Squats require a perfect spinal alignment when done with a meaningful weight. Improper posture and a flexed back should not be tolerated.
If your spine is not aligned properly, it’s in a weak position, and the heavy barbell on top may cause strains.
Of course, if you are doing the exercise with light weights, dumbbells or kettlebells, you may get away with a poor spinal alignment, but if you want to lift heavy barbells, you better learn how to do it right.
Deadlifts fatigue the lower back
Deadlifts exhaust the lower back. There is no eccentric portion, and the lifter uses brute strength to rip the barbell off the floor. The spine is placed under a heavy load and has to do some serious fighting to survive. Without a doubt, the deadlift fatigues the lower back much more than the squat. That’s why you see everyday squatting programs whereas everyday deadlift programs are hard to find, although there are some.
Never squat after deadlifts
The deadlift is the more taxing lift. If you squat after heavy deadlifts, you are putting your spine at risk because you are lifting with weakened stabilizers.
The fragile link is your back, and the chances of it giving up proper alignment are significant. That’s why squatting after deadlifts is not a good idea. For the same reason, powerlifting competitions start with the squat and finish with the deadlift.
Should I squat and deadlift on the same day?
If you follow an intelligent program, you can definitely squat and deadlift safely on the same day. You could also include an upper body exercise in between the two big lifts so that the back could recuperate a bit after the squat.
However, once the poundages start to climb up, you may want to squat and deadlift on a different day. That way the central nervous system (CNS), the muscles and the joints have more time to recover.