Long-term spinal cord injury increases susceptibility to isometric contraction-induced muscle injury

Abstract

Complete spinal cord injury (SCI) results in inactivation and unloading of affected skeletal muscles. Unloading causes an increased susceptibility of muscle to contraction-induced injury. This study used magnetic resonance imaging (MRI) to test the hypothesis that isometric contractions would evoke greater muscle damage to the quadriceps femoris muscle (mQF) of SCI subjects than that of able-bodied (AB) controls. MR images were taken of the mQF prior to, immediately post, and 3 days post electromyostimulation (EMS). EMS consisted of five sets of ten isometric contractions (2 s on/6 s off, 1 min between sets) followed by another three sets of ten isometric contractions (1 s on/1 s off, 30 s between sets). Average muscle cross-sectional area (CSA) and the relative areas of stimulated and injured muscle were obtained from MR images by quantifying the number of pixels with an elevated T2 signal. SCI subjects had significantly greater relative area [90 (2)% versus 66 (4)%, P<0.05; mean (SE)] but a lesser absolute area [16 (3) cm(2) versus 44 (6) cm(2), P<0.05] of mQF stimulated than AB controls. During EMS, peak torque was reduced by 66% and 37% for SCI and control subjects, respectively. Three days post EMS, there was a greater relative area of stimulated mQF injured for the SCI subjects [25 (6)% versus 2 (1)%, P<0.05]. Peak torque remained decreased by 22% on day 3 in the SCI group only. These results indicate that affected muscle years after SCI is more susceptible to contraction-induced muscle damage, as determined by MRI, compared to AB controls. They also support the contention that electrically elicited isometric contractions are sufficient to cause muscle damage after a prolonged period of inactivity.

Electrically stimulated resistance training in SCI individuals increases muscle fatigue resistance but not femoral artery size or blood flow

“…We recently showed that excessive muscle injury occurs with a bout of NMES-induced isometric contractions in humans with SCI. 23 Fatigue with an acute bout of electrical stimulation was 66% (compared to 37% for controls) and area of damage was 25% (compared to 2% for controls) after 3 days. The repeated bout effect of muscle contraction on muscle damage may help explain the decrease in 'fatigue' seen in our study.…”

“…12,23,24 In brief, subjects sat on a specially made chair with a rigid lever arm positioned 701 below horizontal. Subjects received electrical stimulation inducing isometric contraction (30-Hz train of 450-ms biphasic pulse, 50-ms phase delay) of the quadriceps at a current that would elicit 30 Nm of torque with a 1:4 duty cycle for 4 min.…”

Non-invasive assessment of lower extremity muscle composition after incomplete spinal cord injury

“…20 Moreover, based on changes in muscle T 2 after isometric contractions, previous studies have suggested an increased susceptibility to muscle injury after complete SCI in humans. 20 Factors including unloading and inactivation of affected muscle as well as skeletal muscle atrophy seemingly contribute to this phenomenon. Although persons with incomplete SCI have partial sparing of the spinal cord, relative unloading and inactivation of their lower limb muscles might predispose skeletal muscle to injury.…”

Effect of adjusting pulse durations of functional electrical stimulation cycling on energy expenditure and fatigue after spinal cord injury

“…An inherent problem to surface neuromuscular electrical stimulation is the rapid onset of muscle fatigue [7][8][9][10][11]. This well-studied phenomenon is known to interfere with optimizing neuromuscular and cardiovascular performance in persons with SCI.…”

“…This well-studied phenomenon is known to interfere with optimizing neuromuscular and cardiovascular performance in persons with SCI. Rapid onset muscle fatigue is characterized by rapid decline in performance during repetitive activity [8][9][10][11]. Previous work documented that peak torque was reduced in the group with SCI 1.7 times more than in controls after isometric activations with electrical stimulation and remained declined by 22 percent on day 3 in the group with SCI [11].…”