How a walking regimen improves fitness and reduces pain caused by poor blood flow in the legs.
Peripheral arterial disease (PAD) occurs when plaque accumulates in the arteries of the legs. Reduced blood flow and loss of oxygen in the tissues beyond the obstruction cause localized muscular pain, or claudication, especially during exercise (Bulmer & Coombes 2004; Womack & Gardner 2003).
PAD decreases the functional capacity of older adults, who during physical activity often experience intermittent claudication, which can impair their ability to do everyday tasks. Exercise can be an effective, drug-free treatment that enhances functional capacity by altering hemodynamic and metabolic efficiencies.
Pathophysiology of Peripheral Arterial Disease
PAD affects more than 8 million Americans (Rosamond et al. 2008) and is associated with a high risk of cardiovascular death because narrowed arteries limit blood flow to the limbs. Risk factors for PAD include hypertension, diabetes mellitus, hyperlipidemia, premature atherosclerosis and smoking.
Limb ischemia (reduced blood flow) in turn triggers muscle pain (especially in the legs) during weight-bearing exercises; rest usually brings relief. This chronic vascular insufficiency can lead to significant functional impairment (Regensteiner et al. 1993a). As the disease progresses, people may become increasingly incapacitated and lose the ability to perform simple tasks like walking without becoming fatigued. This may lead to muscle fiber denervation, atrophy and altered metabolism (Regensteiner et al. 1993b; Kemp et al. 2001). Thus, it is thought that PAD is a disease characterized not only by hemodynamic insufficiency, but also by subsequent metabolic and mechanical impairments.
In healthy people, blood flow is by far the most important determinant of aerobic capacity. In people with PAD, the contribution of O2 extraction to the aerobic capacity may be more even. The ischemic muscle must work harder to compensate for inadequate blood supply for a given power output. Consequently, the lack of O2 supply favors anaerobic metabolism, leading to an early accumulation of lactate and ending exercise prematurely (Kemp et al. 1995).
It is clear there is a mismatch in O2 delivery and utilization in individuals with PAD. Although revascularization surgery can improve calf-muscle blood flow, studies have not found consistent evidence of an increase in exercise performance (Regensteiner et al. 1993a). Thus, engaging in a long-term, continuous exercise training program to improve metabolic capacity is recommended.
Exercise Testing And Prescription
Older adults with PAD should obtain medical clearance and complete an exercise test before participating in an exercise program. Evaluation protocols include a graded treadmill test and a 6-minute walk test (Womack & Gardner 2003). The degree of claudication pain and time of onset should be recorded during the exercise test. The test should be terminated if a client experiences intense pain or if a cardiovascular abnormality is observed. Questionnaires (such as the Walking Impairment Questionnaire, Physical Activity Recall or Medical Outcomes Study) can be used if a treadmill or walking test cannot be performed (Womack & Gardner 2003).
Exercise can significantly improve functional capacity in older adults with PAD and is therefore considered one of the best ways to treat limb ischemia. The exercise program should aim to relieve symptoms, reduce pain and improve functional performance and quality of life (Wang et al. 2010).
Chronic exercise has been shown to increase walking distance before the onset of leg pain (McDermott et al. 2008). Furthermore, 3 months of exercise has been shown to improve maximum walking distance by as much as 80% (Tan et al. 2000). Even 14 days of physical exercise enhanced blood flow enough to induce improvements in claudication in study participants (Arosioetal. 1999). Aerobic adaptation can also play a significant role in improving functional performance. Exercise training may augment metabolic activity by improving oxidative metabolism and O2 extraction, thus reducing O2 tension and the cost of exercise—and lessening cardiac burden.
Exercise sessions for older adults with PAD mainly focus on aerobic training to optimize functional performance. The preferred training method is walking, because it improves gait patterns and quality of life (Womack & Gardner 2003). Aerobic training is performed in intervals because older adults may be able to walk for only a short time before claudication pain begins. For most, the pain subsides in 5 minutes and the activity can resume (Bulmer & Coombes 2004). This cycle of walking until pain and then resting should continue until the person has achieved the desired duration. For instance, an older adult with PAD may be able to walk for only 5 minutes before the onset of mild to moderate claudication pain. The individual should rest until the pain subsides (about 5 minutes) and then complete another bout of walking. Thus, 20 minutes of exercise will require a 40-minute timeframe.
The recommended frequency for aerobic training is 2–3 days per week (Bulmer & Coombes 2004), with 3 being ideal. Initially, the session should last 20 minutes, at ~40% of heart rate reserve (HRR), and should progress toward 50 minutes with an increase in intensity, up to 70% of HRR. Walking speed is determined by the point where moderate claudication pain occurs within 5 minutes (Womack & Gardner 2003). The grade or speed of the treadmill is increased once a client can complete 8–10 minutes of pain-free walking. If the speed is under 2 miles per hour, then speed is increased. If the speed is over 2 mph, then the grade is increased.
The overall goal is to reach 35–50 minutes of continuous pain-free walking (Lampman & Wolk 2009). Intensity will be gradually advanced as functional performance improves and pain decreases. Peak walking ability should occur after 12–24 weeks of continuous training (Bulmer & Coombes 2004).
While the benefits of aerobic training have been clearly documented to improve functional performance in PAD clients, there is little information on resistance training. Some research has shown that people with PAD lose muscular strength in their lower extremities (McDermott et al. 2008; Wang et al. 2010). Investigators have found that resistance training can increase walking performance (Hiatt et al. 1990), leg strength and rate of force development in people with PAD (Wang et al. 2010). Therefore, older adults with PAD can benefit from resistance training in addition to intermittent walking.
Resistance training should initially focus on major muscle groups in the legs and should progress to including the arms to help with activities of daily living. Intensity should be easy to moderate. Duration should start with 1 set of 8–10 repetitions and gradually progress to 3 sets. Frequency should be 2–3 days per week, and 1 day should be added every 2–3 weeks, as tolerated, to progress toward 5 days of combined aerobic and resistance training (Lampman & Wolk 2009).
Older adults with PAD have reduced functional capacity because of claudication. Thus, health and fitness professionals need to recognize the basic physiological phenomenon behind PAD and develop exercise programs to improve quality of life. Intermittent exercise 2–3 days per week is recommended to achieve 35–50 minutes of continuous pain-free walking.
Older adults should walk until the onset of moderate claudication, then rest and resume activity once the pain subsides. The primary goal is to improve walking efficiency through aerobic training. Resistance training should be a complement to aerobic training and not a substitute.