ranathari

Depends on where you're getting the pins and needles (paraesthesiae is the technical name). If it's present throughout your entire hand then it's probably an excessively tight grip on the bars or excessive vibration from one of the things other people have suggested above. If you're getting it only in specific fingers and/or specific parts of your fingers and hand then it could well be an underlying nerve compression/entrapment and seeing your GP for a referral onto the orthopaedic surgeons will be more helpful (or post a more specific description of where the paraesthesiae are in here).