The health benefits of physical activity and regular exercise are hard to ignore. However, limited studies have demonstrated the effects of exercise on seniors with reduced cognition. In this paper, four studies on the effects of exercise on cognitive function will be examined chronologically.
A study by Lautenschlager et al. (2008) aimed to show the effect of exercise on cognitive function in seniors prone to Alzheimer’s disease after six, 12 and 18 months. A total of 170 participants, aged 50 years and above, were accepted. A randomized, single-blind, controlled trial was carried out for 24 weeks. Participants with subjective or objective memory loss were included. Those with serious medical conditions, drinking problems and low fluency in English were excluded. The intervention group was encouraged to do three 50-minute exercise sessions each week with a pedometer and record the activities into a diary. Compliance was reinforced through telephone calls, a workshop, a manual and newsletters. The control group was given educational materials only. Follow-ups were done at the sixth, 12th, 18th month after 24 weeks of intervention. A total of 138 participants completed the 18th-month follow-up assessment. The Alzheimer Disease Assessment Scale – Cognitive subscale (ADAS-Cog) was used as the main outcome measure. At the end of the study, the intervention group was found to have statistically significant improvement in the ADAS-Cog score compared to the control group (p=0.04). At the 18th month follow-up, the intervention group had an improvement of 0.73 points while the control group improved 0.04 points. Although the study included participants with subjective and objective memory loss, the authors also analysed the results of participants with only objective memory loss. This increased the validity of the results and reduced biasness.
Similarly, Baker et al. (2010) investigated the effects of aerobic exercise and the role of gender on cognition in elderly with mild cognitive impairment (MCI). A randomized, controlled trial was carried out for six months. Participants were recruited from a memory disorders clinic. The inclusion criterion was having an inactive lifestyle (<30 minutes of exercise <3 times per week). Participants with any significant medical conditions were excluded. Thirty-three participants with a mean age of 70 years were accepted and randomized using a 2:1 ratio. Four dropouts occurred in the intervention group due to non-compliance and musculoskeletal issues. Cognitive testing protocols were conducted at baseline, third month and sixth month. The intervention consisted of exercising on cardio machines and the duration and intensity were progressed until the participant’s hit 75-85% HRR. The control group consisted of stretching and balance exercises with HRR maintained at or below 50%. Each group carried out the respective exercises for four days/week, duration of 45-60 mins each session for 6 months. The results showed an improvement in processing speed (P=0.05), verbal fluency (P=0.04) in the intervention group. Women in the intervention group were found to have increased cardiorespiratory fitness along with improved executive functions (p=0.05) as well as improvement in executive processing abilities (p=0.02) but not men. The results of this study might not truly represent the true population of elderly with MCI as participants were recruited from a single-site. Moreover, the exclusion criteria were very strict which was not accurate of the clinical population. Although the authors did not state the reason for unequal randomization, the statistical power was not affected which increased the validity of the results.
The study by Nagamatsu et al. (2012) aimed to show that aerobic and resistance training improves executive function and brain plasticity in senior women with mild MCI. The study was a proof-to-concept, single-blinded, randomized controlled trial. The duration of the trial was 26 weeks. Participants with a score lower than 26 on the Montreal Cognitive Assessment (MoCA) or complained of memory loss were included. Eighty-six community-dwelling women, aged 70 – 80 years old, were recruited. Seventy-seven of them completed the study. Twenty-six women were allocated to the resistance training (RT) group, 24 to the aerobic training (AT) group and 27 to the control (BAT) group. Each session lasted for 60 mins, twice weekly. The RT group performed two sets of six – eight repetitions with free weights and a resistance machine. The AT group carried out an outdoor walking programme and intensity is maintained once 70 – 80% of the heart rate reserve (HRR) was reached. The control group carried out stretching, balance and relaxation exercises. The results showed that the RT group had a significant improvement on the selective attention/conflict resolution (P=0.04) and associative memory task (P=0.03) compared to the control group. This study failed to address their aim with regards to the effect of aerobic exercise on cognitive function. The study also lacked important information such as the method of recruitment and why the study only included women.
Lastly, to build on the previous studies, Hsu et al. (2017) aimed to illustrate that moderate-intensity aerobic training would improve executive functions and functional neural activity in elderly with subcortical ischemia vascular cognitive impairment (SIVCI). The study was a planned secondary analysis of fMRI scans from a randomized, single blinded, controlled trial. A total of 21 out of 38 participants completed the trial. Intervention consisted of a 60 min class with 10 mins warm up, 40 mins walking and 10 mins cool down with an intensity of 60-70% HRR. Sessions were carried out thrice weekly for 6 months. Heart rate and rate of perceived exertion were monitored and recorded. The control group was not provided any recommendation on exercise. MRI scanning was done while the participants performed a modified flanker test and the data were collected at baseline and at end of study. Results showed that the intervention group had marked improvement in reaction time during congruent (p<0.01) and incongruent trials (p=0.03). The intervention group also showed decreased neural activity in some regions of the brain that correlated to improved executive functions. Thus, the authors conclude that thrice weekly of aerobic exercise for at least six months notably boost task performances in older adults with SIVCI. This study was well designed, with clear information on methodology and relevant inclusion and exclusion criteria. As SIVCI is only a subcategory of MCI, the results might not be able to translate to the MCI population. Although there was an improvement in selective attention/information processing from the results of the flanker test, the other domains of cognition need to be considered.
There are noticeably many stark differences in all four studies. In the studies, the dosages of exercise were not consistent and varied from twice weekly to 4x weekly, a total of 120 mins to 180 mins each week and the intensities varied from moderate to high. The common factor is a minimum duration of 6 months was needed for statistically significant improvement (Baker et al., 2010; Hsu et al., 2017; Lautenschlager et al., 2008; Nagamatsu et al., 2012). It will be useful to know the minimum dosage of exercise required to elicit a significant change in cognitive function.
Only the study by Lautenschlager et al. (2008) studied the effects of exercise post-intervention. The sustained benefit of exercise on cognitive function 18 months after six months of aerobic exercise was small but encouraging (Lautenschlager et al., 2008) although this may be attributed to the patients that are self-motivated to exercise. More research has to be done on the sustained effects of exercise on cognition.
The study by Baker et al. (2010) studied the effects of exercise on cognition and analyzed the results between gender. Women that exercised were found to have significant improvement in executive functions such as selective attention, cognitive flexibility and processing speed (p=0.04) as compared to the men who only had an improvement in task switching (p=0.04). This result could be due to the difference in mean age. The mean age of women in the aerobic group was 65.3 compared to 74.6 in the control group. The women in the aerobic group could generally be more able to carry out the exercises. In contrast, the difference in the mean age of the men was small, which provided more validity to the result.
Nagamatsu et al. (2012) is the only study that used resistance training as an intervention. Although, the study showed resistance training improved associative memory performance and brain plasticity in senior women with MCI but not aerobic training, this result should be taken with caution. In comparison to the study by Baker et al. (2010), the intensity and duration of aerobic exercise by were similar; however, Baker et al. (2010) conducted the session 4x/week compared to twice a week. The study by Baker et al. (2010) illustrated a significant improvement in processing speed (P=0.05) and verbal fluency (P=0.04). Hence, the dosage in Nagamatsu’s study might not be enough to elicit a positive result. More research will be required for the effect of resistance training on cognitive function.
In conclusion, aerobic exercise has a beneficial effect on cognitive function when performed for six months at moderate to high intensity. However, more multi-centered studies are needed to ascertain if other types and combinations of exercises can provide the same or more benefits on cognitive function.