Motor unit behavior of lumbar multifidus during a forward trunk bending task performed under different speeds and loads in asymptomatic participants.
Level 4 - case-series / case-control
Laboratory-based repeated-measures physiological study in healthy volunteers (graded by design analogy)
PubMed 41462500 · doi:10.1038/s41598-025-28869-8
What was done
Surface electromyography decomposition (dEMG) was evaluated in 29 asymptomatic male and female adults performing active forward trunk flexion. Participants completed two sets of 60-second exercises across two movement speeds (15 and 25 repetitions/minute) and two external loads (5% and 10% body weight). Action potential amplitudes and motor unit firing rates of the lumbar multifidus were derived. Within-session test-retest reliability was evaluated using intraclass correlation coefficients (ICCs), and the effects of speed and load were analyzed using a two-factor repeated-measures ANOVA.
What was found
Most dEMG parameters demonstrated acceptable within-session test-retest reliability (ICC > 0.70). Increasing trunk flexion speed resulted in significantly greater peak amplitudes, average amplitudes, and average motor unit firing rates. Increasing load resulted in significantly greater average amplitudes and average firing rates. The abstract did not report exact numeric values, confidence intervals, or p-values for the amplitude and firing rate comparisons.
Why it matters
The study shows that non-invasive dEMG of the lumbar multifidus has acceptable within-session reliability and that motor unit recruitment and firing scale with both movement speed and external load. This provides baseline physiological data to guide biomechanical understanding and exercise design for trunk stability.
Limits
The sample size was small (n = 29) and limited entirely to asymptomatic participants, preventing direct generalization to clinical populations with low back pain. Only within-session reliability was assessed rather than inter-day reproducibility. Specific quantitative values, effect sizes, and dispersion metrics were not provided in the abstract.
Cited by
- supports The lumbar paraspinal muscles function to control forward trunk flexion to protect the spine.