If you allow TennisKeeper to access data from the Health app, with your permission, TennisKeeper will read your entries for Steps, Walking + Running Distance and Heart Rate if such data exist. TennisKeeper will aggregate and correlate those data back to your tennis activities so that you can understand your stats (e.g. your footwork on the court) when you are playing a tennis match.
Your health data will not be passed on to any servers, third parties or used for any marketing or promotional purposes. The data is only used by TennisKeeper to provide the functionality outlined above.