Available in sizes 35-85 centimetres, these exercise balls are made of PVC plastic and are used for balance and control, in turn helping strengthen the overall body (in particular the core muscles).  Exercises can be as simple as sitting on the ball with an aim to stay centered, or to more advanced moves such as laying on your back in the ‘bridge’ or ‘rollover’ as seen in pictures above.  

Originally created by an Italian plastics manufacturer in 1963, the ball was later made famous by British physiotherapist Mary Quinton who was living in Switzerland – thus the creation of the ‘Swiss ball’.  They became popular with American physios, and can now be found at most gyms or online for as little as £3.30 each on Amazon.  The work-out can be challenging, but is wonderful at keeping your core in check (otherwise it can be a nasty drop!).