I am a beginner and can squat upto 175lbs but the same weight if I deadlift I feel my lower back .This is certainly problem as most people normally can deadlift much more than squat max.Maybe it's something to do with my form or depth,my body structure.I am a short guy about 168 cm.
“most people normally can deadlift much more than squat “
I tend to disagree with this assertion. There's no “rule” per se that suggests you should be able to deadlift more than you squat. Each of us, as individuals, may have one or more lifts that are more difficult than others. However, there's nothing stopping you from improving an individual exercise. Rather than spending time worrying bout the discrepancy, you should work to improve your weaknesses by concentrating on strengthening the muscles that are involved in the particular exercise you'd like to improve.
The bar location and forwardly located load are key differences between these exercises. Due to this resulting compensation is lower back activation to "complete the lift" (otherwise you would fall forward).
To lift the bar, you're generating the force using a hip hinge -- literally like a pelvic thrust. Your back should remain neutral.
As this will take's some time to learn, it's common to see people lifting with their lower back simply poor mechanics / improper form.
- Another cause is using too much weight. If the barbell is too heavy the force of your hip hinge isn't enough - so your lower back contracts and "compensates" to assists in completing the lift.
To learn the thrusting movement while you're maintaining a neutral back start with a slightly raised bar (with no weight) or kettle bells.
During a squat the force of the bar is instead behind your neck, so if you can't get back up to complete the rep you'd tend to fall backwards.
Contracting your lower back in this case will not help you complete the lift -- so it's not a compensation seen here.
Also please note, while it's important to keep your back straight while squatting, unlike an incorrect deadlift, your lower back musculature is not forcefully contracting and pulling on a flexed spine (which is a very unstable position for your spine).