Symptom Intensity and Subjective Limitation to Exercise in Patients With Cardiorespiratory Disorders* Alan L. Hamilton, PhD; Kieran J. Killian, MD; Edie Summers, RRT; and Norman L. Jones, MD The aim ofthe study was to compare (1) the intensity of leg effort and dyspnea during exercise and (2) subjective limitations to performance in normal subjects, patients receiving medication for car¬ diac disorders, patients with pulmonary impairment, patients with pulmonary impairment who were also receiving cardiac medications, patients experiencing chest pain during exercise, and patients who had a reduced exercise capacity but did not have pulmonary impairment and were not receiv¬ ing cardiac medication. Five hundred seventy-eight subjects rated the intensity of leg effort, discomfort with breathing (dyspnea), and chest pain every minute (Borg scale) during an incremental exercise task (100 kpm/min each minute) to maximum work capacity on a cycle ergometer and fol¬ lowing exercise indicated their subjective limitation by completing a simple questionnaire. Leg ef¬ fort and dyspnea increased systematically with power output in a positively accelerating manner in all groups; both symptoms were significantly more intense in the impaired groups compared with the normal group at submaximal power outputs. In all groups, there was a significant relationship between symptom intensity at submaximal power outputs and the maximal power output achieved. Leg discomfort in combination with breathing discomfort was the predominant subjective limitation in all groups; chest pain in combination with leg and breathing discomfort was the major subjective limitation in individuals with angina. Activation of the sensory systems during exercise is accompa¬ nied by a perception of discomfort associated with the peripheral exercising muscles and discom¬ fort with breathing; both discomfort associated with the exercising muscles and discomfort associ¬ ated with breathing contribute to exercise limitation to a large degree in normal subjects and patients with cardiorespiratory diseases. CHEST 1996; 110:1255-63) Key words: dyspnea; exercise; fatigue; muscle senses; symptom limitation Abbreviations: AN OVA=analysis of variance; Wcap=work capacity A sense of exertional discomfort is experienced and ^¦**associated with exercising muscle, becoming more intense as either the power output or the duration of exercise increases. This discomfort is closely related to the sense of effort,1'2 which is regarded as the conscious awareness of the central outgoing motor command.3"6 During activities involving large muscle groups, such as cycling or running, there is also a sense of discomfort closely related to inspiratory muscle activity (exertional dyspnea).7,8 When the degree of discomfort associated with the peripheral exercising or respiratory muscles exceeds that which an individual is willing to tolerate, activity is volitionally terminated. Hence, exertional discomfort and exertional dyspnea may be viewed as the proximal limitations to muscular performance. *From the Department of Medicine, McMaster University Medi¬ cal Centre, Hamilton, Ontario, Canada. Supported by Ontario Thoracic Society, SERC (UK). Manuscript received September 22, 1995; revision accepted June 6, 1996. ^ In the presence of cardiorespiratory disorders, im¬ pairments in ventilatory, gas exchange, and circulatory processes restrict the aerobic capacity ofthe exercising muscle and are frequently considered to limit exercise performance when finite boundaries in these processes are reached. However, the recognition of intolerable symptom intensity as the proximal limitation to exer¬ cise presents an opportunity to consider limitation in cardiorespiratory disorders in terms of the expression of impairment through the sensory system. For exam¬ ple, excessive inspiratory effort and exertional dyspnea may be caused by increased activity of the inspiratory muscles due to added mechanical loads, increased ve¬ locity of contraction at shortened muscle length, me¬ chanical disadvantages imposed on the diaphragm, and reduced efficiency of gas exchange.9 In addition, excessive peripheral muscle effort must arise if there is a reduced responsiveness to motor activation as a consequence of disturbances in its metabolic, electro¬ lyte, and acid-base integrity, due to impairments in the cardiorespiratory support to the muscle. Furthermore, CHEST 7110/5/ NOVEMBER, 1996 1255