No abstract

No abstract

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ABSTRACT:The purpose of this study was to compare the effects of different footwear (bare feet, flat-soled shoes, and weightlifting shoes) on balance during a barbell back squat in novice and advanced participants. It was hypothesized that i) weightlifting shoes would increase balance performance in the anterior-posterior (AP) and medial-lateral (ML) directions, and ii) advanced participants would demonstrate increased balance performance in the AP and ML direction compared to novice participants. 17 participants (9 novice and 8 advanced) performed 3 trials of a single squat repetition, using a 45lb Olympic standard barbell on a force plate, with bare feet, flat shoes, and weightlifting shoes. Squat 1 and 2 were used as warm-up repetitions and data was collected during squat 3 of each condition. Participants were characterized as either novice or advanced based on the number of training sessions they performed squats each week. Novice participants squatted with a barbell less than once per week, and advanced squatted with a barbell more than once per week. Balance performance was quantified by the percentage of time the centre of pressure (CoP) had the smallest displacement from the average CoP location. A chi-square test was performed to determine the statistically significant changes in CoP displacement between the 3 footwear conditions; accordingly, the post hoc significance interval was calculated to P0.0167). Using a 2-way ANOVA, no significant differences were found between novice and advanced participants' root mean square values for normalized CoP in the AP or ML directions (P>0.05). Participants during the weightlifting shoe condition were found to have better regulation of balance compared to bare feet or flat shoes conditions. Additionally, it was found that novice and advanced participants did not regulate balance differently from each other during the squat movement.

It has been shown that when humans lean in various directions, the central nervous system (CNS) recruits different motoneuron pools for task completion; common units that are active during different leaning directions, and unique units that are active in only one leaning direction. We used high-density surface electromyography (HD-sEMG) to examine if motor unit (MU) firing behaviour was dependent on leaning direction, muscle (medial and lateral gastrocnemius; soleus), limits of stability, or whether a MU is considered common or unique. Fourteen healthy participants stood on a force platform and maintained their center of pressure in five different leaning directions. HD-sEMG recordings were decomposed into MU action potentials and the average firing rate (AFR), coefficient of variation (CoVISI) and firing intermittency were calculated on the MU spike trains. During the leaning directions that demanded larger force production, both unique and common units had higher firing rates (F = 31.31, p < 0.0001). However, the unique units achieved higher firing rates compared to the common units (mean estimate difference = 3.48 Hz, p < 0.0001). The CoVISI increased across directions for the unique units but not for the common units (F = 23.65. p < 0.0001). Finally, intermittent activation of MUs was dependent on the leaning direction (F = 11.15, p < 0.0001), with less intermittent activity occurring during diagonal and forward-leaning directions. These results provide evidence that the CNS can preferentially control separate motoneuron pools within the ankle plantarflexors during voluntary leaning tasks for the maintenance of standing balance.