The Effects of High-Intensity Functional Training Compared with Traditional Strength or Endurance Training on Physical Performance in Adolescents: A Randomized Controlled Trial

High-intensity functional training (HIFT) integrates different modes of exercise into training sessions performed at a relatively high intensity. Although HIFT is becoming more popular in youth strength and conditioning programs, research comparing the effects of HIFT with traditional forms of training, such as strength training (ST) or endurance training (ET) in younger populations are limited. Therefore, the aim of this study was to compare the effects of HIFT with those of ST and ET on strength and endurance performance in adolescents. Fifty-two untrained adolescents (male = 26; female = 26; 17.3 +/- 1.0 years) were randomly assigned to a HIFT, ST, ET, or control group. The intervention groups trained twice a week for 6 weeks with a training duration of 60-75 minutes per session. Performance was assessed before and after the intervention with the countermovement jump (CMJ), 20-m sprint (20 m), 3-repetition maximum back squat (3RM), and Yo-Yo test. The HIFT group made significant improvements in all performance tests (CMJ, +28.5 +/- 27.6%; p > 0.001; 20-m time, -3.9 +/- 5.0%; p = 0.002; 3RM, +34.3 +/- 23.3%; p > 0.001; Yo-Yo, +14.5 +/- 15.2%; p = 0.003), whereas the ST group improved in CMJ (+38.3 +/- 27.7%; p > 0.001), 3RM (+22.2 +/- 11.2%; p > 0.001), and Yo-Yo (+12.2 +/- 21.4%; p = 0.013) and the ET group improved in CMJ (+23.4 +/- 29.9%; p = 0.001), 20-m time (-5.2 +/- 4.6%; p > 0.001), and Yo-Yo (+30.7 +/- 37.3%; p > 0.001). No significant differences between the groups were evident when the results were compared for sex. These results indicate that HIFT is an effective training method for eliciting multifaceted improvements in strength, power, and endurance measures as compared with ET or ST alone in untrained adolescents.