Exercise-related fatigue affects joint-driven resistance: comparison of flexor and extensor.
Shigeru Terada, Masahiro Goto, Hiroto Honda and 1 others
PMID 34219959WHAT IT FOUND
Fatiguing elbow exercises increased joint resistance in healthy men.
The effect was strongest in the distal range of motion after biceps fatigue. Triceps fatigue caused smaller, less consistent increases in resistance.
Key findings
01Following a fatiguing elbow flexion task, the elastic coefficient (a measure of joint resistance) increased significantly across the entire range of motion, as well as in the proximal and distal sub-ranges.
02Following a fatiguing elbow extension task, the flexion elastic coefficient increased significantly only in the distal range, while the extension elastic coefficient showed no significant differences in any range.
03The rate of increase in the elastic coefficient was generally higher in the distal movement range compared to the proximal range after both flexion and extension tasks.
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 25 healthy men, limiting generalizability to women, older adults, or clinical populations. Muscle mass and composition were not controlled for, which can influence stiffness measurements. The order of tasks (biceps then triceps) and the same-day completion may have affected motivation and load consistency. Electromyography was not used during the fatiguing tasks, so compensatory muscle activity could not be ruled out. The study measured passive resistance but did not examine active muscle dynamics or stretch mechanics.
Declared interests
The authors declared no conflicts of interest.
The easy way to misread this
Do not interpret the increased joint resistance as a permanent change in muscle tone or a therapeutic effect. The stiffness was transient, measured immediately after fatigue, and did not distinguish between neural, mechanical, or fluid-based causes.