Open Access Study protocol

Cardiorespiratory fitness, cardiovascular workload and risk factors among cleaners; a cluster randomized worksite intervention

Mette Korshøj12, Peter Krustrup23, Marie Birk Jørgensen1, Eva Prescott5, Åse Marie Hansen16, Jesper Kristiansen1, Jørgen Henrik Skotte1, Ole Steen Mortensen17, Karen Søgaard4 and Andreas Holtermann1*

Author affiliations

1 National Research Centre for the Working Environment, Lersø Parkallé 105, 2100, Copenhagen Ø, Denmark

2 Department of Exercise and Sport Sciences, Section of Human Physiology, University of Copenhagen, Nørre Allé 51, 2200, Copenhagen, N Denmark

3 Sport and Health Sciences, College of Life and Environmental Sciences, St. Luke's Campus, University of Exeter, Exeter, UK

4 Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark

5 Department of Cardiology, Bispebjerg University Hospital, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark

6 Department of Public Health, University of Copenhagen, Øster Farimagsgade 5, 1014, Copenhagen K, Denmark

7 Bispebjerg University Hospital, Bispebjerg Bakke 23, 2400, Copenhagen, NV, Denmark

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Citation and License

BMC Public Health 2012, 12:645  doi:10.1186/1471-2458-12-645

Published: 13 August 2012



Prevalence of cardiovascular risk factors is unevenly distributed among occupational groups. The working environment, as well as lifestyle and socioeconomic status contribute to the disparity and variation in prevalence of these risk factors. High physical work demands have been shown to increase the risk for cardiovascular disease and mortality, contrary to leisure time physical activity. High physical work demands in combination with a low cardiorespiratory fitness infer a high relative workload and an excessive risk for cardiovascular mortality. Therefore, the aim of this study is to examine whether a worksite aerobic exercise intervention will reduce the relative workload and cardiovascular risk factors by an increased cardiorespiratory fitness.


A cluster-randomized controlled trial is performed to evaluate the effect of the worksite aerobic exercise intervention on cardiorespiratory fitness and cardiovascular risk factors among cleaners. Cleaners are eligible if they are employed ≥ 20 hours/week, at one of the enrolled companies. In the randomization, strata are formed according to the manager the participant reports to. The clusters will be balanced on the following criteria: Geographical work location, gender, age and seniority. Cleaners are randomized to either I) a reference group, receiving lectures concerning healthy living, or II) an intervention group, performing worksite aerobic exercise “60 min per week”. Data collection will be conducted at baseline, four months and 12 months after baseline, at the worksite during working hours. The data collection will consist of a questionnaire-based interview, physiological testing of health and capacity-related measures, and objective diurnal measures of heart rate, physical activity and blood pressure. Primary outcome is cardiorespiratory fitness.


Information is lacking about whether an improved cardiorespiratory fitness will affect the cardiovascular health, and additionally decrease the objectively measured relative workload, in a population with high physical work demands. Previous intervention studies have lacked robust objective measurements of the relative workload and physical work demands. This study will monitor the relative workload and general physical activity before, during after the intervention, and contribute to the understanding of the previously observed opposing effects on cardiovascular health and mortality from occupational and leisure time physical activity.

Trial registration

The study is registered as ISRCTN86682076.

Worksite intervention; Cleaners; Aerobic exercise; Work demands; Physical activity; Ambulatory blood pressure