Exercise reduces obesity and related glucose tolerance, but whether increasing exercise intensity offers additional benefit at fixed exercise amounts is unknown.

To determine the separate effects of exercise amount and intensity on abdominal obesity and glucose tolerance.

24-week, single-center, parallel-group trial from 2009 to 2013. (ClinicalTrials.gov: NCT00955071)

Kingston, Ontario, Canada.

300 abdominally obese adults.

Control (no exercise) (n = 75) or 5 weekly sessions of low-amount, low-intensity exercise (LALI) (180 and 300 kcal/session for women and men, respectively, at 50% of maximum oxygen consumption [V̇o ₂peak]) (n = 73); high-amount, low-intensity exercise (HALI) (360 and 600 kcal/session, respectively, at 50% of V̇o ₂peak) (n = 76); or high-amount, high-intensity exercise (HAHI) (360 and 600 kcal/session, respectively, at 75% of V̇o ₂peak) (n = 76). Daily unsupervised physical activity and sedentary time were measured by accelerometer.

Waist circumference and 2-hour glucose level (primary outcomes) and cardiorespiratory fitness and measures of insulin action (secondary measurements).

217 participants (72.3%) completed the intervention. Mean exercise time in minutes per session was 31 (SD, 4.4) for LALI, 58 (SD, 7.6) for HALI, and 40 (SD, 6.2) for HAHI. Daily unsupervised physical activity and sedentary time did not change in any exercise group versus control (P > 0.33). After adjustment for age and sex in a linear mixed model, reductions in waist circumference were greater in the LALI (−3.9 cm [95% CI, −5.6 to −2.3 cm]; P < 0.001), HALI (−4.6 cm [CI, −6.2 to −3.0 cm]; P < 0.001), and HAHI (−4.6 cm [CI, −6.3 to −2.9 cm]; P < 0.001) groups than the control group but did not differ among the exercise groups (P > 0.43). After adjustment for covariates, reductions in 2-hour glucose level were greater in the HAHI group (−0.7 mmol/L [−12.5 mg/dL] [CI, −1.3 to −0.1 mmol/L {−23.5 to −1.5 mg/dL}]; P = 0.027) than the control group but did not differ for the LALI or HALI group versus the control group (P > 0.159). Weight loss was greater in all exercise groups than the control group (P < 0.001); however, reduction in body weight did not differ among the exercise groups (P > 0.182).

The clinical importance of reducing 2-hour glucose level in nondiabetic adults remains undetermined.

Fixed amounts of exercise independent of exercise intensity resulted in similar reductions in abdominal obesity. Reduction in 2-hour glucose level was restricted to high-intensity exercise.

Canadian Institutes of Health Research.