Exercise linked to pleasure, stress

Popular New Year's resolutions include getting better grades and taking on new weight loss efforts. But for some, exercise can prove daunting and even stress-inducing, regardless of its habit of releasing endorphins into the bloodstream. New research into the nervous system has shed light on why some people are likely to quit their exercise routines sooner than others.

The study was conducted jointly by French company Ipsos and the University of Bordeaux, published last week in the journal Biological Psychiatry. Researchers found for the first time that a protein, the CB1 cannabinoid receptor, plays a key role in motivation and reward systems involved during physical exercise. The activity of this protein can vary significantly from person to person, leading scientists to believe that those who enjoy exercise less have CB1 cannabinoid receptors that are not as active.

Why does exercise make some people happier?
"The inability to experience pleasure during physical activity, which is often quoted as one explanation why people partially or completely drop out of physical exercise programs, is a clear sign that the biology of the nervous system is involved," said Francis Chaouloff, M.D., lead researcher in the Ipsos study.

According to the researchers, this is not the first study to link exercise and the endocannabinoid system, although it is the first to locate a specific, gene-targeted action of the CB1 receptor. Ten years ago, researchers found that the endocannabinoid system lights up during physical activity, but for many years the reason for this was unknown. Scientists now believe that the endocannabinoid system is among the most significant pleasure-seeking regions of the brain.

During the study, researchers used mice to test the effects of the CB1 receptor. Mice with the receptor jumped on their running wheels at a normal rate, but those without it experienced 20 to 30 percent less exercise time. Researchers found that not only does the receptor influence the duration of exercise, but also the severity.

Can exercise make you happy?
Yes and no. The Mayo Clinic reports that exercise can, for some, lead to higher endorphin levels, which scientists often equate with greater feelings of happiness. But some don't experience physical activity in the same way, instead becoming more aggravated the longer an exercise goes on. Study researchers believe this is because the same receptors involved in pleasure (reward) are also linked to stress (punishment). Therefore exercise, while promoting happiness for most of the population, could sometimes stimulate unhappiness, according to Ipsos researchers.

However, everyone has the potential to be happy through exercise, and there is no evidence that shows that exercise actually harms stress management. Athletes will often say that mindset is key to any exercise, and they're right. If you go into an exercise thinking you're going to fail, it's likely you're not going to be too happy with the results. But if you look on the bright side, it's possible you could reap more benefits.