Two vs. One

For many members, devoting 30 minutes or more on most days of the week to exercise is a lot to ask. However, dividing the workout into two smaller bouts may be more manageable and less intimidating. It might also be more beneficial.

In fact, a recent study in the Journal of Strength and Conditioning Research found that smaller bouts provide physiological and potential health benefits comparable to, and possibly greater than, traditional continuous exercise.

The study examined whether an incremental 12-week intermittent exercise program, similar to the program proposed in the joint statement from the American College of Sports Medicine (ACSM) and the Centers for Disease Control and Prevention (CDC) that 30 minutes of moderate activity accumulated each day, on most days of the week, leads to significant health benefits would result in similar health-related improvements to those found with a more traditional continuous exercise program. The researchers also wanted to see if these health-related improvements from the first 12 weeks could be maintained or improved when switching from continuous exercise to intermittent training and vice versa.

Thirty-seven low to moderately active (exercise one-three times a week) participants (men and women, ages 29–65 years) were randomized into two groups, with one group exercising for 30 continuous minutes each day and the other group exercising 15 minutes twice a day with at least four hours between exercise bouts. All exercise was aerobic, selected from a variety of different modalities.

Exercise intensity was 50–60 percent of heart rate reserve (HRR) for the first two weeks, 60–70 percent HRR for weeks three and four and 70–80 percent HRR from week five throughout the duration of the study. Subjects exercised on their own, turned in weekly exercise logs and were asked to maintain their normal diet and energy intake. After the 12-week program was completed, subjects switched groups and continued exercising at 70–80 percent HRR following the new plan for 12 additional weeks. Researchers conducted pre-12-week, post-12-week and post-24-week assessments to identify any performance or health changes.

After 12 weeks of training, the intermittent group showed significant improvements including improvements to systolic and diastolic blood pressure during walking. The continuous group showed only changes in diastolic blood pressure during walking. Mean VO2 max increased in both groups after 12 weeks with the continuous group improving 4.5 percent and the intermittent group improving 8.7 percent. At 13–24 weeks the continuous group increased 3.6 percent and the intermittent group increased 7.7 percent. Despite the improvements, no significant changes were found in body composition, but this could be attributed to the lack of a strength-training component in either program, according to the study.

“This study utilized safe progression of exercise to show that intermittent exercise can provide physiological and potential health benefits comparable to, and possibly greater than, traditional continuous exercise, and also showed these improvements were maintained when switching from intermittent to continuous and vice versa,” the authors wrote. “These results support the ACSM/CDC statement that intermittent bouts adding up to 30 minutes of accumulated daily activity can lead to significant physiological benefits.”

Walking Not Enough?

A team from Canada’s University of Alberta compared a 10,000-step exercise program with a more traditional fitness regime of moderate intensity. Researchers found improvements in fitness levels were significantly higher in the second group.

“Generally, low-intensity activity such as walking alone is not likely to give anybody marked health benefits compared to programs that occasionally elevate the intensity,” says lead researcher Vicki Harber.

Researchers compared 128 sedentary people on a 10,000-step exercise regime, which they completed at their own pace, with a group of people whose routine was more difficult but still allowed them to speak one or two sentences with ease at the end. Both routines, which lasted for six months, burned off the same amount of energy.

The researchers assessed walking’s effect on a person’s fitness level by measuring blood pressure and peak oxygen uptake. The step program increased peak oxygen uptake by an average of 4 percent during the six months, but the moderate intensity exercise group increased their peak oxygen uptake by an average of 10 percent.

Other markers of overall health, such as fasting plasma glucose levels and blood fat levels, were unaffected by either exercise.

“Our concern is that people might think what matters most is the total number of daily steps accumulated and not pay much attention to the pace or effort invested in taking those steps,” Harber says.

However, the 10,000-step program does help motivate people to begin exercise, she says.
“Across your day, while you are achieving those 10,000 steps, take 200 to 400 of them at a brisker pace.”

Professor Stuart Biddle, an expert in exercise science at the University of Loughborough, says that the current guidelines on how much exercise is needed might be set too low.

“They are based on a little bit of an educated guess,” he says. “However, you have to strike a compromise between physiology and psychology. The harder you make it, the fewer people will actually do it. It may be that very small changes to the fitness of a large section of the population would have quite a big impact.”

How Much and How Intense to Reduce Heart Disease Risk?

When it comes to reducing the risk of heart disease, high-intensity exercise seems to edge out low and moderate intensity, but how intense and for how long is still being researched.

In a May 2005 study in the Journal of Applied Physiology, researchers investigated the effect of exercise intensity on cardio-respiratory fitness and coronary heart disease risk factors. VO2 max, lipid, lipoprotein and fibrinogen concentrations were measured in 64 previously sedentary men before random allocation to a non-exercise control group, a moderate-intensity exercise group (three, 400-kcal sessions per week at 60 percent of VO2 max) or a high-intensity exercise group (three 400-kcal sessions per week at 80 percent of VO2 max). Subjects were instructed to maintain their normal dietary habits, and training heart rates were modified after monthly fitness tests. Of the 64 participants, 42 men finished the study.

After week 24, VO2 max increased in both groups; however, greater gains were made in the high-intensity group. Trend analysis showed that total cholesterol, low-density lipoprotein cholesterol, non-high-density lipoprotein cholesterol and fibrinogen concentrations changed favorably across the control, moderate-intensity and high-intensity groups. However, significant changes were only observed in the high-intensity group.

“These data suggest that high-intensity training is more effective in improving cardio-respiratory fitness than moderate-intensity training of equal energy cost,” the study’s authors wrote. “These data also suggest that changes in coronary heart disease risk factors are influenced by exercise intensity.”

In another study, published in Chest in October 2005, researchers studied the effects of exercise training amount and intensity on peak oxygen consumption in middle-age men and women at risk for cardiovascular disease. Results showed that exercising at the equivalent of walking 19 kilometers a week at 40-55 percent of peak VO2 is sufficient to increase aerobic fitness levels. However, increasing either exercise intensity or the amount will yield additional separate and combined effects on markers of aerobic fitness.

“Therefore it is appropriate to recommend mild exercise to improve fitness and reduce cardiovascular risk yet encourage higher intensities and amounts for additional benefit,” the authors wrote.

But how much is needed?

An October 2006 study published in the European Journal of Cardiovascular Prevention and Rehabilitation studied the association between the amount and intensity of exercise and cardiovascular mortality in more than 27,000 men and 28,000 women who were free from known cardiovascular disease at the beginning of the study 16 years ago. After adjusting for age and other confounding factors, researchers found that a single weekly bout of high intensity exercise reduced the risk of cardiovascular death, in both men and women, compared with those who reported no activity. However, there was no additional benefit from increasing the duration or the number of exercise sessions per week.

“These results challenge the current recommendation that expenditure of at least 1,000 calories per week is required to achieve exercise-induced protection against premature cardiovascular mortality,” the authors wrote.