Effect of low-level laser therapy on muscle adaptation to knee extensor eccentric training



Eccentric training has been popularized for physical conditioning and prevention/rehabilitation of musculoskeletal disorders, especially due to the expressive responses in terms of muscular strength gain. In view of evidence that low-level laser therapy (LLLT) is able to increase exercise performance and accelerate post-exercise recovery, the aim of this study was to verify the effect of LLLT on hypertrophy and strengthening of knee extensor muscles submitted to eccentric training.


Thirty healthy male subjects were randomized into three groups: Control Group (CG), Training Group (TG) and Training + LLLT Group (TLG). CG received no intervention, while TG and TLG were engaged on an 8-week knee extensor isokinetic eccentric training program. Only subjects from TLG were treated with LLLT (wavelength = 810 nm; power output = 200 mW; total dosage = 240 J) before each training session. Knee extensor muscle thickness and peak torque were assessed through ultrasonography and isokinetic dynamometry, respectively.


CG presented no changes in any variable throughout the study, while eccentric training led to significant increases in muscle thickness and peak torque in TG and TLG. Subjects from TLG reached significantly higher percent changes compared to subjects from TG for sum of muscles’ thicknesses (15.4 vs. 9.4 %), isometric peak torque (20.5 vs. 13.7 %), and eccentric peak torque (32.2 vs. 20.0 %).


LLLT applied before eccentric training sessions seems to improve the hypertrophic response and muscular strength gain in healthy subjects.

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Fig. 1
Fig. 2
Fig. 3



Analysis of variance


Control group


Light-emitting diode therapy


Low-level laser therapy


Rectus femoris muscle thickness


Vastus lateralis muscle thickness


Vastus medialis muscle thickness


Concentric peak torque


Eccentric peak torque


Isometric peak torque


Rectus femoris


Training group


Training + LLLT group


Vastus intermedius


Vastus lateralis


Vastus medialis


Sum of muscles’ thicknesses


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The authors would like to thank Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil) and Fundação de Amparo a Pesquisa do Estado do Rio Grande do Sul (FAPERGS, Brazil) for financial support.

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Correspondence to Bruno Manfredini Baroni.

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Communicated by Martin Flueck.

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Baroni, B.M., Rodrigues, R., Freire, B.B. et al. Effect of low-level laser therapy on muscle adaptation to knee extensor eccentric training. Eur J Appl Physiol 115, 639–647 (2015). https://doi.org/10.1007/s00421-014-3055-y

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  • Phototherapy
  • Resistance training
  • Eccentric exercise
  • Quadriceps femoris