assist an athlete’s recovery after strenuous exercise, what an athlete eats and drinks following exercise will have a significant effect on how the athlete presents for their next training session.

To optimise recovery from a nutritional perspective three important interrelated issues should be considered. These include:

  • refuelling of muscle and liver glycogen stores
  • replacement of fluid and electrolytes lost in sweat
  • regeneration and repair following the catabolic stress and damage caused by exercise, including boosting immune function post-exercise.

Nutritional strategies to optimise post–exercise recovery

This article will detail the key issues that relate to optimising nutritional recovery strategies following strenuous exercise. It is worth noting that many of the studies cited in these articles are purely focused on enhancing post-exercise nutritional status, which for some athletes may not align itself with other nutritional issues they are juggling — for instance body weight reduction. In mentioning this, guidelines developed as a direct result of these studies may need to be modified to accommodate other nutritional goals.

Bottom line — don’t apply these guidelines word for word without considering other nutritional issues that your athletes’ face.

Post-exercise refuelling

The single most important factor driving post-exercise muscle glycogen resynthesis is the amount of carbohydrate consumed following exercise. To date, two studies have investigated the relationship between the amount of carbohydrate consumed following exercise and muscle glycogen refuelling over a 24-hour recovery period. These studies have shaped current daily carbohydrate intake recommendations for athletes and show a glycogen storage threshold at a daily carbohydrate intake of ~7-10 g per kg body mass (Costill et al. 1981; Burke et al. 1995).

Increasing carbohydrate intake above current recommendations may be useful in the case of sports where muscle damage occurs (for example, following eccentric exercise or contact injuries), as damage to muscle is likely to impair the rate of post-exercise glycogen resynthesis. Costill et al. (1991) reported that low rates of glycogen restoration in damaged muscles might be partially overcome by increased amounts of carbohydrate during the first 24 hours of recovery. This strategy may be particularly important for contact, team sport athletes when there is minimum time between exercise bouts.

Immediate post-exercise refuelling

A separate guideline is required to cover the carbohydrate needs of the early phase (0–4 hours) of recovery which can be addressed in a well planned, directed nutritional recovery system. Numerous studies demonstrate that the threshold for early glycogen recovery is reached by feeding carbohydrate at a rate of 1.2g/kg/h(van Loon et al. 2000; Jentjens et al. 2001).

The highest rates of muscle glycogen storage occur during the first hour after exercise (Ivy et al. 1988 ). Failure to consume carbohydrate in the immediate phase of post-exercise recovery leads to very low rates of glycogen restoration. Early feeding of carbohydrate is particularly important when there is limited time between exercise sessions, but is of less importance when there is a longer recovery time (12 or more hours). Overall it appears that when the interval between exercise sessions is short, the athlete should maximise the effective recovery time by consuming carbohydrate rich foods and fluids as soon as possible.

Post-exercise rehydration

In normal healthy people, the daily replacement of fluid losses and maintenance of fluid balance are well regulated by thirst and urine losses. However, under conditions of stress (for example, exercise, environmental heat and cold, altitude) thirst may not be a sufficient stimulus for maintaining optimal hydration levels (Greenleaf 1992).

Studies of voluntary fluid intake patterns across a range of sports show that athletes typically replace only 30–70 per cent of the sweat losses incurred during exercise (Noakes et al. 1998; Broad et al. 1996). As a result, most athletes can expect to finish training or competition sessions with a mild to moderate level of dehydration. Interestingly, studies have shown that after exercise, people fail to drink sufficient volumes of fluid to restore fluid balance, even when drinks are made freely available and there is little else to distract them from drinking adequately (Carter and Gisolfi 1989). In a real life post-game scenario, when athletes have numerous commitments — cool-down, post-game recovery strategies, media, post-game debrief and function — a scheduled plan of fluid intake is paramount.

How much is enough?

To fully replace fluid lost during exercise, research suggests that athletes need to consume 150 per cent of their fluid losses following exercise (Shireffs et al. 1996). It is likely more fluid is required if low sodium choices such as water are consumed as water results in a dilution of body fluids, resulting in increased urine loss.

Sodium is important

Sodium is the principle electrolyte lost in sweat, and during prolonged bouts of heavy sweating, particularly in individuals with high sodium sweat content, a substantial loss of body sodium can occur during exercise.

Although Western dietary patterns are generally considered to be excessive in salt, athletes who lose such large amounts of sodium during exercise may need to undertake special strategies to actively replace sodium losses during and after exercise (Bergeron et al. 2003). Even if the loss of sodium during an exercise session is not substantial and will be eventually replaced by dietary means, there are good reasons for including sodium in recovery fluids and snacks.

Maughan and Leiper (1995) dehydrated subjects by 2 per cent body mass via exercise in a hot environment, then observed them for six hours of recovery after they had consumed 150 per cent of their fluid losses with test drinks providing varying levels of sodium. The research showed greater urine losses when subjects consumed the low sodium drinks (2 mmol/L and 26 mmol/L sodium) compared with higher sodium drinks (52 and 100 mmol/L sodium).

Subjects were found to be in fluid balance by the end of the recovery period when they consumed the two higher sodium beverages, but were still in net negative fluid balance on the lower sodium trials, despite an intake of fluid that was 1.5 times their estimated sweat losses. Overall retention of the ingested fluid was related to the sodium content, however there was no difference in net fluid balance between the two higher sodium fluids.

Given sports drinks typically contain 10–25 mmol/L, additional sodium may need be consumed in order to optimise post-exercise fluid retention. A simple solution you might think is to add additional sodium to the post-exercise fluids provided to athletes. Given that sports drinks have been designed to match a taste profile that optimises fluid intake, offering sodium-containing foods post-exercise may offer a more practical solution. Studies by Maughan et al. (1996) and Ray et al. (1998) have shown that the intake of salt via everyday food choices enhances the retention of fluid consumed to rehydrate after exercise-induced dehydration.

Does protein enhance glycogen refuelling?

On the available evidence it seems that the presence of other macronutrients with carbohydrate immediately following exercise has little influence on muscle glycogen synthesis when total carbohydrate intake is consumed at a rate of 1.2g/kg/h as outlined above. However, when the athlete’s energy intake or food availability does not allow carbohydrate to be consumed at this level, the presence of protein in post-exercise meals and snacks may enhance overall glycogen recovery (Ivy et al. 2002). Of course, protein plays an important role in recovery meals to enhance net protein balance, tissue repair and adaptations involving synthesis of new proteins.

Take home message: for a weight conscious athlete, including a source of protein post-exercise in addition to some carbohydrate may assist muscle glycogen refuelling.

Where to from here?

Now you have part of the necessary technical information to start devising the basis of your post-exercise food and fluid choices, I will tackle post-exercise regeneration and provide some practical suggestions for coaches and athletes striving to optimise post-exercise nutritional strategies.

In the first part of this article I outlined issues relating to post-exercise refuelling and rehydration.  Many athletes and coaches are familiar with these facets of recovery and have strategies in place to ensure optimal recovery.  The area that has attracted significant attention more recently relates to recovery nutritional strategies that facilitate regeneration and repair following the catabolic stress and damage caused by exercise, including boosting immune function and regenerating muscle mass post-exercise. I will focus solely on issues that surround regenerating muscle mass post-exercise as issues relating to immune function for athletes has been discussed in an earlier Sports Coach article - Boosting Immune function in athletes: where should you spend your time and money?' (2005, 28[2]:14-16).

It is worth reiterating that studies cited in this article are purely focused on enhancing post-exercise nutritional status, which for some athletes may not align itself with other nutritional issues they are juggling – for instance body weight reduction.  In mentioning this, guidelines developed as a direct result of these studies may need to be modified to accommodate other nutritional goals.

Bottom line – do not apply these guidelines word for word without considering other nutritional issues that your athletes face.

Only recently have methods been developed and used that enable us to measure protein metabolism particularly muscle protein metabolism, in vivo in humans. Most of the information that can be utilised to develop a post-training/competition nutritional strategy regarding protein and amino acid intake has come from studies conducted only over the last ten to 15 years.  So, it is likely that guidelines will change as we learn more about this very complex area of recovery.

Effects of exercise on muscle protein metabolism

Acute resistance exercise (weight training) has been shown to stimulate muscle protein synthesis and breakdown (Biolo et al. 1995: Chesley et al. 1992: Phillips et al. 1997). Interestingly, in the absence of nutrient intake, muscle protein breakdown outweighs muscle protein synthesis leaving the muscle in negative balance. In other words, resistance exercise without food intake does not stimulate an anabolic state in the muscle.

To date, there are no studies on the impact of chronic endurance training on muscle protein metabolism. However, endurance training increases activity and amount of mitochondrial enzymes and the size and amount of muscle mitochondria (Neufer 1989), suggesting that muscle protein metabolism, at least for some proteins, must be positively influenced by endurance training.

Influence of post-exercise protein intake on protein balance

Amino acid availability is critical to the control of muscle protein metabolism. Thus, a meal or a supplement containing protein or amino acids consumed after exercise will influence muscle protein metabolism.  At rest, elevated blood amino acid levels, from ingestion of amino acids (Tipton et al. 1999) stimulates muscle protein synthesis and results in net muscle protein synthesis (Biolo et al. 1997; Tipton et al. 1999).   To take this one step further, ingesting amino acids post resistance training results in positive protein balance in the muscle.  So eating post-resistance training is as important as the resistance training itself!

Influence of post-exercise carbohydrate intake on protein balance

Any effect of consuming carbohydrate on net muscle protein balance is primarily due to the resulting elevation of hormones, namely insulin. Carbohydrate-containing meals and snacks cause insulin to be released into the body.  Insulin has been shown to reduce muscle protein breakdown post-exercise, resulting in improved net muscle protein balance.

Taken together, the decrease in muscle protein breakdown due to the release of insulin from a carbohydrate meal or snack and the increase in muscle protein synthesis due to the ingestion of amino acids is likely to provide an optimal response on muscle protein balance post-exercise.

How much protein is needed?

The amount of essential amino acids necessary to stimulate muscle protein synthesis appears to be relatively small. Ingestion of as little as six grams of essential amino acids, both with (Tipton et al. 2001) and without  carbohydrate (Borsheim et al. 2002), results in dramatic elevations in muscle protein synthesis leading to net muscle protein balance. So more may not be better!!

At this juncture, the minimum dose of essential amino acids necessary to stimulate net muscle protein synthesis and the amount necessary to stimulate the maximum response remain to be determined.  Despite clear evidence for ingesting amino acids following resistance training, the influence of amino acid ingestion on recovery following endurance training is currently unclear.

Are amino acid supplements better than food protein sources?

Free form amino acids from supplements are not the only protein form that has been shown to increase muscle protein synthesis post-exercise.  Studies have demonstrated that ingestion of both whey protein and casein following resistance exercise also results in net muscle protein synthesis (Tipton et al. 2004). On a whole body level, recent studies demonstrated that a response characterised by a prolonged amino acid appearance of lesser magnitude is superior to a response with greater magnitude, but more transient response (Boirie et al. 1997; Dangin et al. 2001).

Hence food forms of protein maybe provide an advantage over free form amino acids from supplements as individual amino acids from foods are released more slowly over a longer period of time.

Importance of timing nutrient intake post-exercise

The timing of nutrient ingestion has also been shown to influence muscle protein metabolism following exercise.  In a recent series of studies, subjects ingested six grams of essential amino acids plus 35 grams of carbohydrate at various time points in relation to a strength training session (Tipton et al. 2001; Rasmussen et al. 2000).  The carbohydrate/amino acid solution was ingested either immediately before exercise, immediately following exercise or one hour post-exercise. The response of net muscle protein balance was considerably greater when the solution was ingested immediately prior to exercise compared to either time point following exercise (see Figure 1 in related downloads).

Does alcohol effect post-exercise muscle balance?

One factor that must be considered in the context of muscle protein metabolism and muscle growth following exercise is alcohol consumption.  In Australia, binge drinking is common place following sporting events, particularly amongst male team sport athletes.  There have yet to be studies performed on humans in this area, however, there are studies in rats and in vitro studies that indicate an inhibitory effect of ethanol on protein synthesis (Lang et al. 2001).

Summary points for the coach and athlete

  • A carbohydrate/protein snack provides an excellent combination of nutrients to optimise post-exercise muscle protein balance. Examples of suitable snacks include:
    - yoghurt and cereal bar or banana
    - sports bar (such as PowerBar Performance Bar)
    - liquid meal supplement (such as PowerBar Protein Plus Powder)
    - cereal and milk
    - cheese or tuna sandwich.
  • Only a small amount of protein post-exercise is required to increase muscle protein synthesis.
  • For athletes aiming to increase muscle mass, consumption of a pre-exercise protein/carbohydrate snack appears more important than a post-exercise snack of similar nutritional composition.
  • In directing athletes to pre-exercise eating it’s important to consider the athletes’ tolerance to food prior to exercise.
  • It would seem that food forms that contain protein should be consumed 45 to 60 minutes prior to exercise to allow for digestion and absorption.
  • Real foods may provide a superior source of amino acids to facilitate muscular repair post-exercise as they are released slowly into the body.
  • Alcohol post-exercise is likely to impair muscle protein synthesis.

References

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