Way back when, I hinted at doing a research review of the biomarkers of aging. As class started this fell to the back burner as actually getting work done became somewhat important. However my research methods class had a research review as our main project and thus I had a reason to do the review. I’ve posted the review after the jump but be warned: it’s a 3200+ word monster. I hope you find it, if not interesting, somewhat useful.
Strength Training and its Effects on the Biomarkers of Aging
April 4, 2012
Texas State University – San Marcos
Aging is inevitable but a simple look around will show that people age at different rates regardless of their biological age. In 1992 researchers William Evans, PhD, and Irwin H. Rosenberg (11) professors of nutrition and medicine, respectively, at Tufts University USDA Human Nutrition Research Center on Aging (HNRCA) determined 10 biomarkers of aging. Biomarkers are things that tell how old you would be if you didn’t know how old you were in years. These biomarkers are:
1) Muscle Mass
3) Basal Metabolic Rate
4) Body Fat Percentage
5) Aerobic Capacity
6) Blood-sugar Tolerance
7) Cholesterol/HDL Ratio
8) Blood Pressure
9) Bone density
10) Ability to regulate Internal Temperature
Somewhat radical for the time Evans and Rosenberg found that strength training was the intervention that most positively affected all of the biomarkers. This is a review of the research that has occurred in the past 2 decades, focusing on the physical biomarkers: strength, muscle mass, blood pressure, bone density, cardiometabolic health, and metabolic syndrome.
Muscle Mass and Strength
Muscle mass and strength loss with age are associated with reduction in health status. This loss of muscle is referred to as Sarcopenia, which literally means “poverty of flesh.” Whether it is the goal of a practitioner to improve health status or functional abilities, steps should be taken to reduce risk factors by preventing disability and decreasing disease progression. While common interventions attempt to improve markers of cardiovascular and metabolic functions, strength alone is independently associated with functional ability in the elderly (17,18). Since steady-state aerobic training has not been shown to improve muscular force output in the elderly (22), muscular strength may become a more limiting factor in daily activities than cardiovascular function in elderly individuals. As a result ST may be the training intervention of choice, as loss of muscular ability has been shown to at least be partially responsible for reduced function in the elderly (12,13,19).
Understanding this, specialized measurements have been proposed when dealing with an elderly population in order to determine a reduction of function. Han et al (15) have proposed that a “Lean Mass Index” be used with the elderly in place of the traditionally used “Body Mass Index.” By differentiating between total mass and lean mass, clinicians can more accurately determine the rate of muscle wasting and act accordingly. Further indicators of muscle wasting and reduced function include balance, which is also an indication not only of reduced function but also reduced strength (27), as balance is a combination of central nervous system ability and muscle’s strength-producing ability.
The rate of muscle and strength loss has been investigated. Hughes et al (16) found during a 12 year longitudinal study that knee and elbow flexors and extensors lost 20 to 30% strength between the ages of 55 and 65 years. In addition to this, the cross-sectional area (CSA) of all of the thigh muscles reduced by 14.7%. Researchers also found that the stronger the person was during the initial measurement the stronger they were during the measurement 9 years later. To a certain extent this is confirmed in a recent study by Wroblewski et al (35). This study examined the lean muscle mass of master athletes, those aged 40 to 81 years. Researchers found that those training 4 to 5 days per week did not show a significant decrease in strength with age, no loss in total lean mass, and no loss in the CSA of the mid-thigh area. The researchers concluded that “This study contradicts the common observation that muscle mass and strength decline as a function of aging alone. Instead, these declines may signal the effect of chronic disuse rather than muscle aging,” and that “This maintenance of muscle mass and strength may decrease or eliminate the falls, functional decline, and loss of independence that are commonly seen in aging adults.”
While some muscle and strength loss does occur with aging, the rate of muscle and strength loss can be severely truncated with a properly-designed ST program. Rhodes et al (28) found that one year of ST improved by the strength of elderly women by up to 29% with a similar increase in bone mineral density at the hip and back. Lemmer et al (23) demonstrated that elderly individuals are able to gain a significant amount of strength through training, 28% on average, and that these 50% of this improvement is maintained after 31 weeks of detraining.
Osteoporosis is the age-related reduction in bone mineral density (BMD), leading to a reduction in bone mass and thus increased risk for bone breaks. While osteoporosis is most prevalent in postmenopausal women, and thus a greater health concern for women, the prevalence of osteoporosis also increases with age in men. The loss of BMD in postmenopausal women results in a 200% increase of hip fracture risk every 5 years past age 50, with one-third of 80-year-old women having a hip fracture and one third of those will have had 2 hip fractures (5).
The loss of BMD is correlated with strength reductions in women and has promising implications as a measurement for determining the loss of BMD before true osteoporosis is diagnosed (36). It is well understood that physical activity improves BMD while also improve strength and muscle mass in elderly women (28), indicating that sarcopenia and osteoporosis are related. Recent studies suggest that serum osteocalcin, which is secreted during bone remodeling, is correlated with activity and inversely related to fat mass and plasma glucose in elderly men (20). Also of note that ST improves biochemical markers of bone turnover in both elderly men and women, indicating that high osteocalcin levels indicate a sufficient level of physical activity to minimize or stop losses in BMD during aging (34).
While ST has been shown to improve BMD, it is important to note that most studies indicate that it would take an increase of at least 20% to reduce the risk of fracture from a fall in the elderly (6). With this in mind, ST over a lifetime would maintain sufficient BMD to reduce fracture risk but protection in the elderly from a ST intervention would likely occur due to reduction in falls rather than a reduction in fractures after a fall has occurred.
Increases in LBM lead to an overall favorable shift in body composition away from that which precedes metabolic syndrome. An increase in fat mass, specifically in the abdominal region, is thought to be the first step in events that lead to hypertension, glucose intolerance, insulin resistance, and abnormal lipoprotein-lipid profiles. These are concurring risk factors are often referred to as syndrome X or metabolic syndrome (8).
ST improves body composition in men and women, both in studies where calories are controlled for (30,31), and studies where they are not (34). Especially important about this is the reduction of visceral adipose tissue (VAT) seen in both studies. As mentioned above, increase in abdominal fat precedes metabolic syndrome and the majority of this fat is VAT (10). ST has shown to reduce VAT in both elderly men (33) and elderly women (32).
The loss of fat-free mass (FFM) and an increase in fat mass is associated with aging. The loss of FFM is accompanied with a reduction in resting metabolic rate (RMR), which can lead to obesity. While previous studies have shown heavy ST increases FFM and RMR in elderly men and women (3), Campbell et al concluded that the increase in RMR was due to an increase in the metabolic activity of the lean tissue, rather than the increase in FFM, as in their study much of that was reported to by body water. However, as demonstrated by Wroblewski et al (35), chronic exercise preserves FFM and RMR in master athletes, thus making it reasonable that ST over a sufficient period of time would not only improve functional ability but maintain an elevated RMR, thus leading to reductions in obesity risk.
The increase in resting blood pressure (BP) is referred to as hypertension. Hypertension is a major risk factor for heart disease which increases throughout the aging process. By 60 to 70, approximately 50% of men and women are hypertensive and this remains a risk factor for heart disease until a person is over the age of 85 (20).
Studies regarding the effects of ST on hypertension are mixed. Cononie and Graves (4) studied the effects of a 6 month moderate ST on resting BP in normal to moderately high BP 70-to 79-year-old men and women. Researchers observed no changes following ST in either systolic blood pressure (SBP) or diastolic blood pressure (DBP). A more recent study challenges the conclusion, showing that heavy ST can reduce resting BP in 65- to 73-year-old men and women with high normal resting BP (24). The reductions in blood pressure were seen up to 48 hours post-exercise and the mean BP values shifted from high normal into the normal range.
While these studies indicate contradictory results, there is emerging evidence that different genotypes respond differently to ST with regards to BP reduction in the elderly. Delmonico et al (7) indicate that elderly men and women with a specific gene expression see a greater decrease in BP compared to those with a different gene expression. To quote the authors, “The AGT A–20C and AGTR1 A1166C genotypes may influence resting BP response to ST, such that C-allele carriers at each of these loci reduce their resting BP in response to ST to a greater extent than A homozygotes.” Clearly more research is needed to determine at ST dose to elicit BP improvements.
Cardiovascular fitness, as assessed by treadmill test, is an important risk factor for all-cause mortality. It also indicates mortality and morbidity associated with coronary heart disease (CHD) in both men and women. As noted by Blair et al, ““Higher levels of physical fitness appear to delay all-cause mortality primarily due to lowered rates of cardiovascular disease…(2).” In addition to reductions in cardiovascular disease, improved cardiometabolic health by way of physical activity shows a reduction in relative risk (RR) for a variety of other ailments. The RR of developing CHD from being physically inactive (RR=1.9) is similar to the RR associated with cigarette smoking (2.5), hypertension (2.3) and hypercholesterolemia (2.1) (26).
It is well understood that aerobic exercise training leads to improvements in cardiovascular fitness, but the effects of ST have been somewhat controversial. Ades et al. found that 12 weeks of ST increased treadmill walking endurance at 80% VO2max by 38% in 65- to 79-year-old women, even though their VO2max did not change (1). These improvements were correlated with improvements in leg strength. Parker et al showed that 16 weeks of ST with 60- to 77- year-old women decreased heart rate, blood pressure, and rate pressure product significantly during a weight-loaded treadmill walking test (25). Thus cardiovascular endurance may increase due to ST in spite of little or no change in VO2max.
When comparing aerobic exercise to ST, neither training modality improved plasma lipoprotein-lipid profiles significantly (32). Improvements shown in studies on younger individuals are thought to occur due to bodyweight loss rather than ST or aerobic exercise (9). Rhea et al (29) showed that 16 weeks of heavy ST in obese postmenopausal women, aged 50 to 69 years, did not elicit positive changes in lipoprotein levels regardless of bodyweight loss.
There is evidence to suggest that different genotypes respond differently to aerobic activity may be an important determinant as to whether aerobic exercise training improves lipoprotein-lipid profiles (14). It is conceivable that the same is true for lipoprotein-lipid responses to ST but no evidence exists at present time.
Conclusions and Criticisms
The effects of ST on biomarkers of aging are as follows:
(1) Decades of strength and muscle mass losses can be regained very quickly with heavy resistance ST.
(2) Substantial changes in VO2max do not occur due to ST but endurance performance can be improved due to ST.
(3) While recent research suggests that there is potential for ST to improve lipoprotein-lipid profiles in certain genotypes, there is no supporting this at present time.
(4) Evidence shows that ST can normalize BP in the high normal category but no evidence exists that demonstrates ST can reduce BP in elderly hypertensives.
(5) Reductions in body fat and VAT have been shown but diet cannot be ruled out as the cause of this reduction.
(6) Evidence for improvements in BMD due to ST is mixed. There is good evidence for ST as a means of preventing BMD loss due to aging however ST by itself has yet to have been shown to replace BMD sufficiently enough to prevent breaks due a fall. There is, however, strong evidence that ST reduces several risk factors for falls.
Research continues to show the benefit of strength training on the biomarkers of aging. While it is clear that more research is needed to determine specific protocols that address the specific circumstances of elderly individuals, what is clear is that strength training is of benefit for all persons of any age. The research is clear: intelligently prescribed strength training can improve the quality of life for elderly individuals.
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