I am trying to improve my deadlifts. One trouble area is the bottom of the deadlift when I just pick up the barbell and my back wants to round--though I resist that. I want to figure out what muscle/muscle group it is that works at the bottom of the deadlift to stabilize the back and prevent it from rounding? I want to find exercises to strengthen those muscles.
There's a lot of them. At first blush, you have the erector spinea muscles which you can imagine like a bundle of angel hair pasta running along the sides of your vertebrae.
Collectively, everything from your posterior deltoids to your heels is affectionately known as your posterior chain, because like a chain any given single link is irrelevant unless it can rely on its neighboring link to be steadfast.
Specifically answering this in your question:
I want to figure out what muscle/muscle group it is that works at the bottom of the deadlift to stabilize the back and prevent it from rounding? I want to find exercises to strengthen those muscles.
This answer can vary for a lot of people depending on their body dimensions, level of training, and deadlift form. Longer femurs, a bar too far away from your shins, and a gym career of out-of-balance broscience lifting will cause a very different set of challenges than someone who's been attacking the problem directly and following a solid strength training program for some time.
Some key pointers I would give anyone for deadlifting:
- Keep your chest up. Don't drop your hips. If your chest is up, your back is probably plenty flat.
- Use the Valsalva technique. Hold a bunch of air in your lungs, and tighten your abdominals like you're readying for a sucker punch to the gut. This isn't going to increase your strength, but it will increase your safety and cause you to have a strong brace up front.
- Focus on engaging your abs. If you're doing it right, your abs will be a smidge sore after deadlifting, in the beginning at least.
- Try to "screw" your feet into the floor. Don't let your feet move, but apply force like you're trying to rotate your toes outward while keeping your heels planted. This will cause your glutes to engage in a serious way.
- Tight abs. Tighter.
First and foremost ensure that you are using the proper lifting techniques. This means you should be able to lift in slow, controlled movements as opposed to jerky and unstable movements. If your new to lifting, you may see lifters who are capable of working out with 85% of their 1RM and you may struggle with 85%. Keep in mind that they may have been doing it a long while and that they have conditioned their antagonist, synergists, and fixators muscles to be able to control the weight better. This is essential to preventing injury.
The deadlift involves many muscles and stabilizers, so the answer to your question likewise involves may different muscles but often there are lifting techniques that will help as well. This is a great site for information on proper techniques for deadlift.
One technique to avoid rounding is to simply take a wider stance. This will naturally make your back want to be less rounded. I am not suggesting the sumo stance, although you can try this and see how it feels. I am suggesting to try a stance that places your feet slightly wider than your shoulders.
Another technique is to incorporate 'pause Deadlifts' into your workouts. See illustration:
Pick up your weight just a few inches off the ground and pause for a few seconds. This will have the effect of forcing your body to be in the right position and help strengthen your supporting muscles (the Synergists and Fixators) and thereby help you maintain proper form as you progress in weight, but don't do these with a lot of weight.
Lastly, if you increase the strength and flexibility hamstrings, along with the all the other muscles involved, this will improve your control over your form. See Deadlift anatomy illistration: [ Also the antagonist muscles are helpful in controlling the weight as you come back down. If you struggle with maintaining proper form and controlling the weight coming down then also consider strengthening the antagonists.
More on proper lifting techniques: