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HomeA FocusIs interval training the magic bullet for fat loss? — Systematic review

Is interval training the magic bullet for fat loss? — Systematic review

IntervaltrainingInterval training may shed almost 30% more kilos than a continuous moderate intensity workout, suggests an international pooled analysis of the available evidence in the British Journal of Sports Medicine. And sprint interval training may be most effective for weight loss, the analysis indicates, although the breadth of training programmes studied makes it difficult to recommend one particular approach over another, caution the researchers. The international study was led by researchers at the Federal University of Goiás and Federal University of Pará in Brazil.

Most physical activity guidelines recommend a high volume of exercise for weight loss, equivalent to an hour or more every day (420 minutes+/week). But few people can carve out the time needed to meet this recommendation, say the researchers.

They wanted to find out if interval training might match a continuous moderate intensity workout for overall weight loss (total absolute fat mass) and reductions in percentage body fat-the percentage of fat that makes up body weight-despite taking less time to do.

Interval training describes intermittent intense effort, interspersed with recovery periods. The two most common types are high intensity interval training, or HIIT for short, which includes various exercises; and sprint interval training, which includes running, jogging, speed walking, and cycling.

So, they searched research databases for relevant studies that directly or indirectly compared interval training with continuous moderate intensity exercise over a period of at least four weeks.

The data from 41 studies involving 1,115 people were combined for thematic analysis and the results data from 36 studies involving 1012 people were pooled. Both interval training and a continuous workout reduced overall weight and percentage body fat, irrespective of starting weight or gender, the findings showed.

But while there was no significant difference in percentage body fat reduction between the two approaches, there was a significant difference in the amount of weight lost, with interval training proving the more effective method.

Interval training provided a 28.5% greater reduction in weight, overall (1.58 kg vs 1.13 kg). Further analysis, comparing sprint interval training with a continuous moderate intensity workout, revealed an even larger difference in weight loss.

Factors such as supervision; age under 30; walking, running, and jogging; study quality; and studies lasting more than 12 weeks all influenced weight loss in the interval training programmes.

"It is important to be aware of the possible risks and caveats associated with higher intensity training," the researchers point out. "For example, it might increase the risk of injury and impose higher cardiovascular stress. Adherence should also be examined as higher intensity protocols can result in higher discomfort."

And before anyone decides to take up sprint interval training as the most effective exercise for losing weight, the researchers sound a note of caution.

The wide variety of different interval training programmes included in their analysis "makes it difficult to generally recommend that one particular protocol is 'best' for modulating body adiposity," they conclude.

Objectives: To compare the effects of interval training and moderate-intensity continuous training (MOD) on body adiposity in humans, and to perform subgroup analyses that consider the type and duration of interval training in different groups.
Design: Systematic review and meta-analysis.
Data sources: English-language, Spanish-language and Portuguese-language searches of the electronic databases PubMed and Scopus were conducted from inception to 11 December 2017.
Eligibility criteria for selecting studies: Studies that met the following criteria were included: (1) original articles, (2) human trials, (3) minimum exercise training duration of 4 weeks, and (4) directly or indirectly compared interval training with MOD as the primary or secondary aim.
Results: Of the 786 studies found, 41 and 36 were included in the qualitative analysis and meta-analysis, respectively. Within-group analyses showed significant reductions in total body fat percentage (%) (interval training: −1.50 [95% CI −2.14 to −0.86, p<0.00001] and MOD: −1.44 [95% CI −2.00 to −0.89, p<0.00001]) and in total absolute fat mass (kg) (interval training: −1.58 [95% CI −2.74 to −0.43, p=0.007] and MOD: −1.13 [95% CI −2.18 to −0.08, p=0.04]), with no significant differences between interval training and MOD for total body fat percentage reduction (−0.23 [95% CI −1.43 to 0.97], p=0.705). However, there was a significant difference between the groups in total absolute fat mass (kg) reduction (−2.28 [95% CI −4.00 to −0.56], p=0.0094). Subgroup analyses comparing sprint interval training (SIT) with MOD protocols favour SIT for loss of total absolute fat mass (kg) (−3.22 [95% CI −5.71 to −0.73], p=0.01). Supervised training, walking/running/jogging, age (<30 years), study quality and intervention duration (<12 weeks) favourably influence the decreases in total absolute fat mass (kg) observed from interval training programmes; however, no significant effect was found on total body fat percentage (%). No effect of sex or body mass index was observed on total absolute fat mass (kg) or total body fat percentage (%).
Conclusion: Interval training and MOD both reduce body fat percentage (%). Interval training provided 28.5% greater reductions in total absolute fat mass (kg) than MOD.

Ricardo Borges Viana, João Pedro Araújo Naves, Victor Silveira Coswig, Claudio Andre Barbosa de Lira, James Steele, James Peter Fisher, Paulo Gentil

[link url=""]BMJ material[/link]
[link url=""]British Journal of Sports Medicine abstract[/link]

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