The Effects of High-Intensity Multimodal Training in Apparently Healthy Populations: A Systematic Review

Background High-intensity multimodal training (HIMT) is emerging as a popular training method that combines aerobic and resistance training throughout a single exercise session. The current literature is limited by a lack of terminology that broadly encompasses all styles of combined aerobic and resistance training. The magnitude of chronic or long-term (i.e. >= 4 weeks) effects of HIMT participation on aerobic and muscular fitness also remains unclear. Additionally, one of many complex reasons for the growing popularity of HIMT may be attributed to the affective response to exercise, namely levels of enjoyment. However, this concept is not yet well understood across all styles of HIMT. A comprehensive systematic review is required to synthesise the available literature and attempt to provide an operational definition of HIMT to capture the breadth of combined training styles that exist. Objective The objective of this systematic review was to determine the chronic effects of HIMT participation on aerobic and muscular fitness and to compare HIMT to established concurrent training methods. Enjoyability and other adherence-related subjective responses were also examined in HIMT participants. This review critically assessed the level of evidence and feasibility of current HIMT guidelines. Methods A systematic literature search was conducted on PubMed, Web of Science and SPORTDiscus to identify studies up until March 2021. Results A total of 20 studies were included for review. Studies generally reported moderate to large effects on aerobic fitness and subjective responses in favour of HIMT interventions. Mixed outcomes were demonstrated in muscular fitness. These results should be treated with caution due to high risk of bias among included studies. Conclusions Few studies have assessed the chronic effects of HIMT participation on aerobic, and musculoskeletal adaptations and subjective responses, in particular exercise enjoyment. Research conclusions are limited by heterogeneity of experimental protocols and outcome measures. Furthermore, the inability of the literature to make adequate comparisons between various styles of HIMT and other concurrent training protocols limits understandings of the efficacy of HIMT. Registration This systematic review was registered on the Open Science Framework (10.17605/OSF.IO/2RE4B; 26 March 2021).