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

Preconditioning skeletal muscle with phototherapy is anexperimental technique for producing resistance against muscularfatigue during and after strenuous exercise. This study examinedthe ergogenic effects of phototherapy when applied intermittentlyduring passive recovery between repeated bouts of isokineticquadriceps exercise. A triple-blind, repeated measures, placebocontrolled,cross-over design was used in this study to comparethe effects of phototherapy on torque/work and power outputof the knee extensors in 20 healthy individuals (10 men, 10women). The exercise protocol consisted of four repeated boutsof isokinetic exercise. Each bout consisted of 30 continuousknee extension concentric contractions at an angular velocityof 75°/s with a 4min recovery interval between bouts. Subjectsreceived active and sham phototherapy in random order duringpassive recovery between exercise bouts. Phototherapy wasadministered using a near-infrared laser to the quadricepsfemoris 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 averagepower [W]. During the second, third and fourth exercise bouts,subjects produced significantly more torque (normalized andaverage) and total work/average power output during the activephototherapy condition compared to the sham phototherapycondition. Phototherapy applied as a preconditioning treatmentduring passive recovery intervals between bouts high of intensityand high volume resistance exercise significantly attenuatedfatigue and maintained muscular performance of the quadricepsfemoris muscle group. Preconditioning skeletal muscle withphototherapy intermittently during recovery intervals with fatiguingexercise may be a beneficial, non-invasive and safe ergogenic aidfor athletes that require high levels of muscular endurance.