The interesting video attached below gives some of the latest findings on how Yoga is so beneficial.

http://upliftconnect.com/watch-science-behind-yoga/

1 - The physical postures work the body to improve how it functions.  These can be modified for anyone.  They can be done lying down or sitting in a chair.  Poses strengthen and create space in the body so energy can flow (oxygen, heat, synovial fluid, glucose etc plus information through nerves, hormones etc  which brings health).


2 - Breath is slowed down and breath capacity is increased, which affects the parasympathetic nervous system, reduces blood pressure and changes our response to stress.


So working with attention to the breath we reduce stress and then, when challenge is introduced in the form of poses, we use our breath control and our focussed mind to deal with the challenge in our practice and continue to pay attention to this in our everyday lives.


90% of illness is stress related.  15 minutes yoga daily over 6 weeks was effective in trials to significantly reduce the anxiety and depression felt by participants and to increase their positive experiences.  By focussing attention you change brain activity and structure.  Even gene activity like our immune response is changed.  


Yoga develops our mind body awareness, which helps us move through mental and emotional blockages, transforms our relationships with others and our environment and gives us a clearer sense of ourselves and our purpose.

We should try to practise so that every visit to the mat is a ritual revision of living mindfully. 
Whatever state of mind we are in and no matter how tough it was to drag ourselves to practise, try to be really present.  
Whether you are energised and wanting to go straight into some fast sun salutations and standing poses or exhausted and needing 'savasana', take a moment to make the transition to the time you have set aside.
Notice your mind/emotions and how chaotic or sluggish your thoughts are.
Notice your body, the tension you might feel and where it is.
Notice your breath, how fast it is and where in your body you notice it.
Observe yourself in whatever position you are in, earth below supporting, space above and around.
Set an intention for your practice in that moment of observing, just being aware of who might benefit from a calmer or stronger you, just telling yourself that 'you are enough' or holding in your mind something that you want for someone you care for or those you empathise with.
When you start to move, notice what movements your body wants and how.  Don't impose a pace of action or breath on the body, let it emerge.  If you notice you are holding your breath, try to focus particularly on that, so that it keeps flowing.  Holding breath will inevitably mean holding tension and that should be done as and when you want and not unconsciously.
In any new position be aware again of your points of contact with the earth.  Build the pose up from the earth.
Be aware of the sky above you and sense the space all around you.
As you feel the breath entering and leaving the body, notice the expansion and contraction and the way we draw energy to the core of our being from our connection with our breath.

We breathe in ‘prana’ (life force) and are aware of it penetrating us and every atom of the space around us and through our moving meditation we feel one with our universe.  We connect to the energy that moves within and without ourselves and practise without strain or force.  By listening to and observing our bodies and taking sustenance from the air we breathe, expanding in to the space around us, we move uninhibitedly, joyfully.  

We come to a yoga class to work and to be guided through the poses because there is a supportive environment and we will be able to focus on a voice or a demonstration telling us what to do.  In our own practice, we may find that despite making a mindful transition to our poses, our mind wanders.  So we continue to bring it gently back to awareness of the breath, of the instructions that we give the body to be balanced evenly on both feet or sitting bones, to keep knees or elbows soft, to lengthen through the crown, engage the belly and pelvic floor on the outbreath etc.

If we continually, without judgement, bring the mind back to the job in hand of being present in the pose, we are developing this ability to mindfully focus in all areas of our life.  Through constantly feeling the duality - inbreath/outbreath, earth/sky, left/right, up/down, open/close, front/back, tension/release, active/passive, give/take, it begins to inform everything we do and we become our own teacher.  We confidently develop the ability to respond to conditions as they arise.  Every queue could be a ‘tadasana - mountain pose', every sitting - a ‘dandasana - staff pose’, until every short moment becomes its own practice and through our yoga practice we learn how to respond in every moment. ​

Lie on your back and support the knees with a bolster if that is more comfortable for the back.
Notice where the back of the body is supported by the ground and let yourself relax into those points of contact.
Then be aware of the front of the body and where you are in contact with clothes or air and consciously relax related muscles.
Having brought the mind to an awareness of the body start to observe the breath.
Observe where in the body you feel the breath, at the nostrils, in the belly, in the chest, or maybe as a whole openness and expansion of the body at the inhalation and a deeper relaxation of the body on the exhalation.
Observe whether the breath starts to slow down as you relax and bring attention to it.
Observe whether the inbreath and outbreath are the same length.  In a state of relaxation and in an ideal state for our practise and normal activities, the in and out breath will be long and fine, opening and relaxing as much as possible as many muscles as possible.  Slow diaphragmatic breathing will calm the mind and reactivate the parasympathetic nervous system.
Start guiding the breath - relax the belly completely and allow the inbreath to fill the belly and gently on the outbreath allow the belly to draw towards the spine and the pelvic floor and perineum to draw upwards, to fully squeeze the air out.
Next, relax totally on the inhalation and allow the breath to fill the belly and also continue up to the floating ribs and upper side ribs.  Actively squeeze the side ribs in, draw the front ribs down and draw the belly towards the spine and pelvic floor and perineum upwards.
Breathe like this for a couple more breaths.
Next breath, relax totally and allow the breath to fill the belly, the ribs and continue up until the collarbones and the upper chest and shoulder blades feel like they are filled with breath.
As you exhale allow the chest to drop, the ribs to draw in and down, the belly to draw towards the spine and the perineum and pelvic floor to draw upwards.
This is a full yogic breath.  Continue doing this while counting.  Inhale one, two, three to the belly, one, two, three to the ribs, one, two, three to the chest and exhale from the chest one, two, three from the floating ribs and front ribs one, two, three and from the belly one, two, three.
Make sure the tension isn't creeping into any part of the body as you breathe slowly in and out paying attention to the specific parts of the body where you are inviting the breath.
If possible increase this count to 4 for each part.  Once you have found your ultimate capacity, continue to allow the breath to flow in and out in this way, relaxing and engaging the appropriate muscles, without counting, but just focusing on the path of the breath.
Introduce ujjayi breath - slightly constrict the throat so that the sound is as if you were steaming up a mirror while still breathing through the nose.  This has various benefits. It has an effect of slowing down the breath further, of keeping the inhalation and the exhalation of equal length, and of making you more aware of your breath, so that as you practice you will notice if you are straining, holding onto the breath, or panting.  
Next we will do some exercises in a semisupine position in order to work on keeping the breath full like this as we introduce movement.