Pilates, Yoga and back pain.

What is the difference between Pilates and Yoga, and why would you choose to take up one or the other?
Frequently either are recommended by physio’s or doctors for back pain and can be very beneficial under the right circumstances. Unfortunately both carry inherent risks, particularly for people with back issues, and Yoga tends to be less useful than Pilates in these circumstances.

Yoga
Yoga was developed in India hundreds of years ago to address a whole range of human issues, from the physical to the psychological. It would normally include a significant spiritual aspect as well as extreme body positioning, providing a 'whole body' (holistic) teaching and healing.
More recently popular Bikram and Ashtanga developments of this teaching include a dynamic approach, which can be difficult for less able (normal) people to handle.
Many Yoga teachings, including the Bikram and Ashtanga methods, aim to stretch the body as far as possible and to target the maximum range of movement through each joint. While this may be considered beneficial for a person with no history of joint pain or injury, it is not recommended from a bio-mechanical view. One reputable source recommended that only the under 25’s should be allowed into this type of yoga class.
I feel it is not developed from a physiology base, and not all positions nor movements would be recommended by up to date research into human physiology.
There are Yoga classes that focus on the spiritual elements and relaxation. These can be perfect if you are looking for stress relief or a meditation like class. The spiritual element actually enables some people to really connect their mind and body and gain a tangible benefit from this.

Pilates
Pilates is an exercise method developed by Joseph Pilates, an injured gymnast and body builder, in the 1920's. It was developed from exercises from all the programmes available at the time along with some innovation from Joseph P. This included Yoga and several fundamental Pilates exercises clearly come from this discipline. Joseph understood the need for “core strength” and this is the focus for most Pilates forms.
Whilst there are still trainers that teach “pure” Pilates (as Joseph would have done), other professionals have modified and developed the exercises ever since. There is no copyright on the word 'Pilates' so the content of classes can vary hugely.

Back Pain
Many of the Yoga movements are medically contra-indicated for the back (i.e. the risk of making matters worse, by doing the exercise, is greater than the likely benefit). Some of the Pilates movements are also contra-indicated for the back (mostly derived from Yoga movements).
For an example of a Yoga inspired Pilates exercise which can cause back pain we can take a bio-mechanical look at the ‘roll down’.
Yoga and Pilates both use the ‘roll down’, a movement from sitting to lying where the back curls round to allow vertebra by vertebra to reach the floor. The intention being to strengthen the abdominal muscles.
But what actually happens to your body when doing this?
The intervertebral disc space is opened which can aggravate or even cause bulging (herniation/slipped disc). A little like squeezing a jam donut until the jam pops out.
In fact not only the abdominal muscles but also the hip flexors, hold the body as it rolls down.
The shoulders curl forward shortening the pectoral muscle group and the mid trapezius lengthens.
For many people these muscles are either already tight (pectorals) or already long (mid trapezius) from daily repetitive movements such as computer work or driving. The hip flexors are frequently tight just from sitting down for too long.
It turns out that this exercise provides no real benefit but potentially compounds the postural issues that everyday life gives most of us. Worse still it can aggravate back pain and intervertebral disc issues, rather than helping.

My training as a back pain specialist made me question the validity of some of these exercises, particularly when clients have back problems (slipped or bulging vertebral discs, degeneration of facet joints or osteoporosis). My bio-mechanic training has encouraged me to question each exercise that I teach. What is the benefit? What is the risk? Why am I teaching it to this particular group? Is there a better way to gain the desired result? There should always be a clear answer to all these questions.
I have been teaching Pilates and Yoga, in various forms, for more than 20 years. Over the last 10 years I have developed “I move freely” Pilates as an exercise form that carries most of the Pilates benefits with few of the risks.
I Move Freely Pilates takes the principles of Pilates but integrates Bio Mechanic coaching techniques to offer an up to date way of keeping mobile, strong and with the optimum amount of flexibility. Mobility work is essential to keep the whole body moving easily.  I feel that mobility and balance are key skills that deteriorate with age but which with work can be improved reducing the risk of stiff joints and falls in old age.
The strengthening work uses the body's ability to statically contract or 'engage' a muscle as well as using controlled lengthening and contracting of specific muscle groups. It works on the muscles of the abdomen, buttocks (glutes) and back, many of which you can't see (most people don’t even know they have them), but which should perform functional roles of support throughout daily life.
  It is this functional supporting role that reduces back and other joint pain. Each exercise involves a very precise movement and often it is impossible for anyone else to 'see' how hard a person is working as the work is in 'engaging' a specific muscle.  This often leads people to do the exercises at a level below that of which they are capable and so they don't achieve the full benefit but feel they are 'stretching out' rather than 'working'.
Performed correctly Pilates can achieve great core stability and it is as useful to elite sportsmen and women as it is to the general public. 
This link (from my Norfolk Studio) explains more about stretching v working a muscle:
http://thestudionorfolk.wordpress.com/2013/08/12/are-you-stretching-or-working-your-muscles/

To Conclude
Most Yoga teachers have spent time in India studying and practicing so they are expert in their knowledge. Most Pilates instructors have studied the teachings of Joseph Pilates and have an in depth knowledge of the exercises and breathing techniques he espoused. However this does not make any of them experts in back pain management. They are unlikely to have had the training to working with particular conditions, such as arthritis, or liaising with physio’s as to the correct exercise programme for someone with a recently herniated (slipped) disc. For this you need a back pain specialist.
All forms of Pilates and Yoga can offer some people real benefits. To choose which would suit you best give some thought to what you hope to achieve and how your body will respond to the challenges of each class. Do try several before deciding which suits you and don’t be put off if your back aches after one class, try another – they are all different.
I also strongly recommend taking at least one consultation with a back pain trained exercise professional, since it is essential to know some basic information about how to perform Pilates exercises that is not usually covered in the class situation.