Muscle fiber type-specific myofibrillar Ca(2+) ATPase activity after spinal cord injury

Biopsies of the vastus lateralis muscle were analyzed to determine if increased energy demand of contraction, as indirectly reflected by myofibrillar Ca(2+) adenosine triphosphate activity (qATPase), contributes to greater fatigue in affected muscle of spinal cord injured (SCI) patients. The qATPase activity showed a fiber-type effect, IIax + IIx > IIa > I. Average fiber qATPase and fiber specific qATPase activities were not different between SCI and able-bodied controls, nor did they change over time. We suggest greater fatigue in SCI subjects early after injury does not reflect increased energy demand of contraction.