Electromyographic evaluation of the clinical and biomechanical effects of yoga on the flexion-relaxation phenomenon: a Prophet approach

Abstract

Myoelectric silencing of the spinal erector muscles in the trunk flexion posture is indicative of greater spine sharing loads. The evaluation of the flexion relaxation phenomenon is a valid clinical tool able to contribute to the low back pain management [1]. In the broad scenario of low back pain therapy, there is increasing interest in non-traditional interventions such as Yoga, although the scientific evidence does not always analyze the biomechanical significance [2]. Therefore, the aim of this observational study was to evaluate the clinical and biomechanical effects of Yoga on the flexion-relaxation phenomenon of the lumbar erector muscles, through surface electromyography (sEMG) combined with an inertial sensor. Healthy young adults (ages 18 to 40) were selected as participants without chronic nonspecific low back pain for at least three months. The intervention consisted of a Yoga program lasting one hour specific for the lumbar spine Asana, for 4 sessions (2 times/week for 2 weeks), the first in presence and the other three in tele-approach. At the end of each session an evaluation was carried out, thus setting the T0 as the baseline, until the end of the fourth session as T4. The trunk flexion-relaxation phenomenon was performed by asking the participant to slowly flex the trunk forward to full flexion, pausing for 3 seconds and then returning to the standing starting position. The sEMG signal coupled to an inertial sensor was collected to quantify the flexion-relaxation ratio (FRR). Then, using a Prophet model, which allows time series prediction, we have traced the forecast of the FRR trend of the erector spinal muscles of the lumbar spine (Fig. 1). We included 13 healthy women (mean age: 28±8 years; BMI 20.0±0.9 kg/m2). No significant asymmetries were evaluated and Friedman's test reported slight significant differences (left L1-L2 p=.039, right p=0.041; left L4-L5 p=0.045, right p=0.040). Therefore, we performed a Prophet evaluation to analyze FRR trends, finding a growth rate of 0.45±0.3 for left L1-L2, 0.38±0.4 on the right, 0.25±0.4 for L4-L5 on the left and 0.25±0.3 on the right. With an Rhat≤1.01, excluding possible convergence problems. At one month from the end of the intervention, all lower confidence intervals curve remained above the thresholds of the baseline assessments. This study aimed to evaluate the role of Yoga in the prevention of lumbar spine disorders through the kinematic and electromyographic evaluation of the flexion-relaxation phenomenon. Processing the results using a Prophet approach predicts a positive influence even after the end of the Yoga sessions. Surface electromyography coupled to an inertial sensor provides reliable assessments of the lumbar spine, a prediction model can guarantee evidence on the positive introduction of Yoga asanas in the clinical management of any development of low back pain. In light of these results, future prospective studies might focus on the effects of yoga in clinical and biomechanical terms on patients with chronic nonspecific low back pain.