Assessment of skeletal muscle fatigue in men with coronary artery disease using surface electromyography during isometric contraction of quadriceps muscles.

OBJECTIVE To evaluate whether using surface electromyography to assess skeletal muscle fatigue during an isometric exercise has the potential to be clinically useful in patients with coronary artery disease (CAD). DESIGN Double sample comparative study. SETTING Cardiac rehabilitation service in France. PARTICIPANTS Sixteen men with documented CAD and 9 age-matched healthy men. INTERVENTIONS Assessment of quadriceps skeletal muscle fatigue on an isokinetic apparatus with surface electromyography measurements and a symptom-limited exercise test in a laboratory. MAIN OUTCOME MEASURES The maximal voluntary isometric force (MVIF) of the quadriceps was quantified as a measure of muscle strength and isometric endurance was defined as the time required to sustain a contraction at 50% of MVIF until exhaustion. Surface electromyography signals were recorded from the vastus lateralis, rectus femoris, and vastus medialis during isometric endurance. The root mean square (RMS) and the median frequency (MF) were directly calculated on a computer and then normalized (as a percentage of the initial value). RESULTS Muscle strength did not differ significantly between the patients with CAD and the healthy subjects (229+/-21N/m vs 228+/-52N/m), but isometric endurance was reduced (64+/-17s vs 90+/-7s, P <.01). The RMS values showed a significantly higher increase in the healthy subjects versus the patients with CAD for the vastus lateralis and vastus medialis ( P <.001). The MF values were significantly lower for the vastus lateralis, rectus femoris ( P <.01), and vastus medialis ( P <.05) in patients with CAD compared with the healthy subjects. CONCLUSIONS Skeletal muscle fatigue occurs sooner in men with CAD relative to matched healthy men, despite similar muscle strength. This finding may be the result of an abnormality of skeletal muscle function and may play an important role in measuring functional capacity. In addition, it may be a useful tool to assess the efficacy of cardiac rehabilitation interventions.