Ultrasound irradiation before high-load exercise reduces muscle rigidity associated with delayed-onset muscle soreness

[Purpose] We investigated the occurrence of delayed-onset muscle soreness and the suppression of muscle rigidity by ultrasound irradiation before high-load exercise. [Participants and Methods] The study was a randomized crossover controlled trial. The participants were 28 healthy university students (12 males, 16 females). Delayed-onset muscle soreness was induced in the biceps brachii muscle; ultrasound (3 MHz, 1.5 W/cm2, 10 min) was applied before high-load exercise. Pain during elbow motion was evaluated on a visual analog scale. Muscle rigidity was evaluated using a muscle rigidity meter. [Results] After exercise on the second day, the ultrasound group showed significantly less muscle rigidity. [Conclusion] The heat stimulus of ultrasound therapy before high-load exercise reduces muscle rigidity.