What a Bulgarian split squat asks of the lower back, and what no study has countedEmerging evidence
The legs do the work; the trunk has to stay steady over a narrow, split base while you hold the weight and keep your balance, and the back leg's hip is pushed past straight at the bottom. Compared with a back squat, the trunk is more upright and the weight much lighter: in 8 rugby players the front hip worked harder in the Bulgarian even with a smaller load and a more upright trunk, and in 14 trained men, single-leg squats with 28 kg drew less lower back muscle activity than two-leg squats with 135 kg, for the same load per leg. The authors suggest that means less load on the spine; that is an inference, not a measurement.
No study has measured spinal load, the angle of the lower back or the tilt of the pelvis in a Bulgarian split squat, and none counts back pain from one. So this page's map is built from lab studies of healthy people, lifting surveys, a hip physiotherapist's published advice (expert opinion) and the back pain evidence.
Sources 1, 2, 3, 4
The usual cause: the back muscles working hard, or ordinary back painMixed evidence
The commonest pattern, in our reading, is an ache or pump across the lower back that builds through loaded sets, easing between sets or by the next day. The trunk muscles work harder when the set-up is wobbly: unstable loads raised core muscle activity in Bulgarian squats in 21 adults. Holding one dumbbell on one side made the back and tummy muscles on the other side work harder in 42 athletes, while a dumbbell in each hand kept the sides even.
The lean is mixed. In 12 trained women lunging with 30% of their body weight, leaning forward doubled lower back muscle activity (about 40% against 20% of a maximal effort), but in 21 female athletes doing body-weight Bulgarians a 40-degree lean didn't change it. The National Academy of Sports Medicine (NASM) calls excessive forward lean a mistake that increases lower back strain. This is ordinary back pain brought on by the load, the lean or a jump in volume, which the NHS says usually improves within a few weeks, though it can last longer or come back.
Sources 5, 6, 7, 4, 8, 9
A pinch with an arch at the bottom: our readingEmerging evidence
A pinch in the lower back at the bottom of each rep, worse with a long stance, a high bench or a very upright trunk, can come from the back hip running out of room so the lower back arches to make up the difference. This is our reading, not a measured fact. Holding a lunge on low-dose X-ray, 120 healthy young adults had on average about 16 degrees of hip extension left at the back hip, with a wide spread, and on average the pelvis tipped slightly back, not forward; the pattern varied with the shape of the lower spine. In 9 trained men the back hip went about 10 degrees further past straight with an upright trunk.
A hip physiotherapist keeps the shoulder, hip and back knee in a fairly straight line so the back hip doesn't pass straight: expert opinion, not a study. Back pain that dislikes arching has its own guide.
Sources 10, 3, 11
One side by the pelvis, a sudden catch, and pain down a legEmerging evidence
Pain on one side below the belt, by the dimple at the back of the pelvis and into the buttock, worse standing on one leg, is where the sacroiliac (SI) joint refers pain. The hip physiotherapist describes twisting forces across the pelvis in a split squat, larger with the back foot raised, and calls the exercise potentially very provocative for SI joint pain. In a review of 13 studies of 2,842 athletes, SI joint pain was reported in about 11% of athletes and about a third of athletes with low back pain, but the authors say an accurate figure isn't possible.
A sudden sharp twinge mid-rep, picking the dumbbells up with the back foot already on the bench, or after losing balance, then stiffness, is usually a strain or spasm, which settles over days to weeks. Pain, tingling or numbness travelling below the knee is a trapped nerve (sciatica); the NHS says that even if moving hurts, it isn't harmful and can help you get better faster.
Sources 11, 12, 13
Who gets itEmerging evidence
No study counts it. In our reading it mostly bothers people new to Bulgarians or jumping to heavy dumbbells or a barbell, people who hold one heavy weight on one side, people who set a long stance or a high bench and stay very upright, people who wobble and twist to balance, people whose back already hurts, teenagers in sports that arch the back, and women in pregnancy.
In lifting surveys the lower back is always among the commonest sore areas: the spine was among the commonest sites in weightlifters and powerlifters, the lower back in 245 powerlifters and in reviews of the weight-training sports, and the back 11% of injuries in 494 Dutch gym users. In CrossFit, the lower back was most often hurt in the heavy lifting movements. None of these surveys names the split squat, and injury rates in the lifting sports are low. Most lifters with pain keep training with changes: only 16% of injured Swedish powerlifters stopped completely.
Sources 14, 15, 16, 17, 18, 19
When a scan or test mattersStrong evidence
Not at first. The National Institute for Health and Care Excellence (NICE) says don't routinely offer imaging outside specialist care for low back pain with or without sciatica. In 33 studies of 3,110 people without back pain, disc wear showed in 37% of 20-year-olds and 96% of 80-year-olds, and disc bulges in 30% and 84%; the NHS says many people will never know they have slipped a disc. Tests matter for the warning signs, for a teenager whose back hurts arching (a doctor's check, which may include imaging), and for leg symptoms that aren't settling.
Sources 20, 21, 22
How it usually goesStrong evidence
No study follows back pain from Bulgarian split squats. In new episodes of low back pain, average pain fell from 56 to 26 out of 100 within 6 weeks and was 21 at a year (moderate-certainty evidence, the 2024 update of a 2012 review that had given 6 at a year), so it usually eases a lot, though a little often lingers. The NHS says back pain usually improves within a few weeks. Teenage athletes with a stress fracture of the spine returned to sport in about 92% of cases without surgery across 11 studies. No one can promise a date.
Sources 23, 24, 9, 25
