Almost one in five people lacks the protein α-actinin-3 in their muscle fibre. Researchers at Karolinska Institutet now show that more of the skeletal muscle of these individuals comprises slow-twitch muscle fibres, which are more durable and energy-efficient and provide better tolerance to low temperatures than fast-twitch muscle fibres. The results are published in The American Journal of Human Genetics.

Skeletal muscle comprises fast-twitch (white) fibres that fatigue quickly and slow-twitch (red) fibres that are more resistant to fatigue. The protein α-actinin-3, which is found only in fast-twitch fibres, is absent in almost 20 per cent of people – almost 1.5 billion individuals – due to a mutation in the gene that codes for it. In evolutionary terms, the presence of the mutated gene increased when humans migrated from Africa to the colder climates of central and northern Europe.

The results showed that the skeletal muscle of people lacking α-actinin-3 contains a larger proportion of slow-twitch fibres. On cooling, these individuals were able to maintain their body temperature in a more energy-efficient way. Rather than activating fast-twitch fibres, which results in overt shivering, they increased the activation of slow-twitch fibers that produce heat by increasing baseline contraction (tonus).

Release date: 17 February 2021
Source: Karolinska Institutet