How many classes a day? And what style? Certain styles of yoga might put a bit more strain on the musculoskeletal system, but generally speaking doing an hour of such exercise daily should not lead to overtraining.
He/she is also not doing a single repetitive activity, but varying the stresses with different disciplines. And each of these activities has similar, but unique movement patterns and benefits.
The only thing I would say is that it is important understand that although these practices are not (usually, though I’ve seen yoga done with impact) low impact, they are not going to be the same as a low impact cardio workout. Tai chi, perhaps… I am less familiar with that. But even power yoga is not going to give the same benefits as walking, or biking etc. So it might be helpful to them as they are getting the flexibility, balance, core training, etc, they might want to consider adding some cardio work, if is possible for them.
And it is fine to have a regular day off, to recharge if they start to feel overtrained. No schedule has to be set in stone forever.
I agree with Ariadne. Yoga may seem gentle, but as with any exercise, you can always overdo it. If you do not allow your muscles to recover between workouts, or if you conduct marathon-worthy yoga sessions, your body may cry out for help. Overtraining syndrome comes from exercising too much and is not to be taken lightly; it increases your risk of injury, lowers immune system capability and can even cause depression. If you feel severely run down, consult a physician for proper treatment.
Hope this helps
No matter what she should take 1 day off each week with ZERO exercise. Even if her classes are low impact the body needs rest. The other factors that determine if she needs to take more then 1 day off per week are her age, her job, possible injuries, how many classes she takes per day, etc. Lots of factors here. Some people become addicted to exercise but there are certainly worse addictions! So, for the moment I suggest 1 day off per week no matter what. I don’t want to see her burn out and quit.
Best of luck!
Coach John Kane CPT