Effects of high-intensity interval training on physical fitness and body composition in recreationally active females: a systematic review and meta- analysis.

High-intensity interval training (HIIT) is recognized as a time-efficient and effective strategy for enhancing physical fitness and body composition in a shorter duration compared to traditional training protocols. However, there is limited evidence regarding its effects in recreationally active females, as physiological adaptations may differ from those observed in elite athletes and clinical populations. This systematic review and meta-analysis aimed to evaluate the efficacy of HIIT in improving physical fitness and body composition in recreationally active females and to identify potential moderators influencing training outcomes. A comprehensive literature search was conducted across three databases (PubMed, Web of Science, and Scopus) up to February 2024. Studies were included if they examined the effects of HIIT interventions on physical fitness and body composition in recreationally active females (≥ 150-300 min/week moderate-intensity or ≥ 75-150 min/week vigorous-intensity aerobic activity, ≥ 2 days/week muscle-strengthening exercise) without age restrictions. A total of 15 studies met the inclusion criteria, comprising a pooled sample of 304 female participants (age: 25.1 ± 4.2 years old). The findings demonstrated significant, yet small, improvements in maximal oxygen uptake (VO2max) (Hedges'g [g] = 0.40 , 95% confidence interval [CI]  0.19 to 0.61, p < 0.01) and peak oxygen uptake (VO2peak) (g = 1.27, 95% CI 0.62 to 1.93, p < 0.01). Additionally, HIIT interventions led to a significant reduction in body fat percentage (g = -0.3, 95% CI -0.47 to -0.13, p < 0.01). However, no significant changes were observed in body mass or fat mass following HIIT interventions. Moreover, the meta-regression analysis did not find any moderating effect on cardiorespiratory fitness and body composition. These findings suggest that HIIT is an effective modality for enhancing cardiorespiratory fitness and reducing body fat percentage in recreationally active females.