Portable Low-Level Laser Therapy for Recovery After a Quadriceps-Dominant Fatiguing Task in Recreational Runners

Effects of Portable Low-Level Laser Therapy on Running Kinematics in Recreational Runners With Quadriceps Fatigue

This randomized, sham-controlled, two-period crossover study evaluated the effects of portable 808-nm low-level laser therapy (LLLT) on acute recovery and running biomechanics following a quadriceps-dominant fatiguing task in recreational runners. Twenty male recreational runners completed both active LLLT and sham conditions, separated by a 2-week washout period. After the fatiguing task, participants received 10 minutes of bilateral quadriceps LLLT or sham treatment, followed by treadmill running at the same fixed self-selected speed. Quadriceps soreness, heart rate, running spatiotemporal parameters, and kinematic responses were assessed using a verbal numerical rating scale, heart-rate monitoring, two-dimensional video analysis, and inertial measurement units.

Each participant completed two experimental visits in randomized order, with one active LLLT condition and one sham condition separated by a 2-week washout period. At each visit, participants completed a 5-minute treadmill warm-up followed by a 3-minute pre-fatigue running trial at a fixed self-selected running speed. They then performed a repeated stand-sit-stand task designed to produce quadriceps-dominant lower-limb fatigue.

Immediately after the fatiguing task, participants received either active portable 808-nm LLLT or sham treatment for 10 minutes over the bilateral rectus femoris, vastus lateralis, and vastus medialis muscles. A 3-minute post-intervention treadmill running trial was then performed at the same running speed used before the fatiguing task.

Quadriceps soreness was assessed using a 0-10 verbal numerical rating scale. Heart rate was monitored using a chest-strap heart-rate monitor. Running spatiotemporal and kinematic variables were assessed using high-frame-rate two-dimensional video analysis and three inertial measurement units positioned over the bilateral distal tibiae and sacral region.

Inclusion Criteria:

1. Male recreational runners aged 18-40 years.
2. Recreational running status determined using the World Masters Athletics (WMA) age-graded performance score, with an age-graded score below 60%.
3. Previous experience with treadmill running.
4. Rearfoot-strike running pattern.
5. No running-related lower-limb injury during the preceding 6 months

Exclusion Criteria:

1. WMA age-graded performance score of 60% or higher.
2. Non-rearfoot-strike running pattern.
3. Leg-length discrepancy greater than 3 cm.
4. Use of an orthosis, brace, or other lower-limb medical device that could influence running gait.