I recently started practicing martial arts (Kung Fu) and while I realise that technique, posture and balance will all improve with time my kicks are suffering from something and I think I will have to do something beyond regular practice to improve.

When I lift my leg to perform the waist-high kicks in Tan Tui I have no chance of reaching high enough while keeping my leg straight. If I keep my leg straight I can barely get it 5" off the ground.

At that point, there is a stretch in my upper gastrocnemius (or lower hamstring, I feel it in tendons at the back of the knee joint) and I feel tension rather high up in my front thigh. I can hold the position for probably 3-5 seconds before my leg starts shaking.

Now I suspect I need to work on both flexibility in my calves and strength in my thighs, does this sound right? And, is there anyone out there who have overcome this problem who can share some strength/exercise routine that worked?

Thanks!