Biomechanical responses to repeated stretches in human hamstring muscle in vivo.
To examine stiffness, energy, and passive torque in the dynamic and static phases of a stretch maneuver in the human hamstring muscle in vivo we used a test-retest protocol and a repeated stretches protocol. Resistance to stretch was defined as passive torque (in newton-meters) offered by the hamstring muscle group during passive knee extension as measured using an isokinetic dynamometer with a modified thigh pad. In 13 uninjured subjects, the knee was passively extended to a predetermined final position (0.0875 rad/ sec, dynamic phase) where it remained stationary for 90 seconds (static phase). The test-retest protocol included two tests administered 1 hour apart. On a separate occasion, five consecutive static stretches were administered separated by 30 seconds and followed by a sixth stretch 1 hour later. For the test-retest phase, stiffness and energy in the dynamic phase and passive torque in the static phase did not differ and yielded correlations of r = 0.91 to 0.99. During the static phase, passive torque declined in both tests (P < 0.0001). For the repeated stretches, decreases were observed for energy (P < 0.01) and stiffness (P < 0.05) in the dynamic phase and for passive torque (P < 0.0001) in the static phase. However, the decline in the variables returned to baseline within 1 hour. The data show that the method employed is a useful tool for measuring biomechanical variables during a stretch maneuver. This may provide a more detailed method to examine skeletal muscle flexibility.
Magnusson
S P
SP
Team Denmark Test Center, Rigshospitalet, Copenhagen, Denmark.
Simonsen
E B
EB
Aagaard
P
P
Kjaer
M
M
D000328:Adult; D000704:Analysis of Variance; D019540:Area Under Curve; D001696:Biomechanical Phenomena; D005500:Follow-Up Studies; D006801:Humans; D007700:Kinetics; D007719:Knee Joint / Q000502:physiology; D007866:Leg / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D018583:Pliability; D016059:Range of Motion, Articular; D012815:Signal Processing, Computer-Assisted; D013314:Stress, Mechanical; D019415:Torque