Yoga is an excellent form of exercise but it should be approached with caution by persons with osteoporosis or low bone mass. Although back alignment is usually emphasized, there are many forward-bending, twisting and side-bending postures that should be avoided or at least performed with an elongated spine under the supervision of a skilled teacher.
Everyone should be encouraged to follow the above principles and focus on self-progress, slowly, rather than ‘keeping’ up with their neighbour!