hydration guidelines for athletes, using vibration exercises, asthma drugs ergogenic?

Drinking guidelines under attack

Official advice to athletes to drink enough to replace fluid lost in sweat during endurance events is coming under increasing attack from scientists. Australian researchers have called on the American College of Sports Medicine (ACSM) and other official bodies to revise their current fluid replacement guidelines in the light of their recent finding that even quite large fluid losses don’t lead to dehydration or heat illness (1).

And in a hard-hitting leading article in the British Journal of Sports Medicine, the renowned exercise physiologist Professor Tim Noakes claims that the cases against ‘over-drinking’ was proven 20 years ago and that official advice has been influenced by the marketing needs of the sports drink industry (2).

The Australian researchers set out to measure core temperature in 10 participants in the 2004 Ironman Western Australia event (using a special telemetry system swallowed in a pill), and to relate this to the triathletes’ hydration status after the event.

They considered two alternative possibilities:

• That the progressive dehydration commonly experienced by Ironman triathletes (reflected in body weight reduction) would be linked with rises in core body temperature;
• That the athletes’ bodies would adequately regulate their own body temperature and that no relation would be found between finishing hydration status and core body temperature.

In fact, the second theory won out. While fluid losses led to an average fall in body mass of 2.3kg (about 3% of body weight), the athletes’ core body temperature averaged only a modest 1oC above normal resting temperature, while other measures of dehydration, including plasma levels of sodium and urine concentration, stayed within normal ranges.

‘From these data… we could find no evidence to suggest that a 3% reduction in body mass during an Ironman competition in moderate ambient conditions causes athletes to reach core body temperatures that would lead to heat stroke, as is currently implied by the ACSM hydration guidelines and that of others.’

ACSM guidelines advise endurance athletes to drink to replace the total amount of fluid lost in sweat and not to rely on thirst as a guide to their fluid needs. These guidelines have been roundly criticised by Professor Noakes as ‘linked to an extensive marketing campaign, directed by the sports drink industry’.
His view is not only that this ‘over-drinking’ is not necessary to maintain thermoregulation, but also that it puts people at risk of hyponatraemic encephalopathy – a life-threatening dilution of plasma sodium levels.

In a commentary on the new Australian findings, Professor Noakes writes: ‘This confirms that the body regulates its thermal response during prolonged exercise within a very safe range, independent of the extent of weight lost. Ironman triathletes can be assured that their brains will take care of their bodies during exercise, and that there is no need to follow industry favourable guidelines to drink to excess to ensure their safety.’

1. Br J Sports Med 2006;40:320-325
2. Br J Sports Med 2006;40:567-572

How vibration boosts resistance exercise

Muscle vibration may enhance the training effects of light-to-moderate resistance exercise, according to a new UK study.
Nine healthy men completed four sets of eight repetitions on a knee extension machine under the following conditions, separated by at least three days of recovery:

• Low contraction intensity (35% 1RM)
• High contraction intensity (70% 1RM)
• Low intensity with a superimposed low-frequency vibration-like stimulus from the machine;
• High intensity with the same vibration-like stimulus.

Previous research had shown that vibration can activate large amounts of musculature during a movement. And the researchers set out to test the theory that vibration applied during a single resistance-training session would lead to larger increases in strength than those induced by the same session without vibration.

Their main finding was that vibration during knee extension exercise improved the performance of the rectus femoris and vastus lateralis muscles, as demonstrated by increased dynamic muscle strength and power immediately afterwards. Muscle dynamic strength was increased by similar amounts after high-intensity exercise with and without vibration. But after low-intensity exercise, dynamic strength increased only with the addition of vibration.

‘It seems,’ observe the researchers, ‘that superimposing the vibration-like stimulus during low-intensity exercise simulates the response induced by higher-intensity exercise.’

This would be a great boon for people who are unable to take part in intense exercise programmes, such as the elderly. But meanwhile further studies are needed to find out more about precisely how vibration exerts these effects on muscle.

Med Sci Sports Exerc 2006; 38(7):1317-1328

Asthma drugs are not ergogenic

Inhaled ß2 agonist drugs used to treat asthma do not exert ergogenic effects and should be taken off the World Anti-Doping Agency (WADA) banned list. That’s the key message of a new German study set up to review the literature on the effects of these drugs in non-asthmatic competitive athletes and to assess their performance-enhancing effects.

The researchers found 20 high quality studies (randomised controlled trials) that addressed the effects of inhaled ß2 agonists on physical performance in athletes with documented normal resting lung function. Eighteen of these studies included endurance athletes, one looked at power athletes and one involved recreational subjects. In most of these studies, the drugs were inhaled 15-30 minutes before starting exercise.

Ergogenic effects were demonstrated in only three of these studies, but all of these had design problems, which make their results not completely reliable.

‘Altogether’, the researchers conclude, ‘inhaled ß2 agonists do not seem to affect physical performance in non-asthmatic competitive athletes. In addition, there is no evidence for anabolic effects of [these drugs].’

At present, athletes with chronic or exercise-induced asthma have to prove their illness to a medical committee of their ruling body and wait for the grant of a ‘therapeutic use exception’ (TUE) before they can start treatment.

The researchers comment: ‘Obviously, the administrative burden for acquiring permission to use inhaled ß2 agonists is substantial. The limited financial and human resources of the fight against doping may be better focused on substances and methods which have a proved performance enhancing effect and, therefore, a much larger potential to elicit unfair competition…’

Br J Sports Med 2006;40(Suppl 1):i43-i47

Protein does not improve endurance performance

Some recent research studies have suggested that the addition of small amounts of protein to carbohydrate drinks can increase endurance capacity compared to carbohydrate alone. But a new Canadian study on cyclists has found no benefit whatsoever. In the study, 10 trained male cyclists performed an 80km time trial on three separate occasions separated by seven days during which they consumed one of the following:

• 250mls of 6% carbohydrate solution every 15 minutes;
• As above, but with the addition of 2% protein;
• A sweetened placebo containing no carbohydrate or protein.

As expected, the time taken to complete the time trial was significantly lower when drinks containing carbohydrate and carbohydrate plus protein were taken – 135 minutes compared with 141 minutes for the placebo drink. However, there was no difference between the carbohydrate and carbohydrate plus protein drinks, suggesting that the protein had no additional endurance-enhancing effect.

The researchers speculate that some of the earlier studies showing a positive benefit for the addition of protein were flawed a) because the rate of carbohydrate ingestion administered was less than what is considered optimal for endurance performance and b) because the performance test used (exercise time to fatigue) does not mimic the way in which athletes typically compete – ie racing in which a fixed distance or set amount of work is performed as quickly as possible. They therefore conclude that ‘adding 2% protein to a 6% carbohydrate drink provides no additional performance benefit during a task that closely simulated the manner in which athletes typically compete’.

Med Sci Sports Exerc. 2006;38(8):1476-1483