ACSM: A Peak
Experience
Mary
Ann Wallace,
Snowmass Village, Colorado USA
Sportscience News July-Aug 1997
http://www.sportsci.org/news/news9707/wallace.htm
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ACSM: A Peak
Experience
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The
Obesity Epidemic: If it's in your genes, the more
reason to exercise. |
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Several other presentations are summarized below. The abstracts for these and other talks are published in the Supplement to Medicine & Science in Sports & Exercise (Vol. 29, No. 5, May 1997). Abstract numbers are included to make it easier for you to find them. You can also order tapes of lectures, symposiums, and other major presentations through the communications company which taped the conference, Mobiltape.
Next year the conference will be in Orlando, Florida, from June 2-5, dovetailing with the XXVI FIMS World Congress of Sports Medicine also in Orlando from May 30-June 3, 1998. See you there!
Dr. Claude Bouchard: "The Current Obesity Epidemic: Chaos, Gluttony, Sloth, or Nature?"
The hottest health issue of our times--the increasing growth of obesity was analyzed by one of the world's most influential exercise scientists and currently professor in the Physical Activity Sciences Laboratory at Laval University in Quebec, Canada. Call him obsessed with the Venus of Willendorf, the 25,000 year-old obesity case, Bouchard's years of research on obesity has spread some light on the causes behind this alarming statistic: currently one-third of the population in Germany, Great Britain, Canada and the United States are obese.
Long ago Hippocrates stated, "Repletion, carried to extreme is perilous." And with that thought, Bouchard outlined the health implications of obesity. Nearly a quarter of total mortality can be attributed to obesity through diseases like adult-onset diabetes, coronary heart disease, hypertension, and cerebrovascular disease.
Obesity is hazardous. Excess body fat causes metabolic disturbances with late effects on morbidity and mortality. One thing is clear: obesity involves a positive energy balance. That is, energy balance (EB) > energy intake (EI) - energy expenditure (EE). Only three scenarios could account for it: a positive EB as a result of an increasing EI on a constant EE, a positive EB with a constant EI but a decreasing EE, or a positive EB with a decreasing EI and an even more pronounced decrease in EE.
On the question posed in his lecture topic, why is obesity so common, he focuses on possible reasons. Is it gluttony? are we overfeeding? Are we eating more calories than our ancestors? Would they have been obese in earlier generations? Studies suggest energy intake per capita has not increased over the past fifty years. In fact, it may have even decreased. Can dietary fat be the culprit? The "too much fat in the diet" scenario is popular, but just does not fit with the data: the proportion of fat in the U.S. has dropped from 40% to 33% over the exact time period when obesity incidence has risen at a record pace.
Is the obesity epidemic due to inactivity? Have we become couch potatoes? It is quite likely that our energy expenditure of activity has gone down. Taking a look at the trends, the number of cars per household has gone up, the number of television viewing hours per week has gone up. There's a good fit in a study done in Britain; those most active were the leanest. Bouchard argues that the present epidemic of overweight/obesity cases would be conquered if the individuals at risk were as active as those of previous generations.
But is inactivity the entire culprit? Could nature be playing a role? Are genes involved? Are Body Mass Index (BMI: weight in kg divided by height in meters squared) and other measures of body composition characteristics influenced by genetic transmissions from one generation to the next? If so, which genes are carrying the critical mutations? Over 50 studies have looked into genetics using families with obese members. Bouchard's summation of the existing data is that there is familial aggregation of BMI and other body composition characteristics, and genetic heritability is of the order of 25 to 40%. Bouchard also reported that there are about 70 putative genes or markers associated with obesity.
Bouchard's paradigmatic lecture left us pondering solutions. Obesity costs the US $70 billion in health care related costs. Those numbers will only get worse since if current trends are projected two centuries into the future, 100% of all US adults will be overweight!
Intermittent or Continuous Exercise for Health?
Much has been said about exercising more frequently but for less time each session as a substitute for longer, less frequent exercise. The ACSM previously had recommended 30 minutes continuous exercise 3 times a week. The new recommendation published jointly by the ACSM and Center for Disease Control in 1993 recommends moderate levels of moderate exercise and encourages more frequent sessions of briefer duration as an easier but effective exercise strategy. This concept was examined in a study (MSSE Abstract#502) involving 37 individuals randomly assigned to either continuous 30 minutes, 3 days a week exercise regime over 24 weeks or a program of intermittent exercise consisting of 15 minutes each for two sessions a day, 5 days a week. There were no alterations in diet. The results suggest that the current CDC/ACSM minimum exercise recommendations may not be sufficient without energy restrictions for weight loss. Does this study topple the "exercise lite" recommendation promoted since 1993? No, but it does add to the fuel of a concerned group of exercise researchers who warn that the new CDC/ACSM recommendations were not amply supported by scientific data. A recent issue of Science (30 May 1997) has more on this debate.
Another study found improvements in lowering body weight and improving VO2peak with continuous exercise three times a week. Males diagnosed with elevated blood lipid and blood pressure performed a six months exercising program at 70-85% intensity. The sessions consisted of a 15-minute warm up with light stretches and strengthening exercises followed by 30-40 minutes walking/jogging intervals and 10-15 minutes decreasing intensity cardiovascular and flexibility exercises three days a week. It was found that six months of cardiovascular exercise was beneficial in improving VO2peak, body weight, % body fat, blood lipids and blood pressure. Improvement of VO2peak was correlated with reductions in diastolic blood pressure in those with diastolic blood pressure > 90 mmHg, whereas reduction in body weight and % body fat was correlated with changes in blood lipid levels in those with elevated blood lipids. (#503)
Research on Exercising Women Increases
Female athletes haven't been popular as research study groups in the past, owing to their small numbers and the "fluctuating hormone excuse." Fortunately, a group from the University of Colorado at Boulder has been active in targeting the growing population of female athletes. The result has been some top notch research, funded by grants from The National Institutes of Health. Their papers were well represented at the conference. Women swimmers and runners were matched in terms of endurance training volume and age-adjusted competitive performance and all women including the control group in terms of age and hormonal replacement therapy. Conclusion: higher total and abdominal body fatness is associated with less favorable coronary heart disease risk factors. Total body fat was higher in swimmers than runners, but lower than those of sedentary women. HDL-C, HDL2-C, Triglycerides and HDL/Total Cholesterol were less favorable in swimmers than runners. Ambulatory systolic blood pressure level was 6-10 mmHg higher in swimmers and sedentaries compared to runners. Fasting plasma insulin concentration was higher in swimmers than runners. All hemostatic risk factors (Fibrogen, Fibrin D-dimer, PaI-1 antigen, t-PA activity, t-PA antigen) but PA1-1 activity were less favorable in swimmers than runners. (#507)
Stevenson et al. examined age-related changes in plasma total cholesterol based on physical activity status. Studying 57 women (27 competitive distance runners and 30 sedentary), they found that higher levels of plasma total cholesterol were associated solely with elevated LDL-C in sedentary women, but in physically active women, they are associated in part with elevated HDL-C which may contribute to reduced age-related risk of coronary heart disease in physically active women. (#527)
Older male endurance athletes demonstrate better maintenance of arterial blood pressure and smaller increases in heart rate vs. age-matched untrained males during an orthostatic challenge. Should these findings be generalized to women? The results of one study suggest that endurance trained post-menopausal women had lower body mass and % body fat and a higher maximal uptake than matched sedentary females. However, in contrast to the data for males, endurance trained women have similar blood pressure responses but greater tachycardia in response to standing. (#513)
Prior studies on males have shown some benefit of resistance training on endurance performance. In a study on females, findings suggest that resistance training may not enhance endurance performance in female endurance cyclists. Strength training (2x/wk, five sets to failure) over a period of 12 weeks resulted in no significant changes in average power output during a one hour cycle test. (#1502)
These studies suggest that both basic cardiovascular adjustments and specific adaptations to exercise based on data collected from males should not be directly generalized to females. If we want to understand the female athlete, we have to study the female athlete.
Because aging is associated with regression of most renal functions and increased incidence of kidney disease, there might be some concern that exercise would trigger impairment of renal functions. Other studies have shown that strenuous exercise reduces plasma renal flow and glomerular filtration rate leading to oliguria and induces post exercise proteinura. Results from a longitudinal study now in its third year show that maximal plasma lactate concentration decreases with aging, owing to a lesser work output. Resting creatinine clearance (or glomerular filtration rate) decreases after age 60, and urea clearances at rest and after exhaustive exercises decrease with aging. So, maximal exercise in the older individual results in less urea production and the aging kidney has reduced clearance capacity which means that exercise doesn't overload the older kidney. Conclusion: regular endurance exercise does not have a detrimental effect on the kidneys of a healthy, elderly population. (#514)
Does fitness have an effect on learning functions as you age? To some extent, yes. Eighty-three adults were randomly assigned to either experimental or control groups. Older fit adults were indistinguishable from younger fit participants in cognitive function and in learning. What separates this study from past research was the separation of the learning function into two distinct components; crystallized intelligence tasks which are associated with a positive accumulation of knowledge over a lifetime and fluid intelligence tasks, the ability to perform logical relations. Fitness moderates the influence of age on performance of a fluid intelligence task, but not on performance of a crystallized intelligence task. Physical fitness may contribute to postponing normal age-related declines in cognitive function. (#699)
As more of the older population exercise and participate in competitive sports, questions arise as to whether aerobic or strength training is of superior benefit as a training modality for the older individual. This was the topic at a symposium addressing changes in cardiovascular and metabolic risk factors, energy and protein metabolism, body composition, and osteoporosis. VO2max has been shown to be an important predictor of mortality and morbidity. How does importance of VO2max affect the choice of a training modality? You may want to trade your weights for fitness shoes or swim gear, because studies showed that VO2max did not change significantly with resistance training but can elicit changes with endurance training. Studies investigating blood pressure concluded that endurance exercise training in older men may reduce blood pressure. Indeed both systolic and diastolic blood pressure improved with endurance training with the improvement as great with low intensity exercise as with high intensity exercise. Trainers will have to use caution with their older athletes, though, as far as high intensity exercise goes and judiciously schedule it. Vigorous endurance training (80-85% VO2max) contributes to greater inactivity during the non-exercise time in these subjects.
Does the older athlete experience any difference in protein requirements as a result of the choice in training modality? Strength training lowers dietary protein requirements, owing to increased nitrogen retention, whereas endurance training increases dietary protein requirements. The general consensus at the symposium: endurance training has the edge as a preferred training modality in the older athlete but it wouldn't hurt to add a couple of strength training sessions each week. (#207)
Cycling and Triathlon Research
How often have you heard a cycling coach say, "spin?" Top cyclists often do 100-120 rpm. Are cyclists more efficient at higher cadences? Do cyclists and runners differ in their cycling efficiency? Surprisingly, gross efficiency of cyclists and runners cycling did not differ significantly and gross efficiency is the important thing when it comes to winning a race. In addition, gross efficiency max occured at 60 rpm whereas Delta efficiency increased with cadences up to 95 rpm. Implications: former runners turned triathletes don't have to feel they're at a cycling disadvantage, and you may benefit speed-wise by keeping your cadence at lower levels than previously thought. (#1122)
Increasing crank arm length allows for corresponding reduction in pedal force. There's also the case for increasing pedal rate at constant power and constant crank arm length. To minimize oxygen consumption, combine a shorter crank with high pedaling rotation and a longer crank with lower pedaling. Better yet, an individual's optimum crank arm length can be predicted by leg length. (#1503)
Running kinematics after cycling differed from those after running, and as running time increased, some interesting results occurred. Speed was not significantly different, but running efficiency after cycling was initially less than after running and then gradually increased and actually surpassed running only efficiency. Since the study employed a run distance of only 5 km, the implication for triathletes is that running efficiency is not as significantly impacted by prior cycling as previously thought, especially in a longer race. (#493)
Training, Tapering and Stress-Associated Damage
During heavy training, 24-hour urinary free cortisol is higher than normal, and hormonal imbalance can occur as a result of heavy intensive training. A significant reduction during the taper phase suggests tapering can help reverse the hormonal changes experienced from strenuous training. Elite runners (1500 m and 3000 m) maintained intensity at a high level (90-100%) with interval training volume reduced by approximately 60-80% of base over a 7-10 day taper period. Urinary free cortisol may be a good marker for monitoring changes in physiological status after hard training and taper. (#1265)
Does the volume of regular endurance training reduce the extent of DNA damage in leucocytes after highly intense anaerobic and intense endurance exercise? One day after a half-marathon, 10 of 12 subjects showed a significant increase in DNA migration in leucocytes. Twenty-four hours after a treadmill test, all of the subjects exhibited a significant increase in DNA migration. Percent changes in DNA migration, however, were significantly lower in the endurance trained group than the low-trained group. Results confirm that highly intense anaerobic exercise as well as heavy endurance exercise induce DNA damage in leucocytes; however prior regular training may diminish oxidative stress associated effects such as DNA damage. (#1654)
According to the review at this site, nasal dilatation might enhance exercise performance, but only under conditions where the brain gets too hot. None of the studies at the conference (#1609-1612, 1621, 1670) dealt with exercising in hot conditions. One study did suggest that there may be an effect in cold and arid conditions ( #1609). Another study (#1621) using six females found that for those using a nasal strip, forced expiratory volume was significantly greater. Most of what's been done has been with very small samples. These studies do not raise new questions nor do they add substantially to the conclusions in the review at this site.