Reproducibility of contractile properties of the human paralysed and non-paralysed quadriceps muscle

This study assessed the reproducibility of electrically evoked, isometric q uadriceps contractile properties in eight people with spinal cord injury (S CI) and eight able-bodied (AB) individuals. Over all, the pooled coefficien ts of variation (CV(p)s) in the SCI group were significantly lower (ranging from 0.03 to 0.15) than in the AB group (ranging from 0.08 to 0.21) (P <0. 05). Furthermore, in all subjects, the variability of force production incr eased as stimulation frequency decreased (P <0.01). In subjects with SCI, v ariables of contractile speed are clearly less reproducible than tetanic te nsion or resistance to fatigue. Contractile properties of quadriceps muscle s of SCI subjects were significantly different from that of AB subjects. Mu scles of people with SCI were less fatigue resistant (P <0.05) and produced force-frequency relationships that were shifted to the left, compared with AB controls (P < .01). In addition, fusion of force responses resulting fr om 10 Hz stimulation was reduced (P < .05) and speed of contraction (but no t relaxation) was increased (P <0.05), indicating an increased contractile speed in paralysed muscles compared with non-paralysed muscles. These resul ts correspond with an expected predominance of fast glycolytic muscle fibre s in paralysed muscles. It is concluded that quadriceps dynamometry is a us eful technique to study muscle function in non-paralysed as well as in para lysed muscles. Furthermore, these techniques can be reliably used, for exam ple, to assess therapeutic interventions on paralysed muscles provided that expected differences in relative tetanic tension and fatigue resistance ar e larger than similar to5% and differences in contractile speed are larger than similar to 15%.