What are Asanas?
Asana is a Sanskrit word, which means the “Seat” or the “Posture.” As mentioned earlier, Aasanas constitute the “Eight Limbs of Yoga”. Asanas are around eighty four million in number.
Asanas are not mere physical exercises. Nor are they a collection of complex postures. So, what exactly are asanas?
In fact, asanas are a sublime blend of physical movements and mental drills, which inject vitality in the body and infuse tranquility in the mind. Asanas not only channel one’s energies, but also juxtapose these energies in such a way that they fortify one another to make the mind and body a strong single entity. This makes one stable, supple, composed, and strong.
In simple terms, asanas enable one to realize the stockpiles of strengths and abilities lying wasted in one’s veiled inner self. Asanas awaken the mind and activate the body. Thus, paving the way for a happy and healthy existence.
                         How Asanas help
"Asanas are a Tonic for Mental, Psychological, & Spiritual Health"
Asanas are integral part of yoga. The different postures that are practiced as asanas create a synchronizing harmony between the mind and the body. This harmony kicks off a lot of positive changes that helps one realize the real mirth of life. By continuous practice of asanas,the mind starts chopping its weighty feathers of anxiety, nervousness, restlessness, apprehension, anguish, fear, insecurity, doubt, ambiguity, and dilemma. And, gears itself up to make an unbridled flight in the open and fragrant skies of joy, confidence, hope, faith, contentment, and spiritual bliss.
In short, asanas smartly train the mind to get rid of all the negative thoughts and feelings, which have been clogging it and deterring it from thinking freely, rightly, and quickly. This is how asanas act like a tonic and improve the mental, psychological, and the spiritual health.
      Tonic for Physical Health
Asanas do a cleansing act for the body by wiping out all the toxic substances from it. If these toxic substances are allowed to flourish in the body, they wreak havoc on the body by giving birth to different diseases and ailments. This is where asanas come into play. Yoga emphasizes the fact that your body itself gives birth to various diseases. This happens when you do not have a strong immune system. The immune system acts like a wall that guards the body against various obnoxious germs, infections, viruses etc, which are attacking us all the time without our noticing it. The body becomes a breeding ground for different ailments and the diseases when this wall is in a dilapidated condition.
Asanas provide different techniques and measures that fortify the immune system. Furthermore, regular practice of asanas stimulates the nervous system and ameliorates the functioning of the kidneys, heart, liver, intestines, abdomen, joints etc. Asanas galvanize the various parts of the body. Apart from strengthening the muscles, asanas give flexibility, vigor, and endurance. This is how asanas act like a tonic and improve the physical health.
           Different Types of Asanas
There are whole host of asanas. They are generally categorized on the basis of the position taken while practicing the asana. Following are the positions different asanas can be categorized into:
Standing Asanas – The asanas that are practiced by taking standing positions are called Standing Asanas. These are by and large, the easy ones and equip one with flexibility, balance, and stability. So, a new student of yoga would be better off to start with the standing asanas. This will fine-tune one's body and enables one to move on to the tough asanas without much difficulty. Standing asanas are specially recommended for those who spend most of their time sitting. Such people can immensely benefit from the standing asanas as these asanas tend to improve the body posture. Tadasana, Vrikshasana, and Garudasana are some of the key standing asanas. 
Sitting Asanas – The asanas that are practiced by taking sitting positions are called Sitting Asanas. Sitting asanas relax the mind. Besides, they enhance concentration ability and meditation prowess. In all sitting asanas, one is required to sit erect, therefore, they strengthen the spine. They also help one breathe better by opening up the lungs and inflating the chest. Siddhasana, Padmasana, Sinhasana, and Vajrasana are some of the key sitting asanas. 
Supine Asanas – The asanas that are practiced by lying flat on the back are called Supine Asanas. This position enables one to feel relaxed and to wipe out the tardiness. These asanas freshen one up and activate the whole body. In most of the supine asanas, one is required to stretch one’s legs and the toes. This makes them supple. Uttanpadasana, Shavasana, and Halasana are some of the key supine asanas. 
Prone Asanas – The asanas that are practiced by lying prone or face down are called Prone Asanas.  This position is very beneficial for the abdominal muscles. It really tones up the abdomen as well as the pelvic region. Makarasana, Dhanurasana, and Bhujangasana are some of the key prone asanas.  
Inverted Asanas – The asanas that have one in an upside down position are called Inverted Asanas. In this upside down position, the course of gravitational force is on the head. This stimulates the blood supply towards the brain. This position also stamps out different toxic substances from the body. Besides, such asanas perk up the metabolism and invigorate the pituitary gland, lungs, and the kidneys. Shirshasana, Sarvagasana, and Adhomukha Vrikshasana are some of the key inverted asanas.