Flexibility plays a large part in increasing your range of motion (ROM), which leads to a longer and more efficient stroke. Having flexible muscles and joints also not only makes you more powerful (stronger and faster movements), but also helps to prevent injury.
If you have the opportunity, take some Pilates or yoga classes. If not, I’d definitely advocate stretching whenever you get a chance, especially after a workout or even after a shower.
See: http://www.brianmac.co.uk/articles/scni8a1.htm for more
Lower back flexibility and conditioning:
Shoulder mobility and conditioning:
PNF stretching:Proprioceptive Neuromuscular Facilitation (PNF) involves the use of muscle contraction before the stretch in an attempt to achieve maximum muscle relaxation. You move into the stretch position so that you feel the stretch sensation
Your partner holds the limb in this stretched position
You then push against your partner by contracting the antagonistic muscles for 6 to 10 seconds and then relax. During the contraction, your partner aims to resist any movement of the limb.
Your partner then moves the limb further into the stretch until you feel the stretch sensation
Go back to 2. (Repeat this procedure 3 or 4 times before the stretch is released.)