Exercise has been shown to reduce obesity and the related risk for diabetes. But it has been unclear to date whether increasing the intensity of a workout could offer additional benefit during fixed amounts of exercise.
A study(annals.org) published March 3 in Annals of Internal Medicine sought to answer this question by examining the effects of intensity of exercise on obesity and related glucose levels.
Researchers found that fixed amounts of exercise, whether performed at a low- or high-intensity, resulted in similar reductions in abdominal obesity. But only the high-intensity workouts reduced two-hour glucose levels.
Three hundred participants were randomly assigned to complete five exercise sessions a week for 24 weeks. Each session involved either a lower or higher total amount of low- or high-intensity exercise, according to a study summary(annals.org) for patients. In addition, each session was monitored by a trainer to note the amount and intensity of exercise. A control group of participants was asked not to engage in any structured exercise during the study's duration.
- A study published March 3 in Annals of Internal Medicine found that low- and high-intensity exercise resulted in similar reductions in abdominal obesity.
- Only the high-intensity workouts reduced two-hour glucose levels.
- According to one FP expert, this study reinforces that the "volume" of cardiovascular activity is the most important variable for reducing abdominal adipose tissue and waist circumference.
Researchers measured the waist circumference and weight of all participants at the beginning of and throughout the study, according to the summary. They also measured cardiovascular fitness and analyzed how well the body controlled blood sugar. A total of 217 participants (more than 72 percent) completed the study.
FP Expert Breaks Down Study
Jason Matuszak, M.D., of Buffalo, N.Y., a sports medicine specialist and member of the AAFP Commission on Health of the Public and Science, told AAFP News that this study reinforces that the "volume" of cardiovascular activity is the most important variable for reducing abdominal adipose tissue and waist circumference, and probably weight, as well.
"It confirms that you can do less time at a higher intensity for a more 'dense' workout and have all these same benefits," he said. "The key variable in this study seems to be the number of calories."
Intensity of exercise has to do with cardiorespiratory fitness, which is maximum rate of oxygen consumption (VO2 max), Matuszak said, and a person's ability to maximize his/her body to push itself at a higher intensity for longer periods of time.
"Studies are pretty clear that if you really want to improve VO2 max to the greatest degree, it requires greater intensity," he said. "Even if someone doesn't do all of their workouts at high intensity, doing some brief periods (at a higher intensity) can improve cardiorespiratory fitness more."
Study Links Teen Obesity, Blood Pressure Increases
A study(ajh.oxfordjournals.org) published online March 2 in the American Journal of Hypertension found that body mass index (BMI) in healthy adolescents has a statistically significant association with both systolic and diastolic blood pressures and highlighted the significance of the global trend of rapidly increasing adolescent obesity.
The study examined 715,000 Israeli adolescents, both male and female, ages 16-20, who had received medical exams from 1998 to 2011.
The percentage of overweight adolescents increased from about 13 percent in 1998 to 21 percent in 2011, and the percentage of adolescents with high blood pressure rose from 7 percent to 28 percent in males and from 2 percent to 12 percent in females.
Specifically, the mean systolic and diastolic blood pressures increased with increasing BMI deciles (systolic blood pressure by 10mm Hg and diastolic blood pressure by 3-4mm Hg from the first decile to the 10th decile.) A multivariate analysis found that each increase of 1 unit of BMI was associated with an increased risk of systolic blood pressure above 130mm Hg in both males and females.
The association of BMI to blood pressure was more pronounced in females than males, and researchers hypothesized that it may be attributable to certain hormonal factors.
Matuszak said he would be wary of recommending high-intensity workouts to start with for sedentary individuals because the high-intensity exercise group had a one-in-three dropout rate and much more variability in the number of times people actually attended workouts compared to the low-intensity group.
"It might not be statistically significant, but my gut says that it's not just by chance," said Matuszak. "High-intensity workouts are hard work, even for those of us who are regular exercisers. Some people like the hard work because you feel better afterward, but many others may be averse."
As to why the two-hour glucose levels were reduced only in high-intensity exercise participants, Matuszak said this probably was due to greater glucose uptake into the muscle cells facilitated by endogenous insulin because of the greater amount of work they have to do.
"This is probably independent of the mobilization of adipose tissue and would be an added benefit above and beyond the reduction of waist circumference, central adipose tissue and weight," he added. "Ultimately, one could hypothesize that this would help to reduce the risk of type 2 diabetes, since you are improving insulin sensitivity, and I believe this has been reflected in other studies on intense exercise."
Study Limitations Cause for Scrutiny
Matuszak said limitations of the study included that the population studied was 96 percent white, which limited generalizability. Also, 20 percent of participants were on antihypertensive medication, but the drugs were not analyzed.
"We know that beta-blockers for sure, and possibly calcium channel-blocking medications, can adversely affect VO2, and it's unclear how that would affect the study population or our individual patients," he said.
Matuszak added that it would have been beneficial for the study to have included a group that participated in low-amount, high-intensity exercise to see how it performed comparatively.
He also questioned why the researchers didn't separate the statistics by gender, even though they did separate the groups to categorize dropouts and energy expenditure. There were nearly twice as many women in the study, which might have affected the data.
Matuszak said he wasn't sure if calorie expenditure of participants was the best measurement on which to base results, because higher body weight implies greater number of calories burned per same unit of time.
"So your heavier individuals could do the same caloric 'work' in much less time," he said. "It's not clear that having a fixed number of 600 calories burned would have the same cardiovascular benefit for a 300-pound man as it does for a 220-pound man. I would argue that there is probably less benefit for the heavier person, and, in theory, calories/kg body mass may be a better measurement to reduce discrepancies in volume of activity between individuals of different weight."
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