This simple and inexpensive piece of plastic does an excellent job preventing forearm ache on long rides. It’s known as a crampbuster, named after the company that came up with this idea, but also goes by other names like “throttle assist”. Some even call it “manual cruise control”.
I have one of these wrapped around the throttles of all my motorcycles. With this on I need to simply place my right hand on the throttle and rest the base of my palm on the protruding plastic. There is no need to grip the throttle at all. Acceleration and deceleration is done with the base of the palm.
The way the human brain works, if the right hand is gripping something tight, the left hand involuntarily starts gripping as well. So on a day long ride you end up with aching forearms due to constantly gripping the handlebar. This simple piece of plastic prevents that.
There is another important advantage which isn’t obvious when you look at this piece of plastic. Since my hand rests on the throttle I can uncurl my fingers and rest them on the front brake lever. By doing that I can react faster to any emergency situation and squeeze my front brake the instant I decide to. If my fingers were wrapped around the throttle, it would take me some time to straighten them out, wrap them around the brake lever and squeeze. I know that’s just a fraction of a second. But depending on the speed I am riding, a fraction of a second could cut down my stopping distance by a few meters. Sometimes a fraction of a second is all that separates a crash from a near miss.