A 10-week randomized controlled hip-strengthening intervention in healthy, well-trained runners: longitudinal and cross-sectional analyses of frontal-plane running biomechanics across running speeds

Abstract Background Hip abductor (HABDS) and hip external rotator strength (HERS) are proposed to influence frontal-plane running biomechanics, including characteristics associated with running-related injury risk. Evidence and intervention effects are inconsistent. Sex-specific differences in running biomechanics suggest that the relationship between hip strength and running biomechanics may differ between females and males. Whether relationships or the effects of hip strengthening are consistent across running speeds is unknown. This study aimed to examine the longitudinal effects of isolated hip strengthening on running biomechanics at three speeds and whether hip strength predicted running biomechanics at these speeds, accounting for sex. Methods Forty-eight (23 females, 25 males) healthy, well-trained runners underwent baseline hip strength testing (motor-driven dynamometer) and 3D running analysis at three individually prescribed speeds based on 1000-m time: slow (60%), medium (80%), and fast (100%), corresponding to 2.76 ± 0.29, 3.69 ± 0.39, and 4.61 ± 0.49 m/s (mean ± SD). The primary outcome was frontal-plane knee moment, with frontal-plane hip, knee, and pelvis angles as secondary outcomes. Participants were randomized to a 10-week hip-strengthening intervention or a control group. Longitudinal changes were assessed using SPM t-tests of pre–post change scores between groups, conducted separately by sex and running speed. No sex × intervention or speed × intervention interactions were tested. Strength adaptations were evaluated using analysis of covariance. Cross-sectional analyses used SPM general linear models to determine whether hip strength predicted running biomechanics across running speeds, with sex as a covariate. Results The intervention increased HABDS by 0.20–0.29 Nm/kg (10.9–16.7%), with significant effects for five of six conditions, and increased left eccentric HERS by 0.05 Nm/kg (5.9%). Biomechanical outcomes did not change. At baseline, greater HABDS was associated with higher knee abduction moments during late stance at slow running speed only. No other associations were significant. Conclusion A 10-week hip abductor and external rotator strengthening program improved HABDS but did not alter frontal-plane running biomechanics in healthy, well-trained runners. Although greater HABDS was associated with higher knee abduction moments during slow running, the findings do not support a consistent relationship between hip strength and frontal-plane running biomechanics.