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During slow wrist movements, distance covered affects EMG at a given external force
1Institute for Fundamental and Clinical Human Movement Sciences in the Faculty of Human Movement Sciences, Vrije Universiteit Amsterdam, van der Boechorststraat 9, 1081 BT Amsterdam.
Motor Control
|February 15, 2001
Summary
Muscle activation depends on how far a muscle has shortened, impacting its force production. This study on elbow flexors found greater muscle activity after longer shortening distances, highlighting the importance of contraction history.
Area of Science:
- Biomechanics
- Human Physiology
- Motor Control
Background:
- Muscle force production is influenced by various factors including length, velocity, and activation.
- The impact of prior muscle shortening (contraction history) on subsequent force generation and muscle activation remains an area of investigation.
Purpose of the Study:
- To investigate if electromyography (EMG) measurements from elbow flexor muscles are affected by the distance over which the muscle has previously shortened.
- To determine if contraction history influences the force-producing capacity of muscles at low shortening velocities.
Main Methods:
- Participants performed slow, linear wrist movements involving elbow flexion at a constant force (25 N) and low velocity (<1% max).
- Surface electromyography (REMG) was recorded from biceps brachii (caput longum and breve) after wrist displacements of 6.5 cm and 13 cm.
- Inertial loads were minimized to isolate the effects of muscle shortening history.
Main Results:
- Concentric REMG was significantly higher (14% for biceps caput longum, 24% for biceps breve) after a 13-cm wrist movement compared to a 6.5-cm movement.
- No significant differences in eccentric EMG were observed between the two shortening distances.
- These findings suggest an adaptation in muscle activation patterns based on prior shortening.
Conclusions:
- Muscle activation patterns adapt to counteract the influence of contraction history on force-producing capacity.
- The extent of prior muscle shortening significantly affects subsequent concentric EMG in elbow flexors.
- Understanding contraction history is crucial for accurately interpreting muscle activation and force output in biomechanical studies.