High-energy phosphate compounds in slow-twitch and fast-twitch muscle fibres. Changes during exercise in some neuromuscular diseases.

Concentrations of the high-energy phosphates, ATP and creatine phosphate, were investigated in slow-twitch (ST) and fast-twitch (FT) muscle fibres of patients with myotonia congenita (n = 6), dystrophia myotonica (n = 5), myopathia ocularis (n = 2) and hyperornithinemia with gyrate atrophy (HOGA) (n = 3) and compared with those of normal subjects (n = 4). At rest, the patients with HOGA had lower values of ATP in ST muscle fibres than the controls (P less than 0.05). They also had lower values of creatine phosphate in these fibres than the patients with dystrophia myotonica (P less than 0.03) and myotonia congenita (P less than 0.05). After 30 s bicycle ergometer exercises there was an increase in ATP in the ST muscle fibres of the patients with myotonia congenita, but in all other patient groups there was a decrease.