There was a significant reduction in mean pain and disability in all groups at 6 weeks ( p < 0.005 ) ; NPRS : sham ( -1.5 ( 95 % CI -2.1 to -0.8 ) ) , low dose ( -1.3 ( -2.0 to -0.8 ) ) , high dose ( -1.1 ( -1.7 to -0.5 ) ) .