Effects of voluntary activation level on force exerted by human adductor pollicis muscle during rapid stretches.
We have observed the force resulting from sudden stretches (3-10 mm in 10-20 ms) of human adductor pollicis muscle during voluntary contractions maintaining different proportions of the maximum voluntary force from 20% to 100%. The ratio of the peak force during stretch (S) to the voluntary force (I) just before the start of the stretch was calculated. The S/ I ratio was dependent both on the level of activation and the speed of the stretch. At all levels of activation S/ I increased exponentially with velocity towards a plateau value with an exponential constant of about 150 mm/s. The plateau values reached were dependent on activation level (P<0.02, linear regression, n=24). At 96% activation the plateau value of the S/ I ratio was 1.82+/-0.13 (mean+/-95% confidence limits); at 32% activation the value was 2.72+/-0.23.
Onambele
Gladys N L
GN
Institute of Human Performance, Royal National Orthopaedic Hospital Trust, University College London, Brockley Hill, HA7 4LP, Stanmore, Middlesex, UK.
Bruce
Stuart A
SA
Woledge
Roger C
RC
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D014836:Volition / Q000502:physiology