There are indeed "downsides" to Tai Chi, none for Classical Tai Chi

                    On the "outside looking in"...

          A "Downside to Tai Chi? None That I See"...Not

from the NY Times article of September 27, 2010 by Jane Brody

I think that research on Classical Tai Chi is on the "outside looking in" but one day things will change from the seeds planted here, and it will be on the "inside looking out".  Nowdays  I do not see a downside to Classical Tai Chi, on the other hand there are indeed plenty of downsides to Tai Chi per se:

In the Times article and stating: "It places minimal stress on joints and muscles and thus is far less likely than other forms of exercise to cause muscle soreness or injury."  

This is simply not true, wherein 98% of Tai Chi that is taught will indeed put stress on joints, particularly the knee joints and will indeed cause muscle soreness or injury.  External Tai Chi of these varieties does little to insure that there is no shear force directed toward knees/hips, etc.

The Times article states: "There is no “fake” version that could serve as a proper control to be tested against the real thing". I agree in principle just not with the "principals" used in the studies.  It is indeed true however that it is virtually impossible to design an ideal study of tai chi but not for the reasons of the Times article.  It is because there have been no studies of Classical Tai Chi which uses internal discipline, only of external styles of Tai Chi.  A study of Classical Tai Chi which used external Tai Chi as a control group would show the true "fake". 

I'll let you read the rest of the article:  Downside?

Also, do a search of "Uncovering the Treasure" at Amazon, you can search through the "Look inside" feature for such things as "shear force", "knees", etc.