Purpose: A commonly used method for warm-up before exercise is to stretch muscles. How this benefits performance remains uncertain. After a period of eccentric exercise, there is muscle damage accompanied by an increase in passive tension, perceived as a sensation of increased stiffness in the exercised muscles. We have tested the idea that warm-up stretches might reduce levels of passive tension to reduce sensations of stiffness and soreness after eccentric exercise.
Methods: Subjects eccentrically exercised elbow flexors of one arm on an isokinetic dynamometer. The other arm acted as a control. After the exercise, measurements were made of resting elbow angle, as an indication of passive tension levels, before and after one or five large, passive arm extensions. Additional measurements made at 24 h included soreness levels in response to muscle stretch or vibration.
Results: After the exercise, the relaxed elbow adopted a more flexed posture than normal, an effect that slowly subsided over the next 4 d. Five rapid arm extensions returned arm posture back to near control levels. The flexed posture then gradually re-developed over the next hour. At 24 h postexercise, extending the arm produced some soreness as did muscle vibration. The pain from arm extension and vibration was reduced after a series of arm extensions.
Conclusions: The flexed posture at the elbow is due to an increase in passive tension in elbow flexors as a result of muscle damage from the eccentric exercise. Stretch reduces passive tension. Benefits from the lower tension are reduced sensations of stiffness and soreness. This represents a new proposal for the mechanism for passive stretches as a warm-up strategy.