see i think i was gripping with my legs as well as i have rubbed the inside of my leg sore on the seatstay!!
also remember getting a bit of pain in my leading foot/leg too!!
Thats not what Inzane means (well i don't think it is), as a flat pedal rider, when i am going downhill over anything bumpy or rocky my feet have the heels dropped and my legs bent and loose but not so loose that they aren't supporting the bulk of my body which relieves the preesure on your arms. Its also good to swap your leading foot about so that the back of your legs don't to knackered. Also as others have mentioned move your brakes inboard so that your braking finger lines up with the hook on your lever when your hand is holding onto the bars so its a nice straight line through your arm. And that the angle of the lever is in line with your hand up through your wrist to your shoulder so that the back of your hand and wrist aren't strained either way when at rest on the lever. Grips are a personal thing, i like the ruffian as its skinny and very grippy but some prefer a chunkier grip.
hope that helps oh and relax being relaxed always helps, singing a song helps 🙂