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Trunk kinematics and trunk muscle activity during a rapidly applied load
J S Thomas1, S A Lavender, D M Corcos
1Department of Physical Therapy, University of Illinois at Chicago 60612, USA.
Summary
Anticipating a load increases trunk stiffness by activating trunk muscles beforehand. This proactive muscle engagement reduces peak activity and limits trunk movement during unexpected loading events.
Area of Science:
- Biomechanics
- Motor Control
- Human Movement Science
Background:
- Understanding trunk muscle activation patterns is crucial for preventing injuries.
- The role of anticipatory muscle activity in response to expected versus unexpected loads requires further investigation.
Purpose of the Study:
- To investigate trunk kinematics and electromyographic (EMG) activity of eight trunk muscles under expected and unexpected loading conditions.
- To examine the influence of load expectancy on trunk muscle activation and movement.
Main Methods:
- A mixed-model study involving 20 participants with gender as a between-subjects factor.
- Surface EMG recorded from bilateral longissimus thoracis (LGT), erector spinae (ERS), rectus abdominis (RAB), and external obliques (EXO).
- Trunk kinematics measured using a Lumbar Motion Monitor, with motion restricted to the lumbar spine.
Main Results:
- Expected loading reduced peak muscle activity in RAB, EXO, and ERS(R) compared to unexpected loads.
- Normalized EMG activity prior to load onset increased for ERS, EXO, and RAB(R) during expected loading.
- Trunk motion in sagittal and frontal planes was reduced under expected loading conditions.
Conclusions:
- Anticipatory activation of trunk muscles increases trunk stiffness.
- This increased stiffness effectively reduces trunk displacement and peak muscle activity during rapid loading events.
- Findings highlight the importance of predictive muscle control in load management and injury prevention.