During the past few years, there has been considerable interest in the aging process, and several studies have examined strategies for delaying various degenerative responses. Perhaps the most obvious and misunderstood aspect of the aging process is the undesirable change in body composition and physical appearance. It is estimated that approximately 80 percent of Americans are sedentary and that 75 percent of adults are overweight. There would appear to be a strong association between doing too little exercise and having too much bodyweight.
Generally, men and women add about 10 pounds of bodyweight every decade during the midlife years. The typical response is dieting, and according to a Tufts University study, about 40 percent of American adults are presently following restricted-calorie diets. Unfortunately, dieting without exercise does not have a very high record of success. First, only 50 percent of those who begin dieting complete the program. Second, of those individuals who do lose weight, more than 90 percent regain it within one year. Third, about 25 percent of the weight lost during low-calorie diets is actually muscle tissue, which is already in short supply among most older adults.
Research shows that men and women lose more than five pounds of lean body mass (mostly muscle) every decade of life due to disuse. So the 10 pound per decade increase in bodyweight actually represents a 20 pound problem with respect to body composition. That is, on a decade-by-decade basis, the aging adult has about five pounds less muscle and about 15 pounds more fat for a 20 pound change in physical appearance. This process is illustrated in Figure 1.
Because our muscles are the engines of our bodies, muscle loss has a profound impact on our physical ability and functional capacity. Losing muscle is similar to going from an eight-cylinder engine to a four-cylinder engine. As engine size is closely associated with fuel utilization, it is not hard to understand why less muscle leads to a lower metabolic rate. In fact, the progressive reduction in muscle tissue is largely responsible for a two-to-five percent per decade decrease in our resting metabolism.
When our resting metabolic rate slows down, calories that were previously used by muscle tissue are now routed into fat storage. In other words, the progressive weight gain known as creeping obesity is typically due to fewer calories being burned rather than more calories being consumed. That is why dieting does not solve the problem. In fact, dieting exacerbates the problem by further reducing muscle tissue and metabolic rate.
While adults should perform regular endurance exercise, such as walking and cycling, to enhance cardiovascular function, aerobic activities do little to prevent the gradual deterioration of the musculoskeletal system. In a study of elite middle-aged runners, the subjects lost about five pounds of muscle over a 10-year period in spite of extensive aerobic training.
If losing muscle is the basic problem then adding muscle should be the logical solution. But is it possible for older adults to replace the muscle they have already forfeited? Absolutely. In fact, several studies have shown that both muscle strength and mass can be increased at essentially any age through systematic strength training.
With respect to reversing body composition problems, strength exercise is effective for adding muscle, losing fat, raising resting metabolic rate, and increasing daily energy expenditure. Consider the results of a Tuft University study conducted by Campbell and his colleagues. After 12 weeks of strength training (about 30 minutes per session, three days per week), 12 senior men and women added about three pounds of lean (muscle) weight, lost about four pounds of fat weight, raised their resting metabolism by almost seven percent, and increased their daily energy expenditure by 15 percent. That is, three months of relatively brief strength training sessions enabled these older adults to replace muscle, reduce fat and eat about 350 more calories per day in the process.
In a similar study conducted at the South Shore YMCA, 85 senior men and women performed about 30 minutes of strength exercise and 20 minutes of endurance exercise two days per week for a period of eight weeks. On average, the exercisers added two pounds of lean (muscle) weight, lost four pounds of fat weight, and increased their overall muscle strength by about 50 percent.
In addition to replacing muscle tissue, research reveals that men and women of all ages can increase their bone mineral density through regular strength training. Studies with senior men and senior women have shown significant gains in bone mineral density, indicating that strength exercise may reduce the risk of osteoporosis.
Another benefit of strength training is an enhanced glucose metabolism that may reduce the risk of adult onset diabetes. Research at the University of Maryland showed a 23 percent improvement in glucose metabolism after four months of strength exercise.
Another study at the University of Maryland demonstrated a 56 percent increase in gastrointestinal transit speed following three months of strength exercise. Because faster gastrointestinal transit speed may reduce the risk of colon cancer, this finding has important implications for older adults.
Researchers at the University of Florida have demonstrated that properly performed strength training can significantly reduce low back pain, and researchers at Tufts University have determined that strength exercise can alleviate arthritic discomfort.
Contrary to popular opinion, regular strength training results in lower resting blood pressure in seniors as well as in mildly hypertensive individuals. Strength exercise has also been shown to improve blood cholesterol profiles.
In addition to the physiological benefits associated with strength training, a recent Harvard University study showed significant psychological improvements as well. After 12 weeks of strength exercise 14 of 16 depressed seniors subjects no longer met the criteria for clinical depression.
Of course, for most men and women the major outcomes of strength training are simply looking better, feeling better, and functioning better on a day-to-day basis. Fortunately, seniors respond just as well to strength exercise as younger adults.
Senior Study Results
A large-scale study conducted at the South Shore YMCA compared the results of young, middle, and older adults following an eight-week training program consisting of about 30 minutes of strength exercise and 20 minutes of endurance exercise.
The 1132 participants in this study included 238 young adults (21 to 40 years), 553 middle-aged adults (41 to 60 years), and 341 older adults (61 to 80 years). As shown in Table 2, all three age groups began the program with similar bodyweights (172.7 to 179.9 pounds) and similar percent fat readings (25.6 to 27.2 percent). After eight weeks of exercise, the bodyweight and body composition changes were comparable for the three age groups. The 21 to 40 year olds lowered their bodyweight by 2.6 pounds and their percent fat by 2.3 percent. The 41 to 60 year olds decreased their bodyweight by 2.0 pounds and their percent fat by 2.1 percent. The 61 to 80 year olds reduced their bodyweight by 1.7 pounds and their percent fat by 2.0 percent.
Changes in fat weight and lean (muscle) weight were also similar for the three age groups. The young adults lost 4.9 pounds of fat weight and added 2.3 pounds of lean weight. The middle-aged adults lost 4.4 pounds of fat weight and added 2.3 pounds of lean weight. The older adults lost 4.1 pounds of fat weight and added 2.4 pounds of lean weight.
These findings indicated that senior men and women experience similar body composition improvements as young and middle-aged adults in response to a basic program of strength and endurance exercise. It is interesting to note that the older exercisers replaced muscle at the same rate as the younger program participants.
In addition to body composition assessments, 785 of the study subjects had resting blood pressure readings taken before and after the eight-week exercise program. As presented in Table 3, all three age groups began with similar diastolic blood pressure readings (76.1 to 80.1 mm Hg). However, the systolic blood pressure readings were considerably higher for the 61 to 80 year olds (143.1 mm Hg) than for the 41 to 60 year olds (127.9 mm Hg) and 21 to 40 year olds (121.2 mm Hg).
Although all three age groups recorded significant reductions in resting blood pressure, the senior participants experienced the greatest improvement. Their diastolic blood pressure decreased 3.7 mm Hg, and their systolic blood pressure decreased 6.2 mm Hg. Perhaps most important, the older adult group began the exercise program with a systolic blood pressure above the hypertensive level (143 mm Hg), but ended within the normal systolic range (137 mm Hg).
The results of this large-scale research study should be encouraging news for senior men and women. Consider the following key findings for the 341 older adults who completed the two-month strength training program.
Seniors can safely participate in well-designed and carefully-supervised programs of strength exercise, contingent upon their physician’s approval.
Seniors can reduce their body weight and improve their body composition. The participants in this exercise program decreased their bodyweight by 1.7 pounds and improved their body composition by 2.0 percent.
Seniors can decrease their fat weight and increase their lean (muscle) weight. The subjects in this study lost 4.1 pounds of fat and added 2.4 pounds of muscle.
Seniors can reduce their resting blood pressure. The participants in this exercise program experienced a 3.7 mm Hg decrease in their diastolic blood pressure and a 6.2 mm Hg decrease in their systolic blood pressure.
Seniors can develop physically active lifestyles, even after decades of sedentary behavior. More than 90 percent of the study subjects continued to strength train after completing the exercise program.
It would appear that older adults have much to gain from strength exercise, including increased physical capacity, enhanced personal appearance, improved athletic performance, and reduced injury risk. However, many have limited time and energy to participate in a traditional strength training program. Fortunately, properly performed strength exercise requires a relatively small time commitment. For example, the significant improvements in body composition and muscle strength experienced by 1132 subjects in the Westcott and Guy (1996) study resulted from just two or three short training sessions per week.
Recommendations For Sensible Senior Strength Training
Several national organizations have developed guidelines for safe and effective strength training, including the YMCA of the USA, the American College of Sport Medicine and the American Council on Exercise. In general, all of these organizations promote the following program recommendations for adult strength exercise.
The training guidelines call for one exercise for each of the major muscle groups. Table 4 presents standard machine and free weight exercises for the major muscles of the body.
If training time is really limited, one study reported excellent results from just three multiple-muscle exercises. These were the leg press (quadriceps and hamstrings), bench press (pectoralis major, deltoids and triceps), and compound row (latissimus dorsi and biceps).
Strength exercise may be productively performed two or three days per week. In terms of strength development, a recent study by DeMichele et al found two and three training sessions per week to be equally effective. With respect to body composition changes, subjects in the Westcott and Guy study who trained twice a week attained almost 90 percent as much improvement as subjects who trained three times a week (see Figure 1).
Because two and three training sessions per week appear to produce similar muscular benefits, the exercise frequency factor may be a matter of personal preference and scheduling ability.
Single and multiple-set training protocols have proven effective for increasing muscle strength and mass in senior men and women. However, studies comparing one and three sets of exercise have found no significant developmental differences during the first few months of training. It is therefore suggested that seniors begin strength training with one properly-performed set of each exercise. This time-efficient approach to strength exercise is safe, effective and well-received by senior men and women.
For example, in the Westcott and Guy study, the 341 older adults added 2.4 pounds of muscle and lost 4.1 pounds of fat after two months of single-set strength training. Perhaps more important, 95 percent of the participants continued to strength train after completion of the exercise program. Of course, as the senior exercisers become better conditioned, they may perform additional training sets if they desire to do so.
There is a range of training weightloads, generally between 60 to 90 percent of maximum resistance, that is productive for developing muscle size and strength. Weightloads below 60 percent of maximum are relatively light and provide less muscle building stimulus. Conversely, weightloads above 90 percent of maximum are relatively heavy and may present more injury risk.
For most practical purposes, training with 70 to 80 percent of maximum resistance represents a safe and effective weightload range. In fact, many of the studies with senior subjects have successfully used 70 to 80 percent of maximum resistance in their training programs. As these studies have reported no training-related injuries and high rates of muscle development, exercise weightloads between 70 and 80 percent of maximum resistance are recommended for senior strength training programs.
Research indicates that most people can perform about eight repetitions with 80 percent of their maximum resistance, and about 12 repetitions with 70 percent of their maximum resistance. This represents a moderate number of repetitions per set, and requires about 50 to 70 seconds of continuous training effort when performed at a moderate movement speed. The recommended number of training repetitions for senior exercisers is therefore between 8 and 12 repetitions per set.
Although it is not problematic to train with more than 12 repetitions, the key to muscle development is progressive increases in the exercise resistance. Therefore, it is advisable to add a little weight whenever 12 repetitions can be completed in proper form. The recommended training approach is to work with a given resistance until 12 repetitions are performed, then to raise the weightload by five percent or less. For most senior exercisers, this corresponds to about 2.5 to 5.0 pounds more weight, which in turn reduces the number of repetitions that can be completed. This double-progressive training system gradually increases the exercise demands and reduces the risk of doing too much, too soon.
There is general consensus that older adults should use controlled movement speeds when performing strength exercise. One study showed excellent and almost equal strength gains for subjects training with four-second, six-second, and eight-second repetitions, indicating that there is a range of effective training speeds. Because six-second repetitions have a long and successful history, this repetition speed is recommended for senior exercisers. The preferred cadence is two seconds for the more demanding lifting phase (concentric muscle action), and four seconds for the less demanding lowering phase (eccentric muscle action).
Due to age-related decreases in muscle function and joint flexibility, it is important for seniors to develop strength throughout their full range of joint movement. Research has shown that full-range exercise movements are necessary for building full-range muscle strength. That is, strength gains appear to be limited to the movement range that is trained. For best results, seniors should perform each strength exercise through the complete range of joint movement, working the muscles from their fully stretched position to their fully-contracted position. However, if any part of the exercise action causes discomfort, the movement range should be abbreviated accordingly.
In addition to controlled movement speed and full movement range, exercise technique is a critical training factor for older adults. Seniors should always practice proper posture when performing strength exercises, with particular emphasis on position stability and back support. To avoid unnecessary blood pressure elevation older adults should breathe continuously throughout every repetition. The preferred breathing pattern is to exhale during the more demanding lifting movement (concentric muscle action), and to inhale during the less demanding lowering movement (eccentric muscle action). Most important, senior strength trainers should never hold their breath (valsalva effect) or hold the resistance in a static position (isometric effect).
There are many reasons that men and women over 50 years of age should perform regular strength training. These include physiological benefits for the muscular system, skeletal system, cardiovascular system, and digestive system.
However, the major advantage of strength exercise is to replace the muscle tissue that is lost at the rate of about one pound per year in older adults. Regular strength training has been shown to increase muscle mass by more than one pound per month and to increase resting metabolism by over two percent per month, thereby reversing some of the degenerative processes associated with aging.
Senior exercisers should follow general guidelines for safe, sensible, effective and efficient strength training programs. The basic recommendation for successful strength training experiences are: (1) including exercises for all of the major muscle groups; (2) training two or three non-consecutive days per week; (3) performing one set of each exercise; (4) using between 70 and 80 percent of maximum resistance; (5) performing between 8 and 12 repetitions per set; (6) adding five percent more resistance whenever 12 repetitions are completed; (7) using moderate movement speeds, such as six seconds per repetition; (8) exercising through the full range of joint movement; (9) practicing proper posture; and (10) breathing continuously throughout every exercise repetiton.
Research indicates that 95 percent of previously sedentary seniors who complete a well-designed, short-term strength training program continue to do strength exercise.
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