|Maximizing Functional Abilities in the Older Adult
Jeff M. Janot, Ph.D. and Len Kravitz, Ph.D.
Ask yourself, what are the biggest challenges facing our nations health care system in this new century? One may think of the increasing prevalence of many chronic diseases such as cardiovascular disease or diabetes, finding a cure for many types of diseases, or meeting the legislative challenges of managed care in our hospitals and clinics. One could also argue that the biggest challenge is successfully managing what some may call the aging of America. With life expectancy increasing due to improvements in medical care and technology and the baby-boom generation now reaching middle age, the population of older adults in our country will continue to grow in magnitude. In fact, the number of Americans over the age of 65 years old is expected to double to an astounding 70 million by the year 2040 (Hurley & Hagberg, 1998). Also, by the year 2040, 1 out of 4 Americans will be an older adult and 12 million Americans will be over the age of 85 years old. Undoubtedly, this will place an increasing strain on the medical community to care for an aging population, as health care costs would most likely have to rise to meet these needs. However, we, as health and fitness professionals, should welcome this challenge. As more emphasis is placed on the prevention of age-related diseases and increasing quality of life, we can make a profound impact on the quality and cost of health care and ultimately alleviate some of the future problems facing our health care system.
According to the American College of Sports Medicine (ACSM), the goals of an exercise program for older individuals are maintenance of functional capacity for independent living, reduction in the risk of cardiovascular disease, retardation of the progression of chronic diseases, promotion of psychological well-being, and provision of opportunities for social interaction (ACSM, 2000). With these goals in mind, it is critical for exercise professionals to be well-informed regarding the effects of the aging process on the human body and how exercise can best be used to positively influence this process. Therefore, the purpose of this article is to present information on the physiological effects of the aging process and provide scientific evidence on the effects of both aerobic and resistance training on selected age-related disorders in order to assist exercise professionals in creating safe and effective exercise prescriptions for their older clients.
Physiological effects of the aging process
There are many competing theories on how the aging process occurs and progresses throughout the life span: genetic mutations in DNA, free radical formation and accumulation, cellular wear-and-tear, and immune system dysfunction (Robergs & Roberts, 1997). Although we dont know for a fact how the aging process works, one thing we know for sure is that aging is inevitable. So, what is the best way to define aging? A more direct and less-flattering definition of aging is a progressive loss of physiological capacities that ultimately culminates in death (Robergs & Roberts, 1997). An alternative, more general definition of aging that better suits the purpose of this article is that of a process where normal, yet irreversible, biological changes occur throughout a persons lifetime. These biological changes involve many different organs and systems throughout the body, and will often differ between individuals of similar age (ACSM, 2000). Also, these changes are often associated with specific physiological effects (summarized in Table 1), as well as with underlying disorders and disease processes of the body.
The most notable change in cardiovascular function is observed in the decrement of maximal oxygen consumption (VO2max) with advancing age (10% decrease per decade after 30 years old), which can be considered as an indirect measure of cardiovascular function (Hurley & Roth, 2000; Robergs & Roberts, 1997). The change in VO2max has been most attributed to age-related decreases in maximal cardiac output, stroke volume, and heart rate (Makrides et al., 1990), which are ultimately affected by a decrease in the systolic (ability to contract) and diastolic (ability to relax) function of the heart. According to Robergs and Roberts (1997), a 30% decrease in stroke volume between the ages of 25-85 years old contributes most to the age-related decreases in VO2max.
Past research shows that blood pressure is increased at rest in older adults (ACSM, 2000; Hurley & Roth, 2000; Robergs & Roberts, 1997). Specifically, systolic blood pressure is elevated at rest due to increases in systemic vascular resistance, which hinders the flow of blood through the cardiovascular system and forces the heart to work harder to eject blood. Decreases in arterial vessel elasticity have also been shown to contribute to elevated SBP at rest with advancing age (Robergs & Roberts, 1997).
The large, age-related decline in muscular strength is probably the most prominent change that occurs in older adults. Losses in muscular strength occur at an approximate rate of 12-14% per decade after the age 50 years old (Hurley & Roth, 2000). Moderate to large decreases in muscular power and endurance are also observed with advancing age. The changes in muscular function associated with aging are most likely secondary to losses in muscle mass and total cross-sectional area (ACSM, 2000; Robergs & Roberts, 1997). Muscular flexibility is also inversely related to age, and is most likely attributable to losses in muscular elasticity and changes in the structure of collagen fibers within joints.
Another very prominent change that occurs with aging is loss in bone mineral mass and density. On average, 10-20% of our total bone mass is lost by the time we reach an age of 65 years old (Robergs & Roberts, 1997). Interestingly, there is also a gender component affecting the rate at which we lose bone mass, with men losing bone at a rate of approximately 1% per year after the age of 50. In contrast, women lose bone at a rate of approximately 2-3% per year after menopause, and are already losing bone mass by the time they reach their early 30s. Unfortunately as women continue to age, the loss of bone mass predisposes them to a greater chance of developing osteoporosis (decreased bone mineral density), and are at increased risk of bone fractures due to falling. Osteoporosis affects approximately 25 million Americans, most prevalent in women, and runs health care costs into the range of 18 billion dollars per year (Hurley & Hagberg, 1998). It is evident by these statistics that the development of effective treatment and prevention programs are much needed to combat this disease.
There are many metabolic changes that occur in the aging process, most notably decreases in glucose tolerance and insulin sensitivity accompanied by moderate to large increases in total body and intra-abdominal fat and decreases in resting metabolic rate (ACSM, 2000; Hurley & Roth, 2000; Robergs & Roberts, 1997). The changes observed in body abdominal fat and resting metabolic rate is commonly referred to as the abdominal obesity syndrome (Hurley & Roth, 2000). This syndrome, in conjunction with abnormal glucose and insulin responses at rest, greatly increases the risk for the development of diabetes mellitus, as well as increased predisposition to developing cardiovascular disease, such as atherosclerosis and stroke. The problem facing older individuals who are at risk for cardiovascular disease is that it is the leading cause of death (along with cancer) in people 65 years of age or older (Robergs & Roberts, 1997). Currently, there are an approximate 15.7 million Americans who have diabetes, which is expected to increase within the next decade and reach epidemic proportions in this country and worldwide (American Diabetics Association, 2000). It is apparent that the development of effective strategies for the prevention and treatment of diabetes are also warranted. Fortunately, the risk factors for developing diabetes can be modifiable by engaging in an effective exercise program and other change of lifestyle factors (Janot & Kravitz, 2000).
Other metabolic changes that occur due to the aging process are abnormal blood cholesterol levels and decreased immune function (ACSM, 2000; Robergs & Roberts, 1997). However, research demonstrating changes in cholesterol levels have produced mixed results (Hurley & Hagberg, 1998). Decreased high-density (HDL) and increased low-density (LDL) lipoprotein and triglyceride concentrations have been shown with increasing age; whereas, total cholesterol may actually decrease or remain constant.
The majority of age-related pulmonary function changes affect the ability to move air in and out of the lungs per minute (minute ventilation) and in one maximal breath (vital capacity), as well as the diffusion of oxygen and carbon dioxide across the alveolar-blood vessel spaces. The observed changes in the ability to adequately ventilate can be traced to losses in respiratory muscle strength (Robergs & Roberts, 1997). The age-related losses in alveolar elasticity combined with decreases in alveolar surface area, which is need for adequate exchange of lung and blood gases, leads to an increase in residual volume and a diminished capacity for gas diffusion (ACSM, 2000). If less air is in contact with blood flowing through the lungs (ventilation/perfusion mismatching), less oxygen can get to the working muscles for the production of energy, thus leading to losses in muscle function and the ability to perform exercise.
Benefits of aerobic and resistance training: which is best for the older adult?
For years, research on the physiological adaptations to aerobic and resistance training has been only focused on younger to middle age individuals. Fortunately, the body of research using older individuals as subjects has continued to steadily increase since the 1980s, with more emphasis placed on understanding adaptations to resistance training. However, much more research studies are needed to understand the physiological responses of the very old to aerobic and resistance training. The following section is meant to present scientific data on the effects of aerobic and resistance training on the age-related changes on selected physiological variables in older individuals (see Table 2).
VO2max and endurance performance. VO2max is a major determinant of functional capacity in individuals of all ages. As mentioned earlier, there is a 10% decrease in VO2max per decade after reaching 30 years of age. Therefore, one of the problems facing older individuals is maintaining an optimal level of functional capacity in order to perform activities of daily living and promote independence. Various research studies have shown that aerobic training is an effective method in combating age-related decreases in functional capacity, and adaptations to training are similar to those in younger subjects (Makrides et al., 1990; Meredith et al., 1989; Suominen et al., 1977).
Spina et al. (1993) investigated the relative contributions of increases in cardiac output and arterial-venous oxygen difference to the aerobic training-induced increases in VO2max in older men and women. After 9-12 months of moderate to high intensity training, VO2max increased by 19% and 22% in men and women, respectively. The increased VO2max values in men were primarily due to increased central cardiovascular function (cardiac output and stroke volume); whereas, women increased their ability to extract oxygen at their working muscles and not central cardiovascular function. Cononie et al. (1991) and Makrides et al. (1990) observed a 20% and 38% increase in VO2max following high-intensity aerobic training in their subjects, respectively. Makrides et al. attributed the increase in VO2max to a 30% increase in cardiac output. Suominen et al. (1977) revealed that increases in aerobic metabolism enzymes in skeletal muscle led to improvements in VO2max (11%) following 8 weeks of aerobic training in men 56 to 70 years old. By combining both aerobic and resistance training, Ferketich et al. (1998) found that VO2peak was increased by 30% compared to only 25% with aerobic training in older women, in addition to also increasing leg strength by 112%.
No substantial increases in VO2max due to resistance training have been observed in the research literature. However, in a study by Ades et al. (1996), subjects did increase their time to exhaustion (~33%) during treadmill walking at 80% of aerobic capacity after a 12-week resistance training program. Wosornu et al. (1996) observed a smaller increase (16%) in walking endurance following 6 months of resistance training, compared to a 30% increase due to aerobic training. The increase in endurance performance after resistance training was attributed to significant increases in lower body strength despite no increases in VO2max. This was an important finding since increased leg strength has now been linked to increases in functional capacity in older adults.
Blood pressure. Since hypertension is a major risk factor for coronary artery disease and the leading cause of stroke in this country, finding meaningful prevention and treatment strategies is imperative. Aerobic exercise was the first training method employed to modify blood pressure in subjects of all ages. In general, aerobic exercise training has been shown to decrease blood pressure by 8-10 mmHg in those individuals who have high normal blood pressure or mild hypertension (ACSM, 2000).
The effects of resistance training on blood pressure have been less clear due to contrasting results in the research literature (ACSM, 2000). Hurley and Roth (2000) stated that resistance training can normalize blood pressure in those individuals with high normal blood pressure (130s/80s). Cononie et al. (1991) and Smutok et al. (1993) compared the effects of aerobic and resistance training on resting blood pressure in older adults. Smutok et al. found no effects of 20-weeks of aerobic or resistance training on blood pressure in men at risk for coronary artery disease. In contrast, Cononie et al. observed modest reductions of 8 and 9 mmHg in systolic and diastolic pressure, respectively, following 6 months of aerobic training, but not resistance training, in subjects who had mild hypertension at rest.
Muscular strength, mass, and cross-sectional area. Resistance training is generally thought to be a promising intervention for reversing the loss of muscle function and deterioration of muscle structure associated with the aging process (Hurley & Roth, 2000). The well-documented losses of muscular strength and mass (called sarcopenia) are associated with increased susceptibility to disability among older adults, decreases in bone mineral density, increased risk of developing diabetes, and increased risk of falls and hip fractures. In fact, age-related losses in muscle mass approximate 6% per decade after age 50, and is further associated with decreases in muscle cross-sectional area with increasing age (Hurley & Roth, 2000). According to Rhodes et al. (2000), 28% of men and 66% of women above the age of 74 can not lift more than 10 pounds. Due to these age-related changes, increasing muscular strength and mass in older adults is important for maintaining health status and functional capacity. Improving muscular strength alone may be more important than increasing cardiovascular function because of its independent association with increased functional ability in older adults (Hurley & Roth, 2000).
According to Hurley and Roth (2000), strength and mass gains can exceed 30% and 12%, respectively, after two months of resistance training in older men and women. Interestingly, two decades of strength and mass loss can be reversed after engaging in resistance training for at least two months. Morganti et al. (1995) studied the effects of one year of progressive, high-intensity (80% 1 RM) resistance training in post-menopausal women, and found that strength increased by 74%, 35%, and 77% in knee extension, leg press, and lateral pull-down exercise following training. Half of the strength gains observed in these subjects occurred in the first 3 months of the training program. Taffe et al. (1999) also documented significant increases in muscular strength after a 1-day per week, high-intensity resistance training program compared to 2 and 3 days per week programs.
Resistance training programs for older adults have also been shown to increase muscular hypertrophy (cross-sectional area) and decrease the risk of falling. Frontera et al. (1988) demonstrated significant increases in knee extensor and flexor strength accompanied by increases in total thigh area (4.8%) following a high-intensity, 12-week resistance program in 60-72 year old men. Regarding the risk of falls, Buchner et al. (1997) reported a 42% risk of falling in their trained subjects compared to 60% in the control group. This is a very important finding when considering that injuries due to falling in older adults, especially older women (Rhodes et al., 2000), severely limit functional capacity and independence, and contribute to increased hospitalization and mortality.
Bone mineral density. Maintaining bone mineral density with advancing age is critical in preventing osteoporosis in older men and women. Physical activity is generally regarded as an important stimulus for bone modeling and remodeling (Hughes et al, 1995). Thus, aerobic and resistance training can have beneficial effects in the prevention of losses of bone mineral density, but resistance training may be more consistent in providing a beneficial effects, especially in postmenopausal women (Hurley & Hagberg, 1998). Weight-bearing aerobic exercise is by far more helpful in maintaining bone mineral density than non-weight-bearing exercise (Hughes et al, 1995). It should also be noted that very few studies have demonstrated an increase in bone mineral density following an exercise training program. However, Dalsky et al. (1988) reported an increase in bone mineral density in postmenopausal women who followed an aerobic training program with calcium supplementation compared to women given only calcium supplementation.
Simultaneous decreases in bone mineral density and muscle mass have been shown with advancing age and a sedentary lifestyle (Hughes et al., 1995). The most effective way to deter these losses is through engaging in a resistance training program. Rhodes et al. (2000) studied the effects of a year-long resistance training program on strength and bone mineral density in postmenopausal women (mean age = 68.8 years). The high-intensity program elicited a 20-30% increase in muscular strength and was moderately correlated with the maintenance of bone mineral density. In addition, Yarasheski et al. (1997) found slight increases in regional bone density following 16 weeks of high-intensity resistance training, but they were not greater than subjects who supplemented growth hormone throughout the study.
Glucose tolerance and insulin sensitivity. Age-related abnormalities in glucose metabolism and insulin resistance are markers of increased risk for developing diabetes. Exercise training can positively alter these variables and prevent the development of diabetes and the complications associated with this disease.
The effects of aerobic and resistance training on glucose tolerance have consistently showed that glucose concentration at rest is not altered, unless it is already elevated above normal levels (DiPietro et al, 1988; Hersey et al, 1994; Kahn et al, 1990; Miller et al, 1994; Ryan et al, 1996; Seals et al, 1984). The explanation for this is that insulin sensitivity, marked by a lower insulin response for a given amount of blood glucose, is most likely improved during both types of training, which maintains a constant blood glucose concentration. The majority of studies show this response in normal, healthy older adults. Hersey et al. (1994) and Seals et al. (1984) reported significant decreases in insulin response to artificial increases in blood glucose after aerobic exercise training. Seals et al. showed a difference in insulin responses after low- and high-intensity training, with the largest decrease (23%) in insulin occurring after the high-intensity training. Kahn et al. (1990) showed the largest decrease (36%) in insulin response in subjects, aged 61-82 years, following 6 months of intensive (5 days/week) aerobic training. When resistance training is employed, Ryan et al. (1996) observed the greatest (43% vs 29%) decrease in insulin response when resistance training is accompanied by weight loss rather than not in obese, postmenopausal women. This study showed that resistance training can make a significant impact on insulin sensitivity and has the potential for preventing the development of type 2 diabetes in this subject population.
Body fat and resting metabolic rate. Resting metabolic rate decreases at an approximate rate of 10% from early adulthood to retirement age, with further decreases beyond age 65. The age-associated decrease in resting energy expenditure accompanied by an inability to maintain adequate energy balance leads to negative changes in body composition (Treuth et al, 1995). The most deleterious effect of this cascade of events is an increase in intra-abdominal fat, which has been strongly linked to the incidence of cardiovascular disease and diabetes (Kohrt et al, 1992). Thus, finding interventions to target this region to decrease body fat is very much needed.
Both aerobic and resistance training have demonstrated effectiveness in decreasing total, as well as intra-abdominal, body fat (Cononie et al, 1991; Kohrt et al, 1992; Treuth et al, 1995). Two studies by Treuth and colleagues clearly presented the effectiveness of resistance training in this regard. In the first study by Treuth and colleagues (1994), 16 weeks of training was shown to significantly increase fat-free mass and decrease total fat mass by 4.5 pounds in older men. In the second study, a significant decrease in intra-abdominal fat with no changes in fat-free mass and total body fat was observed following 16 weeks of resistance training in older women (Treuth et al., 1995). Subjects in both studies significantly increased their lower and upper body muscular strength. Kohrt et al. (1992) evaluated the changes in body composition and fat distribution patterns after 9-12 months of vigorous aerobic training in 60-70 year old men and women. Aerobic training significantly decreased total body fat, most predominately in the abdominal/trunk region, with no change in fat-free mass. It is clear by these studies that aerobic and resistance training can effectively modify the risk of developing cardiovascular disease by decreasing intra-abdominal body fat.
Changes in body fat are most attributable to changes in muscle mass that is associated with increases in resting metabolic rate. If this were in fact true, resistance training would then be the best method for increasing resting metabolic rate and caloric expenditure. Pratley et al. (1994) and Campbell et al. (1994) reported increases in resting metabolic rate following a resistance training program in older men and women. These increases were attributed to increases in fat-free mass. Since aerobic exercise training does not increase fat-free mass, but still elicits increases in resting metabolic rate, other mechanisms must explain these changes in older adults. One explanation that has been theorized is a modulation of sympathetic nervous system activity and its effects on metabolic rate and fat oxidation (Poehlman et al, 1992; Poehlman et al, 1994). Increases in resting metabolic rate were observed in these two studies and ranged from 7-9% following aerobic training. The increases in metabolic rate were independent of increases in fat-free mass, and were attributed to increases in sympathetic nervous system activity.
There is little evidence to support the positive effects of resistance training on blood lipid profiles in older adults (Hurley & Roth, 2000). Most of the studies that are designed to examine the effects of resistance training do not adequately control changes in body weight, nutrition, and day-to-day fluctuations in blood cholesterol. Smutok et al. (1993) and Wosornu et al. (1996) reported no significant effects of either aerobic or resistance training on the blood cholesterol levels in male subjects following a 5-6 month program. However, Seals et al. (1984) showed significant increases in HDL cholesterol, but not LDL, following a 12-month, high-intensity aerobic exercise program in older men and women. In agreement with these findings, Sunami et al. (1999) revealed that aerobic exercise, even at lower-intensities and longer durations, could significantly improve HDL cholesterol profiles in older men and women.
Conclusions and Final Thoughts
As previously discussed, the continued aging of America could very easily burden our nations health care system in such a way as to affect the future quality and cost of medical care. Consider that the one of the main goals of physical activity for older adults is to alter the progression or prevent age-related disorders or diseases that, if left alone, may lead to increased hospitalizations and further disease complications accompanied by losses in functional capacity. It is clear that the greatest impact exercise professionals can make on the lives of older adults is to assist them in regaining or increasing their level of functional capacity and optimize independence and their ability to perform regular activities of daily living. This can be accomplished through creating your clients exercise prescription around the combination of aerobic and resistance training, which will thoroughly maximize the health and fitness benefits of the program and combat the often deleterious effects of aging. Based on the scientific data presented in this article, aerobic or resistance training has been shown to positively affect a number of physiological variables that are influenced by the aging process by increasing muscular strength and endurance, improving glucose tolerance and insulin sensitivity, increasing bone mineral density in order to slow the process of osteoporosis, decreasing total and intra-abdominal fat and increasing resting metabolic rate, normalizing already high normal blood pressure numbers, and possibly improving blood lipid profiles. Finally, putting scientific data aside, the last step is helping your clients understand the important benefits of exercise and how it positively influences the aging process. Remember, keep it simple and just tell them that you dont stop playing because you grow old, you grow old because you stop playing!.
Table 1. Age-related effects on selected physiological variables
Physiological variable: Age-related effect
VO2max: moderate-large decrease
max Q, SV, HR: decrease
resting systolic blood pressure: increase
systemic vascular resistance: increase
blood vessel elasticity: decrease
muscular strength: large decrease
muscular endurance and power: moderate-large decrease
muscle mass: moderate-large decrease
muscle cross-sectional area: decrease
muscular flexibility: decrease
bone mineral density: decrease
glucose tolerance: decrease
insulin sensitivity: decrease
total body fat: moderate-large increase
intra-abdominal fat: increase
resting metabolic rate: decrease
total cholesterol: decrease or remain the same
triglycerides, LDL cholesterol: increase
HDL cholesterol: decrease
immune function: decrease
residual volume: increase
alveolar surface area and elasticity: decrease
gas diffusion ability: decrease
vital capacity: decrease
ventilation/perfusion mismatching: increase
Table 2. Effects of aerobic and resistance training on selected physiological variables in older adults
Physiological variable: Aerobic vs Resistance
VO2max: Increase vs No change
Endurance (time to fatigue): Increase vs Increase
Blood pressure: Decrease vs Decrease or no change
Muscular strength: No change vs Large increase
Muscle mass: No change vs Mod-large increase
Muscle cross-sectional area: No change vs Increase
Bone mineral density: Increase vs Increase
Glucose tolerance: No change if normal vs No change if normal
Insulin sensitivity: Increase vs Increase
Total body fat: Decrease vs Decrease
Intra-abdominal fat: Decrease vs Decrease
Resting metabolic rate: Increase vs Increase (women?)
Total cholesterol: No change vs No change
HDL cholesterol: Increase vs No change
LDL cholesterol: No change vs No change
ACSM. 2000. ACSMs guidelines for exercise testing and prescription (6th ed.). Baltimore, MD: Lippincott, Williams, & Wilkins.
Ades, P., et al. 1996. Weight training improves walking endurance in healthy elderly persons. Annals of Internal Medicine, 124, 568-72.
American Diabetes Association. 2000. www.diabetes.org.
Buchner, D., et al. 1997. The effect of strength and endurance training on gait, balance, fall risk, and health services use in community-living older adults. Journal of Gerontology, 52, M218-M224.
Campbell, W., et al. 1994. Increased energy requirements and changes in body composition with resistive training in older adults. American Journal of Clinical Nutrition, 60, 167-75.
Cononie, C., et al. 1991. Effect of exercise training on blood pressure in 70- to 79-year old men and women. Medicine and Science in Sports and Exercise, 23, 505-11.
Dalsky, G., et al. 1988. Weight-bearing exercise training and lumbar bone mineral content in postmenopausal women. Annals of Internal Medicine, 108, 824-28.
DiPietro, L., et al. 1988. Moderate-intensity aerobic training improves glucose tolerance in aging independent of abdominal adiposity. Journal of the American Geriatric Society, 46, 875-79.
Ferketich, A., et al. 1998. Cardiovascular and muscular adaptations to combined endurance and strength training in elderly women. Acta Physiologica Scandinavica, 164, 259-67.
Frontera, W., et al. 1988. Strength conditioning in older men and skeletal hypertrophy and improved function. Journal of Applied Physiology, 64, 1038-44.
Hersey, L., et al. 1994. Endurance exercise training improves body composition and plasma insulin response in 70-79 year old men and women. Metabolism, 43, 847-54.
Hughes, V., et al. 1995. Muscle strength and body composition: associations with bone density in older subjects. Medicine and Science in Sports and Exercise, 27, 967-74.
Hurley, B. & Hagberg, J. 1998. Optimizing health in older persons: aerobic or strength training?. Exercise and Sports Science Review, 26, 61-89.
Hurley, B. & Roth, S. 2000. Strength training in the elderly: effects on risk factors for age-related diseases. Sports Medicine, 30, 244-68.
Janot, J. & Kravitz, L. 2000. Training clients with diabetes. IDEA Personal Trainer. 5, 15-17.
Kahn, S., et al. 1990. Effect of exercise on insulin action, glucose tolerance, and insulin secretion in aging. American Journal of Physiology, 258, E937-E943.
Kohrt, W., et al. 1992. Exercise training improves fat distribution patterns in 60-70 year old men and women. Journal of Gerontology, 47, M99-M105.
Makrides, L., et al. 1990. High-intensity endurance training in 20- to 30- and 60- to 70-year old healthy men. Journal of Applied Physiology, 69, 1792-98.
Meredith, C., et al. 1989. Peripheral effects of endurance training in young and old subjects. Journal of Applied Physiology, 66, 2844-49.
Miller, J., et al. 1994. Strength training increases insulin action in healthy 50 to 65 yr-old men. Journal of Applied Physiology, 77, 1122-27.
Morganti, C., et al. 1995. Strength improvements with 1 year of progressive resistance training in older women. Medicine and Science in Sports and Exercise, 27, 906-12.
Poehlman et al. 1992. Influence of endurance training on energy intake, norepinephrine kinetics, and metabolic rate in older individuals. Metabolism, 41, 941-48.
Poehlman et al. 1994. Effects of endurance training on total fat oxidation in elderly persons. Journal of Applied Physiology, 76, 2281-87.
Pratley, R., et al. 1994. Strength training increases resting metabolic rate and norepinephrine levels in healthy 50- to 65-yr-old men. Journal of Applied Physiology, 76, 133-37.
Rhodes, E., et al. 2000. Effects of one year of resistance training on the relation between muscular strength and bone density in elderly women. British Journal of Sports Medicine, 34, 18-22.
Robergs, R. & Roberts, S. 1997. Exercise Physiology: exercise, performance, and clinical applications (1st ed.). St. Louis, MO: Mosby-Yearbook, Inc.
Ryan, A., et al. 1996. Resistive training increases insulin action in postmenopausal women. Journal of Gerontology, 51, M199-M205.
Seals, D., et al. 1984. Effects of endurance training on glucose tolerance and plasma lipid levels in older men and women. Journal of the American Medical Association, 252, 645-49.
Smutok, M., et al. 1993. Aerobic versus strength training for risk factor intervention in middle-aged men at high risk for coronary heart disease. Metabolism, 42, 177-84.
Spina, R., et al. 1993. Differences in cardiovascular adaptations to endurance exercise training between older men and women. Journal of Applied Physiology, 75, 844-55.
Sunami, Y., et al. 1999. Effects of low-intensity aerobic training on the high-density lipoprotein cholesterol concentration in healthy elderly subjects. Metabolism, 48, 984-88.
Suominen, H., et al. 1997. Effects of 8 weeks of endurance training on skeletal muscle metabolism in 56-70 year-old sedentary men. European Journal of Applied Physiology, 37, 173-80.
Taaffe, D., et al. 1999. Once-weekly resistance exercise improves muscle strength and neuromuscular performance in older adults. Journal of the American Geriatric Society, 47, 1208-14.
Treuth, M. et al. 1994. Effects of strength training on total and regional body composition in older men. Journal of Applied Physiology, 77, 614-20.
Treuth, M. et al. 1995. Reduction in intra-abdominal adipose tissue after strength training in older women. Journal of Applied Physiology, 78, 1425-31.
Wosornu, D., et al. 1996. A comparison of the effects of strength and aerobic exercise training on exercise capacity and lipids after coronary artery bypass surgery. European Heart Journal, 17, 854-63.
Yarasheski, K., et al. 1997. Effect of resistance exercise and growth hormone on bone density in older men. Clinical Endocrinology, 47, 223-29.