24m, travel daily 3hours n give badminton coaching after that.mid left of back suddenly got stiff like muscle pain can't move left right freely.

Muscular injury: You need an evaluation. You need to keep in muscular shape with a back exercise program to strengthen your back muscles. This will protect this. Your evaluation will see if it is more than muscle. Since you have had a knee ACL you need to be checked for hypermobility - Ehlers Danlos which can put you at risk. Your physician may have you see a rheumatologist