Contractile properties of the quadriceps muscle in individuals with spinal cord injury

Abstract

Selected contractile properties and fatigability of the quadriceps muscle were studied in seven spinal cord–injured (SCI) and 13 able‐bodied control (control) individuals. The SCI muscles demonstrated faster rates of contraction and relaxation than did control muscles and extremely large force oscillation amplitudes in the 10‐Hz signal (65 ± 22% in SCI versus 23 ± 8% in controls). In addition, force loss and slowing of relaxation following repeated fatiguing contractions were greater in SCI compared with controls. The faster contractile properties and greater fatigability of the SCI muscles are in agreement with a characteristic predominance of fast glycolytic muscle fibers. Unexpectedly, the SCI muscles exhibited a force–frequency relationship 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 described and that the transformation to faster properties consequent upon changes in contractile protein expression following SCI can be assessed. These measurements may be useful to optimize stimulation characteristics for functional electrical stimulation and to monitor training effects induced by electrical stimulation during rehabilitation of paralyzed muscles. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 1249–1256, 1999.

Neural and muscular mechanisms of electrically induced fatigue in patients with spinal cord injury

“…Muscle atrophy associated with the conversion of muscle fibers toward a more glycolytic profile 1 lead to increased fatigability in patients with SCI. 2 Neuromuscular electrical stimulation (NMES) is one of the most used techniques to contract paralyzed muscles. This technique is used in rehabilitation settings to supplement for lost functions and can partially counteract the deleterious adaptations that skeletal muscles undergo after SCI.…”

“…The procedure for T max has been previously described. 2 The triceps surae was stimulated using a portable stimulator (Cefar Physio 4, Cefar Medical AB, Lund, Sweden) that delivered constant-current, rectangular, symmetric biphasic pulses. Two rectangular electrodes (10 Â 5 cm) were placed over the triceps surae muscle, one positioned 3 cm beneath the popliteal fossa and the other beneath the insertion point of the two gastrocnemii muscles to the Achilles tendon and just above the EMG recording electrodes.…”

Muscle fatigue characteristics in paralyzed muscle after spinal cord injury

“…This increased fatiguability in paralyzed muscle has been reported previously in the soleus and quadriceps muscle groups. [1][2][3] However, based on the M-wave results of this study, and from earlier work, 2,7 a failure in Na þ /K þ pump activity does not appear to play a significant role in the increased fatiguability during a relatively short period of maximum stimulation in people with SCI. This was an unexpected finding given the reported decrease in Na þ /K þ pump concentration after SCI.…”

“…1,2 This results in many functional limitations and can inhibit rehabilitation efforts. Fatigue resistance has been shown to decrease rapidly for the first 1.7 years post-injury, with smaller decreases occurring in subsequent years.…”

The length–tension relationship of human dorsiflexor and plantarflexor muscles after spinal cord injury

“…These include fibre-type transformation, 1,2 atrophy, 1 faster contractile properties [2][3][4] and a decreased range of motion. 5 These changes, which can be attributed to both paralysis and a loss of functional innervation, greatly diminish the force-generating capacity of the muscle.…”