Carbohydrate drink boost strength even before swallowed

Researchers at The University of Auckland have shown for the first time that the mere presence of carbohydrate solution in the mouth immediately boosts muscle strength, even before it is swallowed.

The results suggest that a previously unknown neural pathway is activated when receptors in the mouth detect carbohydrate, stimulating parts of the brain that control muscle activity and producing an increase in muscle strength.

Previous research had shown that the presence of carbohydrate in the mouth can improve physical performance during prolonged activity, but the mechanism involved was not known and it was unclear whether a person must be fatigued for the effect to be seen.

“There appears to be a pathway in the brain that tells our muscles when energy is on the way,” says lead researcher Dr Nicholas Gant from the Department of Sport and Exercise Science.

“We have shown that carbohydrate in the mouth produces an immediate increase in neural drive to both fresh and fatigued muscle and that the size of the effect is unrelated to the amount of glucose in the blood or the extent of fatigue.”

The current research has been published in the journal Brain Research and has also captured the attention of New Scientist magazine.

In the first of two experiments, 16 healthy young men who had been doing biceps exercises for 11 minutes were given a carbohydrate solution to drink or an identically flavored energy-free placebo. Their biceps strength was measured before and immediately afterward, as was the activity of the brain pathway known to supply the biceps.

Around one second after swallowing the drink, neural activity increased by 30 percent and muscle strength two percent, with the effect lasting for around three minutes. The response was not related to the amount of glucose in the bloodstream or how fatigued the participants were.

“It might not sound like much, but a two percent increase in muscle strength is enormous, especially at the elite level. It’s the difference between winning an Olympic medal or not,” says co-author Dr Cathy Stinear.

As might be expected, a second boost in muscle strength was observed after 10 minutes when carbohydrate reached the bloodstream and muscles through digestion, but no additional boost in neural activity was seen at that time.

“Two quite distinct mechanisms are involved,” says Dr Stinear. “The first is the signal from the mouth via the brain that energy is about to be available and the second is when the carbohydrate actually reaches the muscles and provides that energy,” says Dr Stinear.

“The carbohydrate and placebo solutions used in the experiment were of identical flavor and sweetness, confirming that receptors in the mouth can process other sensory information aside from the basic taste qualities of food. The results suggest that detecting energy may be a sixth taste sense in humans,” says Dr Gant.

In the second experiment, 17 participants who had not been doing exercise and were not fatigued simply held one of the solutions in their mouths without swallowing. Measurements of the muscle between the thumb and index finger were taken while the muscle was either relaxed or active.

A similar, though smaller effect was observed as in the first experiment, with a nine percent increase in neural activity produced by the carbohydrate solution compared with placebo. This showed that the response is seen in both large powerful muscles and in smaller muscles responsible for fine hand movements.

“Together the results show that carbohydrate in the mouth activates the neural pathway whether or not muscles are fatigued. We were surprised by this, because we had expected that the response would be part of the brain’s sophisticated system for monitoring energy levels during exercise,” says Dr Stinear.

“Seeing the same effect in fresh muscle suggests that it’s more of a simple reflex – part of our basic wiring – and it appears that very ancient parts of the brain such as the brainstem are involved. Reflexive movements in response to touch, vision and hearing are well known but this is the first time that a reflex linking taste and muscle activity has been described,” she says.

Further research is required to determine the precise mechanisms involved and to learn more about the size of the effect on fresh versus fatigued muscle.

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Article adapted by MD Sports from original press release.
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Contact: Pauline Curtis
The University of Auckland

Taste of Carbohydrate Increases Muscle Power

Researchers at The University of Auckland have shown for the first time that the mere presence of carbohydrate solution in the mouth immediately boosts muscle strength, even before it is swallowed.

The results suggest that a previously unknown neural pathway is activated when receptors in the mouth detect carbohydrate, stimulating parts of the brain that control muscle activity and producing an increase in muscle strength.

Previous research had shown that the presence of carbohydrate in the mouth can improve physical performance during prolonged activity, but the mechanism involved was not known and it was unclear whether a person must be fatigued for the effect to be seen.

“There appears to be a pathway in the brain that tells our muscles when energy is on the way,” says lead researcher Dr Nicholas Gant from the Department of Sport and Exercise Science.

“We have shown that carbohydrate in the mouth produces an immediate increase in neural drive to both fresh and fatigued muscle and that the size of the effect is unrelated to the amount of glucose in the blood or the extent of fatigue.”

The current research has been published in the journal Brain Research and has also captured the attention of New Scientist magazine.

In the first of two experiments, 16 healthy young men who had been doing biceps exercises for 11 minutes were given a carbohydrate solution to drink or an identically flavored energy-free placebo. Their biceps strength was measured before and immediately afterward, as was the activity of the brain pathway known to supply the biceps.

Around one second after swallowing the drink, neural activity increased by 30 percent and muscle strength two percent, with the effect lasting for around three minutes. The response was not related to the amount of glucose in the bloodstream or how fatigued the participants were.

“It might not sound like much, but a two percent increase in muscle strength is enormous, especially at the elite level. It’s the difference between winning an Olympic medal or not,” says co-author Dr Cathy Stinear.

As might be expected, a second boost in muscle strength was observed after 10 minutes when carbohydrate reached the bloodstream and muscles through digestion, but no additional boost in neural activity was seen at that time.

“Two quite distinct mechanisms are involved,” says Dr Stinear. “The first is the signal from the mouth via the brain that energy is about to be available and the second is when the carbohydrate actually reaches the muscles and provides that energy,” says Dr Stinear.

“The carbohydrate and placebo solutions used in the experiment were of identical flavor and sweetness, confirming that receptors in the mouth can process other sensory information aside from the basic taste qualities of food. The results suggest that detecting energy may be a sixth taste sense in humans,” says Dr Gant.

In the second experiment, 17 participants who had not been doing exercise and were not fatigued simply held one of the solutions in their mouths without swallowing. Measurements of the muscle between the thumb and index finger were taken while the muscle was either relaxed or active.

A similar, though smaller effect was observed as in the first experiment, with a nine percent increase in neural activity produced by the carbohydrate solution compared with placebo. This showed that the response is seen in both large powerful muscles and in smaller muscles responsible for fine hand movements.

“Together the results show that carbohydrate in the mouth activates the neural pathway whether or not muscles are fatigued. We were surprised by this, because we had expected that the response would be part of the brain’s sophisticated system for monitoring energy levels during exercise,” says Dr Stinear.

“Seeing the same effect in fresh muscle suggests that it’s more of a simple reflex – part of our basic wiring – and it appears that very ancient parts of the brain such as the brainstem are involved. Reflexive movements in response to touch, vision and hearing are well known but this is the first time that a reflex linking taste and muscle activity has been described,” she says.

Further research is required to determine the precise mechanisms involved and to learn more about the size of the effect on fresh versus fatigued muscle.

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Article adapted by MD Sports from original press release.
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Contact: Pauline Curtis
The University of Auckland

Insights into how muscle adapts to endurance

Duke University Medical Center researchers have identified the skeletal muscle changes that occur in response to endurance exercise and have better defined the role of vascular endothelial growth factor (VEGF) in creating new blood vessels, known as angiogenesis, in the process.

VEGF is a protein known to trigger blood vessel growth by activating numerous genes involved in angiogenesis.

The researchers’ new insights could provide a roadmap for medical investigators as they seek to use VEGF in treating human conditions characterized by lack of adequate blood flow, such as coronary artery disease or peripheral arterial disease.

Using mice as animal models, the researchers found that exercise initially stimulates the production of VEGF, which then leads to an increase in the number of capillaries within a specific muscle fiber type, ultimately leading to an anaerobic to aerobic change in the muscle fibers supplied by those vessels. The VEGF gene produces a protein that is known to trigger blood vessel growth.

The results of the Duke experiments were presented by cardiologist Richard Waters, M.D., Nov. 8, 2004, at the American Heart Association’s annual scientific sessions in New Orleans.

“It is known that exercise can improve the symptoms of peripheral arterial disease in humans and it has been assumed that angiogenesis played a role in this improvement,” Waters said. “However, the clinical angiogenesis trials to date utilizing VEGF have been marginally successful and largely disappointing, so we felt it would be better at this point to return to animal studies in an attempt to better understand the angiogenic process.”

The Duke team performed their experiments using a mouse model of voluntary exercise. This experimental approach is important, they explained, because most skeletal muscle adaptation studies utilize electrical stimulation of the muscle, which is much less physiologic and does not as closely mimic what would be expected in human exercise.

When placed in the dark with a running wheel, mice will instinctively run, the researchers said. In the Duke experiments, 41 out of 42 mice “ran” up to seven miles each night. At regular intervals over a 28-day period, the researchers then performed detailed analysis of capillary growth and the subsequent changes in muscle fiber type and compared these findings to sedentary mice.

Mammalian muscle is generally made up of two different fiber types – slow-twitch fibers requiring oxygen to function, and the fast-twitch fibers, which function in the absence of oxygen by breaking down glucose. Because of their need for oxygen, slow-twitch fibers tend to have a higher density of capillaries.

“Exercise training is probably the most widely utilized physiological stimulus for skeletal muscle, but the mechanisms underlying the adaptations muscle fibers make in response to exercise is not well understood,” Waters said. “What we have shown in our model is that increases in the capillary density occur before a significant change from fast-twitch to slow-twitch fiber type, and furthermore, that changes in levels of the VEGF protein occur before the increased capillary density.”

“Interestingly, capillary growth appears to occur preferentially among fast-twitch fibers, and it is these very fibers that likely change to slow-twitch fibers,” Waters said. “Since exercise has the potential to impact an enormous number of clinical conditions, therapeutic manipulations intended to alter the response to exercise would benefit from a more detailed understanding of what actually happens to muscle as a result of exercise.”

The exact relationship between VEGF, exercise induced angiogenesis, and muscle fiber type adaptation is still not clear and will become the focus of the group’s continuing research. The findings from the current study, however, are providing important temporal and spatial clues to the adaptability process.

“Our data suggests that angiogenesis is one of the key early steps in skeletal muscle adaptation and may be an essential step in the adaptability process,” Waters continued. “This understanding could be crucial for designing new studies that can be performed to inhibit the angiogenic response to exercise in order to directly test the links between angiogenesis and skeletal muscle plasticity.”

###

The research team was supported by grants from the American Heart Association and the U.S. Department of Veterans Affairs.

Other members of the Duke team were Ping Li, Brian Annex, M.D., and Zhen Yan, Ph.D. Svein Rotevatn, Haukeland University Hospital, Bergen, Norway, was also a member of the team.

Duke University Medical Center researchers have identified the skeletal muscle changes that occur in response to endurance exercise and have better defined the role of vascular endothelial growth factor (VEGF) in creating new blood vessels, known as angiogenesis, in the process.

VEGF is a protein known to trigger blood vessel growth by activating numerous genes involved in angiogenesis.

The researchers’ new insights could provide a roadmap for medical investigators as they seek to use VEGF in treating human conditions characterized by lack of adequate blood flow, such as coronary artery disease or peripheral arterial disease.

Using mice as animal models, the researchers found that exercise initially stimulates the production of VEGF, which then leads to an increase in the number of capillaries within a specific muscle fiber type, ultimately leading to an anaerobic to aerobic change in the muscle fibers supplied by those vessels. The VEGF gene produces a protein that is known to trigger blood vessel growth.

The results of the Duke experiments were presented by cardiologist Richard Waters, M.D., Nov. 8, 2004, at the American Heart Association’s annual scientific sessions in New Orleans.

“It is known that exercise can improve the symptoms of peripheral arterial disease in humans and it has been assumed that angiogenesis played a role in this improvement,” Waters said. “However, the clinical angiogenesis trials to date utilizing VEGF have been marginally successful and largely disappointing, so we felt it would be better at this point to return to animal studies in an attempt to better understand the angiogenic process.”

The Duke team performed their experiments using a mouse model of voluntary exercise. This experimental approach is important, they explained, because most skeletal muscle adaptation studies utilize electrical stimulation of the muscle, which is much less physiologic and does not as closely mimic what would be expected in human exercise.

When placed in the dark with a running wheel, mice will instinctively run, the researchers said. In the Duke experiments, 41 out of 42 mice “ran” up to seven miles each night. At regular intervals over a 28-day period, the researchers then performed detailed analysis of capillary growth and the subsequent changes in muscle fiber type and compared these findings to sedentary mice.

Mammalian muscle is generally made up of two different fiber types – slow-twitch fibers requiring oxygen to function, and the fast-twitch fibers, which function in the absence of oxygen by breaking down glucose. Because of their need for oxygen, slow-twitch fibers tend to have a higher density of capillaries.

“Exercise training is probably the most widely utilized physiological stimulus for skeletal muscle, but the mechanisms underlying the adaptations muscle fibers make in response to exercise is not well understood,” Waters said. “What we have shown in our model is that increases in the capillary density occur before a significant change from fast-twitch to slow-twitch fiber type, and furthermore, that changes in levels of the VEGF protein occur before the increased capillary density.”

“Interestingly, capillary growth appears to occur preferentially among fast-twitch fibers, and it is these very fibers that likely change to slow-twitch fibers,” Waters said. “Since exercise has the potential to impact an enormous number of clinical conditions, therapeutic manipulations intended to alter the response to exercise would benefit from a more detailed understanding of what actually happens to muscle as a result of exercise.”

The exact relationship between VEGF, exercise induced angiogenesis, and muscle fiber type adaptation is still not clear and will become the focus of the group’s continuing research. The findings from the current study, however, are providing important temporal and spatial clues to the adaptability process.

“Our data suggests that angiogenesis is one of the key early steps in skeletal muscle adaptation and may be an essential step in the adaptability process,” Waters continued. “This understanding could be crucial for designing new studies that can be performed to inhibit the angiogenic response to exercise in order to directly test the links between angiogenesis and skeletal muscle plasticity.”

 

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Article adapted by MD Sports from original press release.
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Contact: Richard Merritt
Duke University Medical Center 

The research team was supported by grants from the American Heart Association and the U.S. Department of Veterans Affairs

Cereal and Milk Good for Exercise Muscle Recovery

Cereal and non-fat milk is as good as a commercially-available sports drink in initiating post-exercise muscle recovery.

Background

This study compared the effects of ingesting cereal and nonfat milk (Cereal) and a carbohydrate-electrolyte sports drink (Drink) immediately following endurance exercise on muscle glycogen synthesis and the phosphorylation state of proteins controlling protein synthesis: Akt, mTOR, rpS6 and eIF4E.

Methods

Trained cyclists or triathletes (8 male: 28.0+/-1.6 yrs, 1.8+/-0.0 m, 75.4+/-3.2 kg, 61.0+/-1.6 ml O2 * kg-1 * min-1; 4 female: 25.3+/-1.7 yrs, 1.7+/-0.0 m, 66.9+/-4.6 kg, 46.4+/-1.2 mlO2 * kg-1 * min-1) completed two randomly-ordered trials serving as their own controls. After 2 hours of cycling at 60-65% VO2MAX, a biopsy from the vastus lateralis was obtained (Post0), then subjects consumed either Drink (78.5 g carbohydrate) or Cereal (77 g carbohydrate, 19.5 g protein and 2.7 g fat). Blood was drawn before and at the end of exercise, and at 15, 30 and 60 minutes after treatment. A second biopsy was taken 60 minutes after supplementation (Post60). Differences within and between treatments were tested using repeated measures ANOVA.

Results

At Post60, blood glucose was similar between treatments (Drink 6.1+/-0.3, Cereal 5.6+/-0.2 mmol/L, p<.05), but after Cereal, plasma insulin was significantly higher (Drink 123.1+/-11.8, Cereal 191.0+/-12.3 pmol/L, p<.05), and plasma lactate significantly lower (Drink 1.4+/-0.1, Cereal 1.00+/-0.1 mmol/L, p<.05). Except for higher phosphorylation of mTOR after Cereal, glycogen and muscle proteins were not statistically different between treatments. Significant Post0 to Post60 changes occurred in glycogen (Drink 52.4+/-7.0 to 58.6+/-6.9, Cereal 58.7+/-9.6 to 66.0+/-10.0 mumol/g, p<.05) and rpS6 (Drink 17.9+/-2.5 to 35.2+/-4.9, Cereal 18.6+/-2.2 to 35.4+/-4.4 %Std, p<.05) for each treatment, but only Cereal significantly affected glycogen synthase (Drink 66.6+/-6.9 to 64.9+/-6.9, Cereal 61.1+/-8.0 to 54.2+/-7.2%Std, p<.05), Akt (Drink 57.9+/-3.2 to 55.7+/-3.1, Cereal 53.2+/-4.1 to 60.5+/-3.7 %Std, p<.05) and mTOR (Drink 28.7+/-4.4 to 35.4+/-4.5, Cereal 23.0+/-3.1 to 42.2+/-2.5 %Std, p<.05). eIF4E was unchanged after both treatments.

Conclusion

These results suggest that Cereal is as good as a commercially-available sports drink in initiating post-exercise muscle recovery.

Author: Lynne Kammer, Zhenping Ding, Bei Wang, Daiske Hara, Yi-Hung Liao and John L. Ivy

Credits/Source: Journal of the International Society of Sports Nutrition 2009, 6:11

G-Trainer: Low-gravity training machine reduces joint and muscle discomfort

A University of Colorado at Boulder study of a space-age, low-gravity training machine used by several 2008 Olympic runners showed it reduced impacts on muscles and joints by nearly half when subjects ran at the equivalent of 50 percent of their body weight.

The new study has implications for both competitive runners rehabilitating from injuries and for ordinary people returning from knee and hip surgeries, according to Associate Professor Rodger Kram of CU-Boulder’s integrative physiology department.

Known as the “G-Trainer,” the machine consists of a treadmill surrounded by an inflatable plastic chamber that encases the lower body of the runner, said Kram. Air pumped into the chamber increases the pressure and effectively reduces the weight of runners, who are sealed in the machine at the waist in a donut-shaped device with a special zipper and “literally lifted up by their padded neoprene shorts,” he said.

Published in the August issue of the Journal of Applied Biomechanics, the study is the first to quantify the effects of running in the G-Trainer, built by Alter-G Inc. of Menlo Park, Calif., using technology developed at NASA’s Ames Research Center in California. The paper was authored by Kram and former CU-Boulder doctoral student Alena Grabowski, now a postdoctoral researcher at the Massachusetts Institute of Technology.

Although G-Trainers have been used in some sports clinics and college and professional sports training rooms since 2006, the new study is the first scientific analysis of the device as a training tool for running, said Grabowski.

“The idea was to measure which levels of weight support and speeds give us the best combination of aerobic workout while reducing the impact on joints,” said Kram. “We showed that a person can run faster in the G-Trainer at a lower weight and still get substantial aerobic benefits while maintaining good neuromuscular coordination.”

The results indicated a subject running at the equivalent of half their weight in the G-Trainer at about 10 feet per second, for example — the equivalent of a seven-minute mile — decreased the “peak” force resulting from heel impact by 44 percent, said Grabowski. That is important, she said, because each foot impact at high speed can jar the body with a force equal to twice a runner’s weight.

Several former CU track athletes participating in the 2008 Olympics in Beijing have used the machine, said Kram. Alumna Kara Goucher, who will be running the 5,000- and 10,000-meter races in Beijing, has used the one in Kram’s CU-Boulder lab and one in Eugene, Ore., for rehabilitation, and former CU All-American and Olympic marathoner Dathan Ritzenhein also uses a G-Trainer in his home in Oregon. Other current CU track athletes who have been injured have tried the machine in Kram’s lab and found it helpful to maintain their fitness as they recovered, Kram said.

For the study, the researchers retrofitted the G-Trainer with a force-measuring treadmill invented by Kram’s team that charts vertical and horizontal stress load on each foot during locomotion, measuring the variation of biomechanical forces on the legs during running. Ten subjects each ran at three different speeds at various reduced weights, with each run lasting seven minutes. The researchers also measured oxygen consumption during each test, Kram said.

Grabowski likened the effect of the G-Trainer on a runner to pressurized air pushing on the cork of a bottle. “If you can decrease the intensity of these peak forces during running, then you probably will decrease the risk of injury to the runner.”

The G-Trainer is a spinoff of technology originally developed by Rob Whalen, who conceived the idea while working at NASA Ames as a National Research Council fellow to help astronauts maintain fitness during prolonged space flight. While the NASA technology was designed to effectively increase the weight of the astronauts to stem muscle atrophy and bone loss in low-gravity conditions, the G-Trainer reverses the process, said Grabowski.

In the past, sports trainers and researchers have used climbing harnesses over treadmills or flotation devices in deep-water swimming pools to help support the weight of subjects, said Kram. Harnesses are cumbersome, while pool exercises don’t provide sufficient aerobic stimulation and biomechanical loading on the legs, he said.

Marathon world-record holder Paula Radcliffe of Great Britain is currently using a G-Trainer in her high-altitude training base in Font-Remeu, France. Radcliffe is trying to stay in top running shape while recovering from a stress fracture in her femur in time for the 2008 Olympic women’s marathon on Aug. 17, according to the London Telegraph.

Kram and Grabowski have begun a follow-up study of walking using the G-Trainer. By studying subjects walking at various weights and speeds in the machine, the researchers should be able to quantify its effectiveness as a rehabilitation device for people recovering from surgeries, stress fractures and other lower body injuries, Kram said.

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Article adapted by MD Sports from original press release.
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Contact: Rodger Kram
University of Colorado at Boulder

Individuals take 16 steps more to run a mile than walk

A new pair of studies compare step counts needed to meet 1) ACSM/CDC recommendations for moderate physical activity and 2) a one-mile mark. Both studies are useful as suggested step-based guidelines for meeting physical activity recommendations.

The first study, funded by the Centers for Disease Control and Prevention, was designed to translate ACSM/CDC public health guidelines for 30 minutes of daily moderate-intensity physical activity into steps. Researchers at San Diego State University and Arizona State University utilized commercial pedometers on a community sample of adults. Their results support an approximate 100 step/minute recommendation for minimally moderate intensity. To meet ACSM/CDC recommendations, this equates to 3,000 steps in 30 minutes, or three daily bouts of 1,000 steps in 10 minutes.

While pedometers are useful tools to measure step counts, this team notes pedometer-derived steps should be used with caution for gauging moderate intensity walking. Step counts associated with moderate intensity walking should be individualized based on stride length and level of fitness. ACSM defines moderate intensity walking as “brisk” walking, or “walking with purpose.” Walkers should be able to talk comfortably at a moderate-intensity level, but still feel exertion. Other definitions have included a pace at which you break a sweat and/or have a slight increase in your heart rate.

“Walking is one of the easiest forms of physical activity, and one that most people can do to meet recommendations for daily exercise,” said Simon J. Marshall, Ph.D., lead author of the study. “Most people have an instinct about the length of time or the distance they walk. A pedometer can help count steps, but when you also try to walk at least 1000 steps in 10 minutes on a regular basis, you may gain significant health benefits. For inactive people, setting smaller targets can help them start a program to meet general physical activity guidelines and enhance their health and wellness.”

In the one-mile study, researchers at Boise State University wanted to determine the number of steps individuals take while walking one mile at 20 and 15-minute paces and while running the same distance at 12, 10, eight, and six-minute paces. One mile (1,609 meters) step count varies at different walking and running speeds and can be predicted based on gender, pace, and height or leg length.

The average number of steps required to run/walk a mile ranged from 1,064 steps for a six-minute-mile pace in men to 2,310 steps for a 20-minute per mile walk in women. An interesting finding is that on average, individuals took more steps while running (jogging) a 12-minute mile than while walking a 15-minute mile (1,951 vs.1,935 steps, respectively). This finding is most likely related to the smaller distance between steps that people tend to take while jogging at the slower speed (12-minute mile) compared to walking at a 15-minute per mile pace.

“A ‘mile’ appears to be universally known as a marker of distance for walkers and runners to measure their activity achievements,” said Werner Hoeger, Ed.D., FACSM, lead author. “To estimate the number of steps required to walk or run a mile at selected speeds is likely to help people who monitor their steps with a pedometer with the objective of increasing their fitness by working up the miles.”

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Article adapted by MD Sports Weblog from original press release.
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The American College of Sports Medicine is the largest sports medicine and exercise science organization in the world. More than 20,000 international, national, and regional members are dedicated to advancing and integrating scientific research to provide educational and practical applications of exercise science and sports medicine.

http://www.acsm.org

Candy Bars Not Much Different Than Energy Bars For Athletes

Energy bars, touted for improving athletic performance while providing the right combination of essential nutrients, may not always give endurance athletes the boost they expect.An Ohio State University researcher compared two popular energy bars and found that one of the bars didn’t give the moderate increase in blood sugar known to enhance performance in endurance athletes. Instead, its effect was much like a candy bar – giving a big rush of sugar to the blood, followed by a sharp decline.

“Theoretically, energy bars produce more moderate increases and decreases in blood sugar levels than a typical candy bar,” said Steve Hertzler, an associate professor of medical dietetics at Ohio State. “But these claims aren’t necessarily valid.” His study appears in a recent issue of the Journal of the American Dietetic Association.

Hertzler wanted to know how energy bars affected blood glucose levels. Glucose is a sugar that provides energy to the body’s cells – for example, red-blood cells and most parts of the brain derive most of their energy from glucose.

“Athletes – especially those involved in endurance sports – want to enhance performance, and energy bars claim to help keep blood sugar levels at a moderate level,” Hertzler said.

Volunteers had to fast for at least 12 hours before taking part in each of four experiments. Then, they ate one of four experimental “meals” consisting of either four slices of white bread; a Snickers bar; an Ironman PR Bar; or a PowerBar. Each experimental meal provided the same amount of carbohydrates (50 grams.)

Hertzler then tested the effects these foods had on blood glucose levels at 15-minute intervals for up to two hours after each experimental meal. The volunteers had to wait at least 24 hours between each experimental meal.

Hertzler measured each subject’s blood samples for glucose levels, to determine which food most raised blood sugar levels.

Both energy bars caused blood glucose levels to peak at 30 minutes, while levels peaked at 45 minutes after the bread and candy bar were consumed. Blood glucose levels declined steadily throughout the duration of testing for all foods but the Ironman PR Bar. This bar caused blood glucose rates to remain fairly steady, probably because of the moderate carbohydrate level of the bar, according to Hertzler.

“Though blood glucose rates peaked at 30 minutes with both bars, the high-carbohydrate energy bar – the PowerBar – caused a much sharper decline,” Hertzler said. “In fact, the decline was sharper than with the candy bar.” Much of the energy derived from the bread and the candy bar came from carbohydrate and the same was true for the PowerBar. While the bar is low in protein and fat, more than 70 percent of it is made up of carbohydrate (such as high-fructose corn syrup; oat bran; and brown rice). In contrast, 40 percent of the Ironman PR is comprised of carbohydrate (high fructose corn syrup and fructose.) The rest of the bar was comprised of 30 percent fat and 30 percent protein.

“The composition of this bar may have been responsible for the diminished blood glucose response,” Hertzler said. “Athletes involved in short-duration events who want a quick energy boost should eat a high-carbohydrate energy bar or a candy bar,” he suggests. “However, endurance athletes would do well to consume an energy bar with a moderate carbohydrate level.”

Hertzler conducted this study while at Kent State University in Kent, Ohio. He is continuing similar research at Ohio State.

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Article adapted by MD Sports Weblog from original press release.
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Contact: Steve Hertzler
Ohio State University

Editor’s note: This research was funded by a grant from Kent State University. The researcher received no funding from either energy bar manufacturer.

Negative energy balance, not exercise, causes menstrual disturbance

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

Moderate exercise prevents extreme weight gain with age

The old adage “use it or lose it” is truer than ever. People who maintain a vigorously active lifestyle as they age gain less weight than people who exercise at more moderate levels, according to a first-of-its-kind study that tracked a large group of runners who kept the same exercise regimen as they grew older. The study also found that maintaining exercise with age is particularly effective in preventing extreme weight gain, which is associated with high blood pressure, high cholesterol, diabetes, and other diseases.

The study, conducted by Paul Williams of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), followed 6,119 men and 2,221 women who maintained their weekly running mileage (to within three miles per week) over a seven-year period. On average, the men and women who ran over 30 miles per week gained half the weight of those who ran less than 15 miles per week.

“To my knowledge, this is the only study of its type,” says Williams, a staff scientist in Berkeley Lab’s Life Sciences Division. “Other studies have tracked exercise over time, but the majority of people will have changed their exercise habits considerably.”

The research is the latest report from the National Runners’ Health Study, a 20-year research initiative started by Williams that includes more than 120,000 runners. It appears in the May issue of the journal Medicine and Science in Sports and Exercise.

Specifically, between the time subjects entered the study and when they were re-contacted seven years later, 25-to-34-year-old men gained 1.4 pounds annually if they ran less than 15 miles per week. In addition, male runners gained 0.8 pounds annually if they ran between 15 and 30 miles per week, and 0.6 pounds annually if they ran more than 30 miles per week.

This trend is mirrored in women. Women between the ages of 18 and 25 gained about two pounds annually if they ran less than 15 miles per week, 1.4 pounds annually if they ran 15 to 30 miles per week, and slightly more than three-quarters of a pound annually if they ran more than 30 miles per week. Other benefits to running more miles each week included fewer inches gained around the waist in both men and women, and fewer added inches to the hips in women.

“As these runners aged, the benefits of exercise were not in the changes they saw in their bodies, but how they didn’t change like the people around them,” says Williams.

Although growing older and gaining weight is something of a package deal, it isn’t the same in everyone. The lucky few remain lean as they age, most people pack on several pounds, and some people become obese. The latter group is particularly at risk for high blood pressure, high cholesterol, and diabetes. Fortunately, Williams’ results show that maintaining exercise can combat such extreme weight gain.

“Getting people to commit to a vigorously active lifestyle while young and lean will go a long way to reducing the obesity epidemic in this country,” says Williams.

Another paper published in the November 2006 issue of the journal Obesity by Williams and Paul Thompson of Hartford (CT) Hospital found that runners who increased their running mileage gained less weight than those who remained sedentary, and runners that quit running became fatter.

“The time to think about exercise is before you think you need it,” says Williams. “The medical journals are full of reports on how difficult it is to regain the slenderness of youth. The trick is not to get fat.”

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Article adapted by MD Sports Weblog from original press release.
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Contact: Dan Krotz
DOE/Lawrence Berkeley National Laboratory

Williams’ research was funded by the National Heart, Lung and Blood Institute. The study in the May issue of the journal Medicine and Science in Sports and Exercise is entitled Maintaining Vigorous Activity Attenuates 7-yr Weight Gain in 8,340 Runners.

Low-Fat Diet Hurts Runners Perfomance, Suppresses Immune Function, and Increases Infection Risk

Trained runners who severely limit the amount of fat in their diets may be suppressing their immune system and increasing their susceptibility to infections and inflammation, a University at Buffalo study has shown.In findings presented here today (May 22, 1999) at the fourth International Society for Exercise and Immunology Symposium, lead author Jaya T. Venkatraman, Ph.D., reported that running 40 miles per week on a diet composed of approximately 17 percent fat compromised the runners’ immune response.

The medium and high-fat diets, composed of approximately 32 and 41 percent fat respectively, left the immune system intact, and enhanced certain components, the findings showed.

“The data suggest that higher-fat diets may lower the proinflammatory cytokines, free radicals and hormones, and may enhance the levels of anti-inflammatory cytokines,” Venkatraman said.

Venkatraman is an associate professor of nutrition in the Department of Physical Therapy, Exercise and Nutrition Sciences in the UB School of Health Related Professions.

Earlier studies published by a UB research group headed by David Pendergast, Ed.D., professor of physiology and biophysics, reported that competitive runners who increased the proportion of fat in their diets improved their endurance with no negative effect on weight, body composition, blood pressure, pulse rate or total cholesterol. (See editor’s note)

However, since a high level of fat was thought to be immunosuppressive, the researchers sought to determine if increasing dietary fat would compromise various elements of the immune system, while improving performance.

“In general, moderate levels of exercise are known to enhance the immune system,” said Venkatraman. “But high-intensity exercise and endurance exercise produce excess levels of free radicals, which may place stress on the immune system.

“Since we have shown that athletes perform better on a higher-fat diet than on a low-fat diet, it was important to determine if the higher-fat diet would further compromise the immune system,” she said. “We found that it did not, but the very-low-fat diet did.”

The study involved six female and eight male competitive runners who trained at 40 miles a week and were part of a larger performance study. They spent a month on their normal diets, followed by a month each on diets composed of approximately 17 percent, 32 percent and 41 percent fat. Protein remained stable at 15 percent and carbohydrates made up the difference.

The immune status of the runners was obtained by analyzing concentrations of essential components of the immune system — leukocytes, cytokines and plasma cortisol — in blood samples taken before and after an endurance exercise test. The tests were conducted at the end of each four-week diet period.

Results showed that natural killer cells, a type of leukocyte and one of the body’s defense mechanisms marshaled to fight infection, were more than doubled in runners after the high-fat diet, compared to the low-fat regimen. Levels of PGE2, inflammation-causing prostaglandins, increased after the endurance test and were higher when the runners were on the low-fat diet.

This study is part of a larger investigation to determine the effects of dietary fat on performance, biochemical and nutritional status, and plasma lipids and lipoprotein profiles in distance runners being conducted by a study group composed of — in addition to Venkatraman and Pendergast — Peter Horvath, Ph.D., associate professor in the UB Department of Physical Therapy, Exercise and Nutrition Sciences, and John Leddy, M.D., clinical professor of orthopaedics and associate director of the UB Sports Medicine Institute.

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Article adapted by MD Sports Weblog from original press release.
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Contact: Lois Baker
University at Buffalo