Eccentric and concentric contraction of multifidus lumborum and longissimus muscles during flexion–relaxation test using discrete wavelet transform

Purpose: Muscle activation can reflect the stability of the lumbar spine based on the electrical features and kinematics during a dynamic test. However, there is a lack of knowledge of the activation of paravertebral muscles i.e., during the flexion–relaxation test. Hence, we determine the band frequency differences between eccentric (ECC) and concentric (CON) contraction during the flexion–relaxation test in healthy untrained participants without lumbar pain, both multifidus lumborum and longissimus muscles. Methods: 40 healthy participants (aged 30.6 ± 6.9 years) were recruited. Kinematic and surface electromyography were collected to compare the ECC and CON spectral characteristics of both multifidus lumborum and longissimus. The bursts were transformed using a discrete wavelet transform (Daubechies). The band frequencies were compared through mean comparison test with alpha set to 5%. Results: Both multifidus lumborum and longissimus muscles had higher intensity in ECC contraction than CON for frequency bands lower than 32 Hz (P < 0.05); meanwhile, there was a higher intensity in CON contraction than ECC for frequency bands higher than 32 or 64 Hz until 256 Hz (P < 0.05). Conclusion: For both paravertebral muscles analyzed, discrete wavelet decomposition suggests that during the flexion–relaxation test there is an ECC contraction characterized by low-frequency bands compared with the CON phase characterized by medium- and higher-frequency bands both paravertebral muscles analyzed. The spectral characteristics might be a useful physiological neuromuscular reference to the pathophysiology adaptations of the paravertebral muscle contraction.