1. in tennis, u lock your wrist (except when serving and overhead 開波及高扣), if u let it loose, the ball would lack power and speed. if u drive your wrist for power, u can easily injure them SERIOUSLY.
in badminton, u flex the wirst, the more flex the faster u can hit.
That's why i don't play badminton regularly, mixing them up can lead to an accident...
2. in my opinion, badminton requires faster movement, not very suitable for elderly (at least for competition). u need to go back and front really fast, the knees hurt !
in tennis, u need to cover a bigger area, but u have relatively more time to do that, and it can be easy if u have good footwork and your partner isn't that accurate (aiming for the lines all the time).
3. the court surface is an issue in tennis, not so much for
indoor badm. courts i guess.
In Common:
People spend a lot of $$$ on their rackets and string.
(i guess : )
Also, $$$ goes into the balls and badmintons (don't remember how they call a badm.)
Can injure your knees, ankles and elbow if u don't warm up and condition your body well.