Hello all, I have been a long time lurker and have finally decided to join. I am 19 and have been training for about 2.5 years. I started with strong lifts 5x5, then mad cow, and now on a version of 531. As you can tell from my training history my focus was on getting stronger and bigger in general. I went from 120 to 183 and in the last 3 weeks I have cut down to 173. I am trying to get to roughly 10% body fat and then I'll lean bulk for a while. I am doing a bodybuilding version of 531, with the big lifts for strength, FSL, and then 3-4 bodybuilding focused exercises. For reference, SQ: 335, BP: 185, DL: 445.
Now to get to the core weakness. When I was doing strong lifts and mad cow I just assumed I had a pretty strong core because I could squat and deadlift into the 300s, therefore my core must be strong. However once I switched to a bodybuilding type program I realized this did not seem to be true. The problem is my core and kind of my whole body will shake during certain exercises. For example a tricep pulldown from a high cable. I am fine on the concentric, but on the eccentric when the bar is going back up I kind of shake. I tried to target this by doing planks because I figured I needed to work on core stability. I have worked up to 3 45s or 135 lbs on my back for 20-30 seconds. This has almost solved the problem on the tricep pulldown. However today I was using a crunch machine (had to for a class for school) and on the eccentric I was shaking a ton. The machine is sitting upright and you grab handles and pull down and back up, repeat. My theory is my core is pretty strong when it comes to contracting but it struggles with stability during eccentric movements.
I am not sure what core muscle is causing this weakness or what exercises to do to target it. Or if I am just not bracing my core correctly. I do not think its a bracing problem because I am used to doing this on the squat and deadlift. Any help is greatly appreciated and if you need a better explanation of what is going on let me know, I tried to explain it the best I could but its not the easiest thing to convey.