Yoga Sutra 2.46

Sthira Sukham Asanam

The body at ease is asana. Being at ease is the root of yoga.

Yoga Sutra 2.46

There's a tendency of over-stretching and more of an emphasis on flexibility than ease in most classes. The over-stretching can cause repetitive use injuries over time. Might not hurt today but repeating a pose over and over with incorrect alignment through time will. "We have suffering if we don't honor our bodies natural movement. Trust in the body's natural wisdom rather than what your mind tells you."-- JL