Strong Legs

The first reason you may be feeling the back working more than the legs is that your legs are stronger and are able to deal with the load of the kettlebell during the squats. If the weight isn’t heavy enough to challenge the legs but still challenges the back then it may be time to move towards barbell squat variations. Barbell variations will take pressure away from holding the weight in place and put much more emphasis on pure leg strength. This is a natural progression and should be done when holding the kettlebell in place is more difficult than the loading of the legs.

Rounding the Lower Back

Rounding the lower back is very common in the goblet squat, especially amongst beginners who havn’t become technically proficient in the squat yet. The often happens because a lack of mobility in the hips and or lower back. It can be avoided by not trying to go so deep in the squat, the rule of thumb is to only go as deep as your current range of motion allows with good technique. Good technique involves having a flat back in a strong stable position. This will mean squatting as low as you can while keeping your back positioning perfect. This should take the pain / emphasis away from the lower back.

Poor Lumbar Strength / Endurance

If you have poor lumbar strength and endurance then you will likely find goblet squat challenging. Goblet squats require core stability and endurance of the lumbar spine (lower back muscles) to perform with good positons. If you perform goblet squats with great technique they will still generate a lot of fatigue in the back, this isn’t a negative thing it is just an area where you will create adaptations from performing goblet squats.