Oh, what a wonderful and juicy question.
To answer it, I think we first have to look at the definition of the word Yoga. Yoga is a Sanskrit word which means, to yoke or unite. It connotes a state of union between one's mind, body and spirit. It is actually speaking more to a state of being than an action. The "yoga" that this question refers to is really speaking of yoga asana or yoga postures, the practice of yoga that we have come to know and adore in the West when it first made it's journey here back in the 1960s and exploded in popularity several decades later.
So what is yoga asana, really? What's the purpose of it? Well, when we're practicing yoga asana (from now on I'm just going to call it "asana"), we're working with the physical body. Sometimes we're moving through vigorous sequences and building up a sweat and breathing deeply and sometimes we're very still and calm and introspective, the breath is hardly noticeable at all because we're so at ease.
So like many answers to big questions such as these, the answer is it depends. Asana is meant to act as a balancing force for one's energy levels and state of mind. Feeling sluggish and heavy or anxious and jittery? Sometimes the answer is to move through a difficult flowing sequence of postures if that would be appropriate for your body and sometimes with those symptoms, the remedy is to rest, reset, sit and stay still for sometimes up to 10 minutes at a time per posture.
Now, when a person is exercising, that would typically mean that they're moving their body in such a way as to create internal structural tension and strain in their musculoskeletal system to affect change in their tissues, typically to develop muscular strength, mobility or improve the capacity of their cardiovascular system. Can more vigorous styles of asana achieve the these effects? Yes, absolutely. Especially if one works with one's body weight skilfully to increase the loads exerted through the tissues OR introduces weights or resistance bands to give the body some kind of load to contend with. There are so many creative ways in which a person could create strength and mobility in their practice. But does that mean that that's all that we're doing in our asana practice? No, not at all. Like I mentioned before, sometimes one's yoga practice can be very restorative and still, in which case, I wouldn't call it "exercise" by the Western understanding of the word.
So now let's try a new way of approaching the question. We can also flip the question around as ask: Is all exercise asana? It's important to look at the one big variable that can differentiate asana from being a yogic practice or from it being simple exercise and this requires us to look at how we are engaging our mind in our movement practice. When we're practicing asana we're also layering a quality of attention that is curious, engaged in feeling sensations in our bodies or breath and maybe even aware of our connection to the greater world around us. In other words, we're applying our attention fully to our experience in the present moment. In asana, we aren't watching TV as one might at the gym on a treadmill. We might listen to music but the music serves as inspiration to the movement practice, to compliment what we're doing, rather than to serve as a distraction. So there's a distinct question here around how we're practicing.
By this light, we could say that any form of exercise is also yoga. Any form of exercise where our minds are engaged in curious awareness and attention to our inner developing processes can become a vehicle for union of body, mind and spirit. Can I be out for a run, feeling all the sensations in my legs, aware of the heaving of my chest while I breathe, aware of the dialogue in my mind, and feeling connected to Mother Nature as I move? YES, OF COURSE, YOU CAN! You can apply this train of thought to any other form of exercise and I would argue that it's all gravy. It's all fair game. The key concept here is that through the movement, through the exercise, or activity, one can come closer to themselves in the present moment through awareness.
I really like the inclusivity of all forms of movement being considered yoga because it creates space for experimentation, cross-training, and inclusivity. It invites all forms of exercise to the table and simply asks that their common thread is the approach to practice rather than being so caught up in the form itself. This reminds me of different religions and how each sect can argue over whose form of God is the "True God" but in effect, they're all talking about the same energy.
I used to believe—and I've studied with a major school of yoga who taught— that any other exercise other than yoga asana was in fact taking away from one's yoga practice. After a great amount of personal experimentation and further education, I've discovered this belief does not hold true for me.
Last, let's look at the Sanskrit word "Asana" which translates to "posture" or "seat" in English. Asana is defined by any posture that is balanced in qualities of steadiness and ease. Sometimes we use the phrase "sthira sukkah asanam" to describe the art of finding a posture that is steady (strong) and sweet (easeful). This could refer to how a person is holding their body in a particular shape and it can also refer to their state of mind. And that's where things get interesting. They say that the stillness and the ease that we cultivate in body and mind leads us toward a state of "yogas citta vritti nirodha" or the cessation of the inner fluctuations of the mind — which refers here to a state of union of body, mind and spirit. Now is that a direct road? If you're able to continually keep your mind and body in a sweet and steady state, will one experience perfect Yoga? In my experience, no, this is not a direct road. Often it first requires navigating the imbalances in one's physical, energetic and emotional bodies, which is a whole other blog post in itself. But I felt it necessary to touch back upon the "end of the yogic journey" (and to really confuse things, sometimes it's also considered the beginning of the journey) which is a state of union.
So back to the original question: is yoga (asana) exercise?
Again, I think it depends. I've heard so many of my peers vehemently assert that their yoga practice isn't exercise and that it's strictly a moving meditation for them, but then their practice is highly active and physically demanding which to me, seems like a denial of the fact that they are having a physical experience, doing wonderful things for their tissues and having a powerful experience through their body. Why deny it? Well, I have a hunch that it has something to do with wanting to look "holy" or of a higher level of consciousness than the common people who are just exercising. Perhaps there's also the fear of being shamed by the Purists who would argue that it's all about transcending the physical plane.
But let's call it what it is: if you're doing 30 Chaturanga push ups in a class, I'm pretty sure that that's BOTH yoga asana (remembering of course to include components of self-awareness) AND exercise. It's less about this OR that. I'm more interested in the this AND that. Again, moving away from the notion of "my practice is more superior to your practice" (see: arguments about "My God is truer than your God.")
So, friends, let's create space for it all, let's bring consciousness to all our movement practices and allow for them ALL to be vehicles of coming into Yoga.