NFL Star James Harrison -- Bangs Out Push Ups ... With 300 lb. Man On His Back!!

Age means NOTHING to James Harrison -- especially when it comes to brute strength -- 'cause the Steelers linebacker just knocked out a set of push-ups with a 304 lb. lineman on his back!!The 36-year-old superstar -- one of the oldest guys in the NFL…

Lokelani McMichael Lori Heuring Lorri Bagley Lucy Liu