Like you said, one can only speculate without the video…going off what you have said I think this is the most likely explanation.
Generally, an effective conventional deadlift is quicker off the floor and slows down closer to lockout while a sumo deadlift is slower off the floor (picture squeezing it off the floor) and easier at lockout.
More than likely you started in a relatively good position (i.e. neutral spine, hips fairly low, chest high) but you did not maintain that neutral spine throughout the lift. This could happen either due to upper/lower back rounding during the lift or the hips shooting up at the start of the pull…either would put you out of position at lockout.
This is not a place you want to be; when you approach the last third of the lift the weaker muscles of the upper body are going to have a hard time correcting this postural issue, so recovering to neutral spine (getting chest through, shoulder back) and locking the hips will become much harder.
To remedy this you need to practice more patience off the floor, the weight may move slower for the first few inches but should be much easier at lockout since the spine remains neutral. Many lifters don’t have the upper back and core strength to do this…but I don’t think that’s your issue, you may just be rushing the lift.
Some key cues for the first phase of the lift:
- chest out, shoulders back
- shins within an inch of the bar, toes angled slighty outwards
- neutral spine
- hips back and as low as is ideal (You don’t neccessarly need to have the hips low but rather as close as possible to their usual position when the bar breaks the floor. Many start with the hips to low but lack the ability to pull from that low so their hips shoot up and wreck the pull.)
- arms straight and locked
Just a thought.
