Comparison of the trapezius and serratus anterior muscles isolation ratio during different shoulder abduction exercises.
Won-Gyu Yoo
PMID 28626300WHAT IT FOUND
In 10 healthy men holding a 3 kg weight, the middle trapezius took a larger share of total scapular muscle activity at 60° shoulder abduction, while the serratus anterior took a larger share at 120°.
Upper and lower trapezius shares did not differ.
Key findings
01Upper and lower trapezius isolation ratios were not significantly different between 60° and 120° shoulder abduction.
02Middle trapezius isolation ratio was significantly higher at 60° (19.8 ± 3.7%) than at 120° (13.8 ± 2.8%).
03Serratus anterior isolation ratio was significantly higher at 120° (28.2 ± 4.4%) than at 60° (21.5 ± 6.0%).
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study included only 10 healthy men, so it does not show what happens in women, older adults, or people with shoulder pain or limited range. It measured a single 5 second hold with a 3 kg weight, not repeated exercise over time, so it cannot show strength gain, pain reduction, or functional improvement. The order of the 60° and 120° tests is not reported, so carryover from one angle to the other cannot be ruled out. The isolation ratio is a relative share of measured muscle activity, not an absolute amount of muscle work or a patient outcome.
The easy way to misread this
Do not conclude that 60° shoulder abduction gives the same clinical benefit as 120° for patients. The study measured relative muscle activity in 10 healthy men, not pain, strength, function, or treatment outcomes.