Effect of Exercise Training Intensity on Abdominal Visceral Fat and Body Composition -Medicine & Science in Sport & Exercise

Effect of Exercise Training Intensity on Abdominal Visceral Fat and Body Composition -Medicine & Science in Sport & Exercise

Introduction
The occurrence of metabolic syndrome* is on the rise. The International Diabetes Federation has stated that central obesity (elevated abdominal visceral) is the unifying cardiometabolic risk factor amongst people with metabolic syndrome. Exercise training elicits beneficial adaptations in body composition and cardiometabolic changes. Irving et al. studied obese, middle-aged women with metabolic syndrome* and the effects of exercise training intensity on abdominal visceral fat (AVF) and body composition. High intensity exercise training (HIET) may induce a greater fat loss (specifically AVF) than low intensity exercise training (LIET). The reasoning behind this idea is that HIET (1) stimulates the secretion of lipolytic hormones which increases post-exercise energy expenditure and fat oxidation; (2) HIET creates a greater negative energy balance compared to LIET. It is therefore hypothesized that 16 weeks of endurance training (under equivalent energy expenditures of 2000 kcals/week) above the lactate threshold (HIET) would result in a greater reduction in AVF and more favorable changes in body composition than endurance training below the lactate threshold (LIET) in abdominally obese women with metabolic syndrome.

Methods
The subjects included 27 middle-aged women (51 ± 9 years) meeting the International Diabetes Federation (IDF) criteria for metabolic syndrome*. Hormonal variances were controlled by only admitting subjects at certain times during their menstrual cycle and setting a postmenopausal status. Subjects were assessed before and after the 16 week training program. The assessments consisted of body composition measurements, cardiorespiratory fitness assessments, physical activity and dietary assessments, and basal metabolic rate measurements. Eligible participants were randomly placed into three 16 week exercise training conditions; control group (no exercise training, LIET, and HIET. The 16 week exercise intervention consisted of three groups: no-exercise training (control), LIET, and HIET. The control group was instructed to maintain their current physical activity level for 16 weeks. The LIET group exercised 5 days per week at the intensity at or below their lactate threshold (LT); the duration of their exercise was adjusted so that ~ 400 kcals were expended during their exercise sessions. The HIET group exercised a total of 5 days per week; 3 days per week at the intensity at or above LT and the other 2 days exercise intensity were at or below LT. The HIET group caloric expenditure was ~400 kcals per exercise session. The study was conducted on both and indoor and outdoor track where the subjects were instructed to walk/run the distance associated with their prescribed intensity and caloric expenditure. Adjustments were made to insure that the caloric expenditure remained the same for each exercise session. Exercise intensity prescription was based on the rating of perceived exertion (RPE) obtained from the LT/VO2peak protocol during the cardiorespiratory fitness assessment. Each subject’s RPE was monitored on a lap-by-lap basis. RPE was suggested to be a reference for training intensity prescription because previous data has found it to be an accurate marker of blood lactate response to exercise intensity in obese adults. Heart rate was not monitored during the exercise sessions.

Results
There were no statistically significant differences between the two training groups for total estimated energy expenditure. The average RPE for LIET was ~11; the average RPE for the HIET group on high intensity days was ~15 and on low intensity days was ~13. Both training groups had similar exercise adherences and no differential rates in dropouts were observed amongst all three groups. The results showed that the HIET group had a significantly reduced waist circumference in comparison to the LIET and control groups. HIET also had a significantly reduced total abdominal fat, AVF, and abdominal subcutaneous fat; no significant changes in these parameters in the LIET and control groups. The HIET group also had a significantly larger reduction in mid-thigh fat. HIET also showed a significant reduction in total body weight, body mass index, and fat mass in comparison to the other groups. Both training groups had an increase in VO2peak values but the HIET group’s value increased more than the other two groups. All groups showed an increase in peak treadmill velocity but the HIET showed a larger elevation in peak treadmill velocity in comparison with the other groups. No significant changes in basal metabolic rate or substrate oxidation assessed during the basal RER. No significant changes in total physical activity were shown.
A correlational analysis was done on the measured parameters of the data. Correlations were found between weight loss and reductions in triglycerides and systolic blood pressure. Fat mass loss was also correlated to triglyceride levels.

Discussion and Conclusion
For this study, HIET training is shown to cause more changes in body composition than LIET. HIET reduced body weight, fat mass, BMI, percent body fat, and waist circumference. Therefore exercise training above the lactate threshold may be an effective intensity for inducing weight loss in obese, metabolic syndrome middle-aged females. Both HIET and LIET had increases in VO2peak after 16 weeks of training but HIET had a larger improvement in this parameter compared to LIET. Improvements in cardiometabolic risk factors associated with metabolic syndrome did not reach statistical significance and did not appear to be related to exercise intensity; this study was not designed to induce changes in these risk factors. The correlational analysis performed on cardiometabolic risk factors and AVF loss were not statistically significant; it might take a higher loss of AVF to see improvements in these parameters.

In conclusion HIET is more effective than LIET in altering body composition in obese women with metabolic syndrome. However further research needs done on training duration, sex, age, menopausal status on exercise intensity for assessing changes in abdominal visceral fat and associated cardiometabolic risk factors.

Limitations and Applications
There were several limitations in this study that could have impacted the results. First off, the HIET group’s baseline AVF measurement was higher than the other two groups but when adjusted to baseline levels, it did not impact AVF. Another limitation is the use of a single-slice image in the analysis of body fat. The number of drop-outs exceeded the estimation of drop-outs for the study; luckily a statistically significance was still evident in AVF. The study was also limited by an incomplete dietary analysis; this did not allow for an accurate analysis of caloric intake and expenditure. The subjectivity of the RPE could have been a limitation if subjects inflated their RPE values masking the actual exercise intensity. The number of subjects that participated in the study was small; this could have been the reason why some variables did not reach statistical significance.

One application to this study can be used in exercise prescription in improving body composition in obese individuals. Because HIET has been shown to be more beneficial and the adherence rate to this exercise protocol does not significantly diminish, it can be applied in the clinical setting.