The Addition of High-Load Resistance Exercises to a High-Intensity Functional Training Program Elicits Further Improvements in Body Composition in Trained Healthy Adults ^†

AIM: The aim of this study was to examine whether the addition of high-load resistance exercises to a high-intensity functional training (HIFT) program elicits further improvements in physical fitness-related parameters and body composition. Material & Method: Twenty recreationally active volunteers (8 male, 12 female; age, 30 ± 4 y; body mass, 65.8 ± 12.7 kg; height, 167 ± 7 cm) were randomly assigned to a HIFT-control (HIFT-C, n = 10) or HIFT-power group (HIFT-P, n = 10) and trained 3 times per week for 8 weeks. The HIFT-C protocol consisted of four rounds of an 8-exercise circuit (30:15 s work:rest, 2 min rest after round 2), which included clean-and-press jump box, TRX chest press, wall ball throws, burpees, repeated 10 m sprints, sumo squat-and-upright row (at 65% 1RM), and abdominal crunches. The HIFT-P group replaced the TRX chest press with bench chest press and the squat-and-upright row with squat at 80% 1RM. Before and after training, participants underwent evaluation of body composition, cardiorespiratory fitness (VO₂max), vertical jump, 1RM bench press, and maximum number of abdominal crunches in 1 min. Two-way repeated-measures ANOVA was used to analyze results. Statistical significance was set at p < 0.05. Results: After 8 weeks the following parameters improved in both groups: VO₂max (5.2 ± 5.4%, p = 0.003), squat jump (10.9 ± 9.8%, p < 0.001), countermovement jump (8.0 ± 6.0%, p < 0.001), bench press 1RM (18.6 ± 19.6%, p < 0.001), and body fat mass (0.82 ± 1.65 kg, p < 0.001). However, muscle mass increased only in HIFT-P (3.3 ± 2.3%, p = 0.002) and abdominal muscle endurance improved only in HIFT-C (16.2 ± 12.2%, p = 0.002). Conclusions: Short-term HIFT resulted in improvements in whole-body cardiorespiratory and neuromuscular fitness and reduction of body fat. The addition of high-load resistance exercises to a HIFT training program was well tolerated and resulted in increased muscle mass.