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

The Functional Utilization of Propulsive Capacity During Human Walking

The age-associated decline in propulsive push off power generated during walking plays a central role in the reduction of mobility and independence in older adults. Previous work suggests that this population retains an underutilized propulsive reserve during normal walking that dynamometry assessments fail to effectively assess. This is especially notable when assessing plantarflexor mechanical output, which often yield implausible (i.e., ≥100%) values of ‘functional capacity utilized (FCU)’, most frequently defined as the ratio of the peak ankle moment during the push-off phase of walking to that during a maximum isometric voluntary contraction. Therefore, the extent to which we utilize our propulsive capacity, how utilization changes as we age, and the factors that govern utilization and maximum propulsive capacity remain unclear. Utilizing a feedback controlled, motor driven horizontal impeding force system and a novel maximum force condition which systematically increases applied force, we can find a participant’s maximum propulsive capacity. During this condition, we find that younger adults retain a reserve of 48% in terms of ground reaction force, 22% in terms of ankle moment and 43% in terms of ankle power, which may not be effectively predicted using dynamometry assessments. As an important first step, we present data showing that a more functional task, walking with horizontal impeding forces, could potentially more effectively assess propulsive reserves in younger adults.
Listed In: Biomechanics