SELECTIVE LOW-LEVEL LEG MUSCLE TRAINING ALLEVIATES DYSPNEA IN PATIENTS WITH HEART FAILURE
Beniaminovitz A, Lang CC, LaManca J, Mancini DM J Am Coll Cardiol. 2002;40:1602-1608
Background.
Dyspnea is a frequent limiting symptom in patients (pts) with heart failure (HF) and has been suggested to originate from the various receptors in muscle tissue that respond to changes in metabolic activity and result in increased respiratory drive. Respiratory muscle training reduces dyspnea during submaximal exercise. Aerobic exercise-training, which conditions both respiratory and peripheral muscles, also diminishes exercise dyspnea. However, it is not known whether selective training of limb muscles would have the same effects.
Objective.
To investigate whether dyspnea can be affected by selective exercise training of leg muscles at a low level that does not condition the respiratory muscles.
Methods.
Patients with HF (N = 29) were randomized to exercise training (n = 20) or control (n = 9). Supervised exercise training three times per week consisted of 15 minutes each of bicycle and treadmill workloads corresponding to 50% of peak VO2, minute ventilation < 25 liters per minute and heart rate (HR) < 120 beats per minute. Leg calisthenics, including hip flexion and extension with ankle weights (5 pound per leg) and thigh muscle contraction using Therabands, were performed. Each month, an additional set of exercises was added, ankle weights were increased by 2 pounds per leg, and Theraband resistance was increased. The control group had guided imagery training, including 90 minutes per week of therapist-guided sessions for 1 month, and a series of relaxation and imagery exercises that promoted stress reduction. Patients were provided with a 15-minute audio-imagery tape and were instructed to listen to the tape and perform the mental exercises twice daily.
Results.
Peak oxygen uptake (VO2) and VO2 at anaerobic threshold were unchanged in the control group. However, significant increases were observed in the training group. HR and blood pressure responses to exercise were unchanged in both groups. Submaximal exercise performance assessed by the duration of a single load of exercise was unchanged in the control group but markedly improved in the training group. The 6-minute walk test was significantly improved in the training but not in the control group. With training, peak flexor and extensor torque significantly increased in the training group, but not in the control group. Endurance reflected by the fatigue ratio was unchanged for both flexors and extensors in the control group but was significantly improved with training. Guided imagery did not significantly affect the scoring for the Minnesota Living with Heart Failure or the Guyatt Respiratory Scales. Low-level training significantly improved these scores. Perceived dyspnea and fatigue during maximal exercise was unchanged in both groups, although these were significantly lower during single-load exercise in the training group.
Conclusions.
Exercise training of selective lower-leg muscles improved submaximal and maximal exercise performance and alleviated dyspnea in patients with HF. Perceived dyspnea during a single load of exercise was significantly decreased with training. Quality-of-life scores were all improved by training.
Comment.
This study demonstrates that improved peripheral skeletal muscle function favorably affects dyspnea, and provides additional evidence of the importance of exercise training in reducing symptoms of HF.
EXERCISE TYPE AND INTENSITY IN RELATION TO CORONARY HEART DISEASE IN MEN
Tanasescu M, Leitzmann MF, Rimm EB, et al JAMA. 2002;288:1994-2000
Background.
Previous studies have shown an inverse relationship between exercise and risk of coronary heart disease (CHD), but data on type and intensity are sparse.
Objective.
To assess the amount, type, and intensity of physical activity in relation to risk of CHD among men.
Methods.
Men (N = 44,452) enrolled in the Health Professionals' Follow-up Study were followed at 2-year intervals from 1986-1998 to assess potential CHD risk factors; identify newly diagnosed cases of CHD, including nonfatal myocardial infarction or fatal CHD; and assess levels of leisure-time physical activity. Leisure-time physical activity was assessed every 2 years between 1986 and 1996, using the question: "During the past year what was your average time per week spent at each activity?" Activities were divided into various intensity levels (eg, walking pace) categorized as casual (<= 2 mph), normal (2 to 2.9 mph), brisk (3 to 3.9 mph), or striding (>= 4 mph). The time spent at each activity in hours per week was multiplied by its typical energy expenditure, expressed in metabolic equivalent (MET) tasks, then summed over all activities, to yield a MET-hour score.
Results.
Newly documented CHD were observed in 1700 subjects. Total physical activity, running, weight training, and rowing were each inversely associated with risk of CHD. Men who ran for an hour or more per week had a 42% risk reduction compared with men who did not run. Men who trained with weights for 30 minutes or more per week had a 23% risk reduction compared with men who did not train with weights. Rowing for 1 hour or more per week was associated with an 18% risk reduction. Exercise intensity was associated with reduced CHD risk, independent of the total volume of physical activity. A half-hour or more per day of brisk walking was associated with an 18% risk reduction. Walking pace was associated with reduced CHD risk, independent of the number of walking hours.
Conclusions.
Increased total physical activity was associated with reduced risk of CHD in a dose-dependent manner. The inverse association was not explained by other known coronary risk factors, including body mass index. Exercise intensity was associated with an additional risk reduction. Running, weight training, and rowing were each associated with reduced risk. Walking pace was strongly related to reduced risk, independent of number of walking hours.
Comment.
The size of the study cohort and the prospective study design are significant strengths to this investigation. Although the physical activity portion of the study is a self-report, the magnitude of the project offsets some of the potential impact of this limitation. A particularly interesting finding is the risk reduction associated with resistance training.