In today's world the term "yoga" has become a synonym for asana. Yoga is being propagated as a form of physical exercise or as a work-out technique. Asanas are thought of as just another kind of exercise routine. This culture is especially predominant in the Western world, but it is slowly creeping into other nations as well. However this is a gross misconception.  

Asana is only one the tip of the iceberg. the entirety of yoga can only be understood when we look into the depths of the ocean and discover the submerged part of the iceberg.

The term yoga means union and it signifies the union of the individual soul with the universal soul. The philosophy of yoga is based on the extensive work by Sage Patanjali called the Patanjala Yoga Sutras. The Yoga sutras contain 196 aphorisms on yoga which are all arranged in a scientifically structured manner.

In this exhaustive text on yoga Sage Patanjali describes the eight-fold path of yoga:

  1. Yama
  2. Niyama
  3. Asana
  4. Pranayama
  5. Pratyahara
  6. Dharana
  7. Dhyana
  8. Samadhi

Let's take a look at the differences between asanas and exercises:

Asana Exercise
Performing yogic asana is associated with physical,
mental and spiritual benefits. It increases
flexibility develops a sense of calmness and helps
achieve the ultimate goal of nirvana or salvation.
Physical exercises on the other hand only influence the
physical body and the mind. They are not known to
be associated with spirituality.
Asanas are complete and balanced. They work on the
whole body. All asanas are practised on both right
and left sides along with complementary postures.
These make sure that all the muscles of the body
are worked equally.
Exercises may be lopsided, working only on some
muscles and neglecting others.
Asana practice is slow and conscious and done with
breath awareness. The goal is to keep the mind at
the present moment by concentrating on the breath.
Exercises are fast and allow jerky movements.
Oftentimes the mind is wandering elsewhere
while the body slogs to burn those extra calories.
Research has found that asana practices actually
lead to reduced oxygen consumption. This implies
a parasympathetic dominance which helps calm
down the body and mind, thus relieving stress.
It leaves you feeling refreshed after a good
session of yoga.
Physical exercises lead to increased oxygen
consumption implying sympathetic dominance.
This actually causes exertion and leaves you
feeling tired after a workout.
The body’s physiology is altered so that there is
a reduced respiratory rate, heart rate and pulse
rate with continued asana practice.
Since exercise leads to sympathetic activation,
there is an increase in respiratory rate, heart
rate and pulse rate following a workout.
Normalization of muscle tone is achieved at the end
of a successful yoga session. This is the reason that
yoga is used as a therapy to treat musculoskeletal
disorders.
Exercise is associated with an increased muscle tone,
often leading to cramps.
The practice of asana is non-competitive and
process-oriented. It is important to focus on
the present moment and perform one’s duty without
expecting a result. This principle is called karma yoga.
Exercises are oftentimes competitive and goal-oriented.
Emphasis is given on the number of push-ups or squats
you complete rather than on the act of performing them
correctly.
During the practice of asanas, isometric contraction
of muscles occur. This means that the muscles contract
and muscle tension increases but the length of the
muscle doesn’t change.
During exercises, especially gym workouts isotonic
contraction of muscles occurs. The muscle fibres
either shorten or lengthen.
Perfection in asana is achieved when the practice becomes
effortless.
The Patanjali yoga sutras say:

प्रयत्नशैथिल्यानन्तसमापत्तिभ्याम्
(2.47)


“Letting go of the effort and uniting with the
infinite by contemplation on the soul”
In the practice of exercise, more vigorous efforts
are required as practice progresses.