Effects Of High-intensity Functional Training Using Two Different Resistance Loads On Body Composition And Strength

High intensity functional training (HIFT) includes repeated intense multi-joint exercises performed in a circuit manner with short recovery, resulting in improvements in muscle strength, body composition and aerobic fitness. PURPOSE: To examine the effects of 12 weeks of HIFT using two different resistance loads (heavier and lighter) on body composition and maximal strength (1-RM). METHODS: Thirty-nine healthy young individuals with an experience in HIFT of at least 3 years (19 males and 20 females, age = 28.5 ± 7.0 years) volunteered to take part in this study. Participants were randomly divided into three groups, two experimental and one control (CON). Eight of the participants did not perform >80% of the sessions or did not take part in the final measurement. Both experimental groups performed HIFT three times per week for 12 weeks. Each session lasted 25.5 min and included four circuits of five resistance exercises (squats, bench press, bent back row, shoulder press, dead lifts) performed for 30 s, with 30 s rest between exercises and 2.5 min between rounds. One experimental group (70%-HIFT, n = 13, 6 M, 7 F) performed the exercises against a load of 70% of 1-RM, while the other experimental group used a load of 30% of 1-RM (30%-HIFT, n = 10, 4 M, 6 F). Volume load was similar in the two experimental conditions. The CON group (n = 8, 4 M, 4 F) did not train during this period. Before and after the 12-week HIFT, body composition was assessed using a multifrequency Bioelectrical Impedance Analyzer. Data were analyzed using 2-way repeated measures ANOVA. RESULTS: Body fat was decreased in both experimental groups (p < 0.001), but the drop was greater in the 30-%HIFT compared with 70%-HIFT (3.19 ± 1.59 vs. 1.64 ± 1.44 kg, p = 0.037), while there was no change in CON (0.29 ± 1.08 kg, p = 0.999). There was a similar increase in fat free mass (FFM) in 30-%HIFT and 70%-HIFT (1.11 ± 0.65 vs. 1.25 ± 1.59 kg, p = 0.034 and 0.013, respectively), while no change was observed in CON (0.34 ± .67 kg, p = 0.991). Maximal strength was similarly increased in four out of five exercises for both experimental groups by 9.5 to 16.9% (p < 0.01), with no change in CON (-0.6 to 4.9%, p > 0.465). CONCLUSIONS: HIFT using light or heavy resistance loads results in similar increases in strength and fat-free mass, but different reductions in fat mass after 12 weeks of HIFT.