Measures Performance. Using a coding sheet2, each observation (service game) was coded on the following parameters: (1) first-serve (number of valid first-serves performed); (2) double-faults (number of double-faults); (3) performance efficacy (number of points won in the service game); (4) success (if the athlete won vs lost the service-game). Because, in tennis, each service game is composed by a flexible number of points, the first three scores mentioned above were transformed into percentages.