Many people find exercise "too hard." That may be why only 28% of U.S. adults manage to get even the minimum recommended level of physical activity. (And that's not the minimum for good health and longevity, but the minimum to maintain decent health.)

Researchers from Johns Hopkins Medicine decided to find out why physical effort feels easy to some people and exhausting to others. They used Parkinson's patients — who regularly supplement their dopamine levels — to see what was going on.

Their discovery: When exercise seems too hard to even imagine doing it, it may be the result of low levels of dopamine, the neurotransmitter/hormone that influences pleasure, reward, and motivation, as well as movement. 

If you're exercise-averse, work on naturally raising your dopamine levels and see if the idea of exercising doesn't become more appealing — and when you do it takes less effort, mentally and physically.

Basic dopamine-loving habits include getting enough sleep, moving more, listening to music, meditating, and spending time in the sun. Other tricks:

• Eat protein-rich foods such as salmon, turkey, legumes, and soy. They contain an amino acid that, down the road, helps promote production of dopamine.

• Ditch saturated fats because large amounts may disrupt dopamine functioning in reward areas of the brain. 

• Get enough iron, niacin, folate, and vitamin B6, all of which help form dopamine.