Continuous Ultrasound Decreases Pain Perception and Increases Pain Threshold in Damaged Skeletal Muscle.

OBJECTIVE: Determine whether therapeutic ultrasound (TUS) delivered in a continuous mode reduces pain perception after muscle injury.

DESIGN: Randomized, double-blind trial.

SETTING: Institutional laboratory.

PARTICIPANTS: Twenty young healthy participants (11 females; 9 males; mean age ± SD, 24.1 ± 3.7 years).

INTERVENTION: All subjects performed 50 maximal eccentric contractions of the biceps brachii on a Biodex dynamometer. Criterion measures of isometric force production and serum creatine kinase (CK) activity confirmed tissue damage. Both groups received either TUS or sham treatment everyday starting 24 hours after muscle damage. Muscle soreness and pain were assessed at baseline, 48 hours postdamage, and every other day for 8 days.

MAIN OUTCOME MEASURES: Muscle pain was assessed with a battery of tests: visual analog scale (VAS), Short-form McGill Pain Questionnaire-2, joint angle changes, and mechanical pressure threshold.

RESULTS: Confirmation of damage occurred with baseline compared to 48 hours after damage of isometric peak torque (N·m; P < 0.01) and CK activity (IU/I; P = 0.03). Our results showed significant treatment group differences in VAS (P = 0.01) and mechanical pressure threshold (P = 0.02) after the third TUS treatment in the distal bicep brachii region.

CONCLUSIONS: Continuous TUS reduced pain perception and increased mechanical pressure threshold in the biceps brachii after muscle damage, specifically near the distal musculotendinous junction.