Clinical investigations of muscle contractility

The use of tests of muscle contractility based on electrically stimulated contractions means that information obtained from the more traditional tests of voluntary muscular performance and strength may be complemented by indices which are independent of volition and independent of muscle mass. Such tests are no longer limited to peripheral muscles but may now be applied to a large proximal muscle--the quadriceps femoris. This report describes the in vivo testing of a drug's pharmacological activity on the quadriceps muscle by a study of the relative forces produced by different frequencies of stimulation. It also illustrates that hypothyroidism is not the only endocrine disorder whose treatment may be monitored by measuring the speed of muscle relaxation. Finally, it describes a patient whose quadriceps weakness was explained by the demonstration of the failure of the muscle to maintain tension during prolonged stimulation.