A new study in the journal Behavioral Brain Research paints a fascinating picture of why some people are more motivated to exercise. The study looked at the dopaminergic system to see how people’s genetic variants could alter the ‘reinforcing value’ of exercise.
The majority of people in the US are too sedentary, and 90% of Americans don’t meet the government’s recommendation for physical activity. (In the appendix of the ‘Dietary Guidelines,’ there is a recommendation by the US Department of Health and Human Services that adults need 2 1/2 hours/week of moderate-intensity aerobic exercise and two days/week of strength training.)
According to the researchers, one factor in adhering to the guidelines is “the reinforcing value of exercise relative to a competing alternative behavior”. In other words, would you rather exercise, or do something else…
The study looked at 178 adults (average age 27) who wore activity trackers. The participants also rated how much they liked different exercises and sedentary activities.
The study found four genetic variants to be related to exercise reinforcement and exercise intensity.
The first variant is related to motivation to exercise. It is a dopamine receptor variant in the ANKK1 gene that affects the dopamine 2 receptor. This variant is well studied in relation to addiction, weight gain, ADHD, and suicide risk (read the whole article on dopamine receptor variants).
The results showed that this dopamine related variant was involved in the reinforcement value for exercise — or, in other words, whether people felt that the reward of exercising was greater than doing other non-physical activities such as watching TV, playing video games, etc.
Check your genetic data for rs1800497 (23andMe v4, v5; AncestryDNA):
The other three genetic variants were linked with the intensity of exercise.
The CNR1 gene codes a cannabinoid receptor variant that has also been associated in other studies with exercise tolerance. The cannabinoid receptors are involved in pain tolerance.
Check your genetic data for rs6454672 (23andMe v4 only):
The LEPR gene codes for the leptin receptor. Leptin is a hormone that signals for satiety and for energy homeostasis.
Check your genetic data for rs12405556 (23andMe v5; AncestryDNA):
The GABRG3 gene codes for a GABA receptor that has been associated with exercise tolerance in previous studies. It is thought to decrease pain signaling.
Check your genetic data for rs8036270 (23andMe v4; AncestryDNA):
It is always interesting to see the genetic pathways that are involved in a topic. If you would rather sit on the couch and play video games rather than working out at the gym, perhaps you can blame your dopamine receptors. And if you don’t work out hard because it hurts, well – blame your GABA or cannabinoid receptors.
Perhaps understanding the reason that you don’t want to exercise will motivate you to get beyond that and start working out more :-)