Running is, after all, a very physically demanding activity that raises one's pulse and requires a tremendous amount of physical exertion. Meditation, on the other hand, involves a separation of mind and body in such a way that the individual meditating achieves a state of consciousness entirely separate from his or her surroundings.
Running and the meditative state are not mutually exclusive, and for those who truly enjoy running, it is quite likely that they have already come to think of it as meditative experience. While the latter is typically associated with slowing the heart rate, breathing deeply and rhythmically, and removing one's self from the world around them, running actually can help achieve all of those - aside, of course, from the lowered heart rate.
For those who have achieved what is often referred to as the "runner's high," this concept of running as meditation is even more understandable. While the specific mechanism that triggers the so-called runner's high is not definitively understood, it generally is tied to the release of endorphins, which occurs during exercise.
The feeling of well-being that is achieved with the release of endorphins is analogous to certain drugs, though in this instance, the drugs in question are naturally occurring and not unhealthy. Interestingly, however, the release of endorphins into the bloodstream is concurrent with the body exhausting its supply of glycogen so that only extended periods of exercise result in this feeling. In this sense, there is a threshold that must be crossed before the true runner's high is achieved.
The other phenomenon that runners often describe is a sense of being detached from their bodies, so that they are performing the act of running without actually being aware of it. For those who see running and exercise in general as pure drudgery, this may seem too good to be true but, rest assured, it is a reality.
While this is not to suggest that running or exercise is a cure-all, it is clear that there are anti-depressant properties associated with running and exercise, making the correlation between running and the meditative state - which is also said to assist with overcoming depression - much clearer.
The other similarity that is noteworthy between running and meditation is, the sense of detachment. After having crossed the threshold that triggers the runner's high, the individual attains a sort of Zen-like consciousness, almost as though viewing the world from a third-person perspective rather than as a part of it. The escape is akin to the healing that occurs during the traditional meditation practice, but the results can be exactly the same.
For those who have never thought of running or exercise as meditation, it's likely that this is merely the result of never having experienced the runner's high (which does, as it turns out, apply to other forms of exercise), or thinking of exercise merely as a task to be performed and not something to be enjoyed. With a slightly different mindset and time to build up to longer periods of exercise, running or other forms of activity can indeed, become meditative.