Muscular system
Yoga
It helps develop muscles evenly over the bone surface, thereby increasing flexibility. Yoga is also an energy efficient activity.
Exercise
Exercise usually focuses on increasing muscle mass. As a result, the length of the muscle shortens and flexibility decreases. When we exercise, we use a lot of energy.
The heart
Yoga
In yoga, once the asana has been attained, the body is relaxed and blood requirement is reduced. This relieves the stress on the heart.
Exercise
In exercise, the effect is the opposite. Ordinary exercise puts a strain on the muscles. This increases the speed of blood circulation and blood pressure, which in turn increases the workload on the heart as it needs to pump faster.
Respiratory system
Yoga
In yoga, the body is in a relaxed state, so the workload on the respiratory system is reduced.
Exercise
The constant movement in regular exercise increases the oxygen requirement in the muscles. This increases the speed of breathing, causing the lungs to work harder.
Immune system
Yoga
Yoga boosts the immune system by increasing the number and functioning ability of immune cells.
Exercise
While this is true for exercise as well, it usually depends on the nature, intensity and duration of exercise.
Stress levels
Yoga
Yoga reduces the cortisol levels in the body. Cortisol is a hormone produced from cholesterol that is linked with perceived stress.
Exercise
Exercise may actually increase cortisol levels in the body because the body perceives exercise as a stress.
Yoga also promotes better cognition through specific nostril breathing; this is absent in regular exercise. After yoga, the body experiences relaxation due to the soothing effect on the nervous system. Exercise leads to production of lactic acid, which may cause fatigue and exhaustion. Other benefits of yoga which are absent in exercise are an increased pain tolerance, control over impulsive behavior and resetting the biological rhythm. Overall, yoga provides most of the benefits of exercise and in addition, also improves subjective aspects such as peace, contentment and happiness.