The other trainers will probably come in to give you a few ideas.
A couple of areas you can look at are:
1. Try to release your grip over the jumps and take a breath as well.
2. Check your grips and make sure they are not too thick, you may need to try a few different ones to find what is best.
3. If you use your index finger for the clutch try to use your middle finger instead.
4. Check the vibration on your bike especially at the handlebars, if it is excessive you can fill the bars with a product to lessen the vibration.
5. Make sure the bars and levers are adjusted properly for you.
6. A bump in your seat and some grip tape will help you use your legs and not your arms/hands to hold on.
Let us know how you do.
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Alan Gerkey MXTrainer
http://www.MXTRAINER.comRacer Development Program