Cognitive decline is a normal feature of aging. Memory difficulties, slowing mental speed, and decreased mental flexibility become evident in old age, even in older adults without dementia [1–5]. Normal, age-associated cognitive decline is related to declines in everyday functional abilities, and to increases in both formal and informal service use among older adults [6–8]. Interventions which improve cognitive functioning are therefore important for the well-being and quality of life of older adults.
Exercise has been suggested as an innovative approach to improving cognitive functioning in older adults. The benefits of exercise for general health and well-being in older adults are already well known .
Cross-sectional evidence suggests that older adults who are physically active display better cognitive functioning than their sedentary peers, in areas such as memory, reaction time, and visuospatial skills [10–13]. Prospective and longitudinal findings suggest that physical inactivity is predictive of subsequent cognitive decline and that changes in physical activity patterns over time are associated with changes in cognitive functioning [14–18].
Experimental studies of exercise training programs for older adults have generally shown improvements in cognitive functioning, particularly on measures of information processing speed and executive functioning (e.g. [19–21]). While some experimental studies have been less conclusive (e.g. [22–24]), this discrepancy is most likely attributable to methodological differences. These include differences in duration, intensity, and frequency of exercise training, along with differences in control groups, exclusion criteria, and cognitive outcome measures. A meta-analysis by Colcombe and Kramer  found that, overall, exercise interventions do have the potential to improve cognitive functioning in older adults, particularly mental speed and executive functioning. The meta-analysis also highlighted that the most beneficial programs are those which have exercise sessions of greater than 30 minutes duration, include aerobic and strength training components, and target adults aged between 65 and 70 years . As this is a relatively new area of research, additional evidence is required to further support the claim that exercise training can improve cognition.
Linking exercise and cognitive functioning
Several mechanisms have been suggested to explain the relationship between exercise and cognitive functioning. The main hypothesis is that exercise directly affects the structure and function of the brain. Increases in aerobic capacity (as a result of increases in exercise) are thought to increase cerebral blood flow, improve the transport and utilization of oxygen and glucose in the brain, promote neurogenesis (the creation of new nerve cells), and regulate neurotransmitter synthesis [14, 15, 17, 18, 26–28]. Some studies have found an association between improvements in aerobic capacity and improvements in cognitive function [19, 21]. Other studies, however, have found no relationship [22– 24, 29]. More evidence is required to validate the idea of increased aerobic capacity as a prerequisite for improved cognitive functioning.
Psychological factors may play a role in mediating the relationship between exercise and cognition . Exercise is known to improve psychological well-being , and psychological well-being has been associated with cognitive functioning [32, 33]. A few studies of exercise training and cognitive training have included psychological measures (e.g. [22, 34–38]), but results have been mixed. More research is required to elucidate the mediating role of psychological factors in the exercise-cognition relationship .
Some researchers have suggested that the benefits of exercise may be further enhanced by combining exercise training with cognitive training .
Cognitive training has been the traditional approach to improving cognitive functioning in older adults. It consists of learning and practicing skills and techniques to manage cognitively demanding situations (e.g. using mnemonics to aid recall). While these programs have been successful in improving the specific cognitive function targeted by the training (i.e. memory programs improve memory performance) [39–41], they do not have the potential to provide the physical and cognitive benefits offered by exercise training. A combination of exercise training and cognitive training, however, may provide the best of both worlds.
Fabre and colleagues  conducted an experimental study of combination training with four groups: aerobic training, cognitive training, aerobic and cognitive training, and control. They found that all three training groups improved significantly, with the combination training group (aerobic and cognitive training) improving significantly more than the other groups. These findings are limited, however, by the fact that the combination training group appear to have received a greater total number of training sessions per week than the other groups. Given that engaged lifestyles have been linked to cognitive performance in older adults [42–45], it is possible that the results of the combination training group could be a consequence of increased social interaction, rather than an added benefit of cognitive training. The potential of combined exercise and cognitive training could be better investigated by matching the overall training exposure of participants in a dual group to that of participants in an exercise training group.
Little is known about older adults' perceptions of exercise training programs and combined exercise and cognitive training programs. While adherence and compliance data can provide some insight into the feasibility of a training program, qualitative feedback from participants provides information about satisfaction and acceptability. Collection of this type of information also provides an opportunity to identify specific strengths and weaknesses of a program, and to assess the real-life benefits of the training which cannot be measured with clinical tests or surveys [46, 47].
The aims of the present study are to:
examine the impact of an exercise training program for older adults on cognitive and physical functioning,
compare the impact of exercise training and a combined program of cognitive and exercise training for older adults (which has an equal number of total training sessions per week) on cognitive and physical functioning,
examine associations between changes in aerobic capacity (as a result of exercise) and changes in cognitive functioning;
examine associations between changes in psychological wellbeing (as a result of exercise) and changes in cognitive functioning; and
identify older adults' perceptions of exercise training and combined exercise and cognitive training.
An exercise training program and a cognitive training program have been developed by the first author (SO), and will be evaluated in a randomized controlled trial. The content of these programs is based on previously successful training programs, and current theories regarding the relationships between exercise training, cognitive training, and cognitive functioning.