Hi pyralless

It is a bit risky trying to diagnose the problem over the net and it really needs both a full history being taken and a proper physical examination of the elbow and arm. Therefore I wouldn't be game to give you exercises as they may do you no good if I get the problem wrong

Possibly you have developed some type of insertion injury of the biceps or brachialis tendons - that may account for the pain on suddenly taking the weight, the pain on full extension of the elbow, the tightness of the muscle and the tenderness close to the radioulnar joint.

Why don't you go to a good sports physio in your area and get it properly looked at. You may be eligible for ACC particular if there was an incident at your sport - in which case in won't cost you that much. It would be good to get specific, accurate advice on how to manage it.