The Department of Health and Human Services and the American College of Sports Medicine recommend 150 minutes per week of moderate intensity exercise or 75 minutes per week of vigorous exercise, in addition to at least 2 sessions of resistance training weekly alongside stretching and flexibility work [17]. With those recommendations, that’s 30 minutes of moderate intensity exercise 5 days a week – at the very minimum. Some with obesity who have lost weight may even complete upwards of 300 to 420 minutes a week of moderate intensity exercise to help prevent weight regain [18].
Exercise time, if trying to meet the weekly national guideline recommendations, could be cut in half with more vigorous exercise. Many of us have heard of High Intensity Interval Training (HIIT) as a form of exercise- it has been increasing in popularity over the last few years in the setting of more recent research uncovering its many benefits. What is HIIT and is it the answer for weight loss in obesity?
HIIT is just as it sounds- it is a modality in which a person alternates intervals of nearly maximal intensity (at around 80-95% of his or her maximal heart rate) with intervals of lower intensity work as recovery periods (at 40-50% of his or her maximal heart rate). Otherwise defined, one should not be able to carry out a conversation during the high intensity work, but would be able to during the lower intensity work. It can be completed by adhering to strictly cardio based work (like running, swimming or biking) or by combining resistance work (such as with free weights, resistance bands or even body weight work). The duration of the intervals, the specific intensity of the high intensity bouts and lower intensity recovery periods, and the number of completed cycles within the workout can also vary based on individual preference, fitness level, and goals.
Are there differences in how HIIT influences health and weight loss compared to continuous exercise, particularly in those with obesity? First, studies have demonstrated HIIT to be well tolerated and more enjoyable for those with obesity in comparison to traditional continuous exercise [3, 9]. Second, several HIIT studies have shown significant fat mass loss and waist circumference decrease in comparison to continuous exercise in this population [6-7, 10, 14-15, 20]. However, not all HIIT studies show this effect [2, 13, 14, 16]. There are several proposed ideas as to why there may or may not be a difference. The predominant theory as to the increased weight and/or fat mass loss seen in multiple HIIT studies, even in those with overweight/obesity, is that there is increased fat oxidation (fat breakdown for use as energy) [1-2, 4, 19-20]. Some have also postulated additional contributions from decreased appetite post exercise once chronically adapted, and increased excess post-exercise oxygen consumption (the body burning extra calories post exercise to get itself back to its pre-exercise state) [4-5]. However, some argue that HIIT’s energy expenditure may lead to some increase in caloric intake from its potential appetite stimulating effects on non-exercise adapted folks and from decreased non exercise activity thermogenesis (NEAT) [8, 11]. Some propose that HIIT may be more beneficial accompanied by dietary changes instead of exercise changes alone [12, 16].
Limitations do exist to recommending HIIT exercise in those with obesity. Many of the studies that have been completed have only conducted HIIT training on treadmill or on cycle ergometer, so other modalities of HIIT could potentially show different results on fat loss. More HIIT studies involving people with preexisting conditions (in addition to obesity) need to be completed to further elucidate its impacts on these specific populations, and injuries/safety with HIIT in those with obesity also need to be further studied before more affirmative statements regarding the topic are made [16]. Those with chronic conditions and/ or sedentary lifestyles may consider seeing a physician to be evaluated prior to initiating HIIT to ensure that is completed safely. Although further investigation is warranted, HIIT is a modality of exercise that has shown to be time saving, effective and enjoyable in those with overweight/obesity for weight loss and overall health.
Read more about exercise best practices in “Using SMART Goal Setting for Working Out at Home.”