Development of an Alternative Protocol to Study Muscle Fatigue

When measuring real-time in vivo muscle fatigue with electromyography (<b>EMG</b>), data collection can be compromised by premature sensor removal or environmental noise; therefore, the objective of this study was to develop a postmortem in vivo methodology to induce muscle fatigue and measure it using EMG. Barrows (<i>N</i> = 20) were stratified by weight and randomly allocated into one of two treatments. The treatments consisted of barrows being subjected to a hog electric stunner super-contraction cycle (<b>ES</b>) or not (<b>CON</b>) postmortem. The right hind limb bicep femoris (<b>BF</b>) and semitendinosus (<b>ST</b>) were selected for ambulatory movement simulation using electronic muscle stimulation (<b>EMS</b>). Muscle workload during EMS was measured with EMG using median power frequency (<b>MdPF</b>) and root mean square (<b>RMS</b>) as indicators of action potential velocity and muscle fiber recruitment. Ambulatory movement was induced and recorded for 20 min with a 4:4 duty cycle at 70 Hz. Muscle biopsies were collected pre- and post-EMS for metabolite analyses to corroborate muscle fatigue onset. There was a TRT × Muscle interaction for normalized RMS percentage (<i>p</i> < 0.01), where BF from CON barrows had greater values (<i>p</i> < 0.01). There were no interactions or TRT main effects for the MdPF normalized value (<i>p</i> ≥ 0.25), but there were Period and muscle effects on MdPF (<i>p</i> < 0.01). Bicep femoris had smaller (<i>p</i> < 0.01) MdPF than ST. The percentage of MdPF decreased (<i>p</i> < 0.01) by Period 5 compared to the other Periods, which did not differ from each other (<i>p</i> ≥ 0.38). There were TRT × Muscle and Muscle × Period interactions for ATP muscle concentration (<i>p</i> ≤ 0.03). The concentration of CON BF ATP was greater (<i>p</i> < 0.01) than that of ES BF and CON and ES ST, which did not differ from each other (<i>p</i> ≥ 0.11), but the APT concentration tended to differ between ES BF and ES ST (<i>p</i> = 0.06). Semitendinosus ATP concentration decreased (<i>p</i> < 0.01) post-EMS compared to ST pre- and BF pre- and post-EMS (<i>p</i> ≥ 0.29), but BF and ST concentration tended to differ pre-EMS (<i>p</i> = 0.07). The data indicated that EMS is a valuable tool for replicating ambulatory movement or physical activity, but super-contraction is not a means to accelerate postmortem muscle fatigue onset. Therefore, further refinement, such as longer EMS stimulation time, should be considered.