Last weekend several hundred of the country’s top exercise & sports scientists and sports dietitians gathered on the Gold Coast for the Exercise & Sports Science Australia (ESSA) and Sports Dietitians Australia (SDA) conference. There was a great range of speakers on a variety of topics, and here I thought I’d highlight some of those presentations and posters in the sports nutrition area.
Romain Meeusen – The brain & temperature regulation
Not technically a nutrition topic per se, but Romain gave a very comprehensive overview of the way the brain responds to exercise in the heat. In particular he showed how several drugs that work in particular parts of the brain (such as amphetamines, anti-depressants and most of all Ritalin) can inhibit the body’s natural regulation of exercise intensity. In effect your brain allows exercising muscles to work harder and produce higher core body temperatures without any conscious perception that you’re any more fatigued than normal.
This gives rise to a performance enhancing effect of these drugs, but comes with the danger that the brain cannot protect the body from heat exhaustion. It’s been speculated that the death of British cyclist Tom Simpson on a mountain during the 1967 Tour de France was a result of heat exhaustion, with a combination of amphetamines and champagne the likely contributor. More recently was a case of an NFL footballer who collapsed and died of heat exhaustion. The player was taking Ritalin at the time.
From a nutrition perspective the potential role of caffeine in interrupting this regulation was discussed briefly, but it has not been conclusively shown that the performance benefits from caffeine occur in this manner, or that caffeine is dangerous when exercising in extreme heat.
Carbohydrate availability and team sports performance
One of the abstract presentations that caught my eye was from Melissa Skein from Charles Sturt University, who investigated the effect of the body’s glycogen (ie. carbohydrate) stores on performance in a simulated team sport performance test. Team sport performance is a difficult thing to measure as there are so many variables involved. But video and GPS analysis has allowed sports scientists to develop performance tests that more closely resemble the physical demands of the game.
The test was very well designed, with 15 meter timed sprints every minute, a pattern that simulates the distances and intensity of soccer matches. In between the sprints participants completed a self-paced hard running, jogging, walking or bounding period until the next sprint.
To vary the body’s carbohydrate stores the participants completed a 95 minute exercise bout the day before the test to use up carbohydrate, followed by either a moderate-to-high (7 grams per kilo body weight) or low (2g per kg) carbohydrate diet for the rest of the day. Interestingly the study was designed to disguise the carbohydrate, so the participants didn’t know which diet they were on. This minimised any placebo effect from the two diets when it came to the performance test.
How did they perform? In terms of 15 meter sprint times there was in fact no difference between the two groups. However the difference in carb stores became apparent in the period between sprints, where those on the higher carb diet ran a greater total distance when the recovery period involved hard running. This suggests that the participants on the lower carb diet conserved energy by slowing down during the recovery periods, in order to continue to perform the 15 meter sprints at maximum intensity. The implication on the field is that those who eat a higher carb diet will cover more territory off the ball, enabling them to better get into position when they’re not directly involved in the play.
On a practical note, this study looked at a very low carbohydrate diet that very few team sport athletes would actually consume. Perhaps a better comparison would have been a moderate carb diet (say 5-6 g per kg) compared to full carbohydrate loading (around 10g per kg). And a test of agility or ability to maintain technique under fatigue would have been a great addition to this study too.
Measuring the calories you burn – the Sensewear armband
One of the devices being spruiked at the trade expo this year was a device called the SenseWear armband. The armband takes an accelerometer (which can be used measure movement intensity and track time spent sitting, standing and lying down) and adds sensors that measure galvanic skin response (changes in response to sweating), skin temperature and the amount of heat dissipating from the body. The combination of sensors is designed to provide greater accuracy for measuring energy expenditure compared to an accelerometer alone.
The device uses an algorithm that chooses which sensors to rely on when estimating how many calories the wearer is burning. This allows better measurement of activities that a stand-alone accelerometer would normally either underestimate (eg. cycling on a stationary bike) or overestimate (movement when travelling in a car).
The SenseWear bands are already being tested and used for preliminary studies at the Australian Institute of Sport and the University of Canberra. In fact one of the posters at the conference from the AIS looked at evaluating the SenseWear armband during periods of both weight maintenance and calorie restriction for weight loss. They noted that the band still lacks validation for measuring energy expenditure during high intensity exercise, but is well validated for other times during the day. It even picked up when participants were not complying with instructions to reduce exercise levels on some days of the study!
Ice slushies during an Olympic Distance Triathlon?
Chris Stevens from the University of Newcastle presented his study looking at the ability of ice slushies to reduce body temperature and enhance performance on the run leg of an Olympic distance triathlon. He noted that traditional use of slushies for cooling prior to competition is not effective in triathlon because the event starts with a swim. So in a pool/bike ergo/treadmill simulation participants consumed ice slushies whilst riding the bike leg, using an extra large straw. The swim and bike legs were standardised for intensity, so only the 10km run was measured in terms of performance, where the participants essentially ran a self-paced 10km time trial on a treadmill.
Over 30min during the bike leg the participants took 10g per kilo body weight of either the sports drink slushie or room temperature sports drink. That’s about 700g for a 70kg triathlete, the equivalent of a large Slurpee or Frozen Coke. The effect was an improvement of 10km running time of just over one minute. It was speculated that the benefit from ice slushies (which seems to be greater than external cooling methods) may come from lowering the temperature in the stomach.
From a practical perspective Chris told us that the slushies stay frozen for around one and a half hours when kept in an insulated drink bottle. But he noted that whilst the pros can access the transition area up until just before the race, age group triathletes cannot enter transition in the last three hours before the race. However consuming ice slushies may be a practical and useful strategy to lower body temperature and enhance performance in other endurance sports in the heat such as ultramarathon running, road cycling and endurance mountain biking.
Buffers – Two new Australian studies
Two new studies were presented that looked at the effect of buffers on sports performance. The first from Amelia Carr at the Australian Institute of Sport looked at the effect of optimal dosing of sodium bicarbonate on 2000m rowing time trial performance. The study included groups that took a one-off dose of bicarb, a “chronic loading dose” over 3 days and a placebo. The result however was somewhat disappointing - bicarb made no difference in this study. Interestingly bicarb supplementation in 2000m rowing has been consistently inconsistent as far as results are concerned, so it’s hard to draw any conclusions as to whether it’s beneficial or not.
The other study came from Phillip Bellinger at the University of Tasmania, who looked at the combination of bicarbonate and beta-alanine supplementation on 4km cycling time trial performance, the distance of the track cycling teams pursuit event. Beta-alanine supplementation alone improved power output compared to placebo, however the result was not significantly different (a 63% likelihood that the difference was trivial). Bicarb however improved power output by 3.1%, and the combination of bicarb and beta-alanine improved power output by 3.3% (with no difference between these two groups).
The effect of sodium bicarbonate & beta-alanine on 4km TT cycling performance. Source: Proceedings of the 5th Exercise and Sports Science Australia Conference and 7th Sports Dietitians Australia Update.
Tim Noakes – Hydration, Hyponatraemia and Lessons from the Past
The presentation I was most looking forward to for the conference was from Professor Tim Noakes. You may have heard of Tim from his book The Lore of Running, or may be aware of his outspoken stance on hydration science. I’ve read the majority of Tim’s studies over the past few years, but it was the first time I’ve had the chance to see him present it all in one journey. To do this topic justice I’ve decided to review Tim’s presentation and arguments in a separate entry, which should be ready in about a week.
Overall the ESSA/SDA Conference was another great success in the fields of sports science and sports nutrition. Now the focus for many delegates turns towards the London Olympics in August, when it’ll be time to turn the knowledge and learning from research into action. Then many will reconvene in October for the Sports Medicine Australia conference in Sydney.