Mechanics and energetics of muscle contraction in normal and dystrophic chickens.

Energy liberation and isometric force generation were compared at 25 degrees C in isolated normal (n = 15) and dystrophic (n = 18) posterior latissimus dorsi muscles (PLD) from 16- to 33-day-old chickens. Twitch-energy liberation in dystrophic muscle decreased by 27 +/- 6%, and force per cross-sectional area decreased by 26 +/- 11%. Tetanic energy liberation in dystrophic PLD was depressed by 32 +/- 10% compared with a 22 +/- 9% reduction in peak force per cross-sectional area plus a 26 +/- 3% reduction in ability to maintain force. Normalizing results using the force-time integral demonstrates an unaltered force generation per unit energy liberation in dystrophic PLD (7 +/- 11% difference from normal). Kinetic properties of the mechanical responses were not significantly different in normal compared with dystrophic PLD. Dystrophic PLD demonstrated hyperexcitability to nerve transection and electrical stimulation. Although force-generating capacity is reduced in dystrophic PLD, coupling of force production to energy utilization appears unaltered.