Are you one of those people who wear shorts in the dead of winter, goes swimming when everyone else is still wearing jackets, and who finds they can handle winter camping more comfortably than their friends? If so, you may be one of the many people who has a genetic mutation linked to increased cold resilience, a benefit in cold climates, but one that may come with a sacrifice in sports performance.
The findings come from the Karolinska Institutet, which found that nearly one out of every five people have muscle fibers lacking the protein α-actinin-3. This mutation, which may have been beneficial in the distant past when humans migrated to cold regions, has been found to help keep someone warm.
The protein is only found in fast-twitch muscle fibers — and around 20-percent of the world’s population lacks this protein as the result of a genetic mutation, according to the new study, which is the first to link the loss of this protein with an increase in cold resilience.
The findings are based on a study of 42 healthy male adults who were tasked with sitting in 57F water until their body temperature dropped down to around 96F. Electromyography was used to measure the electrical activity in the participants’ muscles during this time. As well, muscle biopsies were taken to study the fiber composition.
The results showed that participants who lacked the protein had more slow-twitch muscle fibers, which enabled them to conserve body heat in a more efficient way. Whereas fast-twitch muscle fibers result in shivering, the slow-twitch fibers experienced more baseline contractions, producing heat.
One big question remains, however: what effect does this have on exercise performance? While studying this aspect is tricky, the researchers explain:
People who lack α-actinin-3 rarely succeed in sports requiring strength and explosiveness, while a tendency towards greater capacity has been observed in these people in endurance sports.