Archive for the ‘Weight management’ Category

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 Sports Weblog from original press release.
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Contact: A’ndrea Elyse Messer
Penn State

Taking a break in the middle of your workout may metabolize more fat than exercising without stopping, according to a recent study in Japan. Researchers conducted the first known study to compare these two exercise methods—exercising continually in one long bout versus breaking up the same workout with a rest period. The findings could change the way we approach exercise. Who wouldn’t want to take a breather for that”“Many people believe prolonged exercise will be optimal in order to reduce body fat, but our study has shown that repetitions of shorter exercise may cause enhancements of fat mobilization and utilization during and after the exercise. These findings will be informative about the design of [future] exercise regimens,” said lead researcher Kazushige Goto, Ph.D. “Most people are reluctant to perform a single bout of prolonged exercise. The repeated exercise with shorter bouts of exercise will be a great help [in keeping up with fitness].”

This finding is part of a study entitled Enhancement of fat metabolism by repeated bouts of moderate endurance exercise, found in the June 2007 edition of the Journal of Applied Physiology, which is published by the American Physiological Society. It was conducted by Kazushige Goto, of both the Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Tokyo, Japan and the Institute of Sports Medicine, Bispebjerg Hospital, Copenhagen, Denmark; Naokata Ishii, of the Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Tokyo, Japan; and Ayuko Mizuno and Kaoru Takamatsu, both of the Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.

Summary of Methodology

The researchers used seven healthy (avg. body mass: 66.1, percentage fat: 17.6) men with an average age of 25 who were physically active and familiar with exercise and had them perform three separate trials:

  • one single bout of 60-min exercise followed with a 60-min recovery period (Single)
  • two bouts of 30-min exercise with a 20-min rest after the first 30-min bout, along with a 60-min recovery period at the end (Repeated)
  • one 60-min rest period (Control)

The men performed each trial at the same time of day after fasting overnight. They exercised on a single ergometer (cycling machine) at the commonly recommended exercise prescription of 60% maximum oxygen intake. The recovery and rest periods were conducted while the subjects sat in chairs. Blood samples were taken every 15 minutes during the exercise and every 30 minutes during the recovery period. Their respiratory gas and heart rates were monitored continuously throughout the trial.

Summary of Results

The Repeated trial showed a greater amount of lipolysis (fat breakdown) than did the Single trial. This Repeated trial also had a pronounced increase in free fatty acids and glycerol (chemical compounds that are released when stored fat is used) concentrations in the final 15 minutes of exercise, whereas these concentrations only progressively increased throughout the Single trial. Also, the second half of the Repeated trial showed a significantly greater epinephrine response while also having a rapid decrease in insulin concentration as a result of lower plasma glucose. This combination of high epinephrine and low insulin concentration may have also increased the lipolysis. There was also enhanced fat oxidation in the recovery period of the Repeated trial than in the Single trial, but this result may be because the free fatty acids concentration was already high before the recovery period.

Conclusions

The American College of Sports Medicine recommends moderate exercise for the duration of 45 to 60 minutes to ensure a sufficient amount of energy is depleted in obese individuals. This has caused a greater focus on extending exercise sessions in order to burn more fat. However, this study shows that this method may not be the most effective way to enhance fat metabolism, as splitting up a long bout of exercise with a rest period burns more fat than a continuous bout of exercise. This study could help with the practical application of implementing new exercise methods in order to better manage and control weight in individuals in the future. However, Goto and his team of researchers plan on conducting further studies in order to explore the results in a variety of exercise durations as well as in different types of individuals.

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Article adapted by MD Only Weblog from original press release.
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Contact: Celia Lee
American Physiological Society

It actually takes approximately twice as much time to take the elevator when ascending or descending one floor.  To test this, researchers at the University of South Carolina recorded the time required to ascend and descend one floor by taking the stairs and elevator over several days.  A small group of participants were instructed to alternate between elevator and stair use and to take the stairs at a self-selected “normal” pace during the course of their daily routine.

The time required to take the elevator was significantly greater than the time required to use the stairs going both up and down one floor. The excess time required when taking the elevator was attributed to the wait, not the travel time, since the actual elevator ride was measured at approximately 10 seconds.  The time required to ascend the stairs was greater than the time to descend the stairs, while there was no significant difference between taking the elevator up and elevator down one floor.

The study team hopes this information can be used as part of an intervention to increase stair use, where specific and relevant messages have been shown to be effective in encouraging physical activity.

“If climbing the stairs a few floors saves you time and adds to the physical activity you can accumulate throughout the day, it’s a win-win,” said researcher Joshua Westmeier-Shuh, lead author of the study.  “Let’s look first at shifting the perception that the elevator is a better choice when rushing to work or thinking about how to incorporate activity into the day, and then think about the implications this can have for worksite wellness.  Bottom line: stairs win.”

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Article adapted by MD Sports Weblog from original press release.
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Contact: Communications and Public Information
American College of Sports Medicine

The conclusions outlined in this news release are those of the researchers only, and should not be construed as an official statement of the American College of Sports Medicine.

Golfers averaged more than 13,000 steps in walking to play 18 holes, and even those using carts logged more than 6,000 steps. Guidelines published by ACSM and others recommend walking 10,000 steps per day to maintain cardiovascular fitness and effectively control weight.

“This illustrates an enjoyable way to get the health benefits of walking,” said Cristina Sanders, lead researcher for the study, who presented the findings as part of her graduate work at the University of Colorado, Colorado Springs. “Some people play golf for 40 or 50 years, and it can be quite beneficial.” While previous studies have measured the energy expenditure of individual golfers, this study thought to be the first using pedometers.

Researchers asked golfers at three courses to wear a pedometer while they played 18 holes and noted their height, weight, and handicap. They also noted number of players in each subject’s group, whether he would walk or use a cart, and which tee box he played. After the round, researchers recorded how many steps each golfer walked.

“We had expected that golfers using a cart might take one-quarter as many steps as those who walked the course,” Sanders said. “We were surprised to find that, depending on the course, cart users logged up to half as many steps.” Measuring each course by GPS (global positioning satellite) allowed researchers to calculate minimum course distances, including tee-to-green, green-to-tee, and intermediate path point distances (bridges, paths around lakes, etc.) for each tee box on every hole. These minimum course distances averaged 25 percent longer than the published course playing distances.

Walking golfers and cart golfers took 13,145 +/- 1,736 steps and 6,280 +/- 1,428 steps, respectively. Interestingly, Sanders and her colleagues found no correlation between step count and the golfers’ height, handicap or tee box. Self-reported weight of walking golfers, though, averaged about 8.5 pounds less than that of golfers who used carts.

The golfers in Sanders’ study were all men. She proposed that future research include women, who often play from different tees.  Also of interest, she said, would be a large-scale look into golfers’ energy expenditure, accounting for the extra effort associated with carrying clubs or using pull carts.

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Article adapted by MD Sports Weblog from original press release.
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Contact: Communications and Public Information
American College of Sports Medicine