Purpose: This study investigated whether laser displacement mechanomyography (MMG) could detect acute injury of low back muscles following strenuous eccentric exercise.
Methods: Sixteen healthy adults (10 females, 6 males, mean ± standard deviation, age 21 ± 2.90 years, BMI 21.63 ± 1.99 kg/m2), without low back pain or low back resistance training, were recruited. Strength [maximum voluntary isometric contraction force (MVC)], pain intensity [visual analogue scale (VAS)], biological markers of muscle injury (serum myoglobin and creatine kinase levels), and MMG-derived muscle contractile properties were measured at seven different time points. Pre-exercise 'control' measures were taken prior to a strenuous eccentric exercise task, followed by an immediate post-exercise measurement and further four consecutive daily measurements. A final post-exercise measurement was completed on day 12 post-exercise.
Results: Compared to pre-exercise control, MVC was lower immediately post-exercise (day 1) and on days 2-3. VAS scores were higher post-exercise (day 1) and from days 2-5. Myoglobin was significantly higher on day 4, whilst creatine kinase was significantly higher on days 4-5. MMG-derived maximum muscle displacement (Dmax) was significantly diminished post-exercise (day 1) at all vertebral segments (L1-MT), while contraction velocity (Vc) was significantly slower at all segments except sacral multifidus. Vc recovered rapidly (by day 2), while mid-lumbar Dmax resolved on day 12. Dmax had moderate correlations with MVC (R = 0.61) and VAS (R = - 0.50), and low correlations with myoglobin (R = - 0.36).
Conclusion: MMG appears capable of detecting changes in muscle contractile properties associated with an acute bout of low back pain.
Keywords: Acute injury; Erector spinae; Laser displacement mechanomyography (MMG); Low back pain; Multifidus; Spine.