Previously I was studying for a major exam and I abstained from tennis for about two months. When I returned however I find that my performance would fall after like ten to twenty minutes of hitting. The problem is that I feel weaker now when wielding my racquet after a while and can feel the lactic buildup in my wrist. It is as if the racquet is now too heavy for me. And when I try compensating this 'weakness' by increasing my swingspeed, I start swinging out or shanking. Is there any way to get back the strength that I've lost? What exercises are recommended? My racquet isn't heavy at all, at 11oz and its frustrating that my level of play drops after a while.