A type of skeletal muscle fibre that produces relatively slow, low-tension contractions and is highly resistant to fatigue. Slow-twitch fibres can produce lengthy and sustained contractions, as in the muscles that maintain posture when standing. They are well supplied with blood vessels and mitochondria, produce ATP by aerobic respiration, carry substantial reserves of fuel in the form of glycogen and fat, and contain large amounts of the oxygen-storing protein myoglobin; hence they are the chief component of ‘red’ muscle. Athletes whose muscles contain a high proportion of slow-twitch fibres are generally suited to endurance events, such as long-distance running or cycling. Compare fast-twitch fibre.