Discussion
cognitive impairments, cognitive decline, dementia
To our knowledge, this study is the first prospective study to directly compare the effects of combined physical and cognitive training in different frequencies on cognitive function for older adults with cognitive decline. We identified that the different training frequency of combined physical and cognitive training may result in benefits on different cognitive functions in older adults with cognitive decline. These findings are consistent with our hypothesis. The HF group demonstrated greater improvement in immediate memory measured by the WL-IM and in executive function measured by the SCWT than the LF group. Compared with the HF group, the LF group showed a great improvement in delayed memory measured by the WL-DM. Processing speed and global cognitive function increased in both HF and LF groups.The results of this study indicate that improvements in immediate memory were greater after participants received combined training at a high training frequency than after a low training frequency. Immediate memory, a type of short-term memory, is the ability to remember information that has just been presented [Our results are consistent with those of a previous study indicating that high-frequency training may lead to greater improvement of immediate (short-term) memory than long-term memory [The results showed that participants who received combined training at the low-training frequency had better performance in delayed memory (long-term memory) than those who received high-training frequency. It may be because practicing the new skill or activity at a low frequency may give the brain more time to process and consolidate the information that has been learned. Furthermore, the process of long-term memory may take more time, and rehearsing the information could help strengthen the memory trace and improve retention. Consistent with the previous studies, the low-frequency training could allow the participants to have more time to rehearse the skills or strategies they learned and elicit retrieval and reactivation of a memory trace, leading to better memory consolidation and retention [The HF and LF groups both had improvements in processing speed performance and global cognitive function. Global cognitive performance is usually used to screen the cognitive impairments and as the target of an intervention. Processing speed is one of the strongest predictors of age-related cognitive decline and the incidence of dementia [This study may provide evidence and guidance to practitioners that combined physical and cognitive training offering high or low frequency had positive effects on cognitive function for the elderly with cognitive decline. If environmental or personal reasons prevent the elderly with cognitive decline from going out frequently for the training sessions, one training session per week could also enhance cognitive function. Furthermore, different training frequency of combined physical and cognitive training may benefit different cognitive functions for the elderly with cognitive decline. Clinical practitioners could use different frequency training for distinctive intervention purposes. For example, for improving executive function, clinical practitioners could conduct combined physical and cognitive training at a high training frequency.The current study has some limitations. First, although demographic data were similar between the HF and LF groups, the HF group showed better performance of global cognitive function, processing speed, and memory than the LF group at baseline. Thus, there may have been less room for improvement in the HF group after the combined physical and cognitive training. Future studies could adopt a stratified sampling method to avoid or reduce the bias.Second, our results may not be applicable to older adults with a diagnosis of dementia and normal cognitive function. Future studies are needed to recruit participants with different cognitive levels, such as mild dementia or normal cognition, to verify these training effects on the elderly.Third, lack of random assignment of participants to the intervention may have led to differences in baseline characteristics between two groups and affected the results. However, there were no differences in sex, age, educational levels, and the MMSE baseline score between two groups. The demographic and clinical characteristics might not bias the results, and no adjustments for the baseline characteristics were made.Finally, the lack of a nontreatment control group may be considered a limitation. In the absence of a nontreatment control group, we could not control for learning effects that may influence post-training scores. Future studies should include a nontreatment control group that could control for these biases.