Abstract

Skeletal muscles cope with a large range of activities, from supporting the body weight during upright standing to performing explosive movements in response to an unexpected threat or during sport activities. These actions require metabolic systems that can provide energy during prolonged periods of moderately increased energy consumption, as well as during explosive contractions, where the energy demand quickly increases more than 100-fold. In this chapter we discuss how muscles can deal with these divergent demands and how this relates to the development of muscle fatigue; that is, impaired contractile function manifested as decreased force production and slowed contractions. We first outline the metabolic differences between muscle fibre types and their relation to muscle fatigue. Next, we describe the major energy metabolism pathways in skeletal muscle and their relation to muscle fatigue and recovery. Finally, we discuss the ability of muscle fibres to adapt to altered demands and mechanisms behind these adaptations. The accumulated experimental evidence forces us to conclude that most aspects of energy metabolism and fatigue development involve multiple and overlapping pathways, which highlights that these processes are too intricate and important to depend on one single molecule or mechanism.