Contractile Properties of Human Skeletal Muscle

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Abstract
Active state duration and active state intensities of shortening and load-bearing were determined in the adductor pollicis muscle of 20 normal subjects, and seven hyperthyroid and four hypothyroid patients. Normal subjects showed a marked posttetanic and staircase twitch potentiation related primarily to an increase in active state intensity of shortening. In hyperthyroidism, active state duration in the unconditioned twitch was shortened while in hypothyroidism it was prolonged. Active state intensity of load-bearing was normal in hyperthyroidism (five of seven patients) and decreased in hypothyroidism (three of four patients). After repetitive stimulation (tetanus and staircase), both groups showed either a less than normal twitch potentiation (less than normal increase of active state intensity of shortening) or twitch depression below the control level (decreased active state duration without normal increase of active state intensity of shortening).