Thinking of getting a massage soon and wonder if the enthusiasm of the person giving the message is effective by how heavy/overweight the client is???

All that matters to me is that you behave like a gentleman. Arrive clean or in the event you are coming from a job at which you tend to get dirty &/or sweaty or have a long drive, please be willing to hop in the shower upon arrival.  

In either of those events,  yes I would say enthusiasm may be lacking.