Here is another excellent example to show the effects of asanas on human body as is contemplated in the Svetasvatara Upanishad.
    Laghutvam – arogyam – alolupatvam
    Varna prasadam svara – saushtavam cha,
    Gandhas – subho mutra – purisham – alpam
    Yoga pravruttim prathamam vadanti

Feelings of lightness in the body and well-being, good complexion, pleasing voice, agreeable body odour and scantiness of excretions are the first signs of progress in yoga practice.

The Bahiranga (external) yoga, which consists of Asana, Pranayama and Pratyahara – the three among the classical Ashtanga yoga indeed aim at preparing the practitioner psychically and physically to enter the next and final stages of yoga called Antharanga (internal) yoga.

The combined effect of the Asanas, Pranayama and Pratyahara cannot be defined more vividly and meaningfully than is set out in the above lines. Many similar quotations can be cited to show that the pearls of the yoga ideals lay embedded in most of the Upanishadic teachings.