Effects of photobiomodulation therapy on muscle activity parameters, time to exhaustion in a constant load cycling effort at the severe domain and on the central and peripheral aspects of muscle fatigue

The general objective of this dissertation was to investigate the effects of two doses of photobiomodulation (PBM) on time to exhaustion in a constant load cycling effort at severe domain (Δ60%, [CLE60]), exploring during the exercise the physiological responses resulting from muscular activity (ie, metabolic, gasometric, electromyographic and respiratory), as well as the central and peripheral aspects of muscle fatigue after effort. For this, two studies were carried out, study 1 and 2. Twenty-seven volunteers (14 participants in study 1 and 13 in study 2) participated in the study. Study 1 aimed to investigate the effects of two doses of PBM on central and peripheral aspects after CLE60 with equalized duration (ie, isotime) as well as the neuromuscular responses during the exercise. The subjects performed 5 efforts on different days, one in the form of familiarization and one in the control form, both until exhaustion. The last three efforts were performed with the same duration as that reached in the control condition, preceded by one of the three interventions used in the present study: PBM at the dose of 260 J, PBM at 130 J and placebo (PBM with the device switched off, dose of 0 J). During the last 4 exercises, the electromyographic responses of muscles of the dominant lower limb were evaluated and before and after the last three efforts, neuromuscular evaluations associated with peripheral electrical stimulation of the femoral nerve were performed, aiming to investigate central and peripheral aspects of muscle fatigue. In study 2, the volunteers performed on different days, 5 CLE60 to exhaustion, the first 2 in the form of familiarization, the last 3 preceded by one of the three modalities of intervention (PBM at the dose of 260 J, or 130 J, or placebo in a randomized, double-blinding cross-over design). Also, during the last three efforts, the electromyographic responses of dominant lower limb muscles, gasometric capillary responses, blood lactate concentrations and respiratory gas exchange were monitored, with the collections and/or analyzes being performed in identical time windows for the 3 conditions, determined on the basis of the shortest time achieved between the last three efforts. Considering the results obtained in studies 1 and 2, in general, the PBM in the parameters used had a slight positive influence on neuromuscular aspects during effort (significant) and on muscle fatigue after effort (non significant). However, there was no effect of PBM in the time until exhaustion in the type of effort proposed, as well as changes in metabolic, gasometric and respiratory responses during exercise (AU)