Despite the obvious benefits such as building muscular strength, promoting muscle tone, fat loss, improved metabolism, and bone density, many of us equate “strength training” with toilsome weight machines, dumbbells, or resistance cords. Yet if you’ve ever had sore muscles after a yoga session, you may have wondered if you can just do yoga instead. 
Many yoga practitioners look toned as if they go to the gym and lift weights. And the truth is, they do: their own body weight. Quite simply, yoga poses require positions and orientations that engage our muscles. 
“Yoga can be just as effective as weights when it comes to building a stronger, more impressive physique,” says Nicholas DiNubile, M.D. Yet experts agree that whether yoga can be your sole form of strength training depends on your goals. 
“If all you’re looking to do is build muscle, weight training is the more practical approach,” advises DiNubile. In fact, the American Council on Exercise defines strength training as “exercising with progressively heavier resistance for the purpose of strengthening the muscular skeletal system.” 
“Progressively heavier resistance,” meaning your muscles and bones must be overloaded to keep developing. With weight training, your muscles adapt to the resistance and get stronger, that weight no longer being a challenge. Now you have to add more weight to achieve results.
Many believe that yoga, however, is a more balanced approach to strength training. For one, it conditions your body to perform things you do every day: walking, sitting, bending, lifting. Your body moves in the way it was designed to move. 
Yoga also tones both large and small muscles all over your body, in balance with one another, while weight training isolates one muscle group at a time—like the back and forth of a bicep curl. 
More technically, yoga relies on eccentric contraction, where the muscle stretches as it contracts, giving it a sleek, elongated look. Weight training relies on the opposite principle of concentric contraction, where the muscle gets smaller as it contracts. Muscle fibers heal close together, with a compact, bulging appearance. 
Finally, yoga increases muscle endurance since you typically hold a given pose and repeat it several times during a workout. 
By holding positions longer, doing more repetitions, and learning new poses, yoga can become more challenging. Before you try advanced poses like arm balances, start with the basics, use a yoga DVD, or consult videos online at GaiamTV.com.
I advise clients who wish to stay fit and healthy to mix body-weight exercises (pushups, squats, calisthenics) with workouts using weights or resistance tools. Many studies have shown that the more variety in your routine, the faster you’ll see results. 
Further more, my holistic view about strength and fitness is what inspired Mindful Strength Training, and delivers the best qualities of both yoga and strength training. It integrates different forms of meditation, breathing, visualization, energy-work, and focused intention with strength training, and anchors the whole system with daily mindfulness meditation. Collectively, these practices are designed to activate “flow” and harness the power of human consciousness to amplify our energy systems.
This form of strength training directs our attention towards the energetic and spiritual dimensions of our physical existence via mindfulness in the same way traditional Eastern yoga does.
The mind-body connection is alive and well, and the most important thing is to find a form of exercise you can enjoy as a lifelong habit. And if you include a variety of techniques, you’ll continue to test your body in different ways and keep growing in fitness and as an individual.