Training is Medicine for Patients with Peripheral Arterial Disease

Abstract

The objective in the present thesis was to evaluate possible improvements when using training as a treatment for peripheral arterial disease (PAD) patients and to study possible mechanisms behind the adaptations to training. During exercise patients with PAD are limited by muscle pain in the lower extremities, distal to the atherosclerotic lesions, due to lack of oxygen. In the first experiment high aerobic intensity whole body treadmill endurance training was found to be superior to previous recommendations using moderate aerobic intensity. During the 8 weeks of training whole body peak oxygen consumption (VO2peak) and time to exhaustion when walking improved, whereas no changes in blood flow were observed. Since the high aerobic intensity treadmill walking showed muscular, but not cardiac output or stroke volume responses, it was hypothesized in paper II that specific calf muscle individual leg training could result in even better effect on the distal limitations from the PAD. The calf muscle improved its VO2peak by 24%, which resulted in a 12% improvement in treadmill walking VO2peak in line with the hypothesis, and thus demonstrating the muscular limitation to whole body working capacity. The calf muscle endurance training did not improve walking economy and it was hypothesized that maximal strength training could act as a time efficient training intervention to improve walking economy. Paper III documented that leg press maximal strength training effectively increased 1 repetition maximum (1RM), rate of force development (RFD) and peak force (PF). Further, the increased strength led to an increased aerobic endurance performance, measured as improved walking economy. The ~10% improved walking economy resulted in a 14% increase in time to exhaustion when walking, using a ramp protocol. Realizing that the 8 weeks of treadmill training, the calf muscle training as well as the strength training primarily have an effect on the PAD symptoms, and that the underlying atherosclerotic disease is a risk factor for developing cardiovascular disease, the hypothesis in paper IV was that the individual leg calf muscle training can prime PAD patients for improvements in cardiac function in a following whole body training intervention. The 16 weeks training intervention showed an improvement of 27% in VO2peak and a 40% improvement in time to exhaustion using a ramp protocol. Cardiac output and stroke volume improved by 33% and 25% respectively, showing that the primed small muscles’ adaptations do not any longer limit the possibility to address the cardiovascular system efficiently through the treadmill walking training. The structural adaptations in the cardiovascular system represent a substantial risk reduction for other atherosclerotic events. The experiments through this thesis show that the future guidelines for training used as treatment for PAD should imply high aerobic intensity interval training of the calf muscle followed by high aerobic intensity interval training walking on a treadmill. Both interventions should be supported by maximal strength training for the legs. This training regime is designed to treat the disease most efficiently, and to reduce the risk for further cardiovascular disease.