Contractile properties of the quadriceps muscle in individuals with spinalcord injury

Selected contractile properties and fatigability of the quadriceps muscle w ere studied in seven spinal cord-injured (SCI) and 13 able-bodied control ( control) individuals. The SCI muscles demonstrated faster rates of contract ion and relaxation than did control muscles and extremely large force oscil lation amplitudes in the 10-Hz signal (65 +/- 22% in SCI versus 23 +/- 8% i n controls). In addition, force loss and slowing of relaxation following re peated fatiguing contractions were greater in SCI compared with controls. T he faster contractile properties and greater fatigability of the SCI muscle s are in agreement with a characteristic predominance of fast glycolytic mu scle fibers. Unexpectedly, the SCI muscles exhibited a force-frequency rela tionship shifted to the left, most likely as the result of relatively large twitch amplitudes. The results indicate that the contractile properties of large human locomotory muscles can be characterized using the approach des cribed and that the transformation to faster properties consequent upon cha nges in contractile protein expression following SCI can be assessed. These measurements may be useful to optimize stimulation characteristics for fun ctional electrical stimulation and to monitor training effects induced by e lectrical stimulation during rehabilitation of paralyzed muscles. (C) 1999 John Wiley & Sons, Inc.