Fitness Effects On Older Adults: A Meta-Analytic Study Essay

Fitness Effects on Older Adults A Meta-Analytic Study
Abstract
A meta-analytic study was conducted to examine the hypothesis that aerobic fitness training enhances the cognitive vitality of healthy but sedentary older adults. Eighteen intervention studies published between 1966 and 2001 were entered into the analysis. Several theoretically and practically important results were obtained. Most important fitness training was found to have robust but selective benefits for cognition, with the largest fitness-induced benefits occurring for executive-control processes. The magnitude of fitness effects on cognition was also moderated by a number of programmatic and methodological factors, including the length of the fitness-training intervention,
Thus, an important unanswered question concerns why some studies find improvements in performance with enhanced aerobic fitness while other studies have failed to observe such a relationship. This is the question that we addressed in the present study through the application of meta-analytic techniques to longitudinal studies of fitness effects on the cognition of older adults. Research using animal models provides reasonable grounds to expect aerobic exercise to have a positive impact on human cognitive function through a variety of cellular and molecular mechanisms. For example, Black, Isaacs, Anderson, Alcantara, and Greenough (1990) found increases in capillary density in the cerebellum when rats exercised on a running wheel. Other researchers found that increased aerobic fitness, engendered by running, enhanced cortical high-affinity choline uptake and increased dopamine receptor density in the brains of old rats (Fordyce & Farrar, 1991), increased brain-derived neurotrophin factor (BDNF) gene expression in rats (Neeper, Gomez, Choi, & Cotman, 1995), and increased the number of new cells in the hippocampus of mice (van Praag, Kempermann, & Gage, 1999). It is reasonable to speculate that these cellular, molecular, and neurochemical changes observed in rats and mice in response to exercise interventions may underlie the improvements in perceptual, cognitive, and motor
Meta-analysis is a particularly appropriate technique for this purpose because it enables one to summarize the relationship between two variables across different studies—in the present case, the effect of fitness interventions on cognition. However, in addition to yielding an overall effect size, as well as effect sizes for each study, the meta-analytic procedure enables one to determine whether one or more moderator variables (e.g., theoretical distinctions or methodological factors) influenced the outcome of the studies. In several ways, we extended previous qualitative and quantitative analyses of the literature on the fitness-cognition relationship (Dustman et al., 1994; Etnier et al., 1997). First, we examined the theoretical proposals that have been made with regard to the processes expected to benefit most from enhancements in aerobic fitness. Second, we focused specifically on randomized fitness intervention trials that included control groups and on fitness training that extended from several months to several years. Third, we included studies conducted from 1966 to 2001 in our analyses. Finally, we focused on older adults, from 55 to 80 years of age. Identifying the interventions