Dan

There are a number of issues here and a couple of points not raised.

1) The head of the Z Slash is slightly smaller than the rest of Yonex range. This means that the string feels “tighter” because of the shortened string.

2) Playing with plastic shuttles is much harder than feather because of their flight characteristics. I describe the difference in hitting as stroking a feather and thumping a plastic. Generally players use incorrect speeds where blue is too slow and red tends to be too quick. Sadly there isn't an in-between speed. Slow shuttles can cause shoulder/arm injuries as the body compensates by trying to hit so much harder to clear to the rear court or smash. This is the area where I would be most cautious. If you can switch to feather shuttles then I'm sure you'd have a better game, albeit more expensive. Look at my video and article on testing shuttle speeds, as it will help you understand this critical subject.

3) As others have said, you need to understand whether your racquet was factory strung or custom strung. If factory strung, it wouldn't have been strung too tight so you should be fine playing with it. If it was custom strung then there is potential for an injury risk, especially if playing with plastic shuttles. Poor technique combined with high tension has caused many serious arm and shoulder injuries.

If you are going to continue playing with plastic shuttles I would suggest a maximum string tension of 19lbs because Z Slash does string up tighter because of the smaller head. If you know it was factory strung then leave it alone.

The other thing I would do in your shoes is have a few lessons to check you overhead technique. A couple of lessons now, before bad habits set in can reap huge rewards for you in the future.

Hope this helps.

Paul