Sunday, August 26, 2007

Fitness Research

This month's FitBits from Exercise Etc.

August 15, 2007
Exercise ETC’s Review of Exercise Related Research
Compiled by Chris Marino, MS, CSCS Director of Education, Exercise ETC

ACSM Updates Physical Activity Recommendations

It's been more than a decade since the initial guidelines for physical activity were jointly published by the American College of Sports (ACSM) and the Centers for Disease Control (CDC). Unfortunately, Americans have continued to become less active over that duration since slightly less than half of the population currently meets the minimum recommendations for daily/weekly physical activity. This month ACSM and the American Heart Association (AHA) published updated physical activity recommendations for both American Adults and Older Adults. Although the essential recommendations are relatively unchanged, the update more clearly defines exercise duration and intensity to avoid misinterpretation by the general public.

According to the new guidelines, American adults aged 18-65 years should continue to accumulate at least 30 minutes of moderate-intensity aerobic activity 5 days per week (instead of "most days of the week") OR engage in 20-minutes of vigorous activity 3 days per week. Specific examples based on Metabolic Equivalents (METs) are provided. The update clarifies that activity must be at least 10 minutes in duration to count towards daily goals and that a combination of vigorous and moderate-intensity physical activity is acceptable. Once again, strength training at least twice weekly is recommended. Programs should consist of 8-10 exercises for at least 1 set of 8-12 repetitions each.

The update concludes that the guidelines presented are "minimum" requirements for preventing disease and strongly encourages American adults to strive for greater amounts of physical activity to gain advanced protection against "inactivity-related chronic disease".

The guidelines presented for older adults are nearly identical. ACSM/AHA define the older adult as men and women over the age of 65 and includes those adults over age 50 with clinically significant chronic conditions and/or functional limitations.

The older adult's recommendations for aerobic exercise define moderate and vigorous activity based on perceived exertion in addition to METs. Older adults are also encouraged to strength train a minimum of twice weekly. The older adult's strength program should include 8-10 exercises using 10-15 repetitions per exercise. Although there is no specific recommendation for American Adults with respect to flexibility, the older adult is encouraged to maintain flexibility by stretching or other activity at least 10 minutes twice weekly. The update includes a brief recommendation to include balance training, especially for those at risk for falls.

~ Haskell, W.L. et al. (2007) Physical Activity and Public Health: Updated Recommendation for Adults from the American College of Sports Medicine and the American Heart Association. Medicine and Science in Sports and Exercise. 39(8): 1423-1434.

~ Nelson, M.E. et al (2007) Physical Activity and Public Health in Older Adults: Recommendation from the American College of Sports Medicine and the American Heart Association. Medicine and Science in Sports and Exercise. 39(8): 1435-1445.

Weight Loss During Pregnancy May Be Safe for Obese Women

Historically, obstetricians have been cautious when advising pregnant women on exercise and weight loss. The consensus is that physical activities performed prior to pregnancy are safely continued during pregnancy, and that moderate weight gain ensures healthy birth weight and fewer risks for complications. Currently, "normal weight" women are encouraged to gain between 25 and 35 pounds during pregnancy, while obese women should gain ~13 pounds. A recent study suggests that obese women may not need to gain any weight and that weight loss may actually enhance the health of the newborn.

Researchers studied 96 obese pregnant women with gestational diabetes mellitus. The women were divided into two groups: diet only and diet plus exercise. Both programs were designed to produce moderate calorie restriction with the goal of minimizing weight gain. The exercise group was given a recommendation for activity at 60% Vo2 Max or the equivalent of a brisk walk.

In the end the women who either lost or maintained baseline bodyweight were less likely to have a macrosomic newborn (overweight baby). Also, there were no additional pregnancy complications, and fetal growth was not impaired in the weight loss groups.

Reuters Health interviewed the authors of the study who suggest that preventing weight gain during pregnancy in obese women could provide greater long-term health benefits. They suggest that pregnancy may be an opportune time to make lifestyle changes but women are advised to consult their physician and a nutritionist before attempting to implement such a program.

~ Artal, R. et al. (2007) A Lifestyle Intervention of Weight-Gain Restriction: Diet and Exercise in Obese Women with Gestational Diabetes Mellitus. Journal of Applied Physiology, Nutrition and Metabolism. 32(3): 596–601

Explosive Training Increases Energy Expenditure

Most strength professionals advocate slow, controlled concentric contractions during resistance training to best stimulate both muscularity and calorie expenditure. The philosophy has been that slow contractions create greater lactate accumulation and thus greater muscle fatigue providing a better stimulus for hypertrophy and calorie expenditure. New evidence suggests that explosive contractions may best promote energy use both during and after resistance training. In addition, an explosive contraction has greater potential for stimulating type 2B fibers, which have a greater affinity for hypertrophy.

Researchers studied 9 college-age men who each performed three different exercise protocols using a plate-loaded squat machine. Squats were completed either using a slow cadence (2 seconds) or explosively (<1 second) both with a weight equal to 60%1RM for 4 sets of 8 repetitions. The third protocol consisted of 6 sets of 4 repetitions with a heavier resistance (80% 1RM). The eccentric component was controlled at 2 seconds, range of motion was consistent, and rest intervals were maintained at 90 seconds between sets. Researchers collected expired air at 20 min before, during, and 1 hour post-exercise. Four blood samples were collected at 15-minute intervals beginning 15 minutes post-exercise.

Although blood lactate was greater after slow contractions, as expected, the explosive group actually burned more calories both during and after exercise. The results for the heavy explosive group were similar to the slow contraction group.

Given the results of this study, experienced exercisers may benefit from incorporating more explosive contractions during resistance exercise. Beginners should strive to improve exercise technique and form through slow, controlled movements before attempting explosive contractions.

~ Mazzetti, Scott et al. (2007) Effect of Explosive versus Slow Contractions and Exercise Intensity on Energy Expenditure. Medicine and Science in Sports and Exercise. 39(8): 1291-1301.

The Latest Scoop on the Hottest Tool in Fitness: Vibration Exercise

In two separate studies, both published this past May, exercising while standing on a vibrating platform has been shown to positively affect metabolism.

In the first study, researchers set out to determine how strength training on a vibration plate would affect glycemic control in type 2 diabetics. Forty adult type 2 diabetics participated. Researchers assessed fasting glucose and hemoglobin at baseline and after 12 weeks of training. Although fasting glucose was unchanged following training in both groups, both maximal glucose concentration and hemoglobin decreased significantly in the vibration exercise group. Hemoglobin actually increased in both the strength training only and control group. Vibration exercise has previously been shown to increase strength with less volume and at lower relative intensities of exercise. The authors suggest that the low-time commitment may encourage type 2 diabetics to incorporate exercise into their disease management program.

The second study, published in the Journal of Strength and Conditioning Research reported greater energy expenditure and perceived exertion without subsequent increases in heart rate for Vibration Exercise compared to controls: in this case, lower actual effort increased results.

Seventeen college-aged men physical activity participated in 2 exercise protocols; one consisting of a half squat and a second consisting of a half squat with vibration. Researchers measured energy expenditure, respiratory exchange ratio, perceived exertion, and heart rate at baseline, during exercise, and short-recovery conditions.

These findings suggest that individuals seeking weight loss via body fat reduction, along with muscle hypertrophy, would benefit from training on a vibration platform.

~ Baum, K. et al (2007) Efficiency of Vibration Exercise for Glycemic Control in Type 2 Diabetes Physical activity tients. International Journal of Medicine and Science. 31(4): 159-163.

~ Da Silva, M.E. et al (2007) Influence of Vibration Training on Energy Expenditure in Active Men. Journal of Strength and Conditioning Research. 21(2):470-475.

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