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Effects of exercise amount and intensity on abdominal obesity and glucose tolerance in obese adults: a randomized trial

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

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

Methods: 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 [V̇o2peak]) (n = 73); high-amount, low-intensity exercise (HALI) (360 and 600 kcal/session, respectively, at 50% of V̇o2peak) (n = 76); or high-amount, high-intensity exercise (HAHI) (360 and 600 kcal/session, respectively, at 75% of V̇o2peak) (n = 76). Daily unsupervised physical activity and sedentary time were measured by accelerometer.

Results: 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).

Conclusion: 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.

Full-text

Alex’s Notes: The ACSM currently recommends 150 minutes per week of moderate-intensity exercise or 75 minutes per week of vigorous-intensity exercise. These guidelines thus implicitly suggest that there are no added health benefits of high-intensity exercise other than the shorter time frame needed to burn calories.

But this can’t be true can it? After all, we know that high-intensity exercise (HIE) is an effective alternative to moderate intensity exercise (MIE) for improving glucose tolerance and insulin sensitivity in adolescent boys. We also know that HIE may differentially impact muscle fiber adaptations. With over one-third of US adults obese, two-thirds overweight, and type-2 diabetes on the rise, finding specific exercise types that maximize health benefits is needed. Therefore, the current study sought to investigate the effects of habitual exercise differing in amount and intensity on abdominal obesity and glucose tolerance.

Ultimately, 217 sedentary, abdominally obese participants were randomly assigned to one of four groups listed below. None had a history of heart disease, stroke, diabetes, or any condition that would prevent them from engaging in exercise, and none were habitually active.

  • Control; no exercise
  • Low amount, low-intensity (LALI); 180 & 300 kcal/session for women & men @ 50% VO2 peak
  • High amount, low-intensity (HALI); 360 & 600 kcal/session for women & men @ 50% VO2 peak
  • High amount, high-intensity (HAHI); 360 & 600 kcal/session for women & men @ 75% VO2 peak

Over a 24-week period, the participants exercised on a treadmill 5 times/week using heart rate and VO2 data obtained from baseline exercise testing. Follow-up exercise testing was performed at weeks 4, 8, and 16 to ensure changes in fitness were accounted for in the exercise programs. Additionally, all participants were asked to maintain their habitual diets and submit daily food logs in hopes of maintaining weight, and unsupervised physical activity was monitored with an accelerometer for 1-week periods at baseline and weeks 8, 16, and 25.

Six months of pure cardio later…

All three exercise groups significantly reduced body weight (-3.8-4.9 kg) and waist circumference (WC; -3.9-4.6 cm) compared to the control with no differences between them. However, only the HALI and HAHI groups significantly improved their insulin sensitivity (Matsuda index), with only the HAHI group having enough of a change to show a significant difference from the LALI group. Despite this, the total glucose response to the oral glucose tolerance test did not change significantly in any group, and the total insulin response was significantly reduced in all groups. Only the HAHI group showed a significant reduction in their 2-hour glucose level.

The above were the primary outcomes, but some other changes that occurred included a reduction in insulin resistance (HOMA-IR) and fasting insulin in all groups, and a reduction in blood pressure in the HALI group only. Also, cardiorespiratory fitness increased in all groups, as would be expected, but the HALI group showed greater improvement than the LALI group, and the HAHI group showed greater improvements than both other exercise groups.

Bottom line

The average exercise session time for the groups was 30 minutes for LALI, 60 minutes for HALI, and 40 minutes for HAHI. Additionally, the MET for the sessions was 4.4-4.7 for the LALI and HALI groups, and 7 for the HAHI group. Thus, the low-intensity exercise was equivalent to very brisk walking or recreational badminton, while the high-intensity exercise was equivalent to hiking or very light jogging.

This study suggests that waist circumference may be reduced equally by low- or high-intensity exercise as long as the same total amounts of calories are expended. Similarly, many aspects of blood glucose management also appear to be equally approved, although high-intensity exercise may have a slight advantage. However, it is not known what the long-term benefits would be.

With two-thirds of the American adult population being overweight, spending at least 7.5 waking hours being sedentary, and engaging in no moderate-intensity exercise, the results are actually encouraging in that most the benefits of exercise can be seen with 30 minutes of low-intensity exercise five days/week. Although this does indeed correspond to the recommended 150 minutes per week, it is important to ensure that the amount is spread out across the week.

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