Is Strength Training Associated With Mortality Benefits?
A 15 year Cohort Study of US Older Adults

This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to:    Frankp@chiro.org

FROM:   Prev Med. 2016 (Jun); 87: 121–127 ~ FULL TEXT

OPEN ACCESS

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Jennifer L. Kraschnewski, Christopher N. Sciamanna, Jennifer M. Poger, Liza S. Rovniak, Erik B. Lehman, Amanda B. Cooper, Noel H. Ballentine, Joseph T. Ciccolo

Department of Medicine,
Penn State College of Medicine,
United States;
Department of Public Health Sciences,
Penn State College of Medicine,
United States.
jkraschnewski@hmc.psu.edu

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BACKGROUND:   The relationship between strength training (ST) behavior and mortality remains understudied in large, national samples, although smaller studies have observed that greater amounts of muscle strength are associated with lower risks of death. We aimed to understand the association between meeting ST guidelines and future mortality in an older US adult population.

METHODS:   Data were analyzed from the 1997–2001 National Health Interview Survey (NHIS) linked to death certificate data in the National Death Index. The main independent variable was guideline-concordant ST (i.e. twice each week) and dependent variable was all-cause mortality. Covariates identified in the literature and included in our analysis were demographics, past medical history, and other health behaviors (including other physical activity). Given our aim to understand outcomes in older adults, analyses were limited to adults age 65years and older. Multivariate analysis was conducted using multiple logistic regression analysis.

RESULTS:   During the study period, 9.6% of NHIS adults age 65 and older (N=30,162) reported doing guideline-concordant ST and 31.6% died. Older adults who reported guideline-concordant ST had 46% lower odds of all-cause mortality than those who did not (adjusted odds ratio: 0.64; 95% CI: 0.57, 0.70; p<0.001). The association between ST and death remained after adjustment for past medical history and health behaviors.

CONCLUSIONS:   Although a minority of older US adults met ST recommendations, guideline-concordant ST is significantly associated with decreased overall mortality. All-cause mortality may be significantly reduced through the identification of and engagement in guideline-concordant ST interventions by older adults.

Keywords:   strength training; mortality; resistance training; older adults

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From the FULL TEXT Article:

Introduction

Engaging in regular physical activity reaps a multitude of health benefits for adults of all ages; it is perhaps of greatest value in preventing premature mortality associated with all-cause, cardiovascular disease, diabetes, and even some cancers. [1–11] Significant quality of life improvements and decreased risk of mortality have also been observed in physically active, older adults. [4, 9, 12–16] Unlike aerobic exercise’s well-established effects, strength training has only recently garnered attention for its benefits in regaining muscle mass and strength often depleted with age and disability. [17–20] While guidelineconcordant physical activity has consistent and powerful relationships with longer life expectancy, meeting strength training guidelines may also play an important role in decreasing premature mortality and warrants further investigation.

Although physical activity guidelines have been widely available for decades from the American College of Sports Medicine (ACSM), [21] specific recommendations regarding strength training have only been developed more recently; in 2007, the American Heart Association (AHA) together with the ACSM established recommendations encouraging all adults to participate in strength training activities at least twice each week, [19] with a similar emphasis on muscle-strengthening activity for older adults. [22] In addition, the Behavioral Risk Factor Surveillance System (BRFSS), which began assessing aerobic activity with the first survey in 1984, only began assessing strength training in 2011. [23] Over this time, studies have demonstrated robust effects of strength training on strength, muscle mass and physical function as well as improvement in a range of chronic conditions, including diabetes, osteoporosis, low back pain, and obesity. [7, 18, 24–26] Recently, Krist and colleagues observed considerable improvements in muscle strength and mobility among elderly nursing home residents with impaired mobility at baseline after they engaged in a resistance exercise program twice weekly over a two month period. [17] Similarly, Mayer and colleagues found that progressive strength training in the elderly helped retain motor function and reduce sarcopenia.20 Older adults with functional limitations can achieve significant improvements in physical function and muscle strength by engaging in strength training activity. [27]

In addition to improvements in physical function, several clinical studies have demonstrated that higher levels of muscular strength are associated with lower all-cause, cardiovascular, and cancer mortality risk, among both men and the elderly. [28–30] Findings from 15 epidemiological and 8 clinical studies summarized in the 2015 systematic review by Volaklis et al. provides evidence that muscular strength is inversely and independently associated with all-cause and cardiovascular mortality. [31] Although there is increasing evidence illuminating the substantive benefits of muscle strength on decreased mortality risk, [31] no studies to our knowledge describe the relationship between strength training behavior and mortality in a large, nationally representative sample over an extended time period, particularly in older adults.

The aim of this investigation was to understand the association between meeting strength training guidelines and future mortality in older adults. We hypothesized that guideline-concordant strength training is significantly associated with decreased overall mortality in older US adults.

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Discussion

The purpose of the present study was to understand the relationship between meeting strength training guidelines and future mortality. Overall, the results showed a consistent and inverse association in a large, national sample; [42] those who performed guideline-concordant strength training had significantly lower odds of all cause, cancer, and cardiac death than their less-active counterparts. This association remained significant for all-cause mortality after adjusting for each of the covariate groups (demographic, health behavior, and comorbid condition variables, respectively). In addition, these patterns remained significant, albeit less strongly, after adjusting specifically for demographic variables in cancer and cardiac mortalities. Therefore, older adults who perform strength training activities not only improve their physical functioning as previously demonstrated, [17, 20, 43] but their survival rate as well.

Although not statistically significant in cancer and cardiac deaths, point estimates suggest that guidelineconcordant strength training behaviors are associated with decreased risk of cause-specific mortality. This weaker association may be the result of sample size, as a lesser percentage of individuals died from cancer (N=2,192; 7.2%) or cardiac (N=4,275; 13.4%) etiologies than from all-causes.

Results from the propensity score analyses confirmed our findings from the weighted logistic regression models. After matching subjects who strength trained <2 times/week to subjects who strength trained ≥2 times/week in the propensity score matching, there remained a significantly lower odds of all-cause mortality when controlling for all variables (Groups 1, 2, & 3). Although sample size was greatly reduced in the propensity score matching, as those who met strength training guidelines was a much smaller group than those who were not guideline concordant (N=5,408), this reduction in power is balanced by the efficiency in matching. [44]

Although few studies have examined the impact of strength training on future mortality, existing outcomes are similar to the results of the present study. [45, 46] For example, Singh and colleagues performed a randomized controlled trial involving 12 months of high-intensity weight-lifting exercise as part of a multidisciplinary intervention for patients recovering from hip fractures and found an 81% reduction in mortality (N=4) compared to the usual care control condition (N=8) (adjusted odds ratio: 0.19; 95% CI; 0.04, 0.91; p < .04). [45] Similarly, Hardee and colleagues conducted a prospective epidemiological investigation of self-reported physical activity and resistance training among cancer survivors and observed a 33% lower risk of all-cause mortality among those who participated in resistance training ≥ 1 day per week (N=39) (95% CI, 0.45–0.99) after adjusting for potential confounders, including physical activity. No correlation was found with those who engaged in physical activity only. [46] While these studies are limited by sample size, the present study benefits from using a large, nationally representative sample of a range of health outcomes for the US population. [42]

Consistent with prior findings, meeting strength training guidelines was strongly associated with younger age, among other demographic and health behavior variables, including meeting physical activity guidelines and not smoking. [34, 35, 47] Ciccolo and colleagues (2010) in a separate survey of 9,651 US adults observed that only 21.7% of older adults met strength training guidelines versus 37.5% of adults aged 35–54. [38] This was consistent with our small percentage of older adults performing guidelineconcordant strength training activities (N=2,725; 9.6%). After controlling for physical activity level, which was strongly associated with reduced mortality, specifically reporting strength exercises appeared to confer additional benefit beyond reporting physical activity alone.

This study has several important limitations to consider. First, the study design is that of a cohort study, limiting ability to determine cause and effect. In addition, participation in strength training was selfreported without information regarding session quality or length. Self-report measures remain widely used for physical activity assessment, however, typically overestimate activity level when compared with objective measurement. [48] Unmeasured confounders, including diet and self-report of health status could have obscured the data. Unfortunately, dietary habits and objective physical and biological data are difficult to assess and beyond the scope of this secondary data analysis. Although not ideal, selfreport remains a reliable and valid indicator of health. [49] Another limitation is that respondents may have misinterpreted the survey questions or may not have fully understood the definitions of strength training and calisthenics, which may have weakened the accuracy of strength training prevelance. [34] Additionally, given that calisthenics isn’t always categorized as progressive training, the survey question used from the NHIS combining strength training with calisthenics may have undesirably included some aerobic activity as well. Since respondents were not asked to provide details regarding the type of strength training activities performed, some activities such as stair climbing could have been missed. [24]

Although it is possible that a small percentage of older adults were physically unable to perform strength training activities, potentially confounding the data, the literature suggests otherwise; Drey and colleagues (2012), for example, randomized older adults (>65 years) into either a strength training (ST), power training (PT) or control group and found the highest fidelity in the ST group, with 87% attendance rates over 12 weeks. [50] A final limitation is this study relied on death certificate data, which has been previously questioned for its reliability and accuracy in properly identifying cause of death. [51, 52] However, when used for observational studies the National Death Index has been shown to be accurate in ascertaining deaths, with high sensitivity (96%) and specificity (100%). [53]

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Conclusion

Despite guidelines, only 21.7% of older adults currently meet recommendations of strength training at least twice each week, substantially lower than the 2010 national objective of 30%. [54] This underscores the need for additional programs to increase strength training among older adults to help engage patients in the “Exercise is Medicine” campaign. [34] This study further demonstrates the importance of encouraging doctors to recommend physical activity to patients as they would any other effective treatment, particularly since exercise has been shown to be as effective as some medications. [55] Identifying interventions to successfully engage older adults in guideline-concordant strength training has the potential to significantly reduce all-cause mortality in this population.

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