Journal Club May 2018

May, 2018:  Low-Level Laser Therapy and Muscle Strength

Barbosa R et al: Effect of Low-Level Laser Therapy and Strength Training Protocol on Hand Grip by Dynamometry. J Lasers Med Sci. 2017 Summer;8(3):112-117   Free Full Text

Low-level laser therapy (LLLT) has previously been shown to improve muscle performance, delay fatigue, and prevent muscle injuries. The effect is known as photobiomodulation. Various tests, including testing strength and monitoring biomarkers such as lactate, creatine kinase and C-reactive protein, have verified the results. Most studies have looked at large muscle groups including biceps and quadriceps.

Recently, investigators in Brazil studied the effect of LLLT on grip strength and limited the treatment and measurements to the long digital flexor forearm muscles. They divided 45 healthy women (average age 23 years, narrow standard deviation) into three groups.

The control group received sham LLLT with the probe applied to the forearm but the machine turned off. One study group received a 660 nanometer laser treatment of 1.2 Joules of issued energy to 10 points on the middle and proximal forearm to stimulate the deep and superficial digital flexor muscles. The other study group received 904 nanometer laser treatment at the same sites and at the same total energy application. Each subject received twice weekly LLLT (or sham) sessions for two weeks before beginning the strengthening regimen, which was identical for each group.

Dominant hand strength training consisted of using a finger exerciser that calculated the maximum resistance (MR) of the finger flexors. Then the Oxford protocol was performed: 10 repetitions at 100% of MR, 10 reps at 75% of MR, and 10 reps at 50% of MR. The subjects performed the exercises twice weekly for four weeks.

The researchers measured grip strength in each subject’s dominant hand using a standard protocol and body/arm position at the beginning and end of the study.

RESULTS: None of the 45 subjects experienced any adverse events, and 43 completed the study. Grip strength was statistically equal among the groups at the beginning of the study. In the control group and in the 660 nm group, grip strength increased slightly but not to a statistically significant degree. In the 904 nm group, grip strength increased from about 24 kg to about 29 kg, which proved to be a statistically significant difference.

DISCUSSION: The authors compare their results to previous studies that focused on other muscle groups and different protocols for strengthening, LLLT application, and measurements recorded. They also cite other papers that studied light emitting diode therapy as an alternate form of photobiomodulation. The researchers note that although previous studies also show benefits of LLLT on muscle strength and endurance, lack of a standardized protocol makes comparisons difficult. They do not offer any explanation why LLLT works or how it could be applied clinically.

COMMENT: When I first heard about LLLT I was entirely skeptical, and I generally remain so. Its clinical application, in wound healing for instance, has raced far ahead of the basic science that might elucidate its biologic effects. We should demand better explanations than, “It just works, that’s all I know.”

Now having read this paper, however, and seeing that it basically repeats the results of other LLLT protocols in other muscle groups using various methods of measurement, there seems to be something to LLLT.

The question I have been unable to find an answer to is how it works. Light makes muscle strong? Sounds weird. Yet, consider photosynthesis—light modulates a chemical reaction that converts carbon dioxide into water. Or in animals, sunshine stimulates production of vitamin D, melanin production, and skin cancers. So photobiomodulation certainly does exist.

Has anybody heard of LLLT being used clinically for muscle strengthening? If so, please let me know and I will let this newsletter’s readership know. Also, high performance athletes typically have their ears to the ground regarding most anything that might give them a competitive advantage, even without a scientific basis for it. Cupping comes to mind. Has anybody heard of athletes getting their quads zapped with LLLT? If so, let’s get a discussion going. My quads could use a boost.