AUTHOR=Dutra Yago Medeiros , Claus Gabriel Machado , Malta Elvis de Souza , Seda Daniela Moraes de Franco , Zago Anderson Saranz , Campos Eduardo Zapaterra , Ferraresi Cleber , Zagatto Alessandro Moura 

TITLE=Photobiomodulation 30 min or 6 h Prior to Cycling Does Not Alter Resting Blood Flow Velocity, Exercise-Induced Physiological Responses or Time to Exhaustion in Healthy Men

JOURNAL=Frontiers in Physiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2020.607302

DOI=10.3389/fphys.2020.607302

ISSN=1664-042X

ABSTRACT=<sec><title>Purpose</title><p>The 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<sup>+</sup> and lactate concentrations during exercise.</p></sec><sec><title>Methods</title><p>In 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<sup>+</sup> and lactate concentrations were monitored during exercise sessions.</p></sec><sec><title>Results</title><p>PBMT did not improve the time to exhaustion (<italic>p</italic> = 0.30). At rest, no differences were found in the peak systolic velocity (<italic>p</italic> = 0.97) or pulsatility index (<italic>p</italic> = 0.83) in the femoral artery, and in plasma nitrite concentrations (<italic>p</italic> = 0.47). During exercise, there were no differences for any cardiorespiratory response monitored (heart rate, <italic>p</italic> = 0.15; oxygen uptake, <italic>p</italic> = 0.15; pulmonary ventilation, <italic>p</italic> = 0.67; carbon dioxide output, <italic>p</italic> = 0.93; and respiratory exchange ratio, <italic>p</italic> = 0.32), any blood acid-base balance indicator (pH, <italic>p</italic> = 0.74; base excess, <italic>p</italic> = 0.33; bicarbonate concentration, <italic>p</italic> = 0.54), or K<sup>+</sup> (<italic>p</italic> = 0.22) and lactate (<italic>p</italic> = 0.55) concentrations.</p></sec><sec><title>Conclusions</title><p>PBMT 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.</p></sec>