Task-invariance and reliability of anticipatory postural adjustments in healthy young adults.
Jo Armour Smith, Niklas König Ignasiak, Jesse V Jacobs
PMID 31931450WHAT IT FOUND
Trunk muscle timing and size during rapid arm and leg raises were reliably measured, but the specific muscle synergy patterns varied between the two tasks.
Only a few characteristics, like internal oblique timing and amplitude, stayed the same across both movements.
Key findings
01Most EMG variables were reliably quantified in muscles that contribute consistently to the anticipatory postural adjustment.
02Only a small number of anticipatory postural adjustment characteristics are task-invariant across these two contrasting limb motions.
03Latency of onset in the ipsilateral external oblique, amplitude of contralateral external oblique and contralateral internal oblique activity, and coactivation of the bilateral internal obliques were the same during rapid arm raising and supine leg raising.
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 young adults with no history of low back pain, so results may not apply to clinical populations or older adults. The study was designed to test measurement reliability and task-invariance, not the efficacy of any treatment. Participants used their non-dominant limb, which may affect generalizability to dominant-limb tasks. The sample size was determined by a power analysis for latency differences, which may not be sufficient for detecting smaller effects in synergy patterns.
Declared interests
The authors declared no conflicts of interest. One author is employed by Liberty Mutual Insurance, but the work was performed independent of that affiliation.
The easy way to misread this
Do not interpret the reliability of these measurements as evidence that trunk muscle synergies are fixed or generalizable across tasks. The study found that synergy patterns varied significantly between arm and leg raising, suggesting that anticipatory postural adjustments are highly task-specific even in healthy individuals.