Forced Exercise At Work

I work for a large athletic corporation located in MA. Recently they have adapted a new fitness program/regimen that are rolling out to the public, which is rather intense. Last week they sent out a company wide email stating that they are holding a 4 hour event next week where we are all (roughly 1,000 employees) "encouraged and EXPECTED" to partake in the exercise regimen. It should also be noted that the hours of this event are from 2-6PM, when the normal work day ends at 5PM. Since sending out the initial email they have followed it up with a daily "reminder" email basically demanding that we all go online and register for the event.Throughout the company many of the workers in various departments have been approached by their supervisors/management to let us all privately know that attendance and participation in the physical regimen is expected.While I am sure they have been careful by electing to use the word "encouraged", it would appear as though "expected" means mandatory. Many workers are greatly upset by this demand and have taken to posting on the company intranet. The company responded and basically said "tuff", you are expected to attend and participate. In the company wide email it does say that if you have a medical condition you do not have to participate but are still expected to attend and "encourage" your co-workers. Many people don't feel this is right because you will be made to feel awkward and uncomfortable if you don't participate. To sum it all up, I am wondering if it is legal that a company can require its employees to participate in a physical exercise activity. Not only does this feel like harassment but it doesn't seem like this is a reasonable "request".