Bikers this is a good piece of advice - worth a read.

A commonly asked question amongst riders is "How often should I perform rear observations when riding?"

Lifesavers should be done whenever necessary.  When turning right always look over your right shoulder.  You must have a clear picture of what is going on behind you.  Remember rear observations include using lifesavers to get a view of your blind spots (areas not visible in your mirrors).  A common mistake is performing a life-saver without knowing what you are looking for.  You should perform rear observations:
Every 5 or 6 seconds (mirrors) to get a view of traffic following you.
Before you change speed  (e.g. going from a 30 mph limit to a National)
Before you change direction (e.g. turning left or right).
Before you stop or pull over except when performing an emergency stop.
Before you change position in the road (e.g. moving into the centre when approach a junction, to improve your visibility).

The above is as recomended and reported by:
http://www.motorcycle-training.f2s.com/faq.html#observation

The lifesaver causes stress to the muscles of the neck and shoulder regions. This muscle stress in turn causes restrictions in the ability to comfortably carry out the lifesaver which in turn results in a reluctance to use this vital manouvre. Here at ITS we have treated many motor cyclists for this problem. In the main, a series of 3 or 4 neck and shoulder massages can relax  tight muscles in order to help release muscular tension that otherwise often prohibits this essential motorcyclists' action.

Senior Holistic Massage Therapist at ITS, Janet Aldridge says " the older rider should definately own up to their age and have this problem addressed - after all it is not called lifesaver for no good reason and as for younger riders, well, it is easier to maintain supple muscles than unlocking hurt and painful stuck ones later on, so seek a treatment 2 or 3 times a year as a preventative measure"

Those are surely wise words from Janet - Janet has had considerable success with treating this problem so instead of suffering and maybe not using the lifesaver, in Essex at least, expert help is at hand to get treatment and it may just save your life!