Attilio Anthony John Wagstaffe
hold for ten seconds while tensing the muscle (Isometrics) and release..
I had better results when I switched to 2 seconds of active strecting, followed by 1 second of release - repeated much more reps. Try it yourself, do 1 side the 10 second way, and the other side the 2 second way. YMMV (but my bet is on the 2 second method)