Monitoring individual erector spinae fatigue responses using electromyography and near infrared spectroscopy.

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This study examined the utility of electromyography and near-infrared spectroscopy (NIRS) in assessing m. erector spinae activity during the Biering-Sorensen Back Muscle Endurance (BSME) test. Six men and four women (27.0 +/- 7.1 years of age) performed the BSME test (time = 131.5 +/- 43.5 s). EMG was used to quantify neuromuscular activity of the right and left side at the L3 level, and root mean square was scaled for maximum value at the start of the exercise. NIRS was used to evaluate blood volume (BV) and oxygenation (OX) simultaneous with EMG bilaterally at the L3 level. There was a decrease to 49+/- 8% of initial median frequency (mean= 83 Hz) on both right and left sides when the exercise was 90% complete, and the slope of the median frequency/time relationship was significantly related to BSME time (r = 0.82). Group means for BV increased during back exercise while OX decreased and was significantly different between right and left sides of the lower back. However, large OX response differences among individuals and between right and left sides were noted. OX and median frequency were moderately related (r = 0.27-0.38). It appears that NIRS combined with EMG is a promising tool for assessing localized metabolic and neuromuscular activity during static contractions of the lower back.