Actually speaking there should not be any comparison between Yogic practices & Gym workout. Both are entirely different pathways. One is for physical fitness & other for personality evolution.
But still it needs attention, as when it comes to health, someone may get confused as to which path to walk.
Gym workout involves a meticulous study of skeletal muscles & various gadgets to increase the strength & endurance of them .It also pays attention to cardiac fitness by slowly increasing the heart rate in a span of 6 to 8 weeks so that the left ventricular muscles increase in number to increase the stroke volume. This later on reduces the increase in heart rate, which is called cardiac fitness. Gym workout is called Training as it leads to slow & sustained changes in Physiology. This involves multiple endocrine glands to maintain the Homeostasis .For example…release of endorphins, growth hormone, antidiuretic hormone, aldosterone, prolactin etc. Thus initially the body looks at exercise as a stress leading to stress response which slowly gets converted to training effect.
Gym workout thus has a definite role in body build up & fitness. Yoga on other hand is an ancient science which has its roots from Pre Vedic period, Vedic period, Upanishadas & Bhagvatgeeta. It is compounded by Mahamuni Patanjali as Patanjal Sutras (196) about 500 years BC. He has called the Yogic Technique as Ashtang Yoga. This pathway of eight limbs namely Yama, Niyam, Asan, Pranayam, Pratyahar, Dharana, Dhyana & Samadhi teaches us to practice the discipline. This discipline is aimed at self-control of body, sense organs, mind & thought process. It proves an invaluable companion to face the changes & challenges of life.