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SAN FRANCISCO -- While an intensive exercise regimen has been shown to yield the most health benefits in overweight sedentary adults, Duke University Medical Center researchers have found that when given their choice, these adults apparently tend to gravitate toward a moderate exercise program approximately equivalent to 11 miles of brisk walking or jogging each week.
The results of their analysis lead the researchers to conclude that lower amounts of high intensity exercise might lead to increased adherence to an exercise program.
"It is important to remember that the more exercise you do the more benefits you gain, but when focusing on what people will implement into their daily lives outside of a supervised setting, it appears that these adults prefer to do fewer minutes at a higher intensity versus more minutes at a lower intensity regardless what they did in the supervised program," said Lori Aiken, who presented the results of the Duke study today (May 29, 2003) during the 50th annual scientific sessions of the American College of Sports Medicine.
The researchers also found that lack of time was the most common reason given for not continuing to exercise after completing their initial program, and that the most preferred form of exercise was walking.
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For their analysis, the Duke team randomized 87 "couch potatoes" to one of three nine-month supervised exercise programs differing in amount and intensity: low, moderate or high. The amount of exercise was measured in minutes of exercise per week, while intensity was measured by a calculation known as V02max (subscript 2), which is the maximum amount of oxygen that can be delivered by circulating blood to tissues in a given period of time.
Those in the low group exercised on average 187 minutes per week at an intensity of 40 to 55 percent VO2max, or the equivalent of 11 miles per week of walking. The moderate group exercised 123 minutes per week at 65 to 80 percent VO2max, or the equivalent of brisk walking/jogging 11 miles per week. The high group exercised 180 minutes per week at 65 to 80 percent VO2max, or the equivalent of brisk walking/jogging 18 miles per week.
Participants were given individualized exercise "prescriptions" which took into account their particular health and fitness status. During the supervised portion of the study, they used cycle ergometers, treadmills or elliptical trainers to reach their specified training range. After the completion of the supervised program, the researchers then contacted the participants at home to see to what extent they were continuing their exercise programs.
"Although the participants in the high exercise group gained the most health benefits during the supervised part of the program, when they returned home they significantly cut back on the minutes per week and intensity of their exercise," Aiken said. ""Furthermore, the participants in the low exercise group decreased the number of minutes per week but significantly increased the intensity of their exercise during the six-month follow-up period. This suggests to us that most people tend to move toward an exercise regimen more closely resembling the moderate group.
"The number of participants who continued to exercise after the supervised portion of the study remained fairly encouraging, with 69 percent of the low group, 70 percent of the moderate group and 61 percent of the high group still exercising," Aiken continued. "Most exercise studies run for three months. Our program was much longer than most, which may have been a realistic amount of time for exercise to become habitual."
In terms of weekly amount of time spent exercising each week, only the moderate group chose to increase, from 123 minutes to 131 minutes. This group was evenly split between those who increased, decreased or did not change their level of intensity.
The high exercise group chose to change their exercise prescription the most by significantly dropping, from 180 to 135 minutes per week, Aiken said. In terms of intensity, 53 percent cut their intensity, while only 12 percent increased. The remaining 35 percent did not change.
Although participants in the low exercise group chose to exercise fewer minutes per week, dropping from 187 to 159 minutes, 68 percent increased the intensity of their exercise. Only 14 percent decreased intensity and 18 percent remained the same.
In addition to measuring the exercise habits of the study participants, the researchers also sought to discover why the exercisers stopped their exercise programs. Sixty-nine percent of participants cited time constraints as the main issue. Other reasons reported were lack of motivation (45 percent), family obligations and lack of exercise facilities (both 17 percent), illness or injury (14 percent), and lack of support or travel (3 percent).
During the supervised portion of the study, participants exercised at the Duke Center for Living. As part of their survey, the researchers also sought to find out what mode of exercise the participants were likely to follow at home.
"By far, walking was the exercise of choice, with 84 percent of participants reporting this mode of exercise," Aiken said. "For most people, walking is the most comfortable and convenient form of exercise."
Other forms of exercise included elliptical trainers and other machines (22 percent), running (17 percent), bicycling (16 percent) or swimming (9 percent). Additionally, 16 percent reported that they stretched before exercise, while 47 percent said they included some form of weight training.
The Duke team was led by cardiologist William Kraus, M.D., who received a $4.3 million grant from the National Heart, Lung and Blood Institute in 1998 to investigate the effects of exercise on sedentary overweight adults at risk for developing heart disease and/or diabetes. The results of that five-year trial, dubbed STRRIDE (Studies of Targeted Risk Reduction Interventions through Defined Exercise), are now being published and presented.
Joining Aiken were Duke colleagues Johanna Johnson, Brian Duscha, Cris Slentz and Kraus.