Thursday, May 17, 2007

Even low-level physical activity improves the cardiorespiratory fitness

Effects of Different Doses of Physical Activity on Cardiorespiratory Fitness Among Sedentary, Overweight or Obese Postmenopausal Women With Elevated Blood Pressure

A Randomized Controlled Trial

Timothy S. Church, MD, MPH, PhD; Conrad P. Earnest, PhD; James S. Skinner, PhD; Steven N. Blair, PED

JAMA. 2007;297:2081-2091.

Context Low levels of cardiorespiratory fitness are associated with high risk of mortality, and improvements in fitness are associated with reduced mortality risk. However, a poor understanding of the physical activity–fitness dose response relation remains.

Objective To examine the effect of 50%, 100%, and 150% of the NIH Consensus Development Panel recommended physical activity dose on fitness in women.

Design, Setting, and Participants Randomized controlled trial of 464 sedentary, postmenopausal overweight or obese women whose body mass index ranged from 25.0 to 43.0 and whose systolic blood pressure ranged from 120.0 to 159.9 mm Hg. Enrollment took place between April 2001 and June 2005 in the Dallas, Tex, area.

Intervention Participants were randomly assigned to 1 of 4 groups: 102 to the nonexercise control group and 155 to the 4-kcal/kg, 104 to the 8-kcal/kg, and 103 to the 12-kcal/kg per week energy-expenditure groups for the 6-month intervention period. Target training intensity was the heart rate associated with 50% of each woman's peak O2.

Main Outcome Measure The primary outcome was aerobic fitness assessed on a cycle ergometer and quantified as peak absolute oxygen consumption ( O2abs, L/min).

Results The mean (SD) baseline O2abs values were 1.30 (0.25) L/min. The mean (SD) minutes of exercising per week were 72.2 (12.3) for the 4-kcal/kg, 135.8 (19.5) for the 8-kcal/kg, and 191.7 (33.7) for the 12-kcal/kg per week exercise groups. After adjustment for age, race/ethnicity, weight, and peak heart rate, the exercise groups increased their O2abs compared with the control group by 4.2% in the 4-kcal/kg, 6.0% in the 8-kcal/kg, and 8.2% in the 12-kcal/kg per week groups (P<.001 for each vs control; P for trend <.001). There was no treatment x subgroup interaction for age, body mass index, weight, baseline O2abs, race/ethnicity, or baseline hormone therapy use. There were no significant changes in systolic or diastolic blood pressure values from baseline to 6 months in any of the exercise groups vs the control group. Conclusion In this study, previously sedentary, overweight or obese postmenopausal women experienced a graded dose-response change in fitness across levels of exercise training.

COMMENTARIES Even small doses of activity boost heart fitness 16 May 2007 MedWire News: Even low-level physical activity improves the cardiorespiratory fitness of overweight, sedentary individuals, study findings reveal.
National Institutes of Health (NIH) guidelines recommend at least 30 minutes of moderate-intensity physical activity to promote general health, but it is not clear if sedentary people will benefit from lower levels of activity than this, explain Timothy Church (Louisiana State University System, Baton Rouge, USA) and colleagues.
To investigate, the researchers conducted a study in 464 sedentary, postmenopausal overweight or obese women with elevated blood pressure.
The women’s body mass indices ranged from 25.0 to 43.0 and systolic blood pressure from 120.0 to 159.9 mmHg.
The participants were randomly assigned to three different levels of exercise or to a no-exercise control group. The three exercise levels were cycling or walking sessions designed to expend 4 kcal/kg, 8kcal/kg, or 12 kcal/kg per week.
These levels corresponded to 50%, 100%, and 150% of the NIH consensus recommended activity level for such women.
Women who exercised participated in three or four training sessions each week for 6 months, at a training intensity of the heart rate associated with 50% peak oxygen consumption (VO2). Although maximal effort was obtained during exercise testing, the mean peak absolute (VO2abs) and relative (VO2rel) values were very low, at 1.30 l/min and 15.5 ml/kg/min, respectively, at baseline.
This demonstrated that the group had very low fitness levels at the start of the study, the authors note.
The 4-kcal/kg group exercised for a mean of 72.2 minutes per week over 2.6 sessions, the 8-kcal/kg group for 135.8 minutes per week during 2.8 sessions, and the 12-kcal/kg group for 191.7 minutes per week during 3.1 sessions.
There was a strong dose-response relationship between the amount of exercise and change in fitness, Church and team report in the Journal of the American Medical Association.
Peak absolute oxygen consumption VO2abs were significantly increased at all three exercise levels versus no exercise (1.33, 1.35, and 1.39 vs 1.28 l/min).
These values represented a 4.2% increase in VO2abs in the 4-kcal/kg group, a 6.0% increase in 8-kcal/kg group, and an 8.2% increase in the 12-kcal/kg group, compared with the control no-exercise group (all p<0.001 versus control; p for trend <0.001).
The dose-response relationship was seen across age, race, weight, baseline fitness, and hormone therapy subgroups.
Participants’ systolic and diastolic blood pressure levels, weight, and most other cardiovascular risk factors were not significantly altered with any level of exercise.
However, waist circumference, which was similar in each group at baseline, was significantly reduced at the end of the study in all 3 exercise groups compared with the control group (p<0.05 for each).
This was a significant finding given the importance of increased risk of insulin resistance, diabetes, and metabolic syndrome, and mortality associated with abdominal obesity, Church and team emphasize.
“Perhaps the most striking finding of our study is that even activity at the 4-kcal/kg per week level (approximately 72 min per week) was associated with a significant improvement in fitness compared with women in the nonexercise control group,” the team comments. JAMA 2007; 297: 2081-2091

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