Abstract
PurposeThe aim of the current study was to investigate the effects of photobiomodulation therapy (PBMT) applied 30 min or 6 h prior to cycling on blood flow velocity and plasma nitrite concentrations at rest, time to exhaustion, cardiorespiratory responses, blood acid-base balance, and K+ and lactate concentrations during exercise.MethodsIn a randomized, crossover design, 13 healthy untrained men randomly completed four cycling bouts until exhaustion at the severe-intensity domain (i.e., above respiratory compensation point). Thirty minutes or 6 h prior to the cycling trials, participants were treated with PBMT on the quadriceps, hamstrings, and gastrocnemius muscles of both limbs using a multi-diode array (11 cm × 30 cm with 264 diodes) at doses of 152 J or a sham irradiation (with device turned off, placebo). Blood samples were collected before and 30 min or 6 h after treatments to measure plasmatic nitrite concentrations. Doppler ultrasound exams of the femoral artery were also performed at the same time points. Cardiorespiratory responses, blood acid-base balance, and K+ and lactate concentrations were monitored during exercise sessions.ResultsPBMT did not improve the time to exhaustion (p = 0.30). At rest, no differences were found in the peak systolic velocity (p = 0.97) or pulsatility index (p = 0.83) in the femoral artery, and in plasma nitrite concentrations (p = 0.47). During exercise, there were no differences for any cardiorespiratory response monitored (heart rate, p = 0.15; oxygen uptake, p = 0.15; pulmonary ventilation, p = 0.67; carbon dioxide output, p = 0.93; and respiratory exchange ratio, p = 0.32), any blood acid-base balance indicator (pH, p = 0.74; base excess, p = 0.33; bicarbonate concentration, p = 0.54), or K+ (p = 0.22) and lactate (p = 0.55) concentrations.ConclusionsPBMT at 152 J applied 30 min or 6 h before cycling at severe-intensity did not alter resting plasma nitrite and blood flow velocity in the femoral artery, exercise-induced physiological responses, or time to exhaustion in healthy untrained men.
Highlights
Photobiomodulation therapy (PBMT) is a non-thermal electromagnetic radiation treatment that utilizes visible or invisible lights through laser or light-emitting diode sources (Anders et al, 2015)
The different settings of PBMT treatment parameters between studies, such as distinct irradiation power and total energy delivered on the target tissues are generally used to explain the lack of agreement in the reported effects of PBMT on exercise performance (Ferraresi et al, 2016)
These investigations demonstrated that the peak of PBMT efficacy in improving the transfer of hydrogen ions (H+) through the respiratory electron transport chain, adenosine triphosphate (ATP) synthesis (Ferraresi et al, 2015a), and physical performance (Ferraresi et al, 2015b) occurred 6 h after treatment
Summary
Photobiomodulation therapy (PBMT) is a non-thermal electromagnetic radiation treatment that utilizes visible or invisible lights through laser or light-emitting diode sources (Anders et al, 2015). The majority of investigations used PBMT up to 30 min before the exercise (Malta et al, 2016; Lanferdini et al, 2018a; de Carvalho et al, 2020; Dutra et al, 2020) and only one study has been conducted in humans addressing the suggested time-response effect of PBMT (Rossato et al, 2018) In this investigation, the authors observed that PBMT used 6 h or immediately before exercise reduced muscle fatigue induced by a knee extension-flexion exercise protocol in healthy men (Rossato et al, 2018). The current literature precludes definite conclusions about the PBMT time-response effect and its practical applications in whole-body exercises such as cycling, which renews the calls for research to assess this gap
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