Here is a good tip to tenderise meat. Soak in vinegar over night.
If you add a small amount of vinegar when cooking older beef or chicken to make the meat tender and give it a delicious flavor. You can buy all sorts of white wine, red wine vinegar that add a wonderful flavor to meat. I always add about an egg cup full to all my meat dishes.
Tough meat can also be tenderised by marinating with vinegar or pineapple juice for several hours. The marinade must be washed off to get the taste away though.