HIGH-INTENSITY TRAINING FOR PEOPLE WITH OBESITY

Currently, 39% of the world's population has overweight and more than 13% has obesity (1). Excess weight, especially visceral fat, is associated with cardiovascular conditions such as atherosclerosis and hypertension, metabolic conditions such as diabetes, and even a higher cancer risk. Lifestyle change could partially reverse what is considered one of the major epidemics of the XXI century in Western countries. Beyond complex physiological processes—some still debated—body-weight change reflects the balance between energy intake and expenditure. Every weight-loss program should therefore combine appropriate nutrition with physical exercise. Although diet is the most commonly prescribed strategy, exercise is fundamental to reducing visceral fat. Diet may produce greater weight loss, but exercise reduces visceral fat more effectively (2). 

Moderate-intensity continuous exercise is most commonly recommended for weight loss—for example, brisk walking, jogging or cycling for at least 30 minutes at an intensity that permits conversation without excessive breathlessness. High-intensity interval training, or HIIT, consists of short intervals lasting 30 seconds to 5 minutes at an intensity that makes conversation difficult. It has become a safe and effective way to improve fitness and body composition in the general population. Despite requiring less work time, HIIT is at least as effective as traditional training for performance (3–5) and several health markers (6–9). 

Can HIIT effectively reduce fat mass?

A recent meta-analysis in Sports Medicine examined the effects of HIIT on total, visceral and abdominal fat in people with normal weight, overweight or obesity (10). Across 39 studies, HIIT reduced total, visceral and abdominal fat. Intensities above 90% of peak heart rate produced greater effects on total adiposity, somewhat lower intensities had a greater effect on abdominal and visceral fat, and running programs produced greater benefits than cycling programs (10).

Could HIIT be the best option for people with obesity?

Several studies have compared HIIT with traditional moderate-intensity training, or MIT, for body composition in people with overweight or obesity. A PLoS One study randomly assigned participants to HIIT—3 weekly sessions of 4 sets lasting 30 seconds at 85% of maximal anaerobic power, with 4 minutes of active recovery—or MIT—45–60 minutes at 55–65% of VO2max on 5 days per week (11). After 6 weeks, both methods similarly improved body-fat percentage, total cholesterol, VLDL, HDL, triglycerides and insulin sensitivity, although MIT increased VO2peak more than HIIT (11,1% vs 2,83%) (11). A meta-analysis of 13 studies in Obesity Reviews likewise found that both HIIT and MIT improved body composition, reducing fat by 2 kg (6%) and waist circumference by 3 cm even without body-weight change—fat mass, not total weight, should remain the focus (12). The main difference was the time required: 95 minutes per week for HIIT versus 158 minutes for MIT to obtain similar body-composition benefits (12). 

These findings agree with a 2019 American College of Sports Medicine statement concluding that HIIT, especially for people with overweight and obesity, can improve cardiometabolic health—including insulin sensitivity, blood pressure and body composition—as effectively as traditional exercise or MIT (13). 

Although some studies have found HIIT superior to traditional exercise for fitness and body-fat percentage in people with obesity (14), evidence shows that HIIT and MIT can be equally effective for body composition. HIIT sessions can replace or complement traditional long-duration endurance work within an annual plan while requiring much less time—important when schedules are tight—and may even improve adherence. Both are effective tools, so programming should reflect each person's preferences and characteristics, always prioritizing individualization.

AUTHOR

Javier S. Morales
Lecturer and researcher.

Website: www.fissac.com

Twitter: @javi_salud

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REFERENCES:

1. World Health Organization. Obesity and overweight. 2020. Available at https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight
2. Verheggen RJHM, Maessen MFH, Green DJ, Hermus ARMM, Hopman MTE, Thijssen DHT. A systematic review and meta-analysis on the effects of exercise training versus hypocaloric diet: distinct effects on body weight and visceral adipose tissue. Obes Rev. 2016;17(8):664–90. 
3. Milanović Z, Sporiš G, Weston M. Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Med. 2015;45(10):1469–81. 
4. Ní Chéilleachair NJ, Harrison AJ, Warrington GD. HIIT enhances endurance performance and aerobic characteristics more than high-volume training in trained rowers. J Sports Sci. 2017;35(11):1052–8. 
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