Changes in isolation ratios of the trunk muscles during hip adduction.
Won-Gyu Yoo
PMID 28931995WHAT IT FOUND
During hip adduction, the internal oblique muscle contributed more to trunk activation than the external oblique.
The erector spinae contribution did not change. This suggests hip adduction targets the internal oblique specifically, rather than the outer abdominal layer.
Key findings
01The isolation ratio of the internal oblique was significantly higher during hip adduction compared to no adduction.
02The isolation ratio of the external oblique was significantly lower during hip adduction compared to no adduction.
03The isolation ratio of the erector spinae did not differ significantly between conditions.
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 15 healthy males aged 27–35, so results may not apply to women, older adults, or patients with pain or dysfunction. The task was mild hip adduction with visual feedback; it is unclear if these muscle contribution ratios hold during functional movements or higher loads. The study measured proportional muscle contribution (isolation ratio), not actual clinical stability, strength, or injury rates. Electrode placement for the internal oblique noted that signals from the transversus abdominis and internal oblique are blended and cannot be distinguished at that location, so 'internal oblique' activity may include transversus abdominis.
The easy way to misread this
Do not assume this proves hip adduction improves core stability or prevents injury. The study only measured muscle activation ratios in healthy men during a specific seated task, not functional outcomes.