I suppose that would depend on what you mean by meditation, and the reasons why you are meditating. Whether you are seeking relaxation, improved concentration, enhanced creativity and cognition, clearer thinking, deeper awareness, and a more lucid understanding of yourself and the world you live in.
Those are actually all very good reasons for meditating AND exercising.
I like to do both, to sit still and to exercise, to relax and to think deeply upon things, and sometimes to just completely empty my mind and not think about anything at all, experiencing things directly. I like to do both but I have found that getting regular exercise actually enriches the experience of my sitting still time.
Exercise is comparable to giving your car or bicycle a tune-up, where you are prepping your body (mind, brain) for maximum efficiency and productivity.
Physical exercise stimulates blood flow to your brain, improves the efficiency of your oxygen intake, and releases natural endorphins into your bloodstream. The result being that not only is exercise good for your physical health, but by also making you feel better and your thinking clearer, it's also good for your mental health too.
In other words, if you exercise prior to engaging in some form of creative mental activity, such as reading, writing, or meditating, you will see an increase in productivity. At least I do, perhaps I can only speak for myself, but it is difficult for me to imagine this not being true of anyone else. Try it sometime. Make it into a science experiment. Write down your results. See if you notice an improvement.
I've done this several times myself, and I have noticed an improvement. Which is why I speak so highly of exercise, and truly believe it is like a wonder drug that everyone SHOULD liberally partake in.
Anyways, getting back to the original question of how physical exercise is like a moving meditation, I will expand upon that here.
Movement deepens awareness. Vigorous movement outdoors vigorously deepens awareness of the outdoors. Exercising, moving vigorously, running, lifting weights, makes me feel more alive. Being in movement makes me feel more alive and aware.
Think about it. What is the difference between life and death?
Things that are living are in movement, things that are dead are in stagnation, the only visible movement being disintegration, dust unto dust, until nothing visible remains. To be alive is to be in harmonic movement, a dance between your body and your mind, between body and the physical space you occupy. Self and the world. Body and Earth. Earth and Sky. Microcosm and macrocosm. Masculine and feminine. Creation and destruction.
To live is to maintain an equilibrium between the two opposing forces of creation and destruction. Equilibrium is not stationary, it is ever flowing, it is moving with the movement of the universe, dancing with it, like wind, like water, like fire, and the earth dancing through intergalactic space.
Exercise aligns you with this cosmic movement, to momentarily ride the wave of living through movement. Or something like that.
I've also noticed that exercise makes me more alert to my surroundings, where I see more, hear more, and feel more. Pumps me up. Makes life more energized.
If I sit too long I actually feel more sluggish and less aware of my surroundings.
This is why I call exercise a moving meditation, because not only is it simultaneously relaxing and energizing, it also helps deepen your awareness of your surroundings. At least this is true for me. I learn everything through trial and error. All advice I give has been acquired through direct observation by personal experience.
Stillness has its place too. Can't always be in movement. Need time to rest, to reflect, and to introspect. And yet, when is the mind not in movement? When is the breath not in movement? When is the heartbeat not in movement?
There is no stillness in life. Without movement, life ceases to exist.
If there is no absolute stillness in life, what do people mean when they speak of sitting in stillness and stilling the mind? It means to slow down, to relax and to become more aware, not to stop completely. When you stop completely, your body stops completely, and what happens then? You die.
Which is why it is during sleep that you are closer to a state of death than you will ever be so long as you are alive. Because death is more closely associated with stillness, and life with movement, exercising brings you closer to life.
So exercise already! No more excuses. Whether that means running in a circle, lifting some weights, or walking across the country, just do it! Get moving. You'll feel better, and you'll feel more alive, in a good way.
Then afterwards while sitting in stillness, contemplating the things you've learned, letting the insights pour forth freely like a vibrant energizing rain, you can joyously soak it all in.