THE ACCURACY OF FORCE CONTROL WHILE ANKLE MUSCLE IS LENGTHENING EXPLAINS DYNAMIC BALANCE ABILITY ASSESSED BY A CLINICAL TEST

S. Nozu¹, T. Tanaka¹, M. Inoue¹, H. Nishio¹, Y. Takazawa¹

¹Juntendo University, Inzai, Japan

Background: Assessment of motor control following ankle sprains is important for a rehabilitative approach. The Y-Balance Test (YBT), especially the posterior medial (PM) reach direction (PM-YBT), can identify those who have ankle instability. However, there still exists a need to understand how motor control function explains the performance during the PM-YBT. When considering the ankle movement on the sagittal plane during the PM-YBT performance, ankle muscles should properly produce muscle stiffness while lengthening (eccentric contraction) for ankle joint stability under the weight-bearing task. We hypothesized that the accuracy of force control of eccentric ankle muscles is the key function to explain dynamic balance ability in the PM-YBT.

Purpose: To examine if the accuracy of force control of eccentric ankle muscle explains the performance in a clinical dynamic balance test.

Methods: Twelve healthy subjects performed the PM-YBT and force control testing. The maximum reach distance of the PM reach direction (PM-MRD) was normalized by each subject’s leg length. Subjects were asked to complete a maximal voluntary isometric contraction (MVIC) test of the dorsi/plantar flexor muscle to determine target forces using Biodex System 4. We set a novel method to assess motor control performance that provides a pre-determined target force on a screen (connected with the dynamometer) in front of the subject and passive rotations of the ankle joint at 10 degree/sec through 10° plantar flexion to 10° dorsiflexion for 5 trails. Subjects were then asked to produce and adjust the targeted force (dorsiflexor: at 30% MVIC; plantarflexor: at 50% MVIC) while the ankle joint is passively rotated (eccentric contractions). Subjects were allowed to look at the screen and perform the force control trials. We evaluated the accuracy of dorsi/plantar flexor force control by calculating absolute errors between targeted and produced forces. Tibial anterior (TA) and soleus (Sol) muscle activity were simultaneously recorded during trials. A simple linear regression analysis was used to check if the force control performance associates with the PM-MRD.

Results: A strong correlation was found between the PM-MRD and the accuracy of force control for dorsiflexor muscle (r = -0.67; R² = 0.44). We also found that larger TA activity relates to better force control of the dorsiflexor during the force control testing (r = -0.68; R² = 0.46).

Conclusions: The accuracy of force control of eccentric dorsiflexor, which is influenced by greater muscle activity, can explain better performance in the PM-YBT.

Implications: These findings suggest that motor control modulates muscle activity to produce joint force while the ankle muscle is lengthening, and those who accurately control the dorsiflexor can perform a better dynamic balance in the PM-YBT. Rehabilitative approach methods that optimize motor control of the eccentric ankle muscle force control may improve dynamic balance ability.

Funding acknowledgements: This work was supported by the Joint Research Program of Juntendo University, Faculty of Health and Sports Science.

Keywords:
Motor control
Dynamic balance test
Ankle instability

Topics:
Musculoskeletal: lower limb
Sport & sports injuries

Did this work require ethics approval? Yes

Institution: Juntendo University

Committee: The Research Ethics Committee of Juntendo University

Ethics number: 2021-93