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Study plays up skimmed milk sports hydration boost

By Neil Merrett , 30-Jul-2008

Skimmed milk may become an unlikely new secret weapon within an athlete's kit bag, with new research linking the product to a beneficial effect on preventing dehydration after a workout.

The Milk Development Council-funded study, appearing in the European Journal of Applied Physiology, backs similar research suggesting that skimmed milk is more effective at post exercise hydration then a commercially available carbohydrate-electrolyte drink.

Researchers at Loughborough University's School of Sport and Exercise Sciences, said that in trials of seven male subjects, consuming milk after exercising was found to ensure improved fluid balance to the energy drink.

Following post-exercise testing, the study found that subjects who had consumed skimmed milk had a positive fluid balance three hours after exercising, while those consuming electrolyte-fortified products were more negatively affected.

The team, led by Phillip Watson, added that while milk had been found in the study to improve fluid retention over the commercially available carbohydrate-electrolyte drink, Powerade, there were no differences in terms of the exercise capacity of respondents.

However, citing previous research, the study stressed that the link between the availability of carbohydrates and fatigue after prolonged exercise has been widely acknowledged.

"The progressive depletion of the muscle's limited supply of glycogen and reductions in circulating blood glucose concentrations have both been linked to a loss of performance in endurance-type events," said the researchers.

As part of the study's conclusions, replacing electrolyte loss was highlighted an essential factor in restoring water balance in the human body, to which it was claimed that milk is well suited.

"Compared to many other fluid replacement options available to the sports performer, milk contains relatively large quantities of electrolytes," stated the researchers.

Sports drink multi-tasking

While agreeing that being fully hydrated before, during and after exercise was essential to ensuring a strong performance, David Rogerson, a sports nutritionist at Sheffield Hallam University, said other factors often needed to be considered in athlete performance.

Commenting independently on the research, Rogerson added that there were many different types of sports drinks on the market for various purposes, from products to be consumed before training or competition, to formulations designed for use during or after exercise.

He claimed that a number of factors needed to be considered in terms of providing sports benefits.

"[These benefits include] the availability of energy for immediate performance and energy replenishment post exercise, and proteins and amino acids for muscle repair and nerve impulse conduction," Rogerson told DairyReporter.com.

"Sports drinks will often contain additional vitamins, minerals, antioxidants that will assist energy production, help prevent or limit oxidative damage from performance and facilitate the recovery processes as well as assist hydration. "

While sport drinks makers were continuing to research product innovation in a bid to produce more sophisticated energy products, Rogerson said that water should nonetheless remain a starting point in maintaining hydration.

Methodology

In performing the Loughborough testing, the researchers took seven male volunteers with an average age of 23, excluding any lactose intolerant subjects, to test there reaction to hydration under fixed-temperature conditions.

Before exercising, respondents were required to detail dietary intake and physical activity during the 48 hours before the trials, while no alcohol or strenuous exercise was allowed during the 24 hours before testing.

An overnight fast was also required by each subject during the evening before trials took place to ensure better metabolic balance between each subject. Each respondent was then asked to ingest 500ml of plan water 90 minutes before arriving at the laboratory.

Urine and blood tests were then taken along with the application of an absorbent patch on their backs to measure sweat upon arrival.

Each subject was then put into a climatic chamber kept at a temperature of about 35 degrees Celsius and humidity of between 60 to 70 per cent where they were measured for their nude body mass to the nearest 10 grams, the researchers said.

Subject were then required to undergo 10-minute long cycling sessions with five minute breaks in between for towel drying and nude body mass testing.

"Sweat losses were determined for each period of exercise through changes in body mass, and this pattern of activity and rest continued until the subject had lost approximately 1.8 per cent of the initial body mass," stated the researchers.

The sweat patch was then removed after the subjects were found to have lost one per cent of body mass.

Half an hour after testing had finished, respondents were then given either a skimmed milk or commercially available carbohydrate-electrolyte drink measuring 150 per cent of the body mass lost during exercise. The drinks were supplied in four equal helpings every 15 minutes, according to the researchers.

Once the practice was complete, subjects were then asked to rest for an additional three hours without consuming any other food or drink samples, before being asked to empty their bladders as much as possible.

The difference in new fluid balance between pre-exercise to afterwards was measured through sweat lost, beverage ingested and urine produced, according to the researchers.

Source: European Journal of Applied PhysiologyPublished online, DOI 10.1007/s00421-008-0809-4"A comparison of the effects of milk and a carbohydrate-electrolytedrink on the restoration of fluid balance and exercise capacityin a hot, humid environment."Authors: Phillip Watson, Thomas Love, Ronald J. Maughan, Susan M. Shirreffs

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