Study Subjects: This study will recruit healthy males aged 18 to 35 who regularly exercise for at least 2.5 hours per week.

Expected Number of Participants: 20.

Methods and Procedures: This trial will be randomized into two groups, Groups A and B, who will undergo two isokinetic concentric exercise sessions (fatiguing exercise) separated by 15 days. Group A will first receive a fatigue prevention strategy (high-energy laser) followed by a placebo-controlled no-fatigue strategy 15 days later. Group B will first receive a placebo-controlled no-fatigue strategy followed by a fatigue prevention strategy (high-energy laser) 15 days later. The fatigue prevention strategy involves irradiating the quadriceps femoris with a 900-joule high-intensity laser therapy (3-watt output power for 5 minutes) before the isokinetic concentric exercise. The no-fatigue strategy (sham-controlled) involves irradiating the quadriceps femoris with a 0-joule high-energy laser (0-watt output power for 5 minutes) before the isokinetic concentric exercise. Muscle displacement, muscle excursion, as well as muscle electrophysiological changes, force output, and microcirculation parameters were measured before and after exercise to verify the feasibility of muscle displacement and migration for muscle fatigue assessment, and to further establish their impact and application value in muscle fatigue prevention strategies (high-intensity laser therapy).

Inclusion Criteria:

• healthy male aged between 18 and 35 years who engage in regular physical activity for at least 2.5 hours per week

Exclusion Criteria:

• history of musculoskeletal injuries or lower limb muscle strains involving the dominant lower limb within the past six months
• history of surgical interventions on the dominant lower limb