They do absolutely destroy me, both in terms of cardio and the muscle itself. No exercise kicks my ass more.
I don't wear any shoes when I workout (home gym), so my foot usually stays on the bench; when I wear footwear it tends to slide off more. Sometimes I fall off at the very bottom of the ROM when I lean forward a little too much.
On a tangent, if you want it to kick your ass and don't mind feeling it the next day, elevate the working foot.
I've found that a good way to stay stable is to find an adjustable bench and lay the foot of your supporting leg in the gap of the bench pad. It keeps it from sliding about. But yes, these suckass. Nothing thrashes my quads worse, not even front squats. It just takes time.
When I started doing them about a half year ago I was using bodyweight and had to put my hands down on the decent to keep from falling on my ass, but now I can do them for sets of 8-10 reps with 50lb dumbells. I love them after deads because they stretch out the hip flexors.
I'm doing 30 lbs in each hand for 4 sets of 10-12 and they certainly make it hard to walk normally over to the fountain afterwards. At first I had some trouble keeping balance with my back foot but I would recommend keeping the laces of the foot on the end of the bench as opposed to trying to balance the toe on the bench.
And make sure that your working leg is far enough from the bench so that part of the equation isn't throwing off your balance. And don't give up on em . . . . they are too damn good!
They definitly own me too. There have been two or three times after sets that I got so lightheaded I had to sit down. I will also echo the statement that the more you do them, the better you get at them, I try to take a really wide split and lay the top of my back foot on the bench.
I also try to press up and back, rather then letting my knee get forward, I found that takes away the tempatation to push off the bench with the back leg. I'm still pretty weak at these, but am getting better. I've done 70# dumbells for sets of 8, but that's barely 1/3 of my max back squat. Do others seem to have similar ratios?
It just takes practice to get your balance. If you are wearing shoes, try to become aware of and feel the top of your foot on the bench. If you practices a couple times without weight, you will come to the right foot placement.
After you get comfortable try using a barbell on your back. This will really work the entire body, especially the core, as it throws a higher leverage and balance point at the body. For safety sake, do it in a squat rack or power cage, just in case you lose your balance and need to dump the load. It is a real nut buster.
JTrin, I too find a similar ratio. I can do 100's for sets of ten, again not 1/3 of my max back squat. I really put a premium on my knee not going forward at all, focus on sitting down and back and lessening the knee joint angle of the supporting leg. DigiAir, that's really impressive at a BW of 160. Congrats.