Muscle activation patterns in acceleration-based phases during reach-to-grasp movement.
Keisuke Tokuda, Bumsuk Lee, Yasufumi Shiihara and 4 others
PMID 27942129WHAT IT FOUND
In 10 healthy right-hand-dominant adults, shoulder muscles activated differently as the hand accelerated and decelerated toward a bottle.
The non-dominant arm showed greater upper trapezius and biceps activity in several phases.
Key findings
01The reaching movement could be divided into four phases based on acceleration: increasing acceleration, decreasing acceleration, increasing deceleration, and decreasing deceleration.
02Relative to rest, upper trapezius activity increased in the increasing acceleration and decreasing deceleration phases, anterior deltoid activity was present throughout the movement, biceps brachii activity increased in the increasing acceleration, increasing deceleration, and decreasing deceleration phases, and triceps brachii activity increased only in the decreasing deceleration phase.
03The non-dominant arm showed significantly greater upper trapezius activity than the dominant arm in the increasing acceleration and decreasing deceleration phases, and significantly greater biceps brachii activity in the increasing deceleration and decreasing deceleration phases.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
Only 10 healthy young adults were tested, so the findings may not apply to people with shoulder pain, weakness, or neurological disease. The task was a simple tabletop reach to a 0.5 kg bottle, not a real ADL such as combing hair or reaching overhead. Velocity was calculated from acceleration rather than measured directly, so the timing of velocity-related events is less certain. Only four muscles were tested, so the pattern may not show the role of other shoulder or arm muscles. No patients, interventions, or functional outcomes were studied, so the paper cannot show how to treat a clinical problem.
The easy way to misread this
Do not use these healthy-volunteer muscle activation patterns as evidence that a reach-to-grasp training programme works. The study did not test patients, interventions, or functional outcomes.