After the 5-week treatment period, animals were anesthetized (pentobarbitone sodium, 60 mg/kg intraperitoneal), tracheostomized, and placed on mechanical ventilation. Body temperature was maintained at 37°C using a thermostatically controlled heating blanket and radiant heat. A midline incision was made in the neck, and the digastric muscles were separated to reveal the omohyoid muscle, which was cut to expose the underlying geniohyoid muscles. The sternohyoid muscles running from the sternum to the hyoid bone were also exposed. The muscles were removed rapidly and prepared for adenosine triphosphatase (ATPase) staining or for contractile studies. For the latter, longitudinal strips of 1 to 2 mm in diameter were suspended vertically in a water-jacketed bath in warmed (30°C), oxygenated (95% oxygen, 5% carbon dioxide) physiologic saline solution (pH 7.4) containing NaCl, 120 mmol; KCl, 5 mmol; Ca gluconate, 2.5 mmol; MgSO4, 1.2 mmol; NaH2PO4, 1.2 mmol; NaHCO3, 25 mmol; and glucose, 11.5 mmol. The muscle strip was fixed at one end and attached at the other end to an isometric force transducer. Isometric twitch tension, tetanic tension, twitch/tetanic tension ratio, contraction time, half-relaxation time, the tension-frequency relationship, fatigue, and recovery from fatigue were measured using field stimulation (supramaximal voltage, 1 ms in duration) with platinum electrodes and recorded using an analog-to-digital converter and microcomputer.