Muscular Preconditioning Using Phototherapy Improves the Physical Work Capacity of the Quadriceps when Applied between Repeated Bouts of Resistance Exercise

Abstract

Preconditioning skeletal muscle with phototherapy is an experimental technique for producing resistance against muscular fatigue during and after strenuous exercise. This study examined the ergogenic effects of phototherapy when applied intermittently during passive recovery between repeated bouts of isokinetic quadriceps exercise. A triple-blind, repeated measures, placebocontrolled, cross-over design was used in this study to compare the effects of phototherapy on torque/work and power output of the knee extensors in 20 healthy individuals (10 men, 10 women). The exercise protocol consisted of four repeated bouts of isokinetic exercise. Each bout consisted of 30 continuous knee extension concentric contractions at an angular velocity of 75°/s with a 4min recovery interval between bouts. Subjects received active and sham phototherapy in random order during passive recovery between exercise bouts. Phototherapy was administered using a near-infrared laser to the quadriceps femoris muscle group at 10 J/cm2 (total dose of 1600-2400 J). Performance measures included normalized peak torque [Nm/ kg], average peak torque [Nm], total work [Nm], and average power [W]. During the second, third and fourth exercise bouts, subjects produced significantly more torque (normalized and average) and total work/average power output during the active phototherapy condition compared to the sham phototherapy condition. Phototherapy applied as a preconditioning treatment during passive recovery intervals between bouts high of intensity and high volume resistance exercise significantly attenuated fatigue and maintained muscular performance of the quadriceps femoris muscle group. Preconditioning skeletal muscle with phototherapy intermittently during recovery intervals with fatiguing exercise may be a beneficial, non-invasive and safe ergogenic aid for athletes that require high levels of muscular endurance.