Review
Influence of strength training variables on strength gains in adults over 55 years-old: A meta-analysis of dose–response relationships

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Abstract

Objectives

The importance of strength training to elderly individuals is well established. However, the dose–response relationship of the benefits of strength training in this population is unclear. The purpose of the study was to use meta-analysis to investigate the dose–response of the effects of strength training in elderly individuals.

Design

Fifteen studies with a total of 84 effect-sizes were included. The analyses examined the dose–response relationships of the following training variables ‘intensity’, ‘number of sets’, ‘weekly frequency’, and ‘training duration’ on strength improvement.

Methods

The studies selected met the following inclusion criteria: (a) randomized controlled trials; (b) trained healthy subjects of both genders; (c) trained subjects aged 55 years or older; (d) strength increases were determined pre- and post-training; (e) use of similar strength evaluation techniques (strength determined by a repetition maximum test) and training routine (dynamic concentric–eccentric knee extension exercise to train the quadriceps muscle group). The effect-sizes were calculated using fixed and random effect models with the main effects determined by meta-regression.

Results

Many combinations of training variables resulted in strength increases. However meta-regression indicated only “training duration” had a significant dose–response relationship to strength gains (p = 0.001). Over durations of 8–52 weeks, longer training durations had a greater effect on strength gains compared to shorter duration protocols.

Conclusions

Resistive training causes strength gains in elderly individuals, provided the training duration is sufficiently long, regardless of the combination of other training variables.

Introduction

Muscle strength is considered a fundamental component of physical fitness related to quality of life.1, 2 For elderly individuals, strength training is important to maintain functional ability because strength progressively declines with aging,3, 4 which significantly affects the ability to perform activities of daily living.5, 6, 7 Therefore it is important to determine the optimum dose or amount of strength training that should be prescribed to increase strength in this population.

A dose–response relationship between strength increases and training variables such as training volume (number of repetitions per set, number of sets per exercise), training intensity (percent of one repetition maximum), and duration of training may exist in the elderly as such relationships do exist in younger individuals.8, 9, 10 A dose–response relationship may also exist between some combination of the above training variables and strength increases. A previous systematic review by our group11 concluded that there are very few studies investigating the effects of strength training variables on the strength gains in elderly subjects. Unfortunately, much of the available research has been performed with small sample sizes and consequently low statistical power. Additionally, potential confounding variables, such as the training status of subjects, are frequently not adequately controlled. Hence the dose–response relationship between strength training volume and intensity and strength gains in the elderly remains obscure.

Since the term meta-analysis was coined, recognition has grown that reviewing of scientific literature is itself a scientific approach.12 Meta-analysis allows examining the combined results of previous research and comparing the effects of strength training variables, whether or not individual studies actually compared training variables or included a control group. This makes it possible to identify a dose–response trend for a given training variable, a situation that may be difficult to accomplish in a single experimental design.8, 9 A recent study13 was the first to use the meta-analysis approach to investigate the dose–response relationship between strength increases and training variables in older subjects. Conclusions from this meta-analysis suggested that training intensity shows a dose–response to strength gains in individuals 65 years and older, with higher intensity programs being more effective than lower intensity programs. However, this previous meta-analysis did not examine the combined effects of different training variables or domains of strength training, such as intervention duration, number of sets per exercise, and intensity.

Many possible combinations of different strength training variables or domains may lead to positive adaptations and strength gains. Possible interactions of strength training variables or domains cannot be taken into account by evaluating the effect-sizes related to each training variable separately. Using meta-regression techniques such interactions between training variables can be examined. Therefore, the purpose of this investigation was to use meta-regression techniques to investigate the dose–response of combined domains of strength training variables such as training intensity, weekly training frequency, number of sets per exercise, and intervention period on the strength gains in elderly subjects.

Section snippets

Study inclusion criteria

The following inclusion criteria were adopted to select the studies to be included in the meta-analysis: (a) randomized control trials in which only strength training (defined as a structured, planned exercise where the subject exerts an effort against an external resistance) had been performed. The studies having more than one treatment group, using different strength training methodologies, were included in the analysis in the same proportion as the number of treatment groups, as if they were

Results

As of May 2012, the electronic search identified 1183 potentially relevant studies and the manual search of reference lists identified another 12 potentially relevant studies. After excluding 119 studies which were indentified more than once in the different search engines, the remaining 1076 studies were manually reviewed. Abstract examination for eligibility excluded 799 articles due to failure to satisfy pre-established inclusion criteria. Of the original 1183 studies indentified only 277

Discussion

To the best of our knowledge the present meta-analysis is the first to provide information about the dose–response relationship of strength training in the elderly, considering the combined effects of different domains such as training intensity, frequency, number of sets, and intervention duration. In a previous meta-analysis, Steib, Schoene and Pfeife13 also examined the dose–response relationship between strength training variables and strength gains in elderly subjects. However, their

Practical application

From a dose–response perspective the results of the present meta-analysis suggest that the duration of a resistance exercise program is the most determinant training variable in producing strength gains in elderly untrained individuals. Even acknowledging the homogeneity concerning many of the training variables included in the present analysis, it appears that, within the range of 8–52 weeks of training duration, variables such as training frequency, number of sets, and intensity are secondary

Acknowledgements

This research was partially supported by the Brazilian Council for the Research Development (CNPq – process 305729/2006-3) and Carlos Chagas Foundation for the Research Support in Rio de Janeiro (FAPERJ – process E-26/110.022/2007).

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