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Chronic obstructive pulmonary disease (COPD) is a disease that is characterised by persistent respiratory symptoms and airflow limitation. Consequences beyond the airways and lungs are common, and include limb muscle dysfunction. Limb muscle dysfunction is treated with exercise training, and should be preceded by assessments to individualise prescriptions. Guidelines recommend assessment of quadriceps strength, but limb muscle dysfunction affects more than strength. Other less investigated assessments may be of interest. During training, direct physiological (cardiorespiratory, metabolic, and biomechanical) and symptomatic responses are important, since they can affect training effectivity, and they may differ depending on whether arms or legs are used. The main aims of this thesis were to investigate the relevance of assessments of quadriceps function, feasibility and reliability of methods to assess quadriceps endurance, and to compare the direct physiological and symptomatic responses during arm and leg activities in people with COPD.

Method: This thesis is based on four papers. These include one systematic review with a meta-analysis of studies comparing direct physiological and symptomatic responses to activities performed with the arms versus the legs, and three papers based on an international cross-sectional multicentre study investigating reliability, feasibility, and relevance of three leg extension assessments of quadriceps endurance. Relative and absolute reliability were determined via interclass correlation coefficient (ICC), coefficient of variation (CV %), and limits of agreement (LoA %) for measures of isokinetic total work, isokinetic fatigue index, isometric time to exhaustion, and isotonic repetitions to exhaustion. The relevance of the measures of quadriceps endurance and other quadriceps functions were determined by the association to functional capacity and physical activity with Pearson correlation analyses (r) and multiple linear regression models (R², adjusted R², Δ R², and Δ adjusted R²).

Results: Results from the meta-analyses show that leg-cycle ergometer resulted in greater tidal volume (137 mL), minute ventilation (4.8 L/min), and oxygen consumption (164 mL/min) compared to arm cycle ergometer, while symptomatic responses were similar. Physiological responses (e.g., minute ventilation and oxygen consumption) during arm compared to leg resistance training exercises were similar. Results from studies on functional activities depend on the type and intensity of the activity performed. Isokinetic total work was the measurement with the highest relative reliability (ICC = 0.98) and the smallest absolute reliability (e.g., CV% = 6.5). Isokinetic fatigue index, isometric, and isotonic measures demonstrated low-to-high relative reliability (ICC = 0.64, 0.88, 0.91), and absolute reliability was larger (e.g., CV% = 20.3, 14.9, and 15.8%). Participants performed better on the retest for isokinetic total work and isometric measurements (4.8 and 10%, p < 0.001). The feasibility was similar across protocols, with an average time consumption of< 7.5 minutes, limited perceived dyspnoea compared to leg fatigue, and no major adverse advents. The measures of quadriceps function had mostly similar (r = +/- 0.07–0.45) levels of correlations to the functional capacity and physical activity. In multiple regression analyses improved quadriceps power the models to predict functional capacity the most (Δ adjusted R²= 0.10, 0.15, adjusted R² = 0.60, 0.39). Isotonic endurance was the only muscle function that improved all physical activity models (ΔR² = 0.04–0.07, p < 0.05, R² = 0.38–0.49).

Conclusions: The results indicate that if the goal of an activity is to maximise physiological responses such as minute ventilation and oxygen consumption, activities involving the legs should be preferred. Symptomatic responses seems task and intensity dependent, which suggest that strategies used to reduce symptoms should be based on relative intensity. In the assessment of quadriceps endurance, isokinetic, isometric and isotonic protocols present low to very high relative reliability. Differences in reliability and the better performance at retest might reflect differences in ability to detect true change. Quadriceps power seems to be more relevant to functional capacity, and isotonic quadriceps endurance seems to be more relevant to physical activity.