Trunk Angle Modulates Feedforward and Feedback Control during Single-Limb Squatting

Abstract

Trunk positioning and unexpected perturbations are high-risk conditions at the time of anterior cruciate ligament injury. The influence of trunk positioning on motor control responses to perturbation during dynamic performance is not known. We tested the influence of trunk position on feedforward and feedback control during unexpected perturbations while performing a novel single-limb squatting task. We also assessed the degree that feedforward control was predictive of feedback responses. In the flexed trunk condition, there were increased quadriceps (p < 0.026) and gluteus medius long-latency reflexes (p < 0.001) and greater quadriceps-to-hamstrings co-contraction during feedforward (p = 0.017) and feedback (p = 0.007) time bins. Soleus long-latency reflexes increased more than 100% from feedforward muscle activity regardless of trunk condition. Feedforward muscle activity differentially predicted long-latency reflex responses depending on the muscle (R2: 0.47–0.97). These findings support the concept that trunk positioning influences motor control responses to perturbation and that feedback responses may be invariant to the feedforward control strategy.

Influence of the Menstrual Cycle and Training on the Performance of a Perturbed Single-Leg Squatting Task in Female Collegiate Athletes

“…Despite an approximately 5% (%MVIC) reduction in quadriceps activity after training, the perturbation consistently triggered a marked increase in quadriceps activity. High levels of quadriceps activation are common during the SLS task 29 , 53 and replicated by the athletes in this study who engaged 50% to 75% of the muscle. Athletes in the ML phase activated their quadriceps the most and performed the best on the task, another consistent pattern in SLS performance.…”

“…This response was not observed in knee musculature, possibly due to their invariance from feedforward strategies. 29 These findings also indicate that soleus activity may be augmented in different hormonal milieus as athletes in the EF phase responded to the perturbation with greater soleus activity than athletes in the LF phase. This finding coincides with the alteration in soleus presynaptic inhibition (gating of the spinal reflex) that occurs across these phases.…”

“…Reduced hamstrings activity is expected among those who perform better on the SLS task. 29 , 35 This strategy may be counterproductive to injury mitigation as co-contraction of knee musculature helps to stabilize the knee joint when it is perturbed. 57 One way to potentially upregulate protective hamstrings forces during perturbations is to flex the trunk/hip with the knee.…”

“… 57 One way to potentially upregulate protective hamstrings forces during perturbations is to flex the trunk/hip with the knee. 29 , 56 In practice, however, athletes may avoid excessive co-contraction of knee musculature as it would impede performance. Perhaps another way to maintain performance and protect the knee joint when navigating perturbations is to upregulate soleus muscle activity.…”

“…The SLS task assesses visuomotor performance during dynamic weightbearing movement. 29 , 35 , 36 , 42 , 53 During the task, participants stood atop a stool on a single limb (test limb) with the knee strapped to a knee pad at the end of a rack and pinion system. The contralateral leg remained suspended off the ground ( Figure 1B ).…”