Table 7.

The relationship between sedentary behaviour and fitness

No. of participants (No. of studies)	Design	Quality assessment				Absolute effect	Quality
		Risk of bias	Inconsistency	Indirectness	Imprecision
The mean age at exposure measurement ranged from ~29 to 53 months (~2.4 to 4.4 yr). Data were collected longitudinally up to 8 years of follow-up. Fitness was assessed as: lower body explosive strength (standing long jump) and fitness level (parent-report level relative to other children).
1314 (2)	Longitudinala	Serious risk of biasb	No serious inconsistency	Serious indirectnessc	No serious imprecision	Screen-based sedentary behaviours: Higher TV time (hr/day) at age ~29 mo was unfavourably associated with standing long-jump performance (cm) at age 97.8 mo (B = −0.361; 95% CI: −0.576, −0.145; p < 0.001) [89] and physical fitness level (scale from −2 to 2) in Grade 4 (β = −0.09, SE = 0.0004; B = −0.01, 95% CI: −0.002, −0.02; p < 0.01) [90]. A greater increase in TV time (hr/week) between age ~29 and ~53 months was unfavourably associated with standing long-jump performance (cm) at age 97.8 months (B = −0.285; 95% CI: −0.436,-0.134; p < 0.01) [89] and physical fitness level (scale from −2 to 2, relative to other children) in Grade 4 (β = −0.10, SE = 0.0003, p < 0.01) [90].	Very lowd

^aIncludes 2 longitudinal studies [89, 90] from 1 unique sample (QLSCD)

^bSerious risk of bias. Questionable reliability and validity of the exposure [89, 90] and outcome [90] measures; large unexplained loss to follow-up and unclear if included participants differed from missing participants [89]; controlled for physical activity [89, 90]

^cSerious indirectness. Differences between outcomes of included studies and those of interest; only one study reported a measure of lower-body musculoskeletal fitness (lower-body strength assessed by standing long-jump performance) [89], and one study reported an indirect measure of physical fitness [90]. No studies reported direct measures of total body musculoskeletal or cardiovascular fitness

^dThe quality of evidence from the longitudinal studies was downgraded from “low” to “very low” because of: 1) a serious risk of bias that diminished the level of confidence in the observed effects, and 2) indirectness of the comparisons being assessed