There are many similarities between Yoga and Pilates. Their origins are different, but the aim of both is to improve balance, strength and flexibility. While yoga sessions tend to work the whole body, pilates is more focused on the core muscles and your back, aiming to build core and spine strength. Pilates classes are often more structured than that of yoga.
Both yoga and pilates are lovely to do as stand alone activities, but are also great enhancements to your weekly activity or exercise routine. When combined with another exercise form, for example swimming, a session of pilates/yoga acts as a thorough and relaxing cool down for your muscles.