Effect of long-term atorvastatin treatment on the electrophysiological and mechanical functions of muscle

OBJECTIVE: To study alterations in muscle function combining physiological, electrophysiological and metabolic measurements in patients receiving a statin at various dosages during long-term therapy. MATERIAL: A 3-month (D0, D30 and D90) longitudinal physiological and electrophysiological muscle study was performed in 26 patients receiving 10, 40 or 80 mg/day atorvastatin. METHOD: All subjects performed maximal (MVC) and submaximal (60% MVC) isometric thumb adduction, handgrip and knee extension exercises during the recording of surface electromyograms (EMG) of the adductor pollicis (AP), flexor digitorum (FD) and vastus lateralis (VL). The compound muscle potential (M-wave) evoked by direct muscle stimulation was measured at rest and after 60% MVCs and the EMG power spectrum was analyzed during sustained effort. Blood was sampled from an antecubital vein for measurements of pH, lactate and potassium levels after thumb adduction and handgrip exercises. The measurements were repeated on Day 0 (D0), D30 and D90. RESULTS: Atorvastatin did not affect the MVC and endurance time to fatigue. Post-exercise M-wave alterations in the AP began at D30 with the 80 mg/day treatment and there was a reduced or suppressed leftward shift in the EMG power spectrum in the AP and VL with all 3 dosages. In the AP, the EMG changes appeared earlier (D30) with 80 mg/day whereas they only occurred at D90 on the lower dosages. Atorvastatin had no effect on the maximal postexercise variations in pHv and lactate but it significantly reduced the maximal increase in plasma potassium concentration after thumb adduction and handgrip exercise, the effects being only present at D90 on 10 mg/day but occurring as early as D30 with higher dosages. CONCLUSION: A 3-month atorvastatin treatment did not affect the maximal performance of skeletal muscle during voluntary efforts but EMG analysis revealed a reduced muscle excitability and an attenuated adaptation to fatigue. These effects prevailed in muscles containing the largest proportion of slow-oxidative fibers and were associated with a reduced outward flow of potassium.