Table 2

Summary of bidirectional variables

VariableNumber of studiesNumber of studies: Increased riskNumber of studies: Decreased riskNumber of studies not significantStrength of association (95% CI)
Physical activity/work10604

Playing sport OR 9.5 (1.9, 48.2) [11]

White collar work OR 4.9 (1.7, 14.2) [13]

Vigorous intensity physical activity: OR 1.2 (1.0–1.4) (diagnostic spinal pain) OR 1.3 (1.0–1.5) (traumatic) [15]

High level sports activity RR 1.6 (1.1, 2.3) [24], Part-time work RR 1.5 (1.1, 2.1) [24]

Provoked by manual work: OR 9.2 (2.9, 28.8) [33]

Increased physical activity OR 1.9 (1.2, 2.8) [34]

Psychological factors7403

High level of peer problems: RR 2.3 (1.3, 4.2) [23]

High level of psychological factors: RR 1.6 (1.1, 2.3) [24]

Externalising behaviour: RR 1.5 (1.3, 1.7) (boys), RR 1.4 (1.3, 1.5) (girls), RR 3.6 (1.5, 8.5) (girls 18) [28]

High levels of aggressive behaviour OR 1.4 (1.2, 1.6) [34]

High level of somatic complaints OR 1.3 (1.1, 1.5) [34]

Higher BMI8305

OR 1.3 (1.0, 1.5) [11]

RR 1.1 (1.0, 1.2) (girls), RR 1.1 (1.0, 1.3) (boys) [29]

OR 2.9 (1.7, 5.1) (9 yr), 2.2 (1.4, 3.5) (10 yr), 1.6 (1.2, 2.1) (13 yr) [32]

Smoking6600

OR 2.2 (1.4, 3.5) [4]

OR 2.4 (1.3, 6.0) [14]

OR 3.1 (1.1, 9.2) (MB), 1.8 (1.2, 2.8) (BP) [17]

OR 1.7 (1.4, 2.1) [19]

HR 1.6 (1.4, 1.9) [27]

OR 2.5 (1.4, 4.5) (females) [30]

Illness4301

Asthma OR 1.4 (1.1, 1.7) (female) [20]

Headache OR 1.6 (1.1, 2.1) (female), OR 2.4 (1.2, 4.7) (male) [20]

Abdominal pain RR 1.8 (1.1, 3.0) [24]

Headache OR 2.4 (1.8, 3.1) [26]

Posture/sitting position4400

No LB support: OR 1.7 (1.2, 2.6), OR 2.9 (1.1, 3.5) (persistent LBP) [25]

Provoked by sitting OR 3.8 (1.3, 11.3) [33]

Non-neutral standing posture OR 2.2 (1.3, 3.6) [34]

Uncomfortable school desk OR 6.0 (3.7, 9.7) [35]

Insufficient sleep3300

OR 2.9 (1.7, 5.2) (girls), OR 2.4 (1.3, 4.5)(boys) [10]

OR 2.2 (1.7, 3.8) [35]

OR 1.2 (1.1, 1.4) [36]

Flexibility3201

Decreased flexibility: hamstrings OR 1.1 (1.0, 1.1) [4]

Decreased flexibility: quad muscles: OR 1.7 (1.1, 2.8) [25]

Screen time3102Increased TV time OR 2.0 (1.4, 2.9) [35]
Backpack factors3102Heavy school satchel OR 2.2 (1.0, 4.8) [36]
Muscle endurance1100Poor back muscle endurance OR 1.9 (1.2, 3.0) [34]
OR odds ratio, RR relative risk, HR hazard ratio, (c) parameter measure calculated from the provided results within study i.e. percentages converted to odds ratios