As the song goes..."hold on loosely, but don't let go..."
..."if ya squeeze to tightly...you're gone loose contoooool!"
Loose hands, knees BENT, elbows OUT, pointer finger on brake lever. eyes FORWARD.
The moment before an impact or technical move, may tighten hands momentarily.
The looser your grip (within reason) means your blood circulation flows free.
When you grip tightly, your muscles in your forearm and hands will fill up with blood...
...if that blood dos not escape freely...you get soreness and "hand and arm pump".
Also known as "chronic exertional compartment syndrome (CECS)"
Motocross riders get "arm pump" so bad...they often get surgery, to remove the casing of the muscle.
I've even heard of surgery to move the tendons and veins to the outside of the muscle, so that the the pumped up muscle wont compress those veins.