Influence of knee joint angle on muscle properties of paralyzed and nonparalyzed human knee extensors.
Muscles of individuals with a spinal cord injury (SCI) exhibit an unexpected leftward shift in the force (torque)-frequency relationship. We investigated whether differences in torque-angle relationships between SCI and able-bodied control muscles could explain this shift. Electrically stimulated knee-extensor contractions were obtained at knee flexion angles of between 30 degrees and 90 degrees. Torque-frequency relationships were obtained at 30 degrees, 90 degrees, and optimum angle. Optimum angle was not different between groups but SCI-normalized torques were lower at the extreme angles. At all angles, SCI muscles produced higher relative torques at low stimulation frequencies. Thus, there was no evidence of a consistent change in the length of paralyzed SCI muscles, and the anomalous leftward shift in the torque-frequency relationship was not the result of testing the muscle at a relatively long length. The results provide valuable information about muscle changes occurring in various neurological disorders.
Gerrits
Karin H
KH
Institute for Fundamental and Clinical Human Movement Sciences, Vrije University, van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands.
Maganaris
Constantinos N
CN
Reeves
Neil D
ND
Sargeant
Anthony J
AJ
Jones
David A
DA
de Haan
Arnold
A
D000328:Adult; D004558:Electric Stimulation; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009068:Movement; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010243:Paralysis / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D019415:Torque