Not so much a fitness trend but a business trend. At some point in time, personal training studios were all but crowded out by large gyms with a staff of ‘personal trainers’. While some of those trainers were very good, many were novices and more interested in selling than conducting personal training.
I have recently seen a greater number of personal training studios popping up, also in places where there has to be substantial cost for leasing space. While some of them are specialty studio for Pilates, yoga and Gyrotonics, some are more of the traditional type.