Cardiovascular mechanisms of the occupational physical activity health paradox: 24-hour physical activity, blood pressure, and heart rate in active workers

Recent evidence suggests an occupational physical activity (OPA) health paradox where OPA is associated with adverse cardiovascular health. Physiological mechanisms to explain this paradox have not been studied. METHODS: Nineteen male workers (68% White/Caucasian, age=46.6 years, BMI=27.9 kg/m2) with high reported OPA completed a submaximal exercise test and wore ambulatory activity (ActiGraph and activPAL) and cardiovascular (blood pressure (BP) and heart rate (HR)) monitors for 7days, including at least one workday and non-workday. Individuals recorded work stress levels, work-time, nonwork-time, and sleep times in a diary. Physical activity profiles were described and compared to aerobic physical activity and OPA recommendations. 24-hour cardiovascular load (HR, systolic and diastolic BP) and nocturnal HRV were compared on workdays vs. non-workdays using adjusted linear mixed models. Effect modification by fitness level was explored using interaction models. The effect of work-related stress was analyzed by comparing workdays with low and high stress to non-workdays. RESULTS: Participants were significantly less sedentary and more active on workdays vs. non-workdays (all p<0.05). While most participants met aerobic activity guidelines, OPA exceeded recommended intensity level and upright time limits. 24-hour HR and diastolic BP were significantly higher on workdays vs. non-workdays (β=5.4 beats/min, p<0.001 and β=2.7 mmHg, p=0.019, respectively) but systolic BP did not differ (β=2.0 mmHg, p=0.317). Nocturnal HRV (low and high frequency power) was significantly lower on workdays vs. non-workdays (β=-0.27, p=0.025 and β=-0.33, p=0.014, respectively); other parameters (RMSSD, SDNN, LF/HF) were similar. Workday vs. non-workday cardiovascular load was not modified by fitness level (p-for-interactions>0.703). When stratified by stress level and compared to non-workdays, 24-hour HR was elevated on both low- (β=4.7 beats/min, p<0.002) and high-stress workdays (β=5.4 beats/min, p<0.001), 24-hour diastolic BP was only elevated on high-stress workdays (β=4.4 mmHg, p=0.023), and 24-hour systolic BP was never elevated (p>0.05). CONCLUSIONS: Activity was higher and exceeded OPA recommendations on workdays versus non-workdays. Workdays were also associated with elevated 24-hour cardiovascular load and reduced HRV. Fitness did not modify this relationship, but high job stress seemed to exaggerate it. These results suggest high 24-hour cardiovascular load and job stress as potential mechanisms contributing to the OPA health paradox.