Research has proven that the practice of Yoga is enough to keep you fit as well as key to improving the results of weight lifting. What is keep fit anyway? According to The American College of Sports Medicine (ACSM), fitness is defined as the ability to maintain good health and physical activity which is measured under four categories: cardiorespiratory fitness, muscular fitness, flexibility, and body composition.
The results of one of the studies done in the United States that examines the relationship between yoga and fitness showed that the muscular strength of the subjects had increased by as much as 31%, muscular endurance by 57%, flexibility by as much as 188%, and VO2max (milliliters of oxygen per your body weight per minute that you can move or utilize) by 7%. Another study showed the improved lung capacity of subjects involved including athletes, asthmatics, and smokers. Other beneficial results of yoga include weight loss, increased energy, better sleep, risk reduction of injury and speedier recoveries. 
So how does yoga build fitness and how does it support weightlifting? It depends on who you ask.
– Robert Holly, PhD, a senior lecturer in the Department of Exercise Biology at U. C. Davis says, “Muscles respond to stretching by becoming larger and capable of extracting and using more oxygen more quickly, which result in muscle strength and endurance. An increase in muscle endurance allows subjects to exercise longer, extract more oxygen, and reach an increased maximal oxygen uptake.”
– Study author Dee Ann Birkel, an emeritus professor at Ball State’s School of Physical Education says, “Yoga poses help increase lung capacity by improving the flexibility of the rib area, shoulders, and back, allowing the lungs to expand more fully. Breathwork further boosts lung capacity and VO2max, by conditioning the diaphragm and helping to more fully oxygenate the blood. Poses also increase the heart rate, making yoga aerobically challenging and standing poses, balancing poses, and inversions build strength because they require sustained isometric contractions of many large and small muscles. Holding the poses longer increases this training effect.”
– Dina Amsterdam, a yoga instructor in San Francisco and graduate student at Stanford University, is one of many researchers conducting a three-year study that compares the psychological and physiological benefits of tai chi as to those of traditional forms of Western exercise such as aerobics. She states that, “When you bring your breath, your awareness, and your physical body into harmony, you allow your body to work at its maximum fitness capacity. Yoga class is merely a laboratory for how to be in harmony with the body in every activity outside of yoga. This improved physical wellness and fluidity enhance not just the physical well-being but also permeate all levels of our being.”
Sources
http://www.yogajournal.com/article/practice-section/is-yoga-enough-to-keep-you-fit/
http://www.elephantjournal.com/2015/06/5-reasons-you-need-yoga-to-improve-your-body-building
