Enhanced understanding of dynamic postural stability (DPS) has the potential to curtail lower extremity injuries with important implications for athletic and scientific populations. The ability to stabilize following dynamic tasks such as jumping is dependent on several intrinsic factors, including ligamentous laxity, proprioception, and neuromuscular control. Ballet dancers are a unique group of aesthetic performers who frequently must perform unipedal balance during dynamic tasks. The purpose of this study was to evaluate the effects of mirror feedback and ankle laxity on dynamic balance and muscle activation in 15 trained ballet dancers during a hop-to-stabilization task with and without mirror feedback. Anteroposterior and inversion-eversion ankle laxity was measured with an arthrometer. Surface electromyography was then applied to the tibialis anterior, peroneus longus, and lateral gastrocnemius muscles to record activity during the task in question. The main finding was that time-to-stabilization during the task was unaffected by mirror feedback (F = 0.105, p = 0.900; mirror = 3.31 ± 0.10 s; no-mirror = 3.37 ± 0.12 s). Greater antero-posterior laxity, however, negatively affected DPS with (r = 0.655, p = 0.008) and without the mirror (r = 0.858, p < 0.001). These results suggest that visual feedback does not affect performance during a DPS task; however, increased ankle laxity may influence balancing ability in ballet dancers.

Joint immobilization has been demonstrated to modify neural excitability in subsets of healthy populations, leading to disinhibition of cortical and reflexive pathways. However, these findings may have limited clinical application as most models have investigated casting and rigid immobilization, while many musculoskeletal injuries often utilize dynamic immobilization devices such as boot immobilizers and pneumatic splints that allow for modified ambulation. We therefore aimed to determine the short-term effects of ambulation in ankle immobilization devices on nervous system excitability and stiffness in able-bodied individuals. A repeated-measures design was implemented where 12 healthy individuals were tested for cortical excitability to the ankle musculature using transcranial magnetic stimulation, reflexive excitability using the Hoffmann reflex, and ankle joint stiffness using arthrometry before and after 30min of ambulation with a boot immobilizer, pneumatic leg splint, or barefoot. Motor evoked potential (MEP), cortical silent period (CSP), H to M ratio, and ankle joint displacement were extracted as dependent variables. Results indicated that despite the novel motor demands of walking in immobilization devices, no significant changes in cortical excitability (F≥0.335, P≥0.169), reflexive excitability (F≥0.027, P≥0.083), or joint stiffness (F≥0.558, P≥0.169) occurred. These findings indicate that short-term ambulation in dynamic immobilization devices does not modify neural excitability despite forced constraints on the sensorimotor system. We may therefore conclude that modifications to neural excitability in previous immobilization models are mediated by long-term nervous system plasticity rather than acute mechanisms, and there appear to be no robust changes in corticomotor or spinal excitability acutely posed by ambulation with immobilization devices.

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BackgroundAnkle sprains are associated with detrimental long-term sequelae tied to neuromechanical alterations. Neurological adaptations occurring in the initial weeks after injury may be responsible for long-term adaptations resultant in altered movement patterns; however, few studies have quantified neuromechanical and functional adaptations following acute ankle sprains.ObjectiveThis study aims to quantify cortical and reflexive excitability following ankle sprain with concurrent changes in function.DesignPilot cohort study.SettingUniversity laboratory.Participants6 male subjects (age = 20.8 ± 0.8 years, height = 181.2 ± 3.5 cm, body mass = 84.8 ± 9.0 kg) with history of recent ankle sprain volunteered for this investigation.InterventionsParticipants were tested at 1, 2, 4, and 8 weeks from injury. During each session clinical measures of ankle volume, balance (Y-balance test), and dorsiflexion range-of-motion (weight-bearing lunge) were assessed. Electromyography sensors were placed on tibialis anterior (TA), peroneus longus (PL), and soleus (SOL) and cortical and reflexive excitability were assessed bilaterally using transcranial magnetic stimulation (TMS), and Hoffmann reflex, respectively.Main outcome measurementsStimulus- response curves from TMS were used to determine active motor threshold (AMT, %output) and maximal response (MEPmax, %Mmax). Side differences were assessed using descriptive statistics.ResultsDifferences in ankle volume, balance, and dorsiflexion were observed at week 1, and, except dorsiflexion, were no longer present at week 8. Notable side-to-side alterations in cortical excitability were noted for TA AMT and PL and SOL MEPmax. These findings indicated decreased TA excitability, but increased PL and SOL excitability at 1-week (TAINJ = 33.4 ± 15.7%, TANON = 27.7 ± 4.0%; PLINJ = 70.5 ± 35.1%, PLNON = 45.7 ± 34.1%; SOLINJ = 10.6 ± 11.6%, SOLNON = 12.1 ± 5.1%) but the opposite effect 8-weeks after injury (TAINJ = 38.8 ± 2.8%, TANON = 35.6 ± 12.0%; PLINJ = 35.6 ± 9.2%, PLNON = 48.7 ± 9.0%; SOLINJ = 10.5 ± 7.2, SOLNON = 8.1 ± 5.9%). Generally, the H-reflex was slightly elevated for all muscles and time-points on the injured side.ConclusionsChanges in neurological function were observed among this small cohort of participants that reflect both acute and long-term adaptations due to injury. Further analysis is required to determine how these variables might affect functional measures.