What should be the preferred exercise modality for overweight and obese individuals? Protocol for a systematic review and network meta-analysis

A third of the world’s population is overweight or obese [1]. Obesity has immense consequences for both individuals and societies, so there is an urgent need for better treatments and care-delivery strategies [2‐6]. Lifestyle modification programs consisting of diet, physical activity, exercise and behaviour therapy usually are considered to be the first treatment option [7].

Despite much discussion on the relative importance of physical activity and exercise in weight loss [8‐10], it is recognised that physical activity holds a role in weight reduction and weight loss maintenance [7, 11‐13]. In a Cochrane review published in 2006, Shaw et al. [12] concluded that physical exercise has a small effect on weight loss, especially when combined with dietary intervention [12]. However, physical exercise can be performed in numerous ways and designed to target muscle strength (e.g. resistance training), cardiovascular fitness (e.g. aerobic exercise), flexibility or a combination of these aims [14]. Shaw et al. [12] did not discriminate among exercise modalities, making it difficult to draw firm conclusions.

In a 2009 position paper, the American College of Sports Medicine recommended more than 150 min of moderate-intensity physical activity per week to achieve modest weight loss and more time for greater weight loss [15]. It reported that physical activity increases weight loss with modest diet restrictions but not for more severe diet restrictions [15]. They found no evidence supporting that resistance training induces weight loss but some evidence that resistance training improved body composition (increased lean body mass, reduced body fat). It was also noted that some studies found superior effects from combining resistance training and aerobic exercise compared to aerobic training alone. This finding is in line with the results of a systematic review and network meta-analysis by Schwingshackl et al. [16] comparing the effects of aerobic exercise, resistance training and a combination of the two on anthropometric and metabolic outcomes. They concluded that combined exercise induces greater weight loss than resistance training alone and a larger increase in lean body mass than aerobic exercise alone [16]. They did not perform separate analyses for diet status but included interventions with a diet applied to all intervention groups. Furthermore, they reported a general risk of bias for all the included studies, but not for the individual studies [16]. Finally, they did not report an assessment of the strength of the evidence, which is recommended for systematic reviews [17, 18].

In a more recent review and meta-analysis, Clark [19] concluded that treatment should emphasise producing high metabolic stress by engaging in progressive resistance training or high-intensity aerobic exercise (> 70% of maximal heart rate). The author found that the combination of diet and exercise is more effective than diet alone at reducing fat mass while retaining fat-free mass, and the largest effect was observed for the combination of diet and resistance training [19]. However, there was no quality assessment of the included studies, and the review excluded studies with participants on pharmacologic treatment for diabetes mellitus type 2, cardiovascular disease or smoking [19].

In summary, the literature on the effects of various exercise modalities in overweight and obese individuals is unclear. It is also not known whether concurrent caloric restrictions affect the effects of exercise modalities. The research questions the proposed systematic review and network meta-analysis will address, therefore, are the following:

In line with current recommendations, the objective of this article is to describe the protocol for this systematic review and meta-analysis according to the preferred reporting items for systematic reviews and meta-analysis protocols (Additional file 1: PRISMA-P 2015 Guidelines) [17]. The protocol is registered in Prospero, the international prospective register of systematic reviews: CRD42019103371.

Obesity is a growing worldwide epidemic, and effective interventions are needed. Physical exercise is recognised as an important component in weight reduction and weight loss maintenance. We expect that in this systematic review, we will be able to identify whether certain exercise modalities with and without caloric restriction are more effective than others at improving body composition and metabolic health outcomes in overweight and obese adults.

The major strengths of this systematic review are the detailed protocol and search strategy developed with the help of an experienced research librarian. Prior reviews have generated unclear results on whether certain exercise modalities should be preferred. In addition, few systematic reviews have assessed the quality of studies in this area. In this review, we plan to conduct risk of bias assessment and perform network meta-analysis on only studies with low risk of bias. A potential problem is a loss of precision when excluding studies with high and unclear risk of bias. However, we contend that reduced bias is more important than precision. Nevertheless, we will perform sensitivity analyses stratified according to risk of bias and analyses including all studies. Another strength of this systematic review is the plan to present summary assessments using the GRADE approach to rate the quality of evidence, which offers transparent reporting that might help clinicians, patients and policy makers interpret the results. A limitation of this systematic review is the inclusion of only studies published in English, which might introduce bias. However, according to the Cochrane Handbook for Systematic Reviews for Interventions [21], the extent and effects of language bias might be diminished by a recent shift towards more studies published in English.