Insufficient moderate-to-vigorous physical activity (MVPA) and prolonged sedentary behavior (SB) are significant predictors of metabolic disorders, type 2 diabetes, cardiovascular disease (CVD), and premature mortality. A substantial portion of the global population fails to meet MVPA guidelines, and overweight individuals, even those seemingly healthy, are at increased risk for metabolic syndrome and cardiometabolic diseases. Objective measurement of SB, rather than self-reporting, is gaining traction to better understand its association with obesity and metabolic diseases. Previous cross-sectional studies have linked increased SB time to elevated plasma glucose, insulin, and triglyceride levels, lower HDL cholesterol, and larger waist circumference. Furthermore, SB time correlates with glucose intolerance and an elevated risk of metabolic syndrome and type 2 diabetes. However, the literature is not uniform. For example, some studies have shown that MVPA is associated with BMI, waist circumference, HbA1c, and HDL, while sedentary status is linked only to HDL. The impact of breaking up sedentary time with activity breaks is also contested, with some studies reporting benefits and others not. Objective SB measurement methodologies are not without limitations, particularly regarding the measurement duration. In this study, we use four consecutive weeks of accelerometer-based measurements to analyze associations between SB, PA and metabolic health markers, in an overweight population with low self-reported physical activity levels, aiming to address several controversies in the literature.

Existing literature demonstrates a strong link between insufficient physical activity and prolonged sedentary time with various health issues, including metabolic disorders, type 2 diabetes, cardiovascular disease, and premature mortality. The majority of the global adult population does not meet the recommended levels of physical activity, heightening the risk of obesity-related diseases. While self-reported data has been used, objective measurements of sedentary behavior using accelerometers are increasingly employed. Studies have shown a correlation between objectively measured sedentary behavior and higher levels of glucose, insulin, triglycerides, lower HDL cholesterol, and increased waist circumference. Sedentary time is also associated with glucose intolerance, metabolic syndrome, and type 2 diabetes. However, the existing research presents inconsistencies in the association between MVPA and sedentary behavior with specific cardiometabolic markers, particularly when considering the impact of breaking up prolonged periods of sitting with short bursts of physical activity. The optimal duration and methodology for objectively measuring sedentary behavior are also subject to ongoing debate.

This one-arm explorative observational study, part of a larger intervention study, recruited participants (aged 40-65 years, BMI 25-40 kg/m²) from the local community in Turku, Finland (April 2017 - May 2019). Participants were excluded if they had a history of cardiac events, insulin-treated diabetes, excessive alcohol consumption, narcotic use, tobacco use, difficulty understanding written Finnish, or other chronic conditions posing safety risks. Participants were interviewed, and BMI, waist circumference, and blood pressure were measured. They then wore a hip-worn tri-axial accelerometer (UKK AM30) for four consecutive weeks (mean 25 days), during waking hours, maintaining their usual activities. Fasting venous blood samples were collected for analysis of glucose, insulin, HbA1c, triglycerides, total cholesterol, HDL, and LDL cholesterol. HOMA-IR was calculated. Accelerometer data were analyzed in six-second epochs, converting acceleration data to metabolic equivalents (METs). Light PA (LPA) was defined as 1.5 ≤ MET < 3.0, MVPA as MET ≥ 3.0. Body posture (standing vs. SB) was determined using the Angle for Posture Estimation (APE) method. Daily steps were also counted. Linear models were used to examine associations, adjusting for age, sex, BMI, and medication use where appropriate. Log transformations were used to achieve normal distribution.

Of 263 volunteers, 144 (42 men) completed the study. Mean accelerometer wear time was 14.37 hours/day. Participants spent 67% of wear time in sedentary activities and took an average of 5265 steps/day. BMI negatively associated with MVPA and daily steps. BMI positively associated with SB percentage. Fasting insulin and HOMA-IR negatively associated with PA, daily steps, and MET values, and positively with SB percentage. Fasting glucose positively associated with SB percentage and negatively with standing time, MVPA, daily steps, and MET values (but some associations became non-significant after excluding outliers). HbA1c negatively associated with breaks in sedentary time (but became non-significant after excluding outliers). Fasting triglycerides positively associated with SB percentage and negatively with PA. HDL-cholesterol negatively associated with SB time and percentage and positively with PA. No associations were found between total/LDL cholesterol and accelerometer measures or blood pressure and accelerometer measures. Adding BMI to the models reduced the number of significant associations; breaks in sedentary time and metabolic markers became mostly non-significant after adjusting for BMI. Analysis of only the first week of data yielded different results, emphasizing the need for longer measurement periods.

This study demonstrates a clear association between higher sedentary behavior (SB) percentage and insulin resistance in overweight adults with low self-reported physical activity. Higher SB percentage was linked to unfavorable cardiometabolic markers, including elevated insulin, triglycerides, and lower HDL. Conversely, all types of physical activity, regardless of intensity, were associated with improved insulin sensitivity and more favorable lipid profiles. While breaking up sedentary time showed no significant benefit after adjusting for BMI, the total daily duration of physical activity seems more important than intensity for maintaining metabolic health in this population. The findings highlight the potential of reducing sedentary time as an intervention strategy to improve cardiometabolic health, but also emphasize the strong influence of overall BMI.

This study confirms the association between sedentary behavior and insulin resistance in overweight adults, even after adjusting for BMI. Total daily physical activity, regardless of intensity, is a significant factor in improving metabolic health. Light physical activity shows a particularly beneficial association with lipid profiles. Future research should explore longer-term interventions targeting both sedentary behavior reduction and overall lifestyle changes, including dietary habits, in overweight populations. Furthermore, the impact of short bursts of physical activity needs further investigation.

This study's cross-sectional design limits causal inferences. The reliance on accelerometer data during waking hours might underestimate total sedentary time. Dietary intake and other lifestyle factors were not assessed, but the study was designed to be focused on the association of activity and sedentary behavior with metabolic markers. The observed associations are related to a specific population and more generalizability needs to be studied in the future.