Muscle Specific Endurance of the Lower Back Erectors using Electrical Twitch Mechanography

Abstract

Lower back pain is a common symptom that may be associated with skeletal muscle dysfunction. PURPOSE: This study evaluated the endurance of the lower back muscles in healthy participants using accelerometer-based Mechanomyography (aMMG). METHODS: Surface electrodes and a tri-axial aMMG device were placed on the belly of the erector spinae muscles along the T11-L1 vertebrae. Current levels that evoked visible and tolerable twitch contractions were used. The muscles were stimulated for 3 minutes each at 2, 4, and 6 Hz. An endurance index (EI) was calculated as the maintenance of acceleration at the end of each stage of stimulation relative to the peak acceleration. Subjects (N=7) were tested on two separate days to assess reproducibility. Muscle oxygenation (HbO2) was measured with near infrared spectroscopy (NIRS) during stimulation and during a maximal isometric back extension to induce complete ischemia for signal calibration (N=5). EI was measured in the wrist flexor and vastus lateralis muscles for comparison. RESULTS: EI for the erector spinae muscles were 70.3 + 13.4%, 32.6 + 8.4%, and 19.2 + 6.2 % for 2, 4, 6 Hz, respectively. The coefficients of variation were 9.8%, 13.9%, and 20.3% for 2, 4, 6 Hz, respectively. EI values for the erector spinae were significantly lower than EI values for the arm and the leg (all comparisons, p &lt 0.05). HbO2 values for the erector spinae were 86.4 + 10.9 % at rest, and 77.2 + 15.5%, 84.3 + 14.1%, and 84.1 + 18.9% for 2, 4, 6 Hz, respectively. CONCLUSION: EI is a reproducible method of assessing muscle endurance of the lower back erector muscles that is not related to low oxygen levels. The erector spinae muscles have lower muscle endurance relative to limb muscles.: