When Charles Barkley, Shaquille O'Neal, Ernie Johnson, and Kenny Smith tried some goat yoga moves during "Inside the NBA," the results were hilarious.

Although we did worry a bit when, just to get his goat, the 325-pound Shaq climbed on Barkley's back. That's a yoga pose that could crack vertebrae or tear a muscle.

And it turns out that for people who have osteoporosis (brittle bone disease) or osteopenia (low bone mass) — as more than 54 million Americans do — certain yoga poses are risky business.

A Mayo Clinic study looked at 89 patients with vulnerable bones who did yoga and had painful injuries. The patients attributed their woes to 12 poses that had strained their back, neck, shoulder, hip, knee, or a combination.

Diagnosed injuries ranged from overuse problems to aggravation of arthritis pain, compression fractures, and changes in the proper positioning of vertebrae in the neck and spine.

The researchers' conclusion: If you have osteoporosis or osteopenia, it's smart to avoid positions with extreme spinal flexion and extension because they put you at risk for compression fractures or deformities.   

So if you have either of those conditions, say goodbye to the downward dog and check out the Cleveland Clinic's "Two Minute Chair Yoga" and “Destress Monday's Two-Part Chair Yoga” instructions (21 minutes total) on YouTube.

You can do movements and poses that strengthen, lengthen, and stretch major muscle groups and joints without risking injury.

The researchers noted that people who modified their yoga practice gained relief from their discomfort.