What is the ideal dose and power output of low-level laser therapy (810 nm) on muscle performance and post-exercise recovery? Study protocol for a double-blind, randomized, placebo-controlled trial

The researchers planned to test two separate parameters of low-level laser therapy (LLLT) applied to the quadriceps muscle before exercise:

**Phase 1 — Dose finding:** Four groups receiving different total energy doses at a fixed power of 200 mW:

Group A: 2 Joules (J) per point

Group B: 6 J per point

Group C: 10 J per point

Group D: 0 J (placebo)

**Phase 2 — Power finding:** Using the best dose from Phase 1, four groups receiving different power outputs:

Group A: 100 mW

Group B: 200 mW

Group C: 400 mW

Group D: 0 mW (placebo)

The comparator was a placebo group receiving sham laser treatment (device emitted the same sound but delivered no energy). The outcome measures included:

**Primary:** Peak torque / maximum voluntary contraction (MVC) — a measure of muscle strength

**Secondary:** Delayed onset muscle soreness (DOMS) measured by pressure pain threshold (algometer), and biochemical markers of muscle damage (creatine kinase, lactate dehydrogenase), inflammation (IL-1β, IL-6, TNF-α), and oxidative stress (TBARS, carbonylated proteins, catalase, superoxide dismutase)

The protocol planned to recruit **28 male high-level soccer athletes** from the same professional team for each phase (total 56 participants across both phases). Inclusion criteria were:

Professional soccer athletes

Age 18–35 years

Male gender

Minimum 80% participation in team practice sessions

Light or intermediate skin color (to ensure adequate laser penetration)

Signed informed consent

Exclusion criteria included: history of musculoskeletal injury to hips or knees in the previous 2 months, use of pharmacological agents or nutritional supplements, occurrence of musculoskeletal injury during the study, or any change in practice routine during the study.

The researchers planned to use the following instruments and scales:

**Isokinetic dynamometer (Biodex System 4):** For measuring maximum voluntary contraction (MVC) and peak torque — considered the gold standard for musculoskeletal performance assessment. The non-dominant leg was positioned with the knee at 60° of flexion.

**Analog algometer (Baseline®, Rome, Italy):** For measuring pressure pain threshold to quantify delayed onset muscle soreness (DOMS). The device has a 1 cm² rubber tip, measures 0–10 kg with 0.1 kg precision. Readings were taken from three sites on the knee extensors (medial, lateral, central) of the non-dominant limb.

**Blood analysis via spectrophotometry:** For creatine kinase (CK) and lactate dehydrogenase (LDH) as indirect markers of muscle damage

**ELISA assays:** For inflammatory markers IL-1β, IL-6, and TNF-α

**Spectrophotometry with specific reactions:** For oxidative stress markers TBARS, carbonylated proteins, catalase (CAT), and superoxide dismutase (SOD)

**Blood samples (10 ml):** Collected from the antecubital vein before exercise, 1 minute after the eccentric contraction protocol, and at 1, 24, 48, 72, and 96 hours post-exercise

**Questionnaire:** For personal data including age, body mass, height, dominant lower leg, schooling, and marital status

**Study design:** This is a double-blind, randomized, placebo-controlled clinical trial conducted in two sequential phases. It is a study protocol — meaning no actual data collection or results are reported in this paper.

**Randomisation:** Volunteers were to be randomly allocated to four experimental groups (n=7 per group) by simple drawing of lots (A, B, C, or D). Randomization labels were created using a randomization table at a central office, with sealed, opaque, numbered envelopes to ensure confidentiality. A participating researcher (not involved in outcome assessment) was responsible for programming the laser device based on randomization results and was instructed not to inform participants or other researchers about the dose or power applied.

**Blinding:** This is a double-blind design. The researcher administering the LLLT was blinded to the dose and power applied. The researcher performing evaluations (blood collection, algometer readings, isokinetic testing) was also blinded to group allocation. The laser unit emitted the same sound regardless of programmed power output, so participants could not distinguish active from placebo treatment. The nurse collecting blood samples was also blinded.

**Duration:** Each phase involved a single exercise session with follow-up measurements at 1 minute, 1 hour, 24 hours, 48 hours, 72 hours, and 96 hours post-exercise. The protocol does not specify a washout period between phases, but since different participants were used for each phase (28 per phase), no washout was needed.

**Experimental protocol:**

1. Stretching: Three 60-second sets of active stretching of the knee extensors of the non-dominant lower limb

2. Warm-up: Stationary bike at 100 rpm for 5 minutes without load

3. Baseline MVC measurement on isokinetic dynamometer

4. LLLT application (or placebo) to the quadriceps

5. Eccentric contraction protocol on the isokinetic dynamometer (designed to induce muscle damage)

6. Post-exercise MVC measurement

7. Blood samples and DOMS assessment at multiple time points up to 96 hours

**Statistical approach:** Sample size was calculated based on a previous study (Baroni et al., reference 28) using a β of 20% and α of 5%. The calculation used creatine kinase (CK) values: LLLT led to post-exercise recovery of CK to 435.95 U/l (SD: 238.04), while placebo led to CK of 1,327.58 ± 949.82 U/l. This yielded 7 volunteers per group (28 total per phase).

**What this design can and cannot prove:**

**Can prove:** Whether different doses and power outputs of 810 nm LLLT have different effects on muscle strength preservation, soreness reduction, and biochemical markers of muscle damage, inflammation, and oxidative stress in high-performance athletes. The double-blind, placebo-controlled design controls for placebo effects and experimenter bias. The use of a gold-standard isokinetic dynamometer provides objective, reliable strength measurements.

**Cannot prove:** Long-term effects beyond 96 hours (follow-up stops at 96 hours). Effects in female athletes (only males studied). Effects in non-athletes or recreational exercisers. Effects on different muscle groups (only knee extensors tested). Whether LLLT prevents injury in real-world training/competition (laboratory-based eccentric protocol). The mechanism of action (though biochemical markers provide clues). Whether the optimal parameters found in Phase 1 generalize to Phase 2 (since Phase 2 uses the best dose from Phase 1, but the same participants cannot be used for both phases).

**Major methodological weaknesses:**

Very small sample size (n=7 per group) — adequate for detecting large effects on CK based on the power calculation, but underpowered for detecting smaller effects on other outcomes

Single exercise session — does not reflect real-world training loads

Only male athletes studied — limits generalizability

Light/intermediate skin color requirement — excludes darker-skinned individuals, limiting applicability

No washout period between phases is described (though different participants are used)

The protocol does not specify how the "best dose" from Phase 1 will be determined for use in Phase 2 — is it the dose with the largest effect on MVC, or on CK, or on DOMS? This is a critical methodological detail that is left ambiguous.

No mention of controlling for diet, sleep, or prior training load on the days before testing

**This is a study protocol — no results are reported.** The paper describes the planned methodology only. The actual findings would be published in a separate results paper (which may or may not have been subsequently published).

However, the protocol does reference previous findings from the same research group:

Prior studies demonstrated positive results for LLLT applied before exercise, including attenuation of muscle fatigue and favoring recovery of biochemical markers related to muscle damage

The biphasic dose-response pattern has been observed in other musculoskeletal disorders

Both power and irradiation time influence the efficacy of therapy

The sample size calculation was based on a previous study (Baroni et al., 2010) which found:

LLLT led to post-exercise recovery of creatine kinase (CK) to 435.95 U/l (SD: 238.04)

Placebo treatment led to CK increase to 1,327.58 ± 949.82 U/l

This represents a roughly 3-fold difference in CK levels between LLLT and placebo

Since this is a protocol paper, no effect magnitudes from this study are available. However, based on the power calculation reference:

The expected effect on creatine kinase (a marker of muscle damage) was approximately a 67% reduction (from ~1,328 U/l with placebo to ~436 U/l with LLLT) — this is a large effect size

For context, normal resting CK levels in athletes are typically 100–300 U/l, so the placebo group was expected to show a 4–13 fold increase, while the LLLT group was expected to show only a 1.5–4 fold increase

**Acknowledged by authors:**

The biphasic dose-response pattern means that both too little and too much energy could be ineffective or even detrimental — this is why the dose-finding design is necessary

The study is limited to high-performance male athletes, so results may not generalize to other populations

The protocol only tests one wavelength (810 nm) — other wavelengths may have different optimal parameters

**Critical reader observations:**

**Protocol only, no results:** This paper describes what the researchers planned to do, not what they found. Any practical recommendations must wait for the actual results publication.

**Small sample size:** 7 per group is minimal for detecting anything other than very large effects. The power calculation was based on CK only, so other outcomes (DOMS, inflammatory markers, oxidative stress) may be underpowered.

**Single session design:** Real-world training involves repeated sessions over weeks and months. A single bout of eccentric exercise does not capture cumulative effects or adaptation.

**No long-term follow-up:** 96 hours is the maximum follow-up, so effects beyond that are unknown.

**Skin color restriction:** Excluding darker skin tones limits applicability and raises equity concerns, as laser penetration varies with melanin content.

**Industry funding:** The study was supported by a Young Researcher award grant from the Brazilian fostering agency FAPESP (process number 2010/52404-0). No industry funding is declared, but the laser device manufacturer is not specified.

**No sham control for the isokinetic protocol:** All groups performed the same eccentric protocol, so there is no control for the exercise itself — only for the laser treatment.

**The "best dose" selection criteria are not specified:** How will the researchers decide which dose from Phase 1 is "best"? Will it be based on MVC preservation, CK reduction, DOMS reduction, or a composite? This ambiguity could introduce researcher degrees of freedom.

**Important caveat:** This is a study protocol, not a results paper. The following takeaways are based on the planned methodology and prior research cited in the protocol, not on findings from this specific study. For running your own n=1 experiment, wait for the actual results to be published, or use the protocol as a template for your own testing.

**For someone running their own n=1 experiment:**

**What to test:** 810 nm low-level laser therapy applied to the quadriceps muscle before eccentric exercise (e.g., downhill running, heavy eccentric squats, or isokinetic knee extensions). The protocol tests doses of 2 J, 6 J, and 10 J per point at 200 mW, and powers of 100 mW, 200 mW, and 400 mW at the optimal dose. For a self-experiment, start with 6 J per point at 200 mW (the middle dose) and compare to a sham treatment (laser turned off but placed on the skin for the same duration).

**Minimum meaningful duration:** A single session with follow-up for 96 hours (4 days) post-exercise. However, for real-world relevance, repeat the protocol weekly for 4–8 weeks to assess cumulative effects. Measure outcomes at baseline, immediately post-exercise, and at 24, 48, 72, and 96 hours after each session.

**What to measure (specific metrics):**

- **Strength recovery:** Maximum voluntary contraction (MVC) of the quadriceps using a leg extension machine or isokinetic dynamometer. Measure peak torque (in Nm or kg). A positive result would be less than 20% decline from baseline at 24–48 hours post-exercise.

- **Muscle soreness:** Pressure pain threshold using an algometer (or a homemade version: a 1 cm² blunt probe attached to a kitchen scale). Measure at 3 points on the quadriceps (medial, lateral, central). A positive result would be less than 30% reduction in pressure tolerance at 24–48 hours.

- **Blood markers (optional):** Creatine kinase (CK) and lactate dehydrogenase (LDH) via finger-prick blood test kits (available online). Measure at baseline, 1 hour, 24 hours, 48 hours, and 72 hours post-exercise. A positive result would be CK levels less than 500 U/l at 24–48 hours (compared to >1,000 U/l without treatment).

- **Subjective recovery:** Rate of perceived soreness (0–10 scale) and readiness to train (1–10 scale) at each time point.

**Key confounds to control for:**

- **Exercise intensity and volume:** Standardize the eccentric exercise protocol exactly (same number of reps, same load, same range of motion, same rest intervals). Use a metronome for tempo.

- **Time of day:** Perform all sessions at the same time of day (±1 hour) to control for circadian effects on strength and recovery.

- **Prior training load:** Avoid heavy leg training for 72 hours before each test session. Log all training in the 7 days prior.

- **Sleep:** Aim for 7–9 hours of sleep per night for 3 nights before each session. Log sleep quality and duration.

- **Nutrition:** Standardize pre-exercise meals (same macronutrient composition, same timing). Avoid creatine, beta-alanine, and anti-inflammatory supplements (NSAIDs, fish oil, curcumin) for 7 days before and during the testing period.

- **Hydration:** Maintain consistent hydration status (same water intake on test days).

- **Laser placement:** Mark the treatment points with a dermatographic pen to ensure consistent placement across sessions. Use the same laser device with verified power output (use a laser power meter to confirm).

- **Blinding:** Have someone else program the laser so you don't know whether you're receiving active or sham treatment. Use a device that emits the same sound regardless of power output.

**What a positive result would look like:**

- **Strength:** Less than 15% decline in MVC at 1-hour post-exercise (vs. >25% decline with sham), and full recovery to baseline by 48 hours (vs. 72–96 hours with sham)

- **Soreness:** Pressure pain threshold declines less than 20% from baseline at 24 hours (vs. >40% decline with sham), and returns to baseline by 48