Microdosing is a lie perpetrated by drug dealers to sell drugs to sectors of the population that would be otherwise too cautious to take them. The entire concept is based on a logical fallacy. The fallacy is that if you do not get the positive effect (i.e., getting high), you won't get the negative effect (i.e., addiction, tolerance, and the slew of other health damaging effects for each particular drug).
But there is no data to support this and it is unlikely to be true. In fact from what is known about the nervous system, taking small dozes of an addictive drug often and at regular intervals is a great way to increase tolerance. This will cause any positive effects of the drug to quickly diminish, which will cause the user to take larger doses, which will cause more tolerance and larger doses until the health effects associated with the drug start showing up.
So yes do take those walks in the park. One can actually be addicted to exercise too, but that is an addiction that almost always has nothing but positive side effects. It is in very rare cases that people exercise so much that it causes negative effects.