J Korean Phys Ther.  2022 Aug;34(4):175-180. 10.18857/jkpt.2022.34.4.175.

Correlation among Functional Leg Length Discrepancy, Muscle Activity, Muscle Contraction Onset Time and Vertical Ground Reaction Force during Simple Lifting Task

• Jin HY
• Han JT

• KMID: 2536771
• DOI: http://doi.org/10.18857/jkpt.2022.34.4.175

Abstract

Purpose
Leg length discrepancy causes the posture deformation, gait asymmetry, and lower back pain. The purpose of this study is to investigate the correlation among functional leg length discrepancy (FLLD), muscle activity, muscle contraction onset time and vertical ground reaction force (vGRF) during simple lifting task.
Methods
Thirty-nine subjects participated in this study. FLLD was measured from the umbilicus to medial malleolus of left and right leg using a tape. The subjects performed to lift a 10 kg box from the floor to chest. The muscle activity and muscle contraction onset time of rectus abdominis, erector spinae and rectus femoris was measured using EMG system and vGRF was measured by two force plate. Pearson correlation was used to fine out the correlation among FDDL, muscle activity, muscle contraction onset time and vGRF during simple lifting task.
Results
Correlation between FLLD and difference of muscle activity of short-long side was very high (r > 0.9) during simple lifting task. Correlation between FLLD and difference of muscle contraction onset time of short-long side was very high (r > 0.9) during simple lifting task. And correlation between FLLD and difference of vGRF of short-long side was high (r > 0.7) during simple lifting task.
Conclusion
This study suggests that there is high correlation between FLLD and muscle activity, muscle contraction onset time, and ground reaction force during simple lifting task. Therefore, FLLD could negatively affect the postural balance.

Keyword

Leg length discrepancy; Muscle activity; Ground reaction force; Simple lifting