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Background
Age-related decline in strength is associated with loss of mobility, functioning and independence. It is clear that resistance training benefits older people by increasing strength and improving some aspects of functioning.1 However, the optimal dose and type of resistance training is uncertain. While previous reviews have compared intervention and control resistance training programmes, the results of studies directly comparing different doses or types of resistance training have not been combined.
Aims
This systematic review by Steib and colleagues aimed to synthesise the best available evidence comparing the effectiveness of different types, intensities, frequencies, volumes and durations of resistance training on strength and functioning in older adults.
Searches and inclusion criteria
Three databases (Medline, the Cochrane Library and PEDro) were searched up until August 2008 and reference lists of obtained studies were screened. Eligible studies were randomised controlled trials in adults with a mean age of 65 years or older that compared the effects of two or more different doses or types of supervised resistance training on muscle strength, muscle endurance, power and/or physical functioning. The methodological quality of the trial reports was assessed using the 11-point van Tulder scale, but studies were not excluded from the analysis on the basis of the quality assessment.
Interventions
Resistance training was defined as an exercise that involves the participant exerting effort against their body weight or external resistance. Resistance training evaluated in the included studies was classified as power training, progressive resistance training, eccentric resistance training, isokinetic training, isometric training or repeated training of functional tasks.
Main outcome measures
The outcomes were knee extensor muscle strength (measured as maximum voluntary contraction or one-repetition maximum (RM)), muscle endurance and muscle power. Included measures of physical functioning were timed up-and-go test performance, walking speed, chair rise and stair climbing tests.
Statistical methods
Random-effects meta-analysis was used to pool the results of individual studies within each outcome (strength, power, endurance and physical functioning) for each characteristic of strength training (intensity, type, frequency and volume). Sensitivity analysis was conducted to assess the effect of excluding trials with very low methodological quality.
Results
The systematic review included 29 studies with a total of 1313 participants, and 22 studies with 986 participants contained sufficient data to be included in the meta-analysis. The mean age in the included studies ranged from 65 to 82 years. The majority of studies involved healthy community-dwelling participants, with only two studies involving people with frailty or disability. Seven studies were classified as high quality, and of the remaining 15 that scored less than 50% on the quality scale, seven were considered to be of very low quality. The training programmes generally involved two to three sessions per week with approximately three sets of 6–14 repetitions.
Between-group differences are presented as standardised mean difference (SMD), which estimates the number of SD by which the intervention changes the outcome. The pooled analyses showed progressive resistance training had a significant, dose-dependent effect on strength. High intensity training (60–80% of 1 RM) was more effective than moderate intensity training with a SMD of 0.62 (95% CI 0.22 to 1.03). High intensity training was also more effective than low intensity training (SMD 0.88; 95% CI 0.21 to 1.55). These differences between intervention types would be considered moderate to large.2
Meta-analysis also indicated that the effects of power training and progressive resistance exercise programmes were different. Power training was significantly more effective than progressive resistance training in enhancing muscle power (SMD 1.66; 95% CI 0.08 to 3.24), with no evident dose–response relationship. Conversely, progressive resistance exercise caused greater increases in muscle endurance (SMD 2.24; 95% CI 1.41 to 3.07). There was no difference between the two types of intervention on strength and relative effects on physical functioning were inconsistent.
Comparisons in two studies revealed training two or three times per week increased strength significantly more than a single session, but surprisingly few studies have addressed this issue.
Limitations/considerations
The studies were heterogenous and the minority were high quality. The authors took the appropriate step of conducting sensitivity analysis to explore whether the exclusion of very low quality studies influenced the results. The effect of intensity on strength remained essentially unchanged; however, the strengthening benefits of power training compared with progressive resistance training became significant.
A small number (one to three) of the 22 eligible trials could be pooled for each of the four physical functioning outcomes. The low participant numbers and resulting wide CI in the pooled analysis may have limited the ability to detect any effect of the intervention on function.
Adverse aspects of the interventions were not considered in the systematic review. A recent Cochrane review found more than one third (43/121) of progressive resistance training trials in older adults reported some adverse response to the exercise programme.1
Clinical implications
This well-conducted review demonstrates that progressive resistance training improves strength in older people and more intense training results in bigger benefits. At least two training sessions per week are required to increase strength. The effects of different characteristics of resistance training on functional outcomes are unclear.
Footnotes
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Competing interests None.
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Provenance and peer review Commissioned; not externally peer reviewed.