Evenin' All!
Right so MBTs. MBT Website (Masai Barefoot Technology) They are shoes/trainers which increase the muscle activity in your, buttock, rear thigh, lower limb and abdominal muscles whilst reducing stress and impact on your knees and hips.
They can help with hip, leg, knee and back problems by improving your posture and the knock on effect is that the improved posture pulls the rest of your body into line and tones the muscles.
I got some as I was walking in excess of 5 miles a day and as I already had hip and knee problems plus residual problems from SPD, the constant impact was causing quite a lot of pain.
They definitely worked for me. My posture definitely improved, my tum muscles were flatter and tighter and my legs were much more toned.
Be warned though, they are expensive and you have to be fitted for them by a trained fitter who then teaches you how to walk in them as its quite different from walking in normal shoes or trainers.
You can only wear them for 10-15 mintues at a time a first as well, as they really do tax the muscles and you will hurt like hell if you wear them for longer. The upside of this is that you know you haven't wasted your money and they are actually working!
They used to be really really ugly, but have one or two styles that are bearable now.
I had to stop wearing mine in the third trimester cos I couldn't lace them up anymore! 
I'm thinking I will start of with just 10 minutes a day again as my muscles have lost the plot since then.
I think I will probably get some Chapa Caviar Black sports shoes as they are fairly plain and won't stand out under my black joggers. I had a pale pair last time and they are absolutely wrecked now.
DS2 has been a nightmare today, swap your 2 year old tantrums for a great hulking nearly 5 year olds tantrums, including stamping, growling, screaming and punching Mummy!