Reviewed by Tyler Tice, PT, DPT, OCS, ATC
Introduction:
Ankle sprains are one of the most common injuries in athletes and often leave residual effects on postural control post-injury due to the sensorimotor dysfunction. The Y-balance test is a dynamic balance test that is often utilized to assess these patient’s abilities to demonstrate sufficient dynamic postural control to return to sport or other recreational activities safely after ankle injuries. The maximal reach distance (MRD) in the posteromedial direction of the Y-balance test (PM-YBT) is often used to distinguish individuals with ankle instability from healthy people. Sensory processing and the motor output both have an effect on postural control in performance of the PM-YBT, but the amount each contributes is yet to be determined. This study investigated the contribution of eccentric dorsiflexion and plantarflexion torque control on MRD in the PM-YBT performance and therefore determine its contribution to dynamic postural control.
Methods:
This was a cross-sectional study with 12 subjects. Exclusion criteria for subject selection included a history of lower extremity surgery, injuries in the previous 6 months, or neurological diseases with balance impairments. Subjects height (cm), weight (Kg), and limb length of dominant limb that were used for kicking a ball (cm) were taken. Subjects performed the PM direction of the YBT using the Move2Perform YBT kit with several practice attempts prior to testing. The patients also performed a 5-second maximal voluntary isometric contraction (MVIC) of plantarflexion and dorsiflexion and torque control testing of the ankle using a Biodex dynamometer system. The torque control was defined as the ability to match eccentric torque output to a target torque level. The subjects were instructed to eccentrically contract the plantar flexors at 50% of MVIC as the dynamometer moved them into dorsiflexion and contract the dorsiflexors eccentrically at 30% MVIC while being moved into plantarflexion. EMG data was also collected for tibialis anterior and the soleus as representatives to compare activation of the plantar flexors and dorsiflexors during this testing.
Conclusions of the Study:
Statistical analysis revealed a higher torque control during eccentric dorsiflexion predicted higher MRD scores for the participants, however, higher eccentric plantarflexion torque control was not predictive for MRD performance. This is contrary to previous studies, but is likely attributable to methodological differences between the use of the Biodex compared to use of a handheld dynamometer. It was also noted higher tibialis anterior activity during the YBT test also predicted greater accuracy of torque control in the subjects, while higher soleus activity did not. Therefore, eccentric dorsiflexion torque control can be a potential predictive indicator for performance in PM-YBT. It was theorized that the lack of predictability from the plantar flexors eccentric control performance was due to it their primary usage being in single plane of motion while the dorsiflexors have greater impact on multiple planes at a time. Previous EMG data has indicated plantar flexors are activated similarly between healthy individuals and people with ankle instability, while the tibialis anterior was activated less in patients with ankle instability, continuing to support the need for strong dorsiflexors. There needs to be further investigation to confirm the data seen here, since this study was self-limited by the small sample size used.
Clinical Implications:
This article highlights the importance of ensuring patients have sufficient eccentric dorsiflexor torque control. It seems having better motor control within the tibialis anterior and the other dorsiflexors through direct training can assist in improving the patient’s postural control before returning to recreational activities. The application of this data should not be limited to just athletes or other younger adults who are commonly assessed using the YBT. Although older adults may not be able to perform the PM-YBT, improving the eccentric control of the dorsiflexors may be an effective method for improving older adult’s dynamic balance as well, and consequently reduce their fall risk. Unless the patient has high irritability and cannot tolerate the movement or has precautions surrounding performing active dorsiflexion it would be ideal to begin strengthening this muscle group early to aid in their dynamic balance later in treatment.
References:
Nozu, S., Johnson, K. A., Tanaka, T., Inoue, M., Nishio, H., & Takazawa, Y. (2023). The accuracy of ankle eccentric torque control explains dynamic postural control during the Y-balance test. International Journal of Sports Physical Therapy, 18(5). https://doi.org/10.26603/001c.87760