Reduced muscle inactivity, sedentary time and cardio-metabolic benefits : effectiveness of a one-year family-based cluster randomized controlled trial

Abstract

A driving hypothesis of the evolving field of sedentary behavior is that frequent muscle activity short-circuits detrimental physiological effects of sedentary time. However, the field relies mostly on observational health associations of proxy measures of muscle inactivity, like television viewing or lack of accelerometer-derived impacts. This study tested effectiveness of a family-based cluster-randomized controlled trial aimed at reducing and breaking up sedentary time at work and leisure time of families on muscle inactivity patterns, sedentary time and cardio-metabolic biomarkers. The intervention consisted of a lecture, face-to-face tailored counseling, two follow-up calls and five emails during the first six months, and six months follow-up without the intervention. Detailed muscle inactivity and activity patterns of sitting, standing, normal daily life and the short-term efficacy of the counseling were quantified by special shorts capable of measuring average rectified EMG signal. The long-term effectiveness of the intervention was studied in 133 sedentary parents by measuring accelerometer-derived sedentary time, anthropometrics and blooddrawn cardio-metabolic biomarkers to report if short-term changes in muscle inactivity patterns translate to long-term behavioral and physiological benefits. The main findings of this study were that while muscles were inactive 90% of sitting time and the average muscle activity amplitude was threefold higher in standing (1.6% of EMGMVC) than sitting (0.5% of EMGMVC), the inter-individual differences were tenfold. However, within two weeks of the counseling muscle inactivity time decreased by 37 min in intervention group compared to controls without affecting high intensity activities suggesting that sedentary-time targeted intervention can change specifically muscle inactivity patterns. At three months the intervention was successful in reducing accelerometer-derived sedentary leisure time by 27 min in the intervention group as compared to controls. At 12 months the control group’s sedentary leisure time tended to increase whereas that of the intervention group remained at the baseline level suggesting that acutely effective intervention methods may prevent unfavorable long-term changes. Between baseline and endline, significant intervention effects in weight, total lean mass, leg’s lean mass, apoA-1 and apoB/apoA-1 -ratio favored intervention group and remained independent of moderate-to-vigorous -intensity physical activity and energy intake. In conclusion, the family-based tailored counseling was effective in reducing muscle inactivity and sedentary leisure time acutely, and in preventing an increase in sedentary leisure time during one year without reducing work or weekend sedentary time. This resulted also in some modest positive changes in anthropometrics and apolipoproteins independent of moderate-to-vigorous physical activity and energy intake. Reducing muscle inactivity produces causal health benefits and may bear public health potential.