Photobiomodulation therapy (PBMt) has been used to increase muscle performance and improve recovery when applied
before exercise. We aimed to evaluate the effects of PBMt using LASER on muscle oxygenation and performance. The
study was a randomized, participant and assessor-blinded, within-subject crossover trial with placebo control to test the
viability of the methods. Five physically active young women were randomly assigned to either placebo, or active PBMt
(12 diode cluster probe; 904 nm; 60 mW; 250 Hz; 43.2 J per site, 129.6 J total) in contact over rectus femoris (RF)
muscle of the dominant limb immediately before an isokinetic fatigue protocol. A one-week wash-out period preceded
cross-over. Electromyography and isokinetic performance measures were evaluated. Absolute concentrations of
deoxygenated haemoglobin and myoglobin (deoxy[Hb + Mb]) of the RF, an index of local microvascular fractional O2
extraction, was monitored continuously by near-infrared spectroscopy (NIRS). Total haemoglobin concentration as an
indicator of microvascular haematocrit was calculated as the sum of the deoxy[Hb + Mb] and oxy[Hb + Mb] signals.
PBMt pre-conditioning reduced time to peak torque when compared to placebo (P<0.05). PBMt resulted in a noticeably
reduced trend in deoxy[Hb + Mb] during exercise compared to placebo (P>0.05). PBMt before exercise improves
indicators of muscle performance, potentially by increasing local matching of bulk and microvascular O2 delivery
relative to skeletal muscle O2 utilisation. Further work is required to understand the effect of PBMt on haemodynamic
and metabolic characteristics of muscle.
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