Comparison of Medial and Lateral Hamstring Muscle Activation and Strength across Three Resistance Directions during Isometric Knee Flexion in Healthy Participants: A Pilot Study
10.5763/kjsm.2026.44.1.34
- Author:
Jin Seong KIM
1
;
Il Kyu AHN
;
Kyu Sung CHUNG
Author Information
1. Department of Physical Therapy, Inje University Ilsan Paik Hospital, Goyang, Korea
- Publication Type:Clinical Article
- From:The Korean Journal of Sports Medicine
2026;44(1):34-40
- CountryRepublic of Korea
- Language:English
-
Abstract:
Purpose:This study aimed to identify an effective hamstring exercise method that selectively activates the medial and lateral hamstrings.
Methods:Five healthy adults were enrolled in this cross-sectional pilot laboratory study. Surface electromyography was recorded from the semitendinosus and biceps femoris of the dominant limb during prone isometric knee flexion at 90°, with resistance applied at 0° (neutral), 45° (resistance applied from lateral to medial), and −45° (resistance applied from medial to lateral) in randomized order. Three 5-second maximal trials per direction were performed with 30-second rest intervals. Isometric knee flexion strength was measured using a Smart KEMA system (Koreatech Co., Ltd.), and the outcomes were descriptively compared.
Results:The participants (three females and two males; 32.4±4.5 years) demonstrated the highest mean semitendinosus and biceps femoris activity at 0° (154.7±24.1 μ V and 100.2±25.1 μ V, respectively) and the lowest at 45° (105.3±5.6 μ V and 76.9±4.4 μ V) and −45° (129.3±12.1 μ V and 64.7±19.0 μ V). The medial-to-lateral activity ratio was highest at −45° (2.2±0.6), compared with 0° (1.6±0.3) and 45° (1.4±0.1). Strength was the greatest at 0° (7.5±0.5) compared with 45° (6.4±1.3) and −45° (5.5±1.3).
Conclusion:In this pilot study, the medial-to-lateral electromyographic ratio tended to be highest when resistance was applied at −45°, suggesting greater medial hamstring recruitment under this condition. These descriptive findings are preliminary and should be confirmed in adequately powered studies. Modifying the direction of resistance may be a feasible strategy to bias medial (−45°) or lateral (45°) hamstring recruitment depending on rehabilitation goals.
