ABSTRACT
Contraction of skeletal muscle produces the forces that enable movement to occur. When force requirement is low, only a relatively small volume of muscle needs to be recruited. However, as muscle force requirement increases, for example at higher work rates during cycle ergometer exercise, progressively more musele mass has to be recruited. Human skeletal muscle comprises muscle cells (fibres) with distinct metabolic properties. There is generally thought to be an orderly hierarchy in fibre recruitment strategy with smaller low-threshold fibres being recruited first and larger high-threshold fibres being recruited as force requirement increases (Henneman et al., 1965). Furthermore, during sustained exercise at the same constant work rate, there may be alterations in fibre recruitment as ‘fresh’ fibres replace ‘fatigued’ fibres (Vøllestad et al., 1984; Vøllestad and Blom, 1985). There is also evidence that higher-order fibres make a proportionately greater contribution to force production at higher contraction frequencies (e.g. Beelen and Sargeant, 1993).
