The effect of a repeat bout of exercise on muscle injury in persons with spinal cord injury.
Following an initial bout of damaging exercise, a successive bout of similar exercise typically results in less injury, known as the "protective effect". Unloading due to spinal cord injury (SCI) increases the susceptibility to contraction-induced muscle injury. We tested the hypothesis that two bouts of isometric actions would evoke the same damage in the quadriceps femoris (QF) of patients with SCI. Six male subjects [32 (5) years old, 182 (9) cm, 81 (21) kg, injury level C6-T7, 6 (2) years post-injury, mean (SD)] were tested at two time points (Time1, Time2), separated by 8 weeks. Magnetic resonance images were taken of the QF prior to, immediately after, and 3 days after electromyostimulation (EMS) that evoked isometric knee extension. EMS (50 Hz) consisted of five sets of ten contractions (2 s on/6 s off, 1 min b/t sets) followed by three sets of ten contractions (1 s on/1 s off, 30 s b/t sets). Relative cross-sectional area of stimulated and injured skeletal muscle was obtained by quantifying pixels with an elevated T2. Relative area of stimulated QF was the same for both time points [92 (6)% and 89 (7)%] as was torque loss (approximately 55%). Three days post-EMS, the relative area of stimulated QF injured was not different between time points [30 (14)% vs 29 (17)%, P>0.05]. These results indicate an absence of a protective effective for repeat exercise bouts separated by 8 weeks in SCI patients using EMS.
Slade
J M
JM
Department of Exercise Science, University of Georgia, Athens, GA 20602, USA. jslade@msu.edu
Bickel
C S
CS
Dudley
G A
GA
D000328:Adult; D012090:Cumulative Trauma Disorders / Q000175:diagnosis / Q000503:physiopathology*; D004558:Electric Stimulation / Q000009:adverse effects / Q000379:methods; D015444:Exercise; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000293:injuries* / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000175:diagnosis / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000175:diagnosis / Q000503:physiopathology*