Specificity of back muscle response to submaximal fatiguing contractions.
A fatigue-related decrease in quality and accuracy of the proprioceptive feedback from muscle spindles in the back (e.g. stretch reflexes) may lead to a deterioration of spinal stability, thereby making the spine more vulnerable to external perturbations. Endurance time, tissue oxygenation, reflex latency and blood pressure response were studied in twenty subjects during a submaximal endurance test of the back extensors (20 % MVC) performed as either a position task (supporting a weight stack while maintaining trunk position) or a force task (exerting a force against a dynamometer). Mean endurance time was 8.91 (± 2.79) min for the force task and 10.86 (± 6.93) min for the position task. This result is in striking contrast to what has previously been reported from limb muscles, and suggests that back muscles are especially well suited for postural tasks. An increased reflex latency found after the position task indicates that the disadvantage of the prolonged endurance time is a deterioration of the afferent input from the muscle spindles that may potentially hamper the protection of the spine.
Liberty Mutual Research Institute for Safety, 71 Frankland Road, Hopkinton, MA 01748, USA. Nils.Fallentin@LibertyMutual.com
Nils
N
Fallentin
Rammohan
R
Maikala
Jacob
J
Banks
Niall
N
Obrien
Amanda
A
Rivard
D000328:Adult; D064131:Back Muscles / Q000378:metabolism / Q000502:physiology*; D001794:Blood Pressure; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D009470:Muscle Spindles / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D010807:Physical Endurance / Q000502:physiology; D011187:Posture; D011930:Reaction Time; D012018:Reflex; D055815:Young Adult
D010100:Oxygen