Measurement of the cross-sectional area of the hamstring muscles during initial and stretch positions with gravity magnetic resonance imaging.
Dai Nakaizumi, Hitoshi Asai, Pleiades Tiharu Inaoka and 2 others
PMID 30936643WHAT IT FOUND
Hamstring muscles shrink when stretched, but the amount of shrinkage does not predict how flexible a person is.
The semimembranosus resists shape change more than other hamstring muscles. This method measures muscle deformation, not joint range of motion.
Key findings
01The maximum cross-sectional area of all four hamstring muscles was significantly smaller in the stretch position than in the initial position.
02The semimembranosus showed a significantly smaller change in cross-sectional area compared to the other three hamstring muscles, suggesting it is stiffer or more resistant to stretching.
03There was no significant correlation between the change in cross-sectional area of any hamstring muscle and the stretch position angle.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study only included 15 healthy young men, so findings may not apply to women, older adults, or people with hamstring injuries. Only two positions were evaluated, which limits the ability to understand how muscle shape changes across a full range of stretch intensities. The stretch position angle varied between participants based on comfort and ability to hold the position, which may have introduced variability. The lack of correlation between area change and stretch angle suggests individual differences in muscle morphology that this method did not capture.
Declared interests
None declared.
The easy way to misread this
Do not assume that a smaller change in hamstring muscle cross-sectional area on MRI indicates greater clinical flexibility or a lower injury risk. The study found no relationship between the degree of muscle shape change and the stretch angle, and the sample was small and healthy.