PURPOSE: High-intensity functional training (HIFT) has grown in popularity, yet key training effects are unknown. HIFT aims to create simultaneous cardiovascular and muscular improvements through resistance training being performed at high intensity. This study examined the effect of HIFT through CrossFit™ on strength gains over 6 months, accounting for experience and injury.
METHODS: Participants included 23 adults (43% female) ages 18-35. Experience was dichotomized as ≤6 months (M; n=13), or >6M (n=10). Participants indicated previous weightlifting experience. Strength was assessed by 1 repetition maximum (RM) lifts for overhead press (P), back squat (S), and deadlift (D) using standardized warm-up and repetition progressions at baseline (B), 2M and 6M. Subjects were asked at each assessment period if they had any current injuries that would affect testing. Data were entered into SPSS for analysis. Participants reporting injuries affecting testing at any time period were not included. Paired samples t-tests were used to examine within-group differences and ANCOVA with weight lifting as the covariate and experience as the predictor was used to examine between-group differences for each lift.
RESULTS: On average, both groups improved on each lift. Differences for those with ≤6M HIFT experience were significant for P (t=4.9, p=.001), S (t=4.0, p=.002) and D (t=2.5, p=.03). For those with >6M HIFT experience, only difference in S were significant (t=2.5, p=.036). There was a significant effect of HIFT experience on P increases after controlling for weight lifting experience, F(1,18)=9.2, p=.007. For P, those with ≤6M HIFT experience improved M=11.8±8.4-lb while those with >6M experience improved M=3.0±4.2-lb. No significant effects were found for S or D improvements. For S, those with ≤6M HIFT experience improved M=21.5±19.6-lb while those with >6M experience improved M=10.7±12.9-lb. For D, those with ≤6M HIFT experience improved M=21.6±31.8-lb while those with >6M experience improved M=13.7±20.6-lb.
CONCLUSIONS: HIFT participation elicits strength improvements despite a split focus on aerobic and resistance training, with larger improvements among novice participants. The growth in popularity in HIFT could be due to these continued strength gains in both novice and experienced participants.