Ask any serious triathlete what his resting heart rate is, chances are you won't have to wait long for an answer. Likewise, ask a marathoner about her average mile time and the answer will generally come forthwith, and accurate to the hundredth of a second.
And if you're talking tennis, it's all about the NTRP rating.
The USTA's National Tennis Rating Program (NTRP) is the official system for determining the levels of competition for all players. At first, a… Continue