Yoga what you refer to is some superficial physical exercises and breathing techniques. Yoga is primarily psychological. If you read Patanjali yoga sutra only two words are there for pranayama and asanas. Yoga is about being in tune with Nature, is about natural living. If you are a poet writing poem is yoga. Do not be fooled by people who mistake yoga for awkward twisting of bodies. It is an art of transcending the physical nature of your being. Yoga is about experiencing the metaphysical aspect of your being. No one should do yoga rather he or she should be in yoga.