Does Increasing Peak Vertical Ground Reaction Force During Gait Result In Greater Loading Post-ACL Reconstruction?

PURPOSE: Dynamic loading patterns during gait (greater vertical ground reaction force [vGRF] peaks, lesser midstance vGRF) are associated with better long-term outcomes post-ACL reconstruction (ACLR). Real-time gait biofeedback (RTGBF) has been employed to elicit more dynamic loading profiles by cuing an increase in 1st peak vGRF. It remains unknown whether cuing greater 1st peak vGRF results in greater overall limb- and joint-level loading. Thus, we determined the bilateral effects of cuing an increase and decrease in 1st peak vGRF on i) vGRF impulse and ii) knee abduction moment (KAM) impulse in ACLR patients. METHODS: Thirty-nine participants (46% male; 21 ± 4 years; 24.7 ± 3.2 kg/m2; 7 ± 2 months post-ACLR) completed 2 RTGBF conditions (High, Low) wherein High cued a 5% body weight (BW) increase in 1st peak vGRF and Low cued a 5% BW decrease in 1st peak vGRF. RTGBF sessions were randomized and consisted of walking for 3,000 steps on an instrumented treadmill at self-selected speed with RTGBF provided for the entire session. Kinematic and kinetic data were sampled at 120 and 2040 Hz, respectively, and the first 5 steps of the last 20 steps of the session were analyzed. Stance phase vGRF and KAM impulse were calculated; High and Low impulse were compared separately in each limb via paired t-tests. RESULTS: In the ACLR limb, vGRF impulse was significantly lower (p < 0.05) during the High (0.51 ± 0.07 BW*s) compared with the Low (0.54 ± 0.05) condition, and no differences (p > 0.05) in KAM impulse existed between High (5.33 ± 2.99 Nm*s) and Low (5.32 ± 3.19) conditions. In the contralateral limb, vGRF impulse (0.52 ± 0.07 vs 0.55 ± 0.07 BW*s) and KAM impulse (5.53 ± 2.65 vs 5.53 ± 2.69 Nm*s) were not significantly different (p > 0.05) between RTGBF conditions. CONCLUSIONS: Cuing an increase in 1st vGRF peak leads to less overall force directed to the limb (vGRF impulse) and no greater force directed to the knee (KAM impulse) compared to decreasing 1st vGRF peak. The mechanism linking increased vGRF peak to a lesser overall compressive limb loading impulse is likely that cueing a greater 1st vGRF peak causes a more dynamic vGRF waveform with higher peaks and a lower midstance minimum. Our study demonstrates that increasing peak vGRF with RTGBF can improve the dynamic nature of the of the vGRF profile without increasing limb and knee loads across stance. Supported by: 1R21AR074094; T32AR082310; P30AR072580