Author(s): KATSUGE, M., KUROSAKI, H., KAMBAYASHI, S., KITAMURA, H., NAITO, R., HIRATA, K., HIRAYAMA, K., Institution: WASEDA UNIVERSITY, Country: JAPAN, Abstract-ID: 770

INTRODUCTION:
Greater sprint acceleration is achieved by producing large horizontal ground reaction forces (GRFs). Recently, our group found that higher maximal strength and power of the lower-limb, assessed by the force-velocity (F-V) profile in vertical jumps, are associated with greater horizontal GRF during the earlier and later steps of sprint acceleration, respectively. This study examined the effects of maximal strength training and power training on the F-V profile of the lower-limb and sprint acceleration kinetics.
METHODS:
Twenty-three healthy adults (7 females and 16 males, 23 ± 3 years) were assigned into the following three groups: jump squat group (JSQG, n = 7); back squat group (BSQG, n = 8); control group (CG, n = 8). JSQG and BSQG trained three times per week for 11 weeks, performing jump squats (0% and 20% 1RM, 3–5 sets × 4–6 reps at each load) and back squats (85% 1RM, 4 sets × 3–4 reps), respectively. CG was instructed to maintain their daily routines. Before and after the intervention, participants performed 15-m sprint accelerations to evaluate mean horizontal and resultant GRFs and mean angles of the GRF vector during the propulsive phase for the first and ninth steps. Jump squats were performed to evaluate the F-V profile of the lower-limb. Theoretical maximum force (F0), velocity (V0), and power (Pmax) were derived from the F-V profile. Generalized linear mixed-effects models were used to examine main and interaction effects (F-V profile: group × time; 15-m sprint acceleration: group × time × step). Between-group differences in percentage changes were compared using one-way analysis of variance or Kruskal-Wallis test. Cohen’s d effect sizes were calculated to interpret the magnitude of the between-group differences in percentage changes.
RESULTS:
Significant main effects of time were observed for F0, horizontal and resultant GRFs, and the angle of the GRF vector (p = 0.002–0.048), with no significant interaction effects. Between-group differences in percentage changes were not found for any variable of the F-V profile and sprint acceleration. For the F-V profile, JSQG and BSQG showed moderate changes in F0 compared to CG (d = 0.62 and 0.67). JSQG also showed small changes in Pmax compared to BSQG and CG (d = 0.43 and 0.30). For sprint acceleration, JSQG and BSQG showed small to moderate changes in the horizontal and resultant GRFs for the first step compared to CG (d = 0.38–0.99). JSQG also showed small to moderate changes in the horizontal and resultant GRFs (d = 0.25–0.66) and the angle of the GRF vector (d = −0.30 and −0.46) for the ninth step compared to BSQG and CG.
CONCLUSION:
The present results imply that in healthy adults, maximal strength training enhances F0, leading to an increased GRF in the earlier step, whereas power training enhances both F0 and Pmax, leading to increased GRFs in both the earlier and later steps during sprint acceleration.