Is there a U-shaped relationship between physical activity in leisure time and risk of chronic low back pain? A follow-up in the HUNT Study

Table 4 Risk of chronic LBP by combinations of education and physical activity in women^a

Physical activity in leisure time (hours per week)			Duration of education (years)
Physical activity in leisure time (hours per week)			≤9	10–12	≥13
		Total	2817	4043	2339
Light	Hard	Score	RR (95 % CI)	RR (95 % CI)	RR (95 % CI)
<1	0	1	1.00 (reference)	0.92 (0.74–1.13)	0.67 (0.48–0.93)
≥1	0	2	0.84 (0.70–1.01)	0.90 (0.75–1.08)	0.93 (0.74–1.15)
	<1^b	3	0.88 (0.70–1.11)	0.93 (0.76–1.13)	0.83 (0.66–1.04)
	1–2	4	0.73 (0.55–0.97)	0.96 (0.78–1.18)	0.59 (0.45–0.76)
	≥3	5	1.18 (0.86–1.63)	1.06 (0.80–1.40)	0.51 (0.32–0.82)
P, categorical effect^c			0.037	0.69	0.003
P, linear effect^d			0.32	0.18	0.013
P, quadratic effect^e			0.015^f	0.53	0.006^g

LBP low back pain, RR relative risk, CI confidence interval
^a Adjustment for age, work status, physical activity at work, BMI, smoking
^b Must have reported some hard activity
^c For categorical effect of physical activity, within interval for duration of education
^d For linear effect of score for physical activity, within interval for duration of education
^e For quadratic effect of score for physical activity, within interval for duration of education
^f Coefficient of quadratic term > 0, corresponding to a U-shaped relationship
^g Coefficient of quadratic term < 0, corresponding to an inverted U-shaped relationship

ISSN: 1471-2458