With the rise in popularity of exercise programs like CrossFit and P90x, the old days of running for hours on a treadmill to get in shape are over. These classes implement a new type of exercise called high-intensity interval training, and according to a new meta-analysis published in Obesity Reviews , it may be a more effective and efficient way to lose weight, or manage type 2 diabetes.
High-intensity interval training (HIIT) involves bouts of maximum or near-maximum effort, with only a short period of rest in between. For example, instead of running for an hour straight, a person might run 20-yard sprints for, say, 15 minutes with small rest periods in between. Depending on how much effort a person puts into their workout, HIIT can result in as many as 22 calories burned per minute.
For the purpose of their meta-analysis, researchers from the University of Leicester and the National Institute of Health Research Leicester-Loughborough Diet, Lifestyle, and Physical Activity Biomedical Research Unit collected 50 studies that analyzed the effects of HIIT and regular, continuous training. The studies involved a total of 2,033 participants aged 21 to 68, with 1,383 of them undergoing a HIIT intervention. The fitness levels of the participants ranged from very active to sedentary but healthy to overweight or obese — this last group had also developed metabolic syndrome or another chronic disease like cancer or heart failure.
“The overall goal was to pool the available evidence linking HIIT to outcomes relating to type 2 diabetes [i.e. insulin resistance, blood glucose, and HbA1c],” lead researcher Charlotte Jelleyman told Medical Daily in an email. “Prior to our study the overall effect on these outcomes was unclear.”
The researchers compared HIIT to continuous training and control conditions, which meant only moderate-intensity exercise or no exercising at all outside of daily habitual movement. They found HIIT caused a reduction in insulin resistance, weight loss of just over 2 pounds, and lower levels of blood glucose (a common symptom in diabetic patients). The meta-analysis also found respiratory fitness improved to a greater level than it did in those who took part in continuous training, as well as those who were in the control group.
"This study involved a meta-analysis of experimental research, allowing us to pull together evidence and establish cause and effect,” lead researcher Charlotte Jelleyman said in a press release. “We have demonstrated that HIIT conveys benefits to cardiometabolic health, which, in the cases of insulin resistance and aerobic fitness, may be superior to the effect of traditional continuous training.”
Jelleyman also believes HIIT can be a suitable replacement to continuous exercise when promoting metabolic health and weight loss, especially in people who suffer from type 2 diabetes or its predecessor, metabolic syndrome. Still, Jelleyman cautioned more research would be needed to see how HIIT affects people over the long term.
For those who’ve spent most of their lives as a couch potato, but now wish to lose weight or manage improve diabetes management, Jelleyman suggests moderate-intensity interval training to start — after all, HIIT isn’t for everyone.
“Any additional exercise to what an individual is currently doing will be beneficial,” she said. “Short bouts of exercise broken up with recovery periods is a manageable way of beginning an exercise training program and can be built on to longer or more intense bouts.”
Source: Jelleyman C, et al. The effects of high-intensity interval training on glucose regulation and insulin resistance: a meta-analysis. Obesity Reviews. 2015.