Being overweight or obese can decrease your ability to exercise, say researchers in the multicenter Look AHEAD trial, a study of 5,145 overweight or obese men and women between ages 45 and 75 with type 2 diabetes.

The researchers measured the participants’ ability to exercise using treadmill tests. As participants walked on the treadmill, researchers gradually increased the machine’s speed until the participants were walking briskly yet comfortably, but not faster than 4 miles per hour. Then the researchers increased the incline on the machine until the participants reported feeling exhausted. During the test, researchers measured each participant’s heart rate, blood pressure, and respiration.

The researchers found that the lower the body mass index (BMI) and the lower a participant’s waist circumference (an indicator of fat around the waist), the greater the participant’s exercise capacity. After dividing participants into four groups (BMI 25–29.9; BMI 30–34.9; BMI 35–39.9; and BMI over 40), the researchers found a corresponding decline of 10 to 15 percent in exercise capacity with each increase in weight level.

This study was published in the October 2007 issue of Diabetes Care.