Red Light Therapy for Muscle Fatigue: Scientific Evidence

12 healthy non-athlete men received photobiomodulation combined with a static magnetic field between 2 sets of exercise in a 2021 randomized crossover triple-blinded placebo-controlled trial of second-set performance. 12 healthy non-athlete men received a single application at 630-650, 865-885, and 904-906 nm on the muscles at the front of the thigh, at 0.31 mW to 12.5 W, 0.0712 to 180 J and pulse frequencies of 2, 16, and 250 Hz, in 3.8-minute sessions given 2 times per week across 7 days. Performance in the second set improved compared with placebo, though the finding was described as preliminary.

Movement performance in the legs improved after a single dose of light, according to a 2021 randomized clinical trial of photobiomodulation delivered by combined laser and LED. 60 participants received 617 and 830 nm light on the thigh and calf muscles at 150 mW and 4 to 9 J, in 60-second sessions applied on a single day before functional testing. The group treated on both the thigh and the calf, and the group treated on the calf alone, both performed better than the control on the number of repetitions completed and on time to exhaustion. It was concluded that the effect depends on which muscle group receives the light rather than on the moment of application.

Whether light therapy still helps when the muscles doing the work are not the ones being treated was the question behind a 2020 randomized triple-blind placebo-controlled trial. 30 healthy male volunteers were randomized into placebo, local, and non-local groups of 10, receiving photobiomodulation combined with a static magnetic field at 630-650, 865-885, and 904-906 nm in contact with the front of the thigh, at 0.31 to 17.5 mW, 0.0712 to 180 J and pulse frequencies of 2, 16, and 250 Hz, in 3.8-minute sessions on a single day before an exercise protocol that lengthened the muscle under load. Performance improved, and muscle fatigue fell only in the group whose working muscles received the light directly, with statistically significant differences from both the placebo and the non-local group. The authors concluded that the working muscles themselves need to be treated for the effect to appear.

A 2020 randomized crossover trial tested low-level laser therapy (LLLT) as a preparation step before light exercise with restricted blood flow. 15 young adults completed the exercise under 3 conditions, covering LLLT plus restricted blood flow, sham laser plus restricted blood flow, and a control, with 905 nm light applied in contact with the forearm muscles at 100 mW and 60 J, in 10-minute sessions given 3 times per week across 3 days. Oxygen levels in the muscle fell less under the LLLT condition than under the others. They linked the effect to changes in how the nerve signals driving the muscle were recruited.

12 male amateur soccer players who received photobiomodulation therapy (PBMT) before a simulated match lost less strength in the back of the thigh than they did after a placebo, in a 2019 randomized crossover double-blinded trial of muscle fatigue brought on by soccer. Light at 880 nm was applied there at 5 W, 20 and 243 mW/cm², and 300 J per leg, in 60-second sessions given 2 times per week across 7 days, with the 2 match sessions at least 7 days apart. It was found that strength at the back of the thigh, the balance between the front and back thigh muscles, and standing jump height all fell less after PBMT than after placebo. Strength at the front of the thigh was unaffected by the simulated match under either condition.

Researchers examined 904 nm photobiomodulation, an under-studied wavelength, for exercise-induced muscle fatigue in a 2018 randomized crossover trial with placebo control. 18 young women received light in contact with the front of the thigh at 60 mW, 129.6 J and a pulse frequency of 250 Hz, in 60-second sessions given 2 times per week across 7 days, before a fatigue test of 60 knee extensions on a machine that measures muscle force. The researchers reported that the effort felt significantly harder compared with placebo. They described both the wavelength and the participant group as under-studied and called for further work.

Power outputs of 100, 200, and 400 mW per diode were tested against a placebo in a 2017 randomized placebo-controlled double-blind trial of photobiomodulation therapy (PBMT) for muscle performance and recovery after exercise. 28 high-level soccer players received 810 nm light from a 5-diode cluster applied in contact to 6 sites on the front of the thigh at 300 J, in sessions of 25 to 100 seconds given once per week across 4 days, before an exercise protocol that lengthened the muscle under load. Maximum strength rose, and muscle soreness and the blood markers of muscle strain fell at the 100 and 200 mW settings, with the strongest results at 100 mW. The authors concluded that more power output is not necessarily better.

Comparing photobiomodulation therapy (PBMT) with cryotherapy and with a combination of the 2, a 2017 randomized double-blind placebo-controlled clinical trial examined muscle recovery after high-intensity exercise. 40 volunteers were distributed across 5 groups and treated in contact on the biceps with light at 660 and 850 nm, 10 and 30 mW and 0.3 to 41.7 J, in 30-second sessions given 4 times per week on a single day, with treatment applied 2 minutes after a strength test that followed exercise. The study reported that PBMT alone and PBMT combined with cryotherapy were associated with better recovery than cryotherapy alone. Further, the authors also noted that adding cryotherapy did not improve on what the light therapy achieved by itself.

When researchers applied low-level laser therapy (LLLT) to the calf before a fatigue protocol, a 2016 randomized controlled trial tracked its effect in 60 young, physically active volunteers. Participants were distributed to a control group, a placebo group, or a laser group, with 808 nm light applied to the calf at 100 mW, 35700 mW/cm², and 25 J, in 49-second sessions given once per week, before a fatigue protocol of 100 repeated ankle movements against resistance. The laser group's muscles tired significantly more slowly than those of the control and placebo groups. The sensor readings of muscle activity did not differ between the groups.

A crossover design gave each participant all 3 treatment conditions in a 2016 clinical trial of photobiomodulation for muscle fatigue. 9 participants averaging 24.3 years of age received sham light, 240 J and 480 J in randomized order across separate sessions, with near-infrared light at 810 and 980 nm applied in contact with a small muscle in the hand at 2 and 4 W, in 2-minute sessions given 3 times per week over 4 days, while participants held a load set at 30% of the heaviest weight they could lift once. Participants held the load 26% longer after the 240 J dose than after the sham, a statistically significant gain, and the researchers reported it as the more effective of the 2 doses. How steadily they held the load worsened over the course of the task, but did not differ between the conditions.

2016 brought a randomized crossover double-blind placebo-controlled trial asking whether the size of a light therapy cluster probe changes its effect on fatigue in the muscles that bend the elbow. 10 physically active men aged 18 to 35 completed 4 sessions at least 48 hours apart, receiving a large cluster probe, a small cluster probe, or matching placebos in contact with the biceps, with light at 670, 850, 880, and 950 nm delivering 60 J per muscle, given 4 times per week across 4 days before a fatigue protocol. Maximum strength fell sharply after the exhaustion protocol under every condition, with no significant treatment effect. The authors noted this was the first study to compare cluster probes of different sizes at the same total dose.

Among 12 professional volleyball players, a 2015 randomized double-blind placebo-controlled trial tested LED therapy given before official matches to see whether it could prevent the rise in a blood marker of muscle damage. A professional male volleyball team of 12 athletes received LED therapy before 4 matches during a national championship, with light delivered at 630 and 850 nm to the front and back of the thigh and the calves at total energies of 630, 1260, and 1890 J, applied on a single day per match. The marker rose significantly after the lowest dose and after the placebo, while the higher doses held the rise in check. The authors described the effect as dose-dependent and used it to outline a therapeutic window.

Researchers tested near-infrared light therapy as a way to limit strength loss after strenuous resistance exercise in a 2015 randomized crossover trial. 39 healthy men and women averaging 20 years of age received both an active and a sham treatment on the biceps on separate days, with a class 4 laser delivering 800 and 970 nm light at 1.5 and 3 W in contact, in sessions of 3 to 4 seconds given 2 times per week over 10 days for a cumulative dose of 360 J. Strength loss from before to after exercise was smaller after the active treatment than after the sham, though the difference was small and only just reached statistical significance. Near-infrared light therapy may help preserve muscle function during rehabilitation, while noting that higher doses deserve further study.

This 2014 randomized double-blind crossover trial tested whether low-level laser therapy (LLLT) applied during rest intervals could build resistance to muscle fatigue. 7 clinically healthy young men averaging 21 years of age were allocated to an active laser group and a placebo group, with 808 nm light applied in contact with the muscles at the front of the thigh at 100 mW and 4 J per application, in 40-second sessions given 3 times per week across 21 days, between sets of knee bends and extensions on a machine that measures muscle force. Maximum repetitions rose 52% in the laser group, a statistically significant increase, and the sensor readings showed less fatigue in the thigh muscles. The authors suggested that applying the laser during rest intervals and after the final set may raise resistance to muscle fatigue.

Published in 2013, this systematic review evaluated whether light therapy given before resistance exercise could improve muscle function, reduce exercise-induced muscle fatigue, and support recovery afterwards. The review drew on 10 human studies that applied single-diode lasers, multi-diode lasers, or light emitting diodes to the upper arm, thigh, jaw, shin, calf, and lower leg muscles, at wavelengths spanning 400-700, 632.8, 640, 655, 660, 803, 808, 810, 820-904, 830, 850, and 904 nm, with 100 mW and doses of 8.3 to 417 J, applied 2 times per week. Most of the data sets favored active light therapy over sham treatment, with delayed fatigue, better recovery after exercise, and signs that muscle cells were protected. They concluded that pre-exercise light therapy has consistently shown benefits for muscle.

Across 16 human studies, a 2012 review examined low-level laser therapy (LLLT) for muscle performance, fatigue, and repair. The included trials treated the shin, thigh, buttock, calf, and upper arm muscles in contact, using wavelengths of 632.8, 635, 655, 660, 662, 760, 780, 808, and 904 nm, 4 to 60 mW, 0.1 to 31 J and pulse frequencies of 1 to 10000 Hz, in sessions of 40 seconds to 10 minutes given up to 30 times per week over 30 days. Muscle performance and repair improved across the body of work reviewed, and they suggested the therapy may benefit athletes and people recovering from muscle injury.

Among 45 clinically healthy young women taking part in endurance training, a 2012 randomized controlled clinical trial tested whether adding low-level laser therapy (LLLT) could reduce fatigue in the muscles at the front of the thigh. Participants averaging 21 years of age were split into a control group, a training group, and a training-plus-laser group, with an 808 nm laser applied in contact with the thigh at 60 mW and 0.6 to 18 J, in 50-second sessions given 27 times per week across 63 days of exercise-bike work. At the end of the study, it was reported that only the training-plus-laser group showed a statistically significant reduction in how quickly the thigh muscles fatigued in both the dominant and non-dominant legs. The training group alone showed a fall that did not reach significance, and the control group showed no change from baseline.

Whether red or infrared wavelengths work better against muscle fatigue was the question behind a 2012 randomized double-blind placebo-controlled crossover trial. 10 healthy male volunteers were treated with active red low-level laser therapy (LLLT) at 660 nm, active infrared LLLT at 830 nm, or an identical placebo, applied at 4 points on the biceps at 50 mW per point, and 20 J per muscle, in 100-second sessions on a single day, 3 minutes before a 60-second test of holding the elbow bent against resistance. Mean peak force rose 12.14% with red light and 14.49% with infrared, and mean average force rose 13.09% and 13.24%, both measured against placebo. Neither wavelength outperformed the other, and both appeared to delay muscle fatigue.

Comparing LED therapy against cold water immersion and a placebo, a 2011 randomized controlled trial examined muscle fatigue and short-term recovery after hard exercise. 6 male futsal players were treated 5 minutes after each of 3 all-out cycling tests, receiving LED therapy in contact with the calves and the front and back of the thigh at 654-666 and 830-870 nm, 10 and 30 mW and 41.7 J per point, in 30-second sessions given 3 times per week over 14 days. Only the group that received real LED therapy showed lower levels of the blood markers that rise with muscle strain and fatigue, with statistically significant drops after treatment. A marker linked to inflammation did not change after any of the 3 treatments.

A 2010 randomized controlled trial evaluated LED therapy for fatigue in the muscles at the front of the thigh, using force measured on a machine that gauges muscle strength as the main outcome. 17 healthy, physically active men took part in a crossover double-blinded placebo-controlled design, receiving either an active multi-diode cluster probe or a placebo in contact with the thigh before 30 all-out knee bends and extensions, with light delivered at 660 and 850 nm, 10 and 30 mW and 41.7 to 125.1 J, in 30-second sessions 2 times per week across 3 days. Muscle force after exercise came out higher following LED therapy than following placebo, a statistically significant difference. The smaller drop in force was consistent with better performance.

9 healthy male volleyball players who received low-level laser therapy (LLLT) before exercise completed 14.5% more repetitions and lasted 8% longer before exhaustion than after placebo, in a 2010 randomized crossover double-blinded trial of muscle fatigue. The active treatment used a cluster probe with 5 laser diodes at 810 nm and 200 mW, applied in contact to 2 spots over the biceps of the non-dominant arm for 30 seconds, delivering 60 J of total energy, in sessions given 2 times per week over 7 days. The blood markers that rise with muscle strain, fatigue, and inflammation were all lower after active LLLT, with statistically significant differences pointing to faster recovery.

Active LED therapy increased the number of biceps contractions by 12.9% and extended the time taken to perform them by 11.6% against placebo, a 2009 randomized controlled trial of exercise-induced muscle fatigue reported. 10 male professional volleyball players averaging 23.6 years of age entered a double-blinded placebo-controlled crossover trial, receiving either an active 69-diode cluster probe at 660 and 850 nm with 10 and 30 mW and 41.7 J, or an identical placebo, applied for 30 seconds to the middle of the biceps immediately before contractions carried to exhaustion. The blood markers that rise with muscle strain, fatigue, and inflammation all fell significantly with active LED therapy compared with placebo. This dose appeared to cause a slight delay in the development of muscle fatigue.

Only the active LED therapy cluster probe lowered a blood marker of muscle damage after exercise, according to a 2009 randomized controlled trial that set it against a single-diode low-level laser therapy (LLLT) device and a placebo probe for muscle fatigue. 8 young male volleyball players received 4 pretreatments of 30 seconds each to the front of the thigh, using the active cluster probe at 660 and 850 nm with 10 and 30 mW and 41.7 J, a placebo probe with no output, or a single-diode 810 nm laser at 200 mW, before 3 all-out cycling tests. The fall in the muscle-damage marker reached statistical significance against both the placebo probe and the single-diode laser. None of the pretreatments improved cycling performance or lowered the substance that builds up in working muscles.

8.5 more repetitions before muscle failure followed low-level laser therapy (LLLT) than placebo, which allowed just 2.7 extra, in a 2008 randomized controlled trial of exercise-induced muscle fatigue. 12 male professional volleyball players were tested on day 1 and day 8, receiving either 655 nm LLLT at 50 mW and 5 to 20 J applied in contact to 4 points along the biceps, or an identical placebo, just before lifting a weight set at 75% of their maximum strength for as many repetitions as they could manage, in 100-second sessions given once per week across 7 days. The substance that builds up in working muscles rose to a similar level in both groups, showing no significant difference between them. LLLT appeared to delay the onset of muscle fatigue and exhaustion despite the rise.

According to a 2023 systematic review with meta-analysis, researchers assessed photobiomodulation therapy (PBMT) for strength, fatigue, and everyday physical capacity in healthy people. The review pooled 16 randomized clinical trials covering 340 participants, 183 men and 157 women, using wavelengths of 655-905 nm, powers of 0.00001 to 0.0002 mW, energies of 0.6 to 30 J per point, and application times of 30 to 100 seconds per point. Recovery from fatigue improved in the pooled data, with a mean difference of 5.87.

When researchers set out to see whether photobiomodulation changes muscle temperature during a fatigue protocol, a 2021 clinical trial put 14 volunteers through a crossover design. Participants were divided into a placebo group and a laser group and rotated through both conditions, receiving 808 nm light at 100 mW and 27 J on a single day, before holding 3 all-out contractions of 50 seconds each separated by 50-second rests. Muscle strength was tracked with skin sensors alongside the temperature of the biceps. Some effect on temperature during the fatigue protocol was reported, though the benefit did not hold consistently across the measures the researchers tracked.

A 2020 randomized double-blind study examined a single session of photobiomodulation delivered through a cluster device for muscle fatigue in the biceps. 32 young healthy men received light at 630, 660, 808, and 850 nm in contact with the biceps at 100 mW and 4 to 28 J, in 40-second sessions given once per week on a single day. The findings revealed that the sensor readings of muscle fatigue differed between the infrared group and the control group, suggesting that infrared light may be the more effective option for reducing biceps fatigue. Perceived effort and the substance that builds up in working muscles rose significantly in every group.

35 participants received photobiomodulation before a fatiguing exercise protocol in a 2020 double-blind randomized controlled study, where muscle-damage markers rose 14.9% after active treatment and 65% after placebo, a statistically significant gap. 35 participants received light at 670, 850, and 950 nm in contact with the front of the thigh at 10 to 415 mW, 55.3 mW/cm², and 30.2 to 181.2 J, in 73-second sessions on a single day. The timing of the application did not change the results for pain. The authors described a positive effect on controlling muscle damage, while noting that the benefit did not extend to pain.

Percentage drops in muscle force and in the total work done were all smaller after light therapy than after placebo, a 2020 randomized crossover double-blind placebo-controlled trial of muscle fatigue reported. 18 physically active men received photobiomodulation therapy (PBMT) close to the skin over the front of the thigh at 630-950, 670, 850, 880, and 950 nm and doses of 15 to 1080 J, in sessions of 16 to 64 seconds given 4 times per week across 90 days, during a multiple-set knee extension protocol. The researchers reported that the 135, 270, and 540 J doses all showed possibly or likely positive effects against placebo. They suggested that producing the same total work with less fatigue may allow athletes to add sets and raise their training volume.

When researchers varied the moment at which they applied photobiomodulation therapy (PBMT), a 2018 randomized controlled trial found that timing changed the result for fatigue in the muscles at the front of the thigh. 16 male volunteers averaging 26 years of age completed 5 conditions covering control, placebo, PBMT immediately before exercise, PBMT 6 hours before, and PBMT at both times, with light at 650-1200 nm applied close to the skin at 9 sites on the thigh at 120, 200, and 500 mW and 30 to 270 J, in 4.8-minute sessions given 5 times per week across 35 days. Only the combined condition, 6 hours before plus immediately before, produced more muscle force than both control and placebo. Performance during the fatigue protocol itself was similar across all 5 conditions.

Across 861 participants pooled from 39 randomized controlled trials, a 2018 systematic review and meta-analysis assessed photobiomodulation therapy (PBMT) for muscle performance and exercise-related muscle fatigue in healthy people. The included trials, published between 2008 and 2017, ranged from 5 to 60 participants and treated small and large muscle groups at wavelengths of 655-950 nm, 200 mW, 60 to 300 J and a pulse frequency of 100 Hz, in 6-minute sessions given 3 times per week. Some measures of performance and fatigue improved, but results varied widely between trials, and the quality of the evidence was mixed. They cautioned that the benefits cannot be stated with strong certainty.

2 of the 3 light doses tested produced more repetitions before exhaustion in a 2017 clinical trial of LED therapy for fatigue in the muscles at the front of the thigh. 34 recreationally trained athletes, 18 male and 16 female, averaging 21.1 years of age, completed 4 randomized trials covering placebo, 30 seconds, 60 seconds, and 120 seconds per point, with light at 610, 660, and 850 nm applied close to the skin at 6 points on the thigh at 10 mW, 30 mW and 1.39 W, given 4 times per week across 84 days. The 60-second and 120-second doses produced significantly more repetitions on a single-leg knee extension carried to exhaustion, while the 30-second dose did not.

Placebo, laser before fatigue, and laser after fatigue were the 3 arms compared in a 2014 randomized double-blind placebo-controlled trial of muscle fatigue. 27 healthy male soccer players were tested across 2 sessions 1 week apart, with an 830 nm infrared laser applied just off the skin over the front of the thigh at 60 and 360 mW and 0.6 to 50.4 J, in sessions of 10 and 70 seconds given 2 times per week over 7 days. Repetitions, the heaviest weight lifted once, and time to fatigue came out similar across the 3 groups. The blood markers of muscle strain and damage both fell in the group treated after exercise compared with placebo, with the strongest results when the laser came afterwards.

No statistically significant gain in repetitions, in muscle activity readings, or in the substance that builds up in working muscles followed active treatment in a 2013 randomized controlled trial of low-level laser therapy (LLLT) for biceps muscle fatigue. 20 young women completed a crossover design across 2 sessions 7 days apart, receiving either active 808 nm LLLT or a placebo in contact with the biceps at 100 mW and 56 J, in 70-second sessions given 2 times per week, before 60 seconds of bending and straightening the elbow against 75% of the heaviest weight they could lift once. Participants averaged 22.6 repetitions after placebo and 25.1 after active LLLT, a difference that did not reach statistical significance. The authors reported a tendency toward less fatigue on the sensor readings in the active group but described the effect on delaying fatigue as limited.

In 2009, a randomized controlled trial tested whether 830 nm low-level laser therapy (LLLT) could delay exercise-induced muscle fatigue. 10 healthy male professional volleyball players averaging 22 years of age received either active LLLT or an identical placebo, applied in contact to 4 points on the biceps just before they lifted a weight set at 75% of their maximum strength until they could not continue, using 100 mW of output power, and 5 to 20 J, in 50-second sessions delivered 2 times per week over 7 days. Participants completed 4.5 more repetitions on average after active LLLT than after placebo, a statistically significant difference. The substance that builds up in working muscles rose after exercise under both conditions, with no significant difference between them.

Researchers in Japan examined linear polarized near-infrared light (PL) as a recovery aid for muscle fatigue in a 2008 clinical trial. 20 adults, 10 men and 10 women, squeezed a handgrip repeatedly for 9 minutes, rested for 20 minutes while the arms received either PL at 780-1400 nm in a single 20-minute session once per week or a placebo, then repeated the handgrip task for 3 minutes. The study reported that only the PL condition showed a smaller drop in grip force across a 30-second stretch, alongside higher skin temperature during rest. How tired participants felt and the substance that builds up in working muscles did not differ between the conditions, leading the authors to suggest that PL may keep blood flow and skin temperature up without restoring muscle performance.

Among 12 trained men averaging 31 years of age, a 2020 randomized crossover study tested whole-body photobiomodulation delivered from a light bed, looking at the blood and saliva markers that rise with muscle damage and inflammation after high-intensity resistance training. Participants lay in a bed emitting 660-850 nm light at 526 W and 473400 J, in 15-minute sessions given 2 times per week on a single day, before and after workouts of bench press, chin-ups, and repeated sprints. The muscle damage marker spiked from baseline to 24 hours under both conditions, and the light therapy did not blunt that rise. Baseline values did not differ between the treatment and the control weeks.

Published in 2020, this randomized double-blind crossover placebo-controlled study tested photobiomodulation delivered by light emitting diodes for muscle strength and fatigue resistance in young men. 30 participants received light at 625-645 and 860-900 nm in contact with the biceps of the dominant arm, at 1.15 W, 6 and 75 mW/cm², and 60 J, in 52-second sessions given 4 times per week across 28 days, with testing at 5 minutes, 1 hour, 3 hours, and 6 hours. Peak force, how fast that force built, fatigue resistance, and perceived effort showed no advantage for the light therapy at any of the times tested. How fast the force built was the single measure that did not fall significantly after the fatigue test in the treated group.

2 randomized double-blind placebo-controlled crossover experiments made up a 2020 study of photobiomodulation therapy for maximum muscle strength and muscle recovery after resistance exercise. 60 healthy physical education students, 28 men and 32 women aged 20 to 35, received either a real or a sham treatment from a small home-use device, with 808 nm light applied in contact to 3 sites on the front of the thigh at 84.5 mW, 150 J and a pulse frequency of 13000 Hz, in 10-minute sessions given 2 times per week across 7 days. The effect was reported as follows: total work done and peak muscle force did not differ between the real and the sham treatment, either before or after exercise. No benefit for maximum strength or recovery appeared in this group.

Among 14 well-trained adults, a 2020 randomized double-blind placebo-controlled trial tested photobiomodulation therapy (PBMT) for training volume and discomfort. 14 participants received light at 670, 850, 880, and 950 nm close to the skin over the calf muscles at 60 to 360 J, in sessions of 64 seconds and 7 minutes given once per week across 14 days. How quickly the muscle tired and the total number of repetitions completed were much the same after PBMT and after placebo. Participants rated the discomfort as large under both conditions during resistance training carried to failure.

According to a 2020 clinical trial, researchers ran 2 balanced crossover experiments to see whether photobiomodulation delivered by LED changes muscle fatigue and cycling performance. 27 male recreational cyclists completed hard cycling bouts after receiving light at 620-640 and 830-870 nm in contact with the hip and thigh muscles at 50 and 80 mW and doses of 130 J, 260 J, or placebo, in sessions of 40 to 80 seconds given 3 times per week on a single day. Neither the sensor readings of muscle activity, nor the indicators of muscle fatigue, nor the time to exhaustion differed between the light and placebo conditions. The 130 and 260 J doses offered no benefit for muscle fatigue, cycling performance, or muscle activity in these cyclists.

No reduction in fatigue or muscle damage followed treatment in a 2019 randomized triple-blind placebo-controlled trial of photobiomodulation therapy (PBMT) in judo athletes. 16 athletes averaging 23.1 years of age received active therapy on 1 leg and a placebo on the other in a single session, with light at 670, 850, 880, and 950 nm applied in contact with the front and back of the thigh and the calf muscles at 10 to 100 mW, 1.93 to 1666.6 mW/cm², and 0.3 to 450 J, in 32-second sessions across 3 days, before a protocol of repeated jumping. The authors reported that standing jump performance and ultrasound measures of the muscle showed no advantage for the treated leg. They further noted that the finding ran counter to earlier studies in people who were not athletes.

When researchers applied low-level laser therapy (LLLT) to the calves of sedentary adults, a 2015 clinical trial found no measurable gain in vertical jump performance. 22 sedentary volunteers were split into a control group of 8, a 6-day laser group of 7, and a 10-day laser group of 7, with 660 nm light applied in contact to 8 points over the calf at 30 mW and 1.92 J, in 8-second sessions given 6 or 10 times per week across 6 or 10 days. Neither fatigue nor jump power differed significantly between the groups. Muscle soreness was higher at the first assessment than at the later ones, and the authors concluded that the laser had no significant effect on the measures they tracked.

A 2008 randomized crossover pilot trial tested whether low-level laser therapy (LLLT) could reduce muscle fatigue triggered by electrical stimulation in 5 college-age participants. Each completed 2 LLLT sessions and 1 control session on the muscles at the front of the dominant thigh, with 808 nm light at 500 mW delivering either 7 J over 10 minutes or 3 J over 5 minutes, 3 times per week, followed immediately by 3 minutes of electrical stimulation to tire the muscle. Muscle force fell 62% in the control session and 51% after both laser sessions, and the 11% gap between them did not reach statistical significance. It was further noted that the small sample size and the chosen laser settings may explain the lack of an effect.