Relationship between physical activity and aerobic capacity in chronic lung disease and in different occupational groups

Numerous studies provide evidence for the promotion of physical activity to prevent chronic diseases in healthy subjects and reduce the risk of disease progression in chronically ill patients. In addition, the level of physical activity and the resulting aerobic capacity determine the ability to actively participate in the work process. Moreover, the relation of physical activity to aerobic capacity plays a central role in the reintegration of patients after phases of sick leave. Despite the increasing number of patients in need for reintegration into the work process after diseases or medical procedures, no established reference values exist to evaluate point of time and appropriate way of return to work. Therefore, determining physical performance criteria of different occupational groups appears to be important for assessing the individual work capacity and the ability to take over tasks that are potentially physically demanding. The aim of this thesis was to objectively measure physical activity and aerobic capacity in patients with chronic obstructive pulmonary disease (COPD) (part I) as well as in healthy employees (part II) and to investigate their relationship with regard to quality of life and reintegration into employment. In a cross-sectional manner, data of 87 stable patients with COPD were analysed in part I, while 303 healthy and full-time employed adults from different occupational groups were investigated in part II. In both parts, physical activity was quantified by the SenseWear Mini armband on seven consecutive days (23 hours/day). Average daily energy expenditure, physical activity level in metabolic equivalents of task (METs), number of steps and physical activity duration at different intensities were analysed. The submaximal level of aerobic capacity was measured by the 6-minute walk test in patients with COPD, while the maximal level (VO2max) was determined with the 20-meter shuttle run test in healthy employees. Independent associations of physical activity parameters with aerobic capacity and health outcomes were examined using multiple linear regression analysis. To determine physical performance criteria of different occupational groups, the ratio between workload as measured by METs and employees’ work capacity as measured by VO2max was analysed. In patients with COPD, the number of daily steps and aerobic capacity correlated significantly with each other and were independent predictors of quality of life, whereas no relationship was found with moderate-to-high intensity activity. In contrast, in healthy employees, high-to-very high intensity activity during leisure-time was associated with high aerobic capacity. Neither daily steps nor work-related activity revealed an independent association with VO2max. The ratio of physical workload to maximum work capacity was on average one third of VO2max and increased from sedentary occupations (21%) to jobs with moderate (29%) and high (44%) physical demands. Women showed an equal absolute workload as men, but had a higher relative workload due to their lower VO2max (37% vs. 26%). Multiple linear regressions revealed that physical workload correlated positively with moderate-, high- and very high-intensity activity at work, whereas it was negatively associated with flextime, daily working hours, age and VO2max. The findings of this thesis provide evidence that the relationship between physical activity and aerobic capacity is intensity- and type-specific and varies between impaired and healthy subjects. The results emphasise the need for patients with COPD to maintain physical activity as an integral part of everyday life and to remain mobile, whereas healthy employees need to engage in sufficient high-intensity physical activity in recreation for improving VO2max. This could be explained by the fact that patients with chronic lung disease adopt a sedentary lifestyle and get used to the lower level of physical activity, while healthy subjects may require higher-intensity stimuli to achieve health benefits. Since physical activity and aerobic capacity are independent predictors of quality of life in patients with COPD, measuring activity and fitness levels should be an integral part of the assessment of patients. This may help to prevent future disease exacerbations by allowing appropriate education or treatment. Regarding the reintegration of patients after phases of sick leave, the determined gender- and job-specific physical performance criteria may help to develop future guidelines for a safe return to work. If an individual’s job profile needs to be adjusted, the present results suggest considering various personal and job-related factors for evaluating physical workload, besides VO2max. This is an important finding, since up to now work recommendations were primarily based on individuals’ aerobic capacity. An optimised reintegration process might have the potential to reduce future loss of working hours and related health care costs. With the increasing availability of big data, prescriptive analytics might in future be able to disrupt the traditional healthcare system by recommending courses of actions and showing likely outcomes based on population-derived values