Most people don’t have to be convinced that exercise is good for them or their mood. What they may have to be convinced of – especially if they don’t make a habit of exercise – is to do it in the first place.
Yet one fascinating study reveals just why convincing a non-exerciser to exercise may be so challenging.
Studying voluntary wheel running in mice – which can run up to seven kilometers a day – Stephanie Fulton, a professor at Université de Montréal’s Department of Nutrition and her team compared the distance run by mice who underwent a genetic modification to suppress a molecule activated by leptin, STAT3 (signal transducer and activator of transcription-3) to those who had no such modification. Secreted by adipose tissue, leptin is a key hormone in metabolism and helps control the feeling of satiety. As fat levels increase, leptin also increases essentially telling our brains that we are full. The STAT3 molecule is found in the neurons that synthesize dopamine in the midbrain, and has been called the “motivational highway” in the brain. What Fulton and her team wanted to know was: Is there a connection between leptin and motivation to run?
The answer was clear: The mice who had their STAT3 suppressed ran more – substantially more (Fulton, et. al., 2015).
“We discovered that the rewarding effects of endurance activity are modulated by leptin, a key hormone in metabolism. Leptin inhibits physical activity through dopamine neurons in the brain” (Fulton, 2015).
And the reason for the connection, Fulton and her team suggest, is that when body fat levels – and consequently leptin levels – increase, they activate STAT3 in the dopamine neurons which tells the body energy reserves are sufficient and there is no need to get out and run to look for food – by essentially decreasing the dopamine response to running and making it feel less rewarding.
So do these results play out in humans?
According to Fulton they do. She notes, “Previous studies have clearly shown a correlation between leptin and marathon run times” (Fulton, 2015).
“We speculate that for humans, low leptin levels increase motivation to exercise and make it easier to get a runner’s high” (Fulton, 2015).
Here again, the results have an evolutionary basis. As endurance running capacity in mammals, particularly humans, is thought to have evolved to maximize the chances of finding food, leptin appears to play a critical role both in regulating energy balance and encouraging behaviors that are “rewarding” for our survival (i.e. finding food).
And just how beneficial exercise is to our happiness levels depends not on how much we do – or how intense it is – but rather, that we move at all.
Monitoring 419 generally healthy middle-aged adults who wore accelerometers on their hips to track physical activity over four days, and then completed a series of questionnaires asking them to describe their daily exercise habits, psychological well-being, depression level, pain severity, and extent to which pain interfered with their daily activities, researchers from the University of Connecticut Department of Kinesiology, compared the effects of light physical activity – the equivalent of taking a leisurely walk around the mall with no noticeable increase in breathing, heart rate, or sweating – moderate intensity activity – the equivalent to walking a 15-20-minute mile with an increase in breathing, heart rate, and sweating, yet still being able to carry on a conversation – and vigorous activity – the equivalent to a very brisk walk or jogging a 13-minute mile with a very noticeable increase in breathing, heart rate, and sweating to the point of being unable to maintain a conversation – to participants mood and feelings of well-being.
Among their findings: People who reported higher levels of sedentary behavior also reported lower levels of subjective well-being, meaning those who sat around a lot were the least happiest. In general, physical activity improved people’s sense of well-being. Yet, different intensities of physical activity were more beneficial to some people than others. For instance, people who participated in light-intensity physical activity reported higher levels of psychological well-being and lower levels of depression. People who participated in moderate-intensity physical activity reported higher levels of psychological well-being and lower levels of pain severity. People who led sedentary lives and engaged in light or moderate physical activity showed the greatest improvement in overall sense of well-being. While light and moderate physical activity clearly made some people feel better about themselves, when it came to vigorous activity, the results were neutral. There was no positive or negative association found between high intensity physical activity and subjective well-being (Panza, et. al, 2017).
While it is not surprising that exercise makes us feel better, results like this might have us replacing the ‘more is better’ mindset with ‘anything is better’ – especially when our goal is happiness. Yet another way we can interpret these results is that exercises that make us feel good physically – as opposed to the typical ‘no pain, no gain’ mentality – are the ones we are more likely to do.
“We hope this research helps people realize the important public health message that simply going from doing no physical activity to performing some physical activity can improve their subjective well-being” (Panza, 2017)
Supporting these results, another study showed that less intense forms of exercise – in particular yoga – can have dramatic effects on our sense of well-being and happiness.
Following two randomized groups of healthy individuals over a 12-week long period, researchers from the University Of Boston School Of Medicine had one group practice yoga three times a week for one hour, while the remaining subjects walked for the same period of time. Using magnetic resonance spectroscopic (MRS) imaging, the researchers measured the participants’ brain levels of gamma-aminobutyric (GABA) before the study began and at week 12. As low GABA levels are associated with depression and other widespread anxiety disorders, the question the researchers were asking was: Would GABA levels rise more with walking or yoga? To help clarify the results, each subject was also asked to assess his or her psychological state at several points throughout the study.
For those who practiced yoga the results were promising: they showed a more significant decrease in anxiety and greater improvements in mood than those who walked, and these positive changes were associated with increasing GABA levels (Streeter, et. al., 2016).
So yes, it’s fair to conclude that exercise – intense or not – will make us happier. But interestingly, if we flip the equation around, it seems that being happy, in and of itself, will make us more likely to exercise.
Recruiting 9,986 English adults over the age of 50 Julia Boehm, Ph.D and her team from Chapman University, first assessed their psychological well-being, and then following them for 11 years, assessed them six times over the course of the study asking about the frequency and intensity of their physical activity both at work and during leisure time. Participants were then classified into categories of sedentary activity, low activity, moderate activity, and high activity.
What Boehm and her team found was that those participants who had higher levels of psychological well-being at the start of the study had greater levels of physical activity across more than a decade. Moreover, people at the start of the study who had high levels of psychological well-being and who were also physically active initially were less likely to become inactive over time (Boehm, et. al., 2016).
“Results from this study suggest that higher levels of psychological well-being may precede increased physical activity; therefore, it is possible that psychological well-being could be a novel way of not only enhancing psychological health but also increasing physical activity – which in turn could improve the physical health of a large segment of people in an aging society” (Boehm, 2016).
When we are happier we are more likely to exercise, and consequently, the exercise we do, whether it is intense or not, improves our metabolism, and our gene expression such that exercise itself becomes more rewarding.