Interval training may result in greater weight loss than continuous exercise, with sprint interval training (SIT) the most effective, say researchers, who say interval training also may be easier for obese and older individuals to perform.

The findings of Ricardo Borges Viana, MSc, a PhD student in the Faculty of Physical Education and Dance, Federal University of Goiás, Brazil, and colleagues were published online February 14 in the British Journal of Sports Medicine.

Senior author Paulo Gentil, PhD, of the same institution, told Medscape Medical News that interval training “seems to promote many physiological changes that might favor long-term weight loss.

“For example, previous studies have shown that interval training is able to promote upregulation of important enzymes associated with fat degradation, which occurs to a greater extent than with moderate-intensity continuous exercise.”

The team conducted a systematic review and meta-analysis and compared weight loss with interval training, including both high-intensity interval training (HIIT) and SIT with moderate-intensity continuous training (MOD).

After pooling results from over 1000 individuals, they found both interval training and MOD led to significant reductions in both total body fat percentage and total absolute fat mass.

However, interval training was associated with a reduction in total absolute fat mass that was more than 28% greater than that seen with MOD, with the greatest reductions seen with SIT.

Despite the positive results, the team cautions that “it is important to be aware of the possible risks and caveats associated with higher-intensity training.”

For example, they warn that “it might increase the risk of injury and impose higher cardiovascular stress,” and the potential discomfort associated with high-intensity training could affect adherence.

They also highlight that the “methodological diversity” between protocols used in the studies “makes it difficult to generally recommend that one particular protocol is ‘best’ for modulating body adiposity.”

Gentil believes that interval training might also be the better choice for obese and older people.

“For obese people, virtually everything involves high intensity, because of their low fitness level and because they have to carry a heavier load,” he said.

“Older people also might have difficulty sustaining exercise for longer periods, which might make interval training a good alternative,” he added, noting his research team just finished a study showing that interval training increased functional capacity and health parameters more than MOD.

Gentil emphasized the advantage of interval training is that it “can be performed by almost everyone, we just have to know how to adapt it and have in mind that ‘intensity’ is calculated individually.”

He explained: “For a healthy young man, a sprint probably involves running at high velocities, but for a frail elder, slow walking might be enough.”

For individuals who “have knee problems and are not able to run, you can cycle or even swim. If you have heart disease, you can walk at a controlled intensity.”

The authors note that most guidelines for obesity management recommend high exercise volumes, at 150 to 250 minutes/week and up to 60 minutes/day of moderate-intensity aerobic exercise.

However, they point out that “few people meet these guidelines.”

They suggest that interval training may help weight loss, “as it has some benefits similar to MOD, while requiring less time.”

Indeed, HIIT has shown comparable improvements in insulin sensitivity and blood pressure as MOD, with at least as high levels of enjoyment and adherence, and lower perceived exertion.

To compare the impact of interval training and MOD on body adiposity, the team conducted a systematic search of the PubMed and Scopus databases in English, Spanish, and Portuguese.

From an initial 786 studies that included a minimum of 4 weeks of exercise training and compared interval training with MOD, they included 41 in a qualitative appraisal and 36 in a meta-analysis.

The qualitative appraisal included a total of 1115 individuals, whereas the meta-analysis involved 1012, with the number of participants included in each study ranging from seven to 90.

The mean age of participants across all studies ranged from 10.4 to 70.1 years, and there were a total of 576 men and 522 women.

The researchers found that both interval training and MOD were associated with significant reductions in total body fat percentage, at –1.50% and –1.44%, respectively (P = .00001).

Both forms of training were also linked to significant reductions in total absolute fat mass, at –1.58 kg for interval training (P = .007) and –1.13 kg for MOD (P = .04).

There was no significant difference in total body fat percentage reduction between interval training and MOD (P = .705).

However, interval training was associated with a significantly greater reduction in total absolute fat mass versus MOD, at a relative reduction of –2.28 kg, or 28.5% (P = .0094).

In subgroup analyses, SIT was associated with even greater reductions in total absolute fat mass versus MOD, at –3.22 kg (P = .01).

Among people who underwent interval training, factors associated with reductions in total absolute fat mass were supervised training, walking, running or jogging, age younger than 30 years, and the intervention lasting fewer than 12 weeks.

These factors did not have a significant effect on total body fat percentage loss, and neither sex nor body mass index was associated with total absolute fat mass or total body fat percentage.