I think I've confirmed it. After getting a lower back injury a while ago and continuing to do my squats and deadlifts through the pain, I took the last week off because I believed my muscles needed the recovery time. I go back to squatting today and the pain returns almost instantly. I reached 185 lbs on my warmup before calling it quits. I think it's a spinal injury and the limited research I've done indicates that it will take weeks, maybe months to heal properly.
I am devastated right now, especially for having to say the phrase "substitute for squats" as I am one of those who believes in no substitute. But I had made a respectable amount of progress using StrongLifts 5x5. Now, all but one of the exercises on that program is off limits to me. My working weight for both squats and deadlifts was supposed to be 215 lbs a couple of weeks ago. My working weight for Pendlay rows was supposed to be 120 lbs. I've managed to continue my overhead press and I'm working at 110 lbs. My working weight for bench press is 160 lbs. All these exercises put significant stress on the lower back except bench press, so this injury has pretty much brought my StrongLifts routine to an end.
As it were, I was about to start a cut in which I just maintain my strength while losing fat. While I would normally be open to less intense body weight exercises, seeing the above numbers, I'm sure you'll agree that I would still lose strength. I'm not saying those numbers are particularly impressive, but I do weigh only 160 lbs, so they are at least respectable numbers, numbers I would very much like to keep. What I need is a weight lifting substitute for barbell movements.
According to Mehdi of StrongLifts, weight machines are inferior because the machine supports the weight for you. I completely agree, but still wonder if I should make an exception in this case. Doing overhead press and rows with a machine is better than nothing. But before going to the machine for rows, I'm going to see how pullups feel.
But I'm still lost as to how to get an acceptable squat/deadlift substitute. Any of those leg machines would isolate my muscles, allowing my legs to be much stronger than the rest of my posterior chain.
I guess what I'm really after is a way to limit or completely prevent strength loss in my back without actually disturbing the injury for the next several weeks. I would really prefer not to have to start over with the empty bar when I'm finally healed.