|
|
ACSM: Limits to
Sport Performance
|
|
|
|
Endurance Performance in the Heat · Overtraining Summit · Why Johnny Can't Jump · Triathlon Clinical Lecture · Difficult Tendinopathies · Adaptogens · Related Abstracts |
The abstracts for some of these presentations are published in the Supplement to Medicine & Science in Sports & Exercise (Vol. 29, No. 5, May 1998). Where available, I've included abstract numbers. You can also order tapes of lectures, symposiums, and other major presentations through Mobiltape.
Next year the conference will be in Seattle, Washington, from June 2-5. Expect cooler temperatures than Orlando!
Dr Ronald J. Maughan: "What Limits Endurance Performance in the Heat?"
The 1996 Summer Olympics in Atlanta brought everyone's attention to potential problems associated with performing in the heat. Studies of marathons had shown that the winning time was related to ambient temperature. As Dr Maughan said, if it's very hot or very cold, the good guys don't run; but even the athletes who do enter are slowed by the heat.
How hot is hot? What we found out is that it doesn't have to be that hot to have a significant effect on performance. Maughan reported results of a study (Galloway and Maughan, 1997) in which subjects cycled at 70% maximum oxygen consumption at various ambient temperatures. Exercise time was 81 min at 4°C, 94 min at 11°C, 81 min at 21°C and 52 min at 31°C. Most of us wouldn't think that 21°C was hot or that we'd need to acclimatize, but this study clearly showed that athletes may need to take special considerations at normal temperatures.
What causes performance to be reduced in the heat? Most of the research on endurance activities tells us that the point of fatigue coincides with the point at which muscle glycogen becomes depleted. However, these studies were done in generally cool conditions. Febbraio et al. (1996) showed that at temperatures of 3°C, 20°C, 40°C, exercise time ranged from 95 min to 33 min. At the point of fatigue, glycogen concentration was low in cold and temperate conditions, but there was no apparent shortage of glycogen at the point of fatigue in the heat.
A study by Neilson and coworkers points to high core temperature as the factor that causes fatigue, at least in exercise continued to exhaustion. Over a period of 10 days, subjects exercised in the heat. As they acclimatized, they exercised longer each day, but they stopped at the same core temperature. It's good evidence for a protective mechanism preventing us from reaching a dangerously high temperature. Recent research has suggested that the neurotransmitter serotonin is involved in the feeling of fatigue that makes us stop.
Maughan emphasized that increasing heat loss by increasing skin temperature is crucial to prolonging exercise in the heat. If you can maintain a higher skin temperature, you can evaporate more sweat and delay the increase in core temperature. Drinking during exercise in the heat probably enhances performance by this mechanism: core temperature rises more if you take no fluids, so it's possible that the more fluid we replace, the better we maintain our skin blood flow to remove heat, the longer we are able to delay that rise in core temperature, and the better our exercise performance. Precooling--a useful strategy for reducing the effect of heat on performance--also delays the rise in core temperature. Maughan did not discuss the possibility that drinking and precooling might work by making more cardiac output available for the active muscles.
The individual who copes well with heat stress will have a high mechanical efficiency, a low body mass, a high ratio of surface area to mass, an efficient sweating mechanism, and a high skin temperature during exercise. It might be possible to improve mechanical efficiency by increasing training volume. Losing body mass can also increase efficiency and increase the surface-to-mass ratio. Maintaining skin temperature and sweating is achieved more effectively if we take fluids during exercise.
For related articles on heat acclimatization, see our Encyclopedia article as well as Preparing Athletes for Competition in the Heat by Maughan and Shirreffs on the Gatorade Sports Science Exchange.
Is it overtraining? Or is it overreaching, staleness, burnout, underrecovery, inadequate recovery syndrome, overuse syndrome, training stress syndrome, or chronic fatigue syndrome? All of these terms were used at the conference. It was a popular topic: a symposium, a number of related conference sessions, and the Second Annual USOC and ACSM Human Performance Summit. Last year's Summit was sold out. This year's didn't quite have a sell-out crowd, but it may have been because of the coverage the topic received during the regular conference sessions. It's too bad more people didn't attend, because it was an opportunity to interact with researchers and coaches on the panel. Here's a short summary of what we heard at the Summit.
It began with asking a simple question: What's responsible for peak performance? The answer: training. Olympic swimmer Mark Spitz trained by swimming 10,000 yards a day in his time. Today children are swimming that far, and swimmers such as Janet Evans swam more than 50% over that amount. We hear top athletes say "you have to train hard," and we attribute to some extent the Kenyans' success on the fact that they train hard.
But as one panelist said, some athletes may undertrain; that is, not train hard enough. The overload principle is absolutely necessary. By this, we mean a progressive increase in training load with the goal of improving performance. What we need to know is when to cut down the load. Overreaching is excessive overload with inadequate rest resulting in poor performance in training and competition. But overreaching that results in long-term loss of sport performance is overtraining.
A number of factors contribute to overtraining: long-term, high-intensity training; insufficient recovery; frequent competition resulting in mental and physical stress; poor training plan or lack of variety in training. Medical conditions such as illness or allergies may play a role. Also look for poor diet or inadequate caloric intake. There may be environmental stress factors such as altitude, temperature, humidity, or travel. Or there may be psychosocial stressors: conflicts with coach, faculty or friends, problems in work or school. As Tim Noakes, one of the panelists said, "When the hypothalamus isn't able to cope with the total amount of stress, something goes wrong." Harm Kuipers gave us examples: take an athlete over three time zones, or to altitude, put them in a dull environment without contact with family, or train in hot and humid conditions. Work them hard in conditions such as these and they will be overtrained.
The defining characteristic of overtraining: an unexplained drop in performance in training or competition. There are over 100 potential symptoms, but only a few are important: exaggerated fatigue or "heavy legs", a mismatch between training load and perception of effort, and changes in mood, sleep, and concentration.
Prevention techniques for avoiding overtraining:
And if the athlete does overreach to the extent of becoming overtrained? Rest. Giving us a little anecdotal information, Tim Noakes used Mark Allen as an example, who will train at a lower heart rate of around 150 beats per minute for three months and take two months off each year. Tim reminded us that you can't raise performance unless you limit competition, and a very real problem of the Kenyans is their "burnout" rate. Of nine in competition, eight may not return in subsequent years. So perhaps coaches need to address the issue of whether there is a limit of training above which harm, not benefit, results. And for the sport scientists: a need to study how little training one needs, not how much.
Dr David Costill: "Why Johnny Can't Jump"
What impact does training have on muscular strength and performance? This question formed the central theme of the Wolffe Lecture given by David Costill.. Using an example from the 1960s, Costill looked at changes in muscle peak power in two runners detraining over a 4-year period. He found their maximum oxygen consumption dropped from 78 to 46 ml/min/kg, but their vertical jump doubled. Intrigued, Costill took a look at swimmers. He found arm strength is lower when training is heaviest in swimming. As soon as swimmers reduce training, arm power and strength comes back. Studies of isolated single muscle fibers have narrowed the mechanism down to changes in force generation of the fast-twitch fibers. Whether these changes in contractility impact on competitive performance will depend on the demands of the event. If generation of high peak forces is important, as in sprint events, then too much endurance training will be counterproductive.
Those at the triathlon clinical lecture heard a distinction between overreaching and overtraining, studies of hematocrits, drug testing concerns, and other topics. J. Michael Ray organized this session that included talks by Richard Budgett, Mary O’Toole, and Thomas K. Miller and other speakers.
Overreaching vs Overtraining
Dr Richard Budgett, from the British Olympic Association, presented a shortened version of his earlier presentation at the conference on fatigue and underperformance in athletes. Budgett was careful to make a distinction between overreaching and overtraining. Overreaching is what triathletes do all the time, and it applies to other athletes as well. They train, become fatigued, recover to get supercompensation, repeat the cycle, and gradually improve. Some athletes cross the fine line and become overtrained. In other words, they don't get the full recovery after a training stimulus. With overtraining, there is an objective loss of form with no other identifiable cause. This loss of form can be tested in the laboratory or by underperformance in competition which lasts at least two weeks in spite of adequate rest. Temporary fatigue is normal. But when it lasts more than two weeks and has no other identifiable cause, it becomes underrecovery.
So if the athlete is underperforming, what can be done? First, make sure that there isn't a medical reason. There are a series of tests that can help point toward overtraining that involve hormonal, psychological, immunological and other factors. The last thing coaches want to hear, however, is that they've overtrained their athletes, because they'll feel threatened if their athletes underperformed. So if medical reasons are ruled out, it's important to recognize that overtraining is due to underrecovery.
The cure is a tough pill to swallow for both the coach and athlete, who may well be addicted to exercise. In most cases, recovery involves 6-12 weeks of relative rest for the athlete. Light exercise, 10-20 minutes, building up to an hour is part of the recovery process during this time. Only after a gradual buildup is achieved, should intensity be increased, equivalent to very short sprints with rest periods similar to what a 100-m runner would do on a track.
What's the alternative to 6-12 weeks of downtime for the athlete? The same answer we heard at the Summit and worth repeating: Prevention, through good communication between the coach and athlete and careful monitoring of the athlete.
Hematocrits in Triathletes
Dr Mary O'Toole, co-founder of Labman (Ironman Hawaii), discussed studies that attempted to find the optimum hematocrit (concentration of red blood cells) for triathletes. She explained that optimum hematocrit depends upon a balance between oxygen carrying capacity on the one hand and increased viscosity. When hematocrits are increased above 50% there is an exponential rise in blood viscosity. With endurance athlete training, however, there is a decrease in viscosity and also an increase in red-cell deformability, which makes blood more fluid. So perhaps viscosity isn’t as much an issue with endurance athletes as some researchers think. A dangerous hematocrit is considered to be 55%, but we don't know if that applies to endurance athletes. (See related articles at this site: cyclists, skiers, altitude.)
What do we expect the hematocrit of a heavily training triathlete to be? What do we expect the change in the hematocrit to be during the course of a competitive event? Do we have any data to address safety thresholds for triathletes? Do we have data to identify cutoffs for triathletes participation? Are data from other athletes appropriate for triathletes? These are some of the questions that O'Toole addressed.
O'Toole reported data from three different event distances and nine events total: two Olympic, two half-Ironman, and five Ironman races. A total of 412 athletes gave venous-blood samples 24-36 hours before competition. They were sampled within minutes of their event finish. The results were a normal distribution with an average hematocrit of 43% for 289 men and 40% for 123 women. By event distance: (men) Olympic, 45%; Ironman, 42%. She and others also looked at iron status and found it was extremely unusual for the triathlete to be iron deficient.
Cutoffs suggested are 3 standard deviations above the mean, which would work out to 52 for men and 48 for women. In sample of 412 athletes, there was only one man who had a pre-event hematocrit higher than 52%, and that was 52.5%. In sample of 123 women, only one woman was higher than 48%, and that was 48.5%. In the entire sample of 412, only eight athletes, all men, had hematocrits higher than 50%.
In a profile of pros in comparison to amateurs in the Ironman distance, pros had slightly higher hematocrits. She didn't know if it was due to better nutritional status of pros, altitude training, or just a chance finding due to small sample sizes.
She also reported on changes in hematocrits over a period of years in other endurance sports. The mean changes were less than 2%. Changes in individual triathletes showed the greatest range in Iron men: one had an increase in hematocrit of 10%, another had a decrease of 7%. The changes seemed to be more pronounced in men than in the women; but the reasons aren't known.
Finally, O'Toole compared samples taken by fingerstick vs venipuncture. She found they were very similar. If anything, fingerstick may give a little higher hematocrit measure and therefore give a higher margin of safety. If hematocrit is used as a cutoff measure for athlete safety, fingerstick hematocrits may be the most practical.
EPO: Fact, myth, medical control
Dr T. K. Miller, medical director for USA Triathlon took a look at the latest drug to cause concern among the sport and medical science community: recombinant human erythropoietin (EPO). It's difficult to detect, has significant performance enhancement potential and minimal side effects, all of which make EPO the ideal performance enhancing drug. Manufactured by recombinant DNA technology, it has an identical amino acid sequence as native erythropoietin which explains the problem in detection. It doesn’t seem to matter how you give it: weekly or daily, you get the same final hematocrit for the same total dose.
So what are the problems? It should be enough that it threatens the integrity and dignity of sport, but there are very real concerns in the medical community. First, there is significant individual variability. Another issue is lack of control or monitoring: not every athlete who has access to EPO has access to a good physician. It also has a dose-dependent response. If 300 units per kg is good, then 600 has to be better. EPO can thicken the blood and lead to an increased risk of heart attack and stroke. In addition, EPO has been reported to accentuate the increase systolic blood pressure in some individuals during exercise. Add in risk of dehydration, and there are legitimate medical concerns.
What hematocrit testing would require is:
Miller’s opinion: Use of EPO in a regulated manner with careful monitoring and adjustment of hematocrit to an optimal level for a given individual has the potential for significant, competitive, unfair advantage. Misuse has the very real potential for a catastrophic event.
The Difficult Tendinopathies--Are Old Myths Undermining Our Treatment? The speakers in this symposium looked at specific injuries to address this issue. The tendency to simply palliate tendon injuries rather than cure them is due to the fact that research still hasn't uncovered the true nature of the pathology of these injuries--is it degeneration or inflammation? Their conclusion: the disabling tendon injuries that are a curse especially of runners (achilles tendon), cricketers, swimmers, tennis and baseball players (shoulder tendon), basketball players (patella tendon), are due to chronic degenerative changes in the tendons that will not be cured by a few days of physiotherapy and a handful of anti-inflammatory drugs. Rather, they heal poorly and cause prolonged disability. There is a need for new research to identify the most successful ways to treat these conditions and especially for the development of new drugs, because anti-inflammatories have essentially no role in these conditions. As the conditions are degenerative and never fully recover, it's important that they should be prevented in the first place.
Adaptogens are food-grade herbal substances sold under a variety of names by health food companies. It's claimed that they can speed up recovery from physical exercise and gain additional stamina and endurance. It's hard to find good research studies supporting the claims, so I went with interest to two poster sessions that attempted to evaluate whether claims of improved performance associated with the commercially marketed adaptogen, Endurox, were valid.
Triathletes in the United States are familiar with Endurox. Go to any major US triathlon and the odds are that you'll find a sample package of Endurox in your race packet. Clever marketing. What athlete doesn't want to "slow lactic acid buildup that causes muscle soreness and fatigue. Endurox (ciwujia, eleuthera, or a form of Siberian ginseng, a natural root grown in China), like many natural food supplements, is not regulated by the US Food and Drug Administration. Used as directed, the product claims to help an athlete metabolize up to 43% more fat calories per workout.
Cheuvront, Moffatt and other researchers from Florida State University used a double-blind crossover design and randomly assigned subjects to consume the recommended dosage of Endurox for seven days or a placebo. The subjects performed cycle ergometry as researchers collected and continuously analyzed expired gases. The findings did not support the ergogenic claims of Endurox of reduced lactate production or faster heart rate recovery. (#1838)
Dustman and others from Northern Illinois University used a double-blind balanced randomization design to measure physiological response to a stair-stepping exercise session. Results did not support advertised claims by Endurox to increase fat metabolism, decrease lactate accumulation, heart rate and feelings of fatigue during exercise. (#1839)
Overtraining
(#612) Health Maintenance Test responses to five consecutive days of high intensity cycling. Morning heart rates have been used by athletes and coaches to determine the delicate line between optimal training and overtraining. One tool designed to measure changes in morning heart rate is the Health Maintenance Test is designed to measure changes in morning heart rate and appears to be an inexpensive and accurate tool for coaches and athletes to monitor training status during periods of overload.
(#609) Training responses of selected physiological parameters in competitive male cyclists. Heart rate measured during rest and submaximal exercise may be a sensitive indicator of training adaptations in competitive cyclists, who maintain their training mileage but increase their intensity.
(#115) The influence of exercise type on salivary-IgA and mood state. Interval training may have a detrimental effect on mucosal immunity (interval training significantly increased reported fatigue and submaximal exercise significantly decreased reported anger), and the effect of physical activity on mood states may be affected by type of exercise.
Endurance Performance in Heat
(#1612) The effect of hypohydration on the lactate threshold in a hot and humid environment. Lactate threshold occurs at a lower stage and absolute oxygen consumption, and a higher core temperature during exercise in the heat regardless of hydration level.
(#1617) Effects of hydration status on cognitive function during extended exercise in heat. Cognitive function is enhanced when carbohydrate is ingested during extended exercise in the heat. Although glycerol has been suggested to maintain hydration during endurance exercise, it appears that cognitive function is only enhanced when blood glucose homeostasis is maintained.
(#1597) The effects of whole body pre-cooling on soccer-specific intermittent exercise performance. Intermittent activity induces greater increases in rectal temperature compared with endurance exercise. A pre-cooling strategy of exposure to a cold shower for 60 min resulted in a lower average rectal temperature during exercise than if no pre-cooling had taken place. However, when exercise stopped, there were no significant differences in temperature between treatments. Conclusion: any thermoregulatory benefit of whole-body pre-cooling during intermittent exercise is transient in nature.
Blood
(#1901) Greater erythrocyte deformability in elite endurance athletes. Findings indicate larger proportion of young red blood cells in the blood of elite cyclists and provide further evidence that the turnover of red blood cells in endurance athletes is higher than in the general population.
