Dr Paul Batman
Dr Paul Batman reviews the research surrounding high-intensity interval training vs continuous exercise in relation to visceral fat reduction.
Since the 1980s, there has been a dramatic rise in worldwide obesity levels. The accumulation of excess fat in the abdominal area has been strongly correlated with an increase in both diabetes and cardiovascular disease. This is termed ‘metabolic obesity’. It has been widely reported that decreases in abdominal adiposity is responsible for reductions in plasma glucose and triglycerides, and generally has produced favourable effects on all aspects of metabolic disease.
Over the years, strong evidence suggests that high-volume, moderate-intensity continuous exercise can reduce abdominal visceral fat, in conjunction with improvements in all tness and health parameters.
In more recent times there has been a move towards high-intensity interval training reportedly producing similar positive responses. Some researchers have proposed that HIIT is more effective in reducing abdominal adiposity compared to high-volume continuous exercise (>45 minutes). As widespread as this mode of training is within the fitness industry, the comparison between the two systems has not been thoroughly investigated. The different findings from studies could be attributed to differences in: training protocols; volume and intensity; methods of measuring visceral fat; obesity levels; and gender.
This study compared the effect of prolonged moderate-intensity continuous training to high-intensity interval training when the energy expenditure was held constant at 300kJ per session, for both modes, in young obese females.
A combined 52 females acted as subjects for this study and were divided into a HIIT group, an MICT group, and a control group (no exercise). They ranged in years from 18-22 with a BMI >25kg/m2 and percentage body fat >30%.
The MICT group performed continuous exercise on a cycle ergometer at an intensity of 60% VO2 max until 300kJ was expended. The HIIT group performed four-minute cycling bouts at an intensity of 90% VO2 max followed by a three-minute recovery bout until 300kJ was expended. The control group received no training over 12 weeks. These workloads were achieved progressively over a four-week period and the experiment lasted 12 weeks. Measurements pre- and post-study were taken on: total body mass; body fat percentage; fat mass of whole trunk; android and gynoid regions; and aerobic fitness.
Over the 12-week study there was a significant reduction in body mass and body fat percentage in both training groups. There was no significant difference between the two training groups. There was a decrease in total body fat and regional body fat measures in both training groups. Again, there was no significant difference between the two training groups. There was a decrease in
abdominal adiposity in both training groups, with no significant difference observed between each group. Aerobic fitness as measured by VO2 max significantly improved more in the HIIT group compared to the MICT group.
Following 12 weeks of training, both the HIIT and the MICT groups reduced whole-body fat and regional body fat by approximately 10%. Both groups also produced similar improvements in VO2 max, even though HIIT produced high values.
The reduction in all body fat measures in the MICT group were said to be highly dependent upon the volume of training, indicating that a greater time period is required per training session to reduce abdominal adiposity in obese subjects. The HIIT group required less training volume to achieve similar results due, specifically, to the increased intensity rather than the actual energy expended. This would suggest that the actual mechanism for reducing fat mass is specific to each training protocol. Exercise intensity can reduce the rate of fatty acid mobilization from the adipose tissue into the blood, forcing the greater use of carbohydrates as the main fuel source, yet can still cause signi cant reductions in body fat measures. This was partly attributed to the greater EPOC, or post-exercise metabolic rate and fat expenditure during the recovery period.
HIIT also reportedly causes greater increases in catecholamines and growth hormones, both of which cause increased lipolysis in adipose tissue particularly in the B adrenoceptors in abdominal fat compared to subcutaneous fat.
Both MICT and HIIT produced significant results in all measures of body fat and aerobic tness. Ideally, both could be used to produce significant results depending on the needs and motivation of the clients. HIIT appears to be more effective for reducing abdominal fat over shorter training sessions, but can be difficult to maintain in obese groups due to the higher motivation levels required to maintain the increased intensity. Ideally, both MICT and HIIT could be used to reduce body fat levels across all body regions.
Authors: Zang, H., Tong, T., Qiu, W., Zhang, X., Zhou, S., Liu, Y., and He, Y.
Source: Journal of Diabetes Research, volume 2017, article ID 5071740
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