Archive for October 14, 2007

A new study investigating the potential of a circadian rhythm in athletic performance adds further confirmation that it exists. The finding is being published in the Journal of Applied Physiology. The authors of “Circadian Variation in Swim Performance,” are Christopher E. Kline, J. Larry Durstine, J. Mark Davis, Teresa A. Moore, Tina M. Devlin, Mark R. Zielinski, and Shawn D. Youngstedt, all from the Department of Exercise Science, Arnold School of Public Health, University of South Carolina, Columbia, SC. Background

Circadian rhythms are generated within the body, and are “re-set” almost every 24 hours. Human circadian rhythms originate from the tiny hypothalamus residing in the back of the brain. The hypothalamus, working with the endocrine system, drives many of our behavioral and physiological rhythms.

Researchers have speculated that there may be a circadian rhythm inherent in athletic performance and point to research showing that athletic performance varies based on time-of-day. Other studies have shown that peak performance occurs in early evening, at approximately the peak of the body temperature rhythm. Additional studies have found that morning is the worst time for athletic performance.

These findings, however, have limitations. For example, the studies failed to identify the other factors that could cause time-of-day differences that are independent of circadian rhythm. For example, worse performance in the morning could be attributed to nutritional status, joint stiffness following bed-rest, sleep inertia upon arising, lower ambient temperature, and a lack of “warm up” in the muscles.

Methodology

To better understand the potential existence of a circadian rhythm in swimming performance, researchers assessed 25 highly trained swimmers over 50-55 consecutive hours while who were adhering to a 180-minute ultra-short sleep/wake schedule, specifically one hour of sleep in darkness and two hours of wakefulness in dim light, repeated throughout the length of observation. This study design distributed multiple masking factors equally across the 24-hour day and allowed multiple performance assessments to be conducted over a short period of time with relatively little sleep loss.

Each swimmer performed six scheduled maximal-effort 200-meter swim trials that were distributed equally across eight times of day, with nine hours between each trial. Data from the sleep/wake schedules, swim performances, states of sleepiness, physical/mental energy, and physical/mental fatigue and body temperature measurements were collected. The statistical comparisons were performed using SPSS software. All results were presented as mean plus or minus standard error; with significance set at P<0.05.

Results

The primary findings of the study showed:

  • swimming performance had significant circadian variation when expressed relative to the time of day (Tmin). Specifically, swim performance was impaired between 2:00 – 8:00 AM, compared to all other times of day. Peak performance was at 11:00 PM;
  • there was a clear superiority of swim performance in the afternoon/evening compared to in the morning. (The results confirm previous findings of a significant time-of-day variation in swimming performance.);
  • the ultra-short sleep/wake cycle provided the first clear evidence of circadian regulation in athletic performance.

Implications of the Study’s Results

These data suggest a circadian rhythm in athletic performance exists. The circadian range from best to worst performance in this study — 5.84 seconds — could have considerable importance in athletic competition. For example, among females competing in the 200-meter freestyle final at the 2004 Olympics, first and third place were separated by only 0.42 seconds, and first and eighth place were separated by only 1.17 seconds. Among the men, 0.61 seconds separated the winner from third place, and 3.69 seconds separated first from eighth place.

By demonstrating a circadian rhythm in athletic performance, the research provides a stronger theoretical rationale for expecting decrements in performance following circadian desynchronization (multiple time zone travel). However, by knowing the circadian time of peak performance, athletes may be better able to shift their circadian systems so that the peaks of their performance rhythms coincide with the time of desired peak competition.

In the highly competitive sports environment, where financial stakes are often high, team managers will find it useful to add the study of physiological concepts such as circadian rhythms to provide a potential edge for victory.

Contact: Donna Krupa
American Physiological Society

Physiology is the study of how molecules, cells, tissues and organs function to create health or disease. The American Physiological Society (APS) has been an integral part of this scientific discovery process since it was established in 1887.

The majority of non-medical anabolic-androgenic steroid (AAS) users are not cheating athletes or risk-taking teenagers. According to a recent survey, containing the largest sample to date and published in the online open access publication, Journal of the International Society of Sports Nutrition, the typical male user is about 30 years old, well-educated, and earning an above-average income in a white-collar occupation. The majority did not use steroids during adolescence and were not motivated by athletic competition or sports performance.

The study, conducted by a collaboration of researchers from around the country coordinated by Jason Cohen, Psy.D. candidate, used a web-based survey of nearly 2,000 US males. Whereas athletes are tempted to take anabolic steroids to improve sports performance, the study suggests that physical self-improvement motivates the unrecognized majority of non-medical AAS users who particularly want to increase muscle mass, strength, and physical attractiveness. Other significant but less highly ranked factors included increased confidence, decreased fat, improved mood and attraction of sexual partners.

Although often considered similar to abusers of narcotics and other illicit drugs (e.g., heroin or cocaine), non-medical AAS users are remarkably different. These users follow carefully planned drug regimens in conjunction with a healthy diet, ancillary drugs and exercise. As opposed to the spontaneous and haphazard approach seen in abusers of psychotropic drugs, everything is strategically planned to maximize benefits and minimize harm. “This is simply not a style or pattern of use we typically see when we examine substance abuse” said Jack Darkes, Ph.D., one of the authors. “The notions of spontaneous drug seeking and loss of control do not apply to the vast majority of AAS users,” added co-author Daniel Gwartney, M.D.

“These findings question commonly held views of typical AAS users and their underlying motivations,” said Rick Collins, one of the study’s authors. “The focus on ‘cheating’ athletes and at risk youth has led to irrelevant policy as it relates to the predominant group of non-medical AAS users. The vast majority of AAS users are not athletes and hence, are not likely to view themselves as cheaters. The targeting of athletes through drug testing and other adolescent or sports-based interventions has no bearing on non-competitive adult users.” The study concludes that these AAS users are a driven and ambitious group dedicated to gym attendance, diet, occupational goals and educational attainment. “The users we surveyed consider that they are using directed drug technology as one part of a strategy for physical self-improvement within a health-centered lifestyle,” said Collins. “Effective public policy should begin by accurately identifying who’s using steroids and why. We hope our research – the largest adult survey of non-medical AAS use we know of – is a significant step forward in that direction.”

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Charlotte Webber
BioMed Central

Article:
A League of Their Own: Demographics, Motivations and Patterns of Use of 1,955 Male Adult Non-Medical Anabolic Steroid Users in the United States
Jason Cohen, Rick Collins, Jack Darkes and Dan Gwartney
Journal of the International Society of Sports Nutrition (in press)

During embargo, article available at: http://www.jissn.com/imedia/1374735248154681_article.pdf?random=454689

After the embargo, article available from the journal website at: http://www.jissn.com

Drinking water during a long-distance race may do serious harm rather than keep you safe from injury if you’re drinking too much, according to a cardiologist at UT Southwestern Medical Center.Runners or any long-distance athletes who drink too much water during a race could put themselves at jeopardy for developing hyponatremia, a condition marked by a loss in the body’s sodium content that can result in physical symptoms such as lethargy, disorientation, seizures and even respiratory distress.

In a perspectives article in the current issue of The New England Journal of Medicine, Dr. Benjamin Levine, professor of internal medicine at UT Southwestern, said competitive runners are less likely to suffer from hyponatremia.

“Those who are running to finish the race very fast don’t have time to drink a lot of water along the way,” Dr. Levine said. “Those who are not running the race competitively tend to stop at every water station and take a drink. Over the course of a long race, they can dilute themselves.”

In addition popular sports drinks don’t always include enough sodium to offset the body’s loss of the mineral during exercise. The drinks often carry more water with smaller concentrations of salts than are normally found in the human body; therefore, they do not replace salts adequately, said Dr. Levine, medical director of the Institute for Exercise and Environmental Medicine, a collaboration between UT Southwestern and Presbyterian Hospital of Dallas.

The NEJM perspectives article accompanies a study in the same journal by researchers at Children’s Hospital in Boston and Harvard Medical School. The study evaluates the blood concentration of sodium in runners both before and after a long race and examines their risk factors for developing hyponatremia. It recommends individualized fluid-replacement consumption by all competing athletes.

“Researchers of the study found a surprisingly large number of runners had actually gained weight during the race and their sodium concentrations were very low – some were dangerously low,” Dr. Levine said. “The recommendations listed in the study that fluid-replacement schedules be individualized for all athletes competing in long-distance events should be taken seriously by all competitors.”

People lose water and salts from their bodies at different rates during exercise, he said. Heat and humidity also play a role in the rate of this loss. Calculating fluid loss is as simple as weighing yourself before and after exercise and comparing that number to the amount of fluid you consumed throughout.

“All serious distance athletes should find out what their rate of fluid loss is and individualize their fluid intake prior to a distance event,” Dr. Levine said. “It’s also good to accept some mild dehydration during a long race. There are plenty of Web sites available now that show how to customize your fluid intake.”

He also added that taking along salty snacks to eat during the race is a good way of combating hyponatremia. Generally, athletes of all types are instructed prior to activities that water consumption is necessary to prevent illness from heat and to maintain performance levels.

It is also clear, however, that fixed global recommendations for fluid replacement may not be optimal for individual athletes of different body types and with varying degrees of training and heat acclimatization.

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Katherine Morales
UT Southwestern Medical Center

Peak athletic performance may be related to time of day, suggests a University of Chicago study being presented to the Endocrine Society’s annual meeting, ENDO 2001, in Denver, Colorado, on June 22, 2001. The study shows that the response of the systems regulating energy metabolism and some hormones differs according to when in the day exercise is performed.

Subjects who exercised at night had much larger drops in glucose levels in response to exercise than at other times of day. Exercise in the evening and at night elicited large increases in the levels of two hormones important for energy metabolism, cortisol and thyrotropin. Exercise at other times of day had much smaller effects on these hormones. In contrast, marked increases in growth hormone levels in response to exercise were not effected by the time of day.

“The effects of exercise we observed may explain how some times of day could be better than others for regular exercise or athletic performance, as we might expect from anectdotally reported variations in peak athletic performance,” said Orfeu Buxton, Ph.D., a post-doctoral fellow in endocrinology at the University of Chicago. “We found strong evidence for substantial changes in glucose metabolism and an array of hormonal responses to 1-hour, high-intensity exercise, dependent on the timing of the exercise. Circadian rhythms, generated by our 24-hour internal clock, appear to play an important role in the complex response to exercise.”

For the study, conducted in the Clinical Research Center of the University of Chicago, 40 healthy men, between the ages of 20 and 30, were divided into five groups. Four groups exercised vigorously for one hour on a stair-stepper in the morning, afternoon, evening or night. A control group did not exercise. A standard marker, the timing of melatonin secretion, was used to determine the timing of each individual’s daily rhythm, his circadian “clock time.”

When not exercising, the subjects rested in bed with constant glucose infusion to avoid fluctuation in their blood sugar levels caused by intermittent meals. Blood levels of the “circadian hormones,” melatonin, cortisol and thyrotropin, and the levels of growth hormone and glucose were compared to blood levels for the same time of day in the resting control subjects.

The importance of timing for hormonal secretion and energy metabolism is demonstrated by the distinct 24-hour patterns of secretion for each hormonal system. One hormone may be actively secreted in a complex pulsating pattern while another may be in a resting phase.

Many circadian rhythms, such as heart rate, oxygen consumption, and cardio-pulmonary function play a role in athletic performance. Rhythmic patterns of hormonal secretion provide internal temporal organization essential to the coordination of physiological processes. Physical exercise is associated with marked metabolic changes and can elicit a variety of neuroendocrine responses. Although these metabolic and hormonal responses to morning exercise are well-documented, few studies have examined the effects of exercise at other times of day.

“Our study covers new ground, demonstrating variation in the effects of exercise at four different times of day, with circadian time precisely quantified, with a practical duration of exercise, and with a high intensity designed to elicit maximal effects” said Buxton.

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Jeanne Galatzer-Levy
University of Chicago Medical Center

Co-authors on the study include, André J. Scheen, M.D., Division of Diabetes, Nutrition and Metabolic Disorders, University of Liége, Belgium; Mireille L’Hermite-Balériaux, Ph.D., Laboratory of Experimental Medicine, Université Libre de Bruxelles, Belgium and Eve Van Cauter, Ph.D., Department of Medicine, University of Chicago.

This work was supported by grants from the Air Force Office of Scientific Research and from the Department of Defense. The University of Chicago Clinical Research Center is supported by a National Institutes of Health grant.

When it comes to coaching, the pep talk is better than the locker room tirade, University of Florida researchers have found.In a project that applied methods previously used only in classroom settings, a team headed by Professor Robert Singer found that changing people’s attributions, or how they think about themselves, influenced their performance in sports tasks they sought to learn.

“How we think about how we will do and how we’ve just done can very much affect our persistence, our attitudes and our achievements,” said Singer, chair of UF’s department of exercise and sport sciences. “It’s not only a belief in what you can do, it’s also an understanding of thinking more objectively.”

The technique is known as attribution training, which involves using people’s self-perceptions and the extent to which they feel they can control their own behavior to help them succeed at various tasks. Those who believe they can control and change how they feel about themselves are said to have constructive attributions.

In the study, scheduled to be published in March in The Sport Psychologist, Singer and UF colleague Iris Orbach divided 35 college-age beginning tennis players into three groups, each of which was given different instructions regarding personal failure. The first was told they could control their attributions and effort and could change their performance. The second was told their failures were due to a lack of innate ability. The third group was told nothing.

In four trials, the first group scored consistently better in performance, expectation, success perception and emotional control, Singer said. For example, on a test to measure feelings of personal control over behavior, the first group scored twice as high as the control group, while the second group scored below the control group.

In a related study in 1997 that focused on basketball time trials, the first group improved their final time between the first and fourth trials more than twice as much as the control group and more than nine times as much as the second group did.

“When it comes down to it, the primary thing is that you really have to understand what helps you to achieve and what’s under your control,” Singer said. “What has been observed is that those individuals who tend to have more constructive attributions tend to persist longer and tend to achieve more than those who do not have constructive attributions.”

Most studies associated with attribution training techniques have been conducted in the area of education, with the goal of raising the standards for children who are underachievers in the classroom. Singer and Orbach were among the first in the world to apply the techniques to sports.

“Why not try this in a sports setting?” Singer said. “The typical design is to train one group with an attributional orientation that reflects that if you try harder and you try smarter, you’ll have a greater chance of doing well. You’ll learn the skills better and think better things will happen.”

Although it is a common perception that believing in yourself can lead you to success, Singer said his study could have a significant impact on the way people teach and learn athletic activities.

“A lot of times in sports, there’s a negative attitude and a lot of criticism that goes on,” he said. “Probably many athletes and coaches don’t realize the significance of what we’re talking about and the relevance of how people think … I believe that if there’s a better understanding by coaches as to the kind of feedback they give to athletes and how stuff is delivered to them, it could make a difference.”

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Kristin Harmel
University of Florida

Use of growth hormone to boost athletic performance can lead to diabetes, reports a study published ahead of print in the British Journal of Sports Medicine.

The study reports the case of a 36 year old professional body-builder who required emergency care for chest pain.

He had lost 40 kg in 12 months, during which he had also experienced excessive urination, thirst, and appetite.

He admitted to using anabolic steroids for 15 years and artificial growth hormone for the past three. He had also taken insulin, a year after starting on the growth hormone.

This was done to counter the effects of high blood sugar, but he had stopped taking it after a couple of episodes of acute low blood sugar (hypoglycaemia) while at the gym.

Tests revealed that his liver was inflamed, his kidneys were enlarged and that he had very high blood sugar. He was also dehydrated, and diagnosed with diabetes.

He was given intravenous fluids and gradually increasing amounts of insulin over five days, after which he was discharged. His symptoms completely cleared up, and he was no longer diabetic.

The use of growth hormone has steadily risen among amateur athletes and bodybuilders all round the world, say the authors, because it is easy to buy online and difficult to detect in screening tests—unlike anabolic steroids.

The authors believe that this is the first reported case of diabetes associated with the use of high dose growth hormone, and urge anyone taking high doses to regularly check their blood sugar levels.

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Emma Dickinson
BMJ Specialty Journals

Female athletes often lose their menstrual cycle when training strenuously, but researchers have long speculated on whether this infertility was due to low body fat, low weight or exercise itself. Now, researchers have shown that the cause of athletic amenorrhea is more likely a negative energy balance caused by increasing exercise without increasing food intake.”A growing proportion of women are susceptible to losing their menstrual cycle when exercising strenuously,” says Dr. Nancy I. Williams, assistant professor of kineseology and physiology at Penn State. “If women go six to 12 months without having a menstrual cycle, they could show bone loss. Bone densities in some long distance runners who have gone for a prolonged time period without having normal menstrual cycles can be very low.”

In studies done with monkeys, which show menstrual cyclicity much like women, researchers showed that low energy availability associated with strenuous exercise training plays an important role in causing exercise-induced amenorrhea. These researchers, working at the University of Pittsburgh, published findings in the Journal of Clinical Endocrinology and Metabolism showing that exercise-induced amenorrhea was reversible in the monkeys by increasing food intake while the monkeys still exercised.

Williams worked with Judy L. Cameron, associate professor of psychiatry and cell biology and physiology at the University of Pittsburgh. Dana L. Helmreich and David B. Parfitt, then graduate students, and Anne Caston-Balderrama, at that time a post-doctoral fellow at the University of Pittsburgh, were also part of the research team. The researchers decided to look at an animal model to understand the causes of exercise-induced amenorrhea because it is difficult to closely control factors, such as eating habits and exercise, when studying humans. They chose cynomolgus monkeys because, like humans, they have a menstrual cycle of 28 days, ovulate in mid-cycle and show monthly periods of menses.

“It is difficult to obtain rigorous control in human studies, short of locking people up,” says Williams.

Previous cross-sectional studies and short-term studies in humans had shown a correlation between changes in energy availability and changes in the menstrual cycle, but those studies were not definitive.

There was also some indication that metabolic states experienced by strenuously exercising women were similar to those in chronically calorie restricted people. However, whether the increased energy utilization which occurs with exercise or some other effect of exercise caused exercise-induced reproductive dysfunction was unknown.

“The idea that exercise or something about exercise is harmful to females was not definitively ruled out,” says Williams. “That exercise itself is harmful would be a dangerous message to put out there. We needed to look at what it was about exercise that caused amenorrhea, what it was that suppresses ovulation. To do that, we needed a carefully controlled study.”

After the researchers monitored normal menstrual cycles in eight monkeys for a few months, they trained the monkeys to run on treadmills, slowly increasing their daily training schedule to about six miles per day. Throughout the training period the amount of food provided remained the standard amount for a normal 4.5 to 7.5 pound monkey, although the researchers note that some monkeys did not finish all of their food all of the time.

The researchers found that during the study “there were no significant changes in body weight or caloric intake over the course of training and the development of amenorrhea.” While body weight did not change, there were indications of an adaptation in energy expenditure. That is, the monkeys’ metabolic hormones also changed, with a 20 percent drop in circulating thyroid hormone, suggesting that the suppression of ovulation is more closely related to negative energy balance than to a decrease in body weight.

To seal the conclusion that a negative energy balance was the key to exercise-induced amenorrhea, the researchers took four of the previous eight monkeys and, while keeping them on the same exercise program, provided them with more food than they were used to. All the monkeys eventually resumed normal menstrual cycles. However, those monkeys who increased their food consumption most rapidly and consumed the most additional food, resumed ovulation within as little as 12 to 16 days while those who increased their caloric intake more slowly, took almost two months to resume ovulation.

Williams is now conducting studies on women who agree to exercise and eat according to a prescribed regimen for four to six months. She is concerned because recreational exercisers have the first signs of ovulatory suppression and may easily be thrust into amenorrhea if energy availability declines. Many women that exercise also restrict their calories, consciously or unconsciously.

“Our goal is to test whether practical guidelines can be developed regarding the optimal balance between calories of food taken in and calories expended through exercise in order to maintain ovulation and regular menstrual cycles,” says Williams. “This would then ensure that estrogen levels were also maintained at healthy levels. This is important because estrogen is a key hormone in the body for many physiological systems, influencing bone strength and cardiovascular health, not just reproduction.”

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: A’ndrea Elyse Messer
Penn State