Sustained force development: specializations and variation among the vertebrates

The kinds of muscle fibre that are recruited for sustained force production by different vertebrates are described. Although aerobic metabolism always accounts for a significant proportion of their ATP turnover, no single characteristic such as colour, number and form of motor endplates, membrane properties, myosin isotype or contraction speed is diagnostic of such muscles. As mechanical power output increases, there is a tendency for a decrease in fatigue resistance with repetitive usage and an increase in both aerobic capacity and the fraction of energy requirements derived from glycolysis.