High-intensity Functional Training on Physical Performance in Team-sport Athletes: A Systematic Review and Meta-Analysis including CrossFit-Based Interventions

This study is the first systematic review and meta-analysis focusing specifically on the effects of High-Intensity Functional Training (HIFT) on the athletic performance of team sport athletes. Athletes in team sports (such as basketball, football, volleyball, handball, etc.) exhibit highly intermittent characteristics. They perform high-intensity activities including confrontation, sprinting, jumping, and direction changes in short periods, along with the feature of mixed energy supply from multiple energy systems, which places higher requirements on the coordinated development of their various physical fitness components. However, traditional sport-specific physical training often targets only specific muscle groups and the development of single physical fitness components, which may not meet the physical fitness characteristics of team sport athletes. Therefore, training methods that combine aerobic training with resistance or bodyweight training and are performed at high intensity have attracted increasing attention. High-Intensity Functional Training (HIFT) has become a representative term and popular trend for this type of training in the fields of sports and fitness. Its effects on the elderly, healthy populations, athletes, and personnel in special occupations have been extensively explored, covering both physiological and psychological research fields. In 2018, Feito et al. uniformly defined this concept as a training modality that includes a variety of functional movements performed at high intensity (relative to individual capacity), aiming to improve general physical fitness parameters (such as cardiorespiratory endurance, strength, body composition, flexibility, etc.) and performance (such as agility, speed, strength, power). It is a form of high-intensity exercise conducted continuously based on functional movement patterns of resistance training. It emphasizes the combination of endurance and strength to optimize exercise efficiency, and can also bring higher emotional feedback and lower injury risk. Although there is a large number of studies on HIFT currently, evidence demonstrating the effects of this training on the performance of team ball sport athletes is still lacking. Most original experimental studies remain focused on the elderly, healthy populations, and populations with functional disorders. Notably, in 2023, Wang et al. included 13 original studies in a systematic review on the effects of HIFT on athletic performance, among which 11 studies focused on striking sports, and only one study on volleyball (a team sport) was included. We believe that this approach may obscure the gaps and deficiencies in research in this field. Furthermore, our study will not include resistance and functional training conducted in a high-intensity interval mode (with strictly defined rest intervals between movements), making it the first systematic review focusing exclusively on HIFT. Therefore, based on the lack of systematically integrated evidence on the effects of HIFT on the athletic performance of team sport athletes and calls from previous researchers, it is crucial to conduct this comprehensive systematic review. We will objectively evaluate the effects of HIFT on various performance indicators of team sport athletes, including strength, power, speed, agility, flexibility, etc., through meta-analysis, provide a comprehensive report for the current field, and promote more original research in this area. The research hypothesis is that HIFT has significant effects on the strength, aerobic capacity, jumping, agility, sprinting, and endurance of team sport athletes.