When I ride I arch my lower back correctly but my shorlders seem to slouch, is there any way to prevent this ?

Try the "Equifit Shoulders Back"
You can try this exercise; make your shoulder blades touch, push down your shoulder and roll them a bit. Do this a couple of times while on the horse and let your chest out !! Hope this helps.
Just always think chest out, lean away and not foward. That's what my trainer tells me anyways.
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