The Complexity of H-wave Amplitude Fluctuations and Their Bilateral Cross-Covariance Are Modified According to the Previous Fitness History of Young Subjects under Track Training

Abstract

The Hoffmann reflex (H-wave) is produced by alpha-motoneuron activation in the spinal cord. A feature of this electromyography response is that it exhibits fluctuations in amplitude even during repetitive stimulation with the same intensity of current. We herein explore the hypothesis that physical training induces plastic changes in the motor system. Such changes are evaluated with the fractal dimension (FD) analysis of the H-wave amplitude-fluctuations (H-wave FD) and the cross-covariance (CCV) between the bilateral H-wave amplitudes. The aim of this study was to compare the H-wave FD as well as the CCV before and after track training in sedentary individuals and athletes. The training modality in all subjects consisted of running three times per week (for 13 weeks) in a concrete road of 5 km. Given the different physical condition of sedentary vs. athletes, the running time between sedentary and athletes was different. After training, the FD was significantly increased in sedentary individuals but significantly reduced in athletes, although there were no changes in spinal excitability in either group of subjects. Moreover, the CCV between bilateral H-waves exhibited a significant increase in athletes but not in sedentary individuals. These differential changes in the FD and CCV indicate that the plastic changes in the complexity of the H-wave amplitude fluctuations as well as the synaptic inputs to the Ia-motoneuron systems of both legs were correlated to the previous fitness history of the subjects. Furthermore, these findings demonstrate that the FD and CCV can be employed as indexes to study plastic changes in the human motor system.

Exposure to impacts across a competitive rugby season impairs balance and neuromuscular function in female rugby athletes

“…Limited but unfortunately flawed evidence suggests that some athletes may present higher values of H-waves CCV. 40 Significant methodological issues and interpretation within the prior study of Ceballos-Villegas et al 40 prevent firm conclusions for their own data and impair translation to ours. This is an area in which further investigation is needed to translate how an increased CCV reflects the evaluation of plastic changes in the motor reflex responses in humans.…”

Absence of Neuroplastic Changes in the Bilateral H-Reflex Amplitude following Spinal Manipulation with Activator IV

“…Differences may be mediated by neurological or biomechanical factors related to each chiropractic technique [27]. Future investigation is necessary on the complexity of bilateral H-reflexes to clarify whether other variables of the H-reflex or M-wave are affected by the chiropractic intervention [28].…”