Limb Muscle Weakness in Chronic Obstructive Pulmonary Disease: Improving Characterization and Optimizing Exercise Prescription

Limb muscle weakness is a secondary consequence of chronic obstructive pulmonary disease (COPD). It affects approximately 30% of patients and is associated with exercise intolerance, increased health care utilization, and increased risk of mortality. There are still important gaps in the understanding about the development and management of limb muscle weakness in COPD. The overall objective of this thesis was to improve characterization of and optimize strength exercise prescription for limb muscle weakness and n in COPD. The first study of this thesis showed that an increased fatty infiltration accompanies muscle atrophy across thigh and calf muscles in people with COPD. Intramuscular fat infiltration was greater in COPD compared to what was observed in matched healthy controls and more strongly correlated with muscle weakness and impaired mobility than muscle atrophy in these individuals. The second and third studies of this provided insights on how people with COPD may respond to exercise approach that specifically target muscle weakness. In these studies the acute effects of different strength training exercises for upper- and lower-limb muscles were explored in these individuals. In the second study, we showed that immediate cardiorespiratory responses during short bouts of weightlifting in COPD are independent of the exercise intensity. Although people with COPD reported greater levels of perceived exertion and longer time to recover after high vs. low-intensity exercise bouts, responses to different intensities were comparable to their healthy counterparts. The third study showed that responses were also independent of number of exercising limbs (double vs. single limb) during lower and upper-body exercises. In this study, however, we showed a significant effect of limb position during arm exercises in people with COPD where arm exercise overhead (above shoulder level) evoked greater responses and perceived exertion and longer recovery time than other exercise variations. The findings from the three studies reveal the importance of fatty infiltration in the development of limb muscle weakness in COPD and provide insights on tailoring exercise approaches to muscle weaknes3s that better meet the needs of people with COPD. Future studies could assess cardiorespiratory requirements during a full training program to determine the most appropriate intensity-response and to further assist in standardizing training prescription in COPD. As well, the training effects of strength exercises on intramuscular fatty infiltration in people with COPD in an area for future investigation.