Background: The peroneus longus (PL) and peroneus brevis (PB) function as the primary muscles of eversion, a movement closely associated with tibial external rotation for ankle mortise stability. Ankle motion and tibial rotation vary based on different ankle and knee positions. Objects: This study aimed to investigate the PL, PB, and biceps femoris (BF) muscle activation and eversion strength during side-lying isometric eversion exercise based on different ankle positions (neutral [N] and plantarflexion [PF]) and knee positions (90° flexion [KF] and extension [KE]). Methods: Thirty healthy adults with an Ankle Joint Functional Assessment Tool score of ≥ 22 were recruited (mean age = 24.8 ± 3.1 years). Maximal isometric eversion strength and submaximal muscle activation of the PL, PB and BF were measured during isometric eversion exercise in side-lying. A 2 × 2 repeated measures analysis of variance was performed to investigate differences in muscle activation and strength. Results: The PL and PB muscle activation showed significant main effects with the knee and ankle positions (p < 0.05); activation was greater in the KE and PF positions than in the KF and N positions. The BF muscle activation showed a significant interaction effect with knee and ankle positions, which was greater in knee extension and ankle plantarflexed (KEPF) position than in knee flexion and ankle plantarflexed (KFPF) position (p < 0.05). Eversion strength showed a significant main effect only in ankle position (p < 0.05) and was greater in the N position than in the PF position. Conclusion: The results of this study indicate that the KEPF position can be recommended to facilitate contraction of the PL and PB during side-lying eversion exercise. Furthermore, the effects of the knee-ankle positions should be considered for measuring ankle eversion strength and implementing the isometric submaximal side-lying eversion exercise.

INTRODUCTION
MATERIALS AND METHODS
    1. Participants
    2. Smart KEMA Strength Measurements
    3. Surface Electromyography
    4. Procedures
    5. Statistical Analysis
RESULTS
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTION
ORCID
REFERENCES

• Do-eun Lee(Department of Physical Therapy, The Graduate School, Yonsei University, Kinetic Ergocise Based on Movement Analysis Laboratory)
• Jun-hee Kim(Kinetic Ergocise Based on Movement Analysis Laboratory)
• Seung-yoon Han(Department of Physical Therapy, The Graduate School, Yonsei University, Kinetic Ergocise Based on Movement Analysis Laboratory)
• Oh-yun Kwon(Kinetic Ergocise Based on Movement Analysis Laboratory, Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Yonsei University, Wonju, Korea) Corresponding author