Review
Resistance exercise for muscular strength in older adults: A meta-analysis

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Abstract

Purpose

The effectiveness of resistance exercise for strength improvement among aging persons is inconsistent across investigations, and there is a lack of research synthesis for multiple strength outcomes.

Methods

The systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations. A meta-analysis was conducted to determine the effect of resistance exercise (RE) for multiple strength outcomes in aging adults. Randomized-controlled trials and randomized or non-randomized studies among adults  50 years, were included. Data were pooled using random-effect models. Outcomes for 4 common strength tests were analyzed for main effects. Heterogeneity between studies was assessed using the Cochran Q and I2 statistics, and publication bias was evaluated through physical inspection of funnel plots as well as formal rank-correlation statistics. A linear mixed model regression was incorporated to examine differences between outcomes, as well as potential study-level predictor variables.

Results

Forty-seven studies were included, representing 1079 participants. A positive effect for each of the strength outcomes was determined however there was heterogeneity between studies. Regression revealed that higher intensity training was associated with greater improvement. Strength increases ranged from 9.8 to 31.6 kg, and percent changes were 29 ± 2, 24 ± 2, 33 ± 3, and 25 ± 2, respectively for leg press, chest press, knee extension, and lat pull.

Conclusions

RE is effective for improving strength among older adults, particularly with higher intensity training. Findings therefore suggest that RE may be considered a viable strategy to prevent generalized muscular weakness associated with aging.

Introduction

Muscular weakness plays a principal role in the pathogenesis of frailty and functional impairment that occurs with aging, and contributes to numerous disease processes. Maximal strength capacity reaches a peak sometime around the second or third decade of life, and by the fifth decade, begins a gradual decline (Larsson et al., 1979, Lindle et al., 1997, Metter et al., 1997, Narici et al., 1991, Vandervoort and McComas, 1986). This deterioration, which is typically attributed to diminished levels of activity or disuse/immobilization due to disease, has been documented primarily through cross-sectional research, and appears to increase in severity after the age of 65 (Baumgartner et al., 1998). Although losses of strength are rarely tracked longitudinally (Aniansson et al., 1986, Bassey and Harries, 1993, Frontera et al., 2000, Kallman et al., 1990), existing epidemiological studies report a significantly higher prevalence across each decade of late adult life. Sarcopenia and muscular weakness are not considered to be “disease” states, but rather conditions which translate to acute functional deficit and disability, as well as related comorbidity and mortality (Ruiz et al., 2008). Moreover, increased longevity has led to a higher frequency of sarcopenia, and respective escalating health care expenditures for complications associated with declines in functional health and loss of independence.

Numerous investigations have identified a disparate decline of strength and muscle mass, indicating that these age-related debilities are to some extent, independent (Klitgaard et al., 1990, Lynch et al., 1999, Young et al., 1985). However, since strength and muscle mass do not decrease concurrently, strength may be a superior indicator of muscular dysfunction (Doherty, 2003, Klein et al., 2001). Indeed, longitudinal data suggest that muscle strength is a robust predictor of functional decline that may occur during aging (Pendergast et al., 1993, Rantanen et al., 1999a, Rantanen et al., 1999b), and is an important physiological attribute for maintenance of mobility and movement efficiency. Since strength capacity appears to also be indicative of disability (Janssen et al., 2002, Visser et al., 2002), resistance exercise (RE) may serve as an effective mode of physical activity to directly improve functional capacity. There is strong evidence to indicate that muscle weakness is a treatable cause of disability, and that aging persons with early-onset deterioration are probably the most likely to benefit from strategic interventions (Evans, 1996, Frontera et al., 1988, Hakkinen and Hakkinen, 1995, Hurley et al., 1995). Specifically, RE is considered to be a safe and effective method for increasing strength and lean muscle tissue in young (Hubal et al., 2005, Lowndes et al., in press) and older adults (Fiatarone et al., 1990, Frontera et al., 1988, Hakkinen et al., 1998, Hakkinen et al., 2001, Reeves et al., 2004, Vincent et al., 2002, Welle et al., 1995). Even after short bouts of resistance training protocols, aging subjects may experience improvements in protein synthesis rate and neuromuscular adaptation that are comparable to that of younger cohorts, despite a much lower pre-exercise rate (Holviala et al., 2006, Newton et al., 2002, Roth et al., 2001, Yarasheski et al., 1993). These findings imply that disuse may actually be the underlying reason for muscle atrophy and weakness, rather than aging, per se.

The effectiveness of RE for strength improvement among aging persons is inconsistent across investigations. While much research has investigated strength increases accompanying single-cohort interventions, most have examined only one or two training programs, providing only a glimpse of the overall dose–response relationship. Debate concerning the appropriateness of RE among older individuals has been cultivated by questions of the general efficacy and safety for this population. There are very few published accounts that have examined the overall benefit of RE for strength in aging persons while considering a continuum of dosage schemes, treatment durations, and/or age ranges on longitudinal strength adaptation. As a result, it is difficult to evaluate the treatment effects coinciding with these factors. Further, although the existing body of evidence regarding the utility of resistance exercise for strength improvements among older adults has recently been deemed to be supported by the highest category of evidence (i.e. “Evidence Category A.”) (Chodzko-Zajko et al., 2009), a systematic review to assess treatment effects across multiple strength measures, and potential moderating variables more generalizable to RE prescription, is yet to be completed. To date, the most comprehensive reviews related to this topic have either limited the analysis of strength to a single measure (i.e. knee extension) (Latham et al., 2003, Latham et al., 2004, Liu and Latham, 2009), or have compared multimodal exercise regiments for general changes in overall functional capacity (Baker et al., 2007), not specific to strength outcomes. Therefore the purposes of this review and meta-analyses were to examine the effects of resistance exercise among older adults for multiple upper- and lower-body strength outcomes, and across multiple dosing schemes.

Section snippets

Methods

This meta-analysis was conducted in accordance with the recommendations and criteria as outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.

Results

The flow of article search and selection, from “potentially relevant” to final inclusion is depicted in Fig. 1.

Discussion

The primary results of this investigation suggest a robust, significant association between resistance exercise and upper and lower body strength improvement among older individuals. From a public health perspective, these findings confirm the value of full-body RE for the prevention or treatment of age-related declines in muscle function, which may in turn serve as a safeguard against disablement. In particular, we observed significant main effects for lower-body (i.e. leg press = 31.63 kg (29%);

Conclusions

Resistance exercise is an effective modality for aging men and women, and may elicit significant improvements in muscular strength capacity. The current analysis is supportive of previous findings to suggest a positive association between intensity of resistance exercise and degree of strength improvement. As strength decline is highly related with subsequent functional deficit and disease comorbidity, it is conceivable that improvements in this parameter would help to maintain independence,

Acknowledgements

This research is supported by the NIH, NICHD, NCMRR Grant #5-T32-HD007422. The authors thank Dr. Brent Alvar and Dr. Pamela Swan for their support and feedback during the conception of this project. No financial disclosures were reported by the authors of this paper.

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