Lower Extremity Muscle Contributions to Ground Reaction Force during a Stop-Jump Task

Females commonly use a landing technique that creates higher impact forces when contacting the ground, thus leading to higher ground reaction force (GRF) acting upon the lower extremities, leading to an increased risk of injury. The lower extremity musculature plays a critical role in absorbing the energy of these impact forces during landing. Understanding how specific muscle groups contribute to ground reaction force may offer insight to creating more advanced landing retraining protocols. The purpose of this study was to observe how lower extremity muscle groups contribute to GRFs during an unanticipated stop-jump task. 3D musculoskeletal simulations of unanticipated stop-jump tasks were completed for five healthy females. Participant-specific scaled musculoskeletal models (modified gait2392) were generated. A pseudo-inverse induced-acceleration analysis was used to determine individual muscle group contribution to 3D GRFs. Means ± standard deviations were calculated for each muscle group during the landing phase. The vasti, soleus, and the gluteus maximus muscle groups were most responsible for bodyweight support, with the vasti and the soleus being the largest contributors (375.84±88.64 N; 267.39±103.70 N, respectively). The vasti group (165.63±74.94 N) were primarily responsible for braking and propulsion. Finally, the gluteus maximus, gluteus medius, and vasti group were the major generators in producing a medially-directed GRF, with the vasti group as the largest contributor (118.05±32.83 N). The vasti, soleus, and gluteus maximus appears to be the overall largest contributors to 3D GRFs. Landing retraining protocols may want to consider targeting these muscle groups specifically to improve landing performance and decrease injury risk.
Listed In: Biomechanics, Sports Science, Other

Effects of acute plantarflexion stretching on anterior cruciate ligament loading during single-leg landing

Research has shown decreases in dorsiflexion ROM appear to be predictors for non-contact ACL injuries during landing tasks. The gastrocnemius-soleus complex (GSC) plays a critical role in dorsiflexion ROM, with a less compliant GSC decreasing dorsiflexion ROM. However, it is unknown whether acute GSC stretching can decrease ACL loading during landing tasks. Fifteen active participants completed three trials of single-leg drop-landings from a box. 3D-lower extremity kinematics and kinetics were captured using 3D-motion capture system and force plate. Between assessments, all participants completed a three-minute bout of stretching targeting the GSC. Musculoskeletal modeling was used to estimate ACL loading in the sagittal, frontal, and transverse planes, overall peak ACL loading, and time to peak ACL loading. Pretest and posttest ACL loading variables were compared with paired t-tests (p≤0.05). No significant differences were found between pre-stretch and post-stretch peak ACL loading time, peak frontal plane ACL loading, and peak transverse plane ACL loading (p>0.05). However, post-stretch peak sagittal plane ACL loading was significantly higher compared to pre-stretch peak sagittal plane ACL loading (p=0.008). Furthermore, overall post-stretch peak ACL loading was significantly higher compared to overall pre-stretch peak ACL loading (p=0.022). As the gastrocnemius plays a role in knee flexion, it is possible that an acute bout of stretching may increase gastrocnemius compliance, therefore increase in sagittal plane ACL loading. An increase in sagittal plane loading would also lead to an overall loading effect on the ACL. Future studies warrant investigation into the effects of chronic GSC stretching on ACL loading.
Listed In: Biomechanics, Sports Science