A whiff of your gym bag might make you wince, but your nose could be the key to getting fit. New research in mice suggests there is a link between doing voluntary exercise and the expression of genes that relate to scent perception.
Rodents are used in scientific research for various reasons: they’re small, easy to keep, reproduce quickly and are thought to share genetic and behavioural characteristics with humans.
In a study by Sachiko Haga-Yamanaka and colleagues at the University of California, Riverside, mice were placed on a running wheel. “Voluntary wheel running (VWR) is an intrinsically motivated and naturally rewarding behaviour [for mice], and even wild mice run on a wheel placed in nature,” wrote the researchers in their paper.
Watching the mice, they were able to select those who chose to spend more time running at the wheel. The ‘high-runner’ mice were bred together, and then their offspring were watched on the wheel. The high-runners were chosen from this second generation and selectively bred again – so on, until the team had established a line of mice that were genetically engineered to be high-runners.
They then compared these mice to a control group, who had not been genetically modified, to find out what had happened during the evolution by artificial selection.
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Looking specifically at a part of the olfactory system called the vomeronasal organ – located in the nose of rodents – and its corresponding neurons in the brain, the researchers noticed that there were 132 genes changed in the high-runners.
"The olfactory system became genetically differentiated between the high-runner and control lines during the selective breeding process,” said Haga-Yamanaka.
"Our results suggest these chemosensory receptors [which were expressed by the altered genes] are important trait locations for the control of voluntary exercise in mice."
"The high-runners had a unique sense of smell."
The vomeronasal organ detects pheromones, chemicals produced by animals that end up in the air. This new knowledge could one day form the basis of a sensory stimuli for getting fitter.
It’s not yet clear if these odours work by increasing the mouse’s motivation for exercise, or if it boosts the neurological ‘reward’ it gets when it is running.
"While humans do not appear to have a vomeronasal organ, the vomeronasal system in rodents can be a model of human [smell] to some extent," said Haga-Yamanaka. "Some vomeronasal receptors seem to be expressed in the olfactory organ in humans, and some of the central brain circuitry seems to be very similar."
"It's not inconceivable that someday we might be able to isolate the chemicals and use them like air fresheners in gyms to make people even more motivated to exercise," said co-authorTheodore Garland Jr. "In other words: spray, sniff, and squat."
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There are still several studies needed before we get to that point, though.
Researchers still need to determine how the high runners perceive smells differently from regular mice, whether it's concentration of the pheromone detected or something else. "The idea that scents can affect reward received from exercise, or motivation to begin exercising, are both testable hypotheses in the future," adds Haga-Yamanaka.
"In principle, such experiments would not be that difficult to do. For example, you can use surveys of humans before, during, and after exercise to ask how motivated or rewarded they feel, while simultaneously giving some a scent and others no scent.
"Alternatively, you could use functional magnetic resonance imaging (FMRI) to look at the brain and measure patterns of brain activity. There, you'd see if reward centres 'light up' more when given certain scents during exercise," said Haga-Yamanaka.
"So far as we are aware, such studies have not yet been done."
Reader Q&A: Do the benefits of exercise wear off as your body gets used to it?
Asked by Tim Harrison, via email
The benefits definitely diminish, but not because you get used to the exercise – it’s because your fitness level gets closer to the optimal level. Your strength and endurance can’t increase indefinitely, for a variety of biological limits. Your muscles have a maximum size that is strongly affected by genetics, and the same is true of the strength of your tendons and the oxygen-carrying capacity of your lungs.
Sustained exercise at high levels (such as running more than 48 kilometres per week) has actually been shown to have a negative impact on your long-term health, causing permanent damage to the muscle fibres and nerves in the heart. A 2013 study of over 52,000 cross-country skiers found that those who had completed the most races had the highest chance of suffering heart rhythm problems.
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