Exercise training prior to night shift work improves physical work capacity and arterial stiffness

Abstract

Shift work is an independent risk factor for metabolic and cardiovascular diseases (CVDs). Notably, shift workers have a 40% increased risk of suffering CVD in contrast to non-shift workers and the risk increases by 7.1% every five years of night shift duty. Mechanisms linking shift work with increased CVD morbidity and mortality are not fully understood but a tendency toward an unhealthy lifestyle with subsequently deteriorating cardiovascular risk factors has been identified. As a consequence endothelial dysfunction develops, which in the long term leads to a loss of elasticity of the arterial wall, that is, arterial stiffening. Regular aerobic exercise has repeatedly been shown to improve endothelial and vascular function. Recent studies have shown that already in young adults physical work capacity is connected with arterial stiffness and may have long-term protective influences on the development of CVD. So it is important to promote or to maintain regular exercise activities at any age. Further, exercise serves as a non-photic synchronizer of circadian rhythmicity. Therefore, the study aimed to investigate whether timed aerobic exercise prior to night shift work improves the cardiovascular risk profile and arterial stiffness in healthy individuals. The study was performed in accordance with the Declaration of Helsinki and its current amendments, and was approved by the Ethical Committee of the Hamburg State Chamber, Germany and by the Ethical Committee of the State of Salzburg, Austria. The trial is registered at ClinicalTrials.gov (NCT01767181) and was part of the EU funded multicentre trial EuRhythDia under the Framework 7 call. To test the influence of exercise, repeated-measures analysis of variance (three times – before exercise, after exercise (12 weeks) and after a wash-out-phase (24 weeks), with a fixed factor of group) was conducted. In the case of significance, a paired sample t-test, a Friedman test or a Wilcoxon-signed rank test for post hoc analysis was applied. For dependent samples, t-test or a Wilcoxon-signed rank test was conducted to test group differences. p-values of< 0.05 were regarded as statistically significant. All analyses were performed using IBM SPSS Statistics Version 21.0.0.1. Healthy night shift workers (N1⁄4 64, 20.1% male, 36.7 12.2 years) were randomized into a training group (three months’ timed and supervised physical exercise, n1⁄4 52) and a control group (recommendations only, n1⁄4 12). The training group performed 35min of high-intensity interval training (HIIT) on cycle ergometers within 2 h prior to each night shift for 12 consecutive weeks. HIIT was based on the first ergometer test of each participant and started with an initial warm-up for 5min at 60–65% of maximum heart rate (HRmax), following four bouts of 4min intervals at 85– 95% HRmax, with 3min active recovery at 65–75% HRmax. Cool-down was performed for 5min at 60– 65% HRmax. Workload was gradually adapted during the intervention according to the participant’s HR. After 12 weeks a ‘wash-out’ of 12 weeks followed without any intervention. Control group participants were urged to maintain their current lifestyle throughout the entire study and thus not to modify their exercise, lifestyle and eating behaviours. All participants underwent assessment of anthropometric measures, lipid profile,