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A. Farrag1,2, W. Elsayed3, M. Almusallam3, N. Almulhim3, E. Alzahrani1, Z. Alowa4
1Prince Sultan Military College of Health Sciences, Dhahran, Saudi Arabia, 2Cairo University, Basic Science Department, Faculty of Physical Therapy, Cairo, Egypt, 3Imam Abdulrahman Bin Faisal University, Department of Physical Therapy, College of Applied Medical Sciences, Dammam, Saudi Arabia, 4AlJubail General Hospital, Department of Physical Therapy, AlJubail, Saudi Arabia
Background: Assessment of muscular performance is an essential component of physical therapy examination. The isokinetic system has been a robust method for muscular performance assessment and rehabilitation of the plantar flexors. However, the assessment procedures in terms of knee joint angle have been greatly diverse and based on personal preferences rather than standardized guidelines. Accordingly, the need for exploring how knee position would impact the performance of the plantar flexors seems to be of great importance.
Purpose: To examine the muscular performance (isokinetic torque productivity and electromyography) of the plantar flexors (Soleus and Gastrocnemius) under different knee joint angle.
Methods: Volunteers were recruited from the local community. Participants were healthy subjects with age and body mass index (BMI) ranges of 18 – 45 years and 18 – 25, respectively. A Repeated Measures experimental design was implemented. Each subject repeatedly performed the dynamometric test procedures under the different test conditions. Participants were seated in the Biodex system 4 pro multi-joint dynamometer with the back support inclined to 70 degrees. The isokinetic test protocol was set to a movement velocity of 60°/s and ankle movement between 10° dorsiflexion to 30° plantarflexion. Participants performed three repetitions of concentric isokinetic plantar flexion of the dominant side in randomly-ordered three different knee angles; 15°, 45°, and 90°. Surface electrodes of the Delsys Trigno wireless electromyography (EMG) system collected data from the plantar flexors. EMG data were normalized to the greatest root mean square amplitudes recorded during the maximum voluntary isometric contraction (MVIC) of the respective muscle. The outcome measures were plantar flexion peak torque (Pk.TQ), peak torque/bodyweight (Pk.TQ/BW), and EMG activity of the Soleus (SOL) and medial (GM) and lateral (GL) Gastrocnemius muscles.
Results: Data were collected from 33 (13 females) participants with mean (SD) age and BMI of 22.4±3.2 and 22.3±2.6, respectively. One-way ANOVA test showed that Pk.TQ (p=0.004) and Pk.TQ/BW (p=0.005) values were significantly different between different knee joint angles. Post-hoc analysis revealed that the 45° knee angle resulted in the highest Pk.TQ (71.9±36.9 N.m) and Pk.TQ/BW (116.1±52.5 N.m/Kg), which was significantly different from the 15° knee angle (Pk.TQ, p=0.03 and Pk.TQ/BW, p=0.03), but insignificantly different from the 90° knee angle (Pk.TQ, p=0.99 and Pk.TQ/BW, p=0.99). Only the SOL normalized EMG data was significantly impacted by the knee joint angles (p=0.04), and the measurements recorded in the 15° position (86.6%±11.1) was less than that recorded in the 45° (89.5%±7.5, p=0.2) and 90° (91.1%±6.8, p=0.04) knee angles.
Conclusion(s): Knee joint position can impact the torque productivity of the plantar flexors more than its electrical activity. Midway flexion of the knee joint (i.e. 45° flexion) is the optimal position for the plantar flexors to produce the greatest torque compared with other knee angles.
Implications: Knee joint position can influence the plantar flexion torque profile, particularly during isokinetic performance. Accordingly, assessment and rehabilitation protocols should consider the knee joint position when targeting plantar flexion muscular performance, and clinicians ought to prioritize the semiflexed knee position for improving the torque productivity of the calf muscle.
Funding, acknowledgements: The study was funded by the Prince Sultan Military College of Health Sciences – Saudi Arabia.
Keywords: knee position, calf muscle, electromyography
Topic: Sport & sports injuries
Did this work require ethics approval? Yes
Institution: Prince Sultan Military College of Health Sciences – Saudi Arabia.
Committee: Institutional Review Board
Ethics number: IRB-2018-PT-006
All authors, affiliations and abstracts have been published as submitted.
