1. The effect of intravenous aminophylline on the contractility of adductor pollicis has been studied in three subjects both in the fresh state and following the induction of muscle fatigue. 2. Aminophylline had no influence on the frequency—force relationship and relaxation rate of adductor pollicis in the fresh state. 3. Fatigue resulted in a selective depression of the force response to low and moderate frequencies of stimulation and a slight effect on maximum force production 10 and 35 min afterwards. 4. Aminophylline given prior to, during and/or after fatigue did not influence this selective low-frequency fatigue at 10 or 35 min. 5. Aminophylline at the concentrations obtained has no significant effect on muscle contractility or fatiguability in man.
1. A technique has been devised to measure the effect of stimulation frequency on the contraction force in an accessory muscle of respiration, the sternomastoid, in man. The frequency/force curve was found to be very similar to that of the quadriceps and adductor pollicis muscles. 2. Fatigue of the sternomastoid due to inspiratory loading or sustained maximum voluntary ventilation resulted in reduced force generation at low stimulation frequencies compared with maximum force. This type of fatigue frequently persisted for several hours. 3. If low frequency fatigue were to develop in patients with pulmonary disease it could have important consequences for the development of respiratory failure.