Effects of reallocating time in different activity intensities on health and fitness: a cross sectional study.

The effects of replacing time in specific activity categories for other categories (e.g. replacing sedentary time with light activity) on health and fitness are not well known. This study used isotemporal substitution to investigate the effects of substituting activity categories in an equal time exchange fashion on health and fitness in young people. Participants were drawn from schools in Camden, London (n = 353, mean age 9.3 ± 2.3 years). Time sedentary, in light and in moderate-to-vigorous activity (MVPA) was measured via accelerometry. The effects of substituting time in activity categories (sedentary, light and MVPA) with equivalent time in another category on health and fitness were examined using isotemporal substitution. In single and partition models, MVPA was favourably associated with body fat %, horizontal jump distance and flexibility. Time sedentary and in light activity were not associated with health and fitness outcomes in these models. In substitution models, replacing one hour of sedentary time with MVPA was favourably associated with body fat % (B = −4.187; 95 % confidence interval (CI), −7.233, −1.142), horizontal jump distance (B = 16.093; 95 % CI, 7.476, 24.710) and flexibility (B = 4.783; 95 % CI, 1.910, 7.656). Replacing time in light activity with MVPA induced similar benefits but there were null effects for replacing sedentary with light intensity. Substituting time sedentary and in light activity with MVPA was associated with favourable health and fitness. Time in sedentary behaviour may only be detrimental to health and fitness when it replaces time in MVPA in young people. The online version of this article (doi:10.1186/s12966-015-0249-6) contains supplementary material, which is available to authorized users.

将特定活动类别中的时间替换为其他类别（例如用轻度活动替代久坐时间）对健康和体能的影响尚不明确。本研究采用等时替代法，以相等时间交换的方式研究活动类别替代对年轻人健康和体能的影响。 参与者来自伦敦卡姆登的学校（n = 353，平均年龄9.3 ± 2.3岁）。通过加速度计测量久坐时间、轻度活动时间以及中等到剧烈活动（MVPA）时间。采用等时替代法研究将活动类别（久坐、轻度活动和MVPA）中的时间用其他类别中的等量时间替代对健康和体能的影响。 在单一模型和划分模型中，MVPA与体脂百分比、立定跳远距离和柔韧性呈正相关。在这些模型中，久坐时间和轻度活动时间与健康和体能结果无关。在替代模型中，用MVPA替代1小时久坐时间与体脂百分比（B = -4.187；95%置信区间（CI），-7.233，-1.142）、立定跳远距离（B = 16.093；95%CI，7.476，24.710）和柔韧性（B = 4.783；95%CI，1.910，7.656）呈正相关。用MVPA替代轻度活动时间也有类似益处，但用轻度活动替代久坐时间则没有效果。 用MVPA替代久坐时间和轻度活动时间与良好的健康和体能相关。在年轻人中，只有当久坐行为时间替代了MVPA时间时，才可能对健康和体能有害。 本文的网络版（doi:10.1186/s12966 - 015 - 0249 - 6）包含补充材料，授权用户可获取。