By Ceara Higgins, DC, for RRS Education
Study Title: “Exercise interventions for cognitive function in adults older than 50: a systematic review with meta-analysis”
Authors: Northey JM, Cherbuin N, Pumpa KL, et al.
Publication Information: British Journal of Sports Medicine 2018; 52: 154-160.
Comment from Dr. Shawn Thistle:
There are numerous benefits to exercise, which is why chiropractors have always been strong advocates for supporting active lifestyles for our patients. This study is the first I’ve seen summarizing the evidence specific to cognitive benefits of exercise for people over 50…the results are promising for both aerobic and resistance training, reminding us to always incorporate patient preference into exercise prescription.
As any population ages, cognitive decline becomes more of an issue. Maintaining a physically active lifestyle has been shown to help reduce age-related cognitive declines1 and incidence of dementia.2 The most accepted hypothesis to explain this relationship postulates that neural and vascular adaptation to physical exercise promotes neurogenesis, angiogenesis, synaptic plasticity, decreased proinflammatory processes, and reduced cellular damage due to oxidative stress, all leading to improved cognitive function.3
Prior research has shown conflicting results, due in part to the use of restrictive inclusion criteria. Guidelines as to the type or amount of exercise that clinicians should be recommending to their patients are, therefore, needed. The authors of this study performed a comprehensive meta-analysis with no limit on publication date or exercise mode in order to include a larger number of studies. Four key issues were addressed:
- The effects of supervised exercise interventions, including aerobic, resistance, multicomponent, tai chi and yoga, on cognitive function;
- The influence of variables including the duration, frequency, intensity, and length of exercise;
- The differentiation of exercise effects on global cognition and aspects of cognition including attention, executive function, memory, and working memory; and
- The impact of the study design, including the type of control group and baseline cognitive status of participants.
Thirty-nine studies were included in the quantitative analysis. All modes of exercise (except yoga) produced significant positive effects on cognitive function. Studies with a medium duration of exercise (45-60 minutes) showed positive effects, while short- and long-duration exercise did not show statistically significant results. Moderate and vigorous exercise intensity had similar positive effect sizes, while low-intensity exercise did not show statistically significant results.
Exercise in general showed statistically significant effects on all domains except for global cognition. Resistance training showed significant effects on executive function, memory and working memory and tai chi showed significant effects on working memory. Both aerobic and resistance training were shown to have similar effect sizes.
This study showed results contrary to those of recent reviews on aerobic exercise, showing aerobic exercise to be beneficial to the cognitive functioning of older adults. This is likely due to the multilevel analysis model utilized in this study and the absence of restrictions on publication dates, which allowed for a much larger data pool. In addition, this study confirms previous research suggesting that resistance training may play an important role in improving and maintaining cognitive function in older adults.5
Clinical Application and Conclusions
This meta-analysis provides positive evidence supporting the prescription of both aerobic and resistance training, between 45 and 60 minutes in duration, of moderate or vigorous intensity, and of any frequency or length, in adults over 50, specifically to improve cognitive function. Tai chi was also shown to improve cognitive function in this age group, although there were few studies that specifically looked at tai chi. While further studies are needed, this is important as tai chi may be suitable for less functional populations that may not be capable of other forms of aerobic or resistance training. As well, it is important to note that including participants with mild cognitive impairment in the meta-analysis did not change the overall findings, indicating that this group can also benefit from exercise prescription.
In the future, it would be useful to study the effect of unsupervised versus supervised exercise interventions to determine the best way to provide such programs for older patients.
A search was conducted up to November 2016, with all returned titles screened by the first author to exclude all duplicates or clearly non-relevant studies. Next, abstracts were independently reviewed by two authors, then full texts were reviewed independently by three authors using the inclusion and exclusion criteria below. The bibliography of all included articles and prior reviews were also searched. Any disagreements at any stage were resolved through discussion.
- RCTs published in a peer-reviewed journal
- Studies of community dwelling men or women aged 50 years or older
- No limitation was placed on baseline cognitive status
- Studies including a structured exercise program of any type, duration, frequency, or intensity
- Studies with control groups including no contact, waiting list, attention control, sham exercise, or alternative active treatment
- Studies utilizing at least one outcome measure of cognition, measured at baseline and follow-up by any validated neuropsychological test
- Clinical samples with neurological (like stroke) or mental illnesses (like depression)
- Exercise programs that were not explicitly stated as fully supervised, or of less than four weeks’ duration
Two review authors independently extracted data on study population, intervention, control group, and outcome measures into a standardized form. When it was available, the average change from baseline, SD of the mean change, and the number of participants at each assessment for all groups was also extracted. In studies with multiple follow-ups, the longest follow-up period during which the exercise intervention was continued was included.
Mode of exercise was classified as aerobic, resistance training, multicomponent training, tai chi, or yoga. Exercise intensity was classified as low, moderate, or high based upon published guidelines.7 Exercise duration was classified as short (< 45 min), medium (> 45 to < 60 min), or long (> 60 min), including the time spent on warm-up and/or cool-down. Exercise length was defined as the number of weeks of exercise and classified as short (4-12 weeks), medium (13-26 weeks), or long (> 26 weeks) using a prior review as a guide.4 Finally, exercise frequency (number of exercise sessions per week) was classified as low (2 or less), medium (3-4), or high (5-7). Neuropsychological tests were classified according to the domain of cognition they were assessing. These included global cognition, attention, executive function, memory, and working memory.8 Control groups were classified into four categories, including no contact (e.g. advised to maintain current lifestyle), active (e.g. sham exercise such as stretching), educational, or social (e.g. social meeting groups).
Risk of bias was independently assessed as low, high, or unclear, by two authors using the Cochrane Collaboration Guidelines.9 The articles were assessed for randomization, allocation concealment, blinding of therapists, blinding of participants, blinding of outcome assessors, handling of incomplete data, selective reporting, and any other risk of bias. It was found that the majority of studies did not describe their sequence generation nor allocation concealment in enough detail and that in all studies it was not possible to blind the therapists or participants. It was judged that this created a high risk of bias for participants but a low risk of bias for therapists.
- The meta-analysis was conducted utilizing established guidelines from the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA).6
- This study provided an up-to-date summary of supervised RCTs and advanced previous reviews by utilizing a multilevel design and not limiting exercise mode nor publication date.
- Only English language publications were included, introducing the possibility of language bias.
- Studies were only included if exercise was the sole intervention, therefore a large number of studies where exercise was provided as an adjunct to other interventions were excluded.
Dr. Thistle is a practicing chiropractor, educator, international speaker, knowledge-transfer leader, entrepreneur and medicolegal consultant. He is the founder and CEO of RRS Education, a trusted source of continuing education solutions for chiropractors since 2006. RRS Education provides weekly Research Reviews like this one (subscription required) as well as evidence-based online courses to help busy clinicians review and integrate current research into their patient care. For more information, visit: www.rrseducation.com.
- Erickson KI, Gildengers AG, Butters MA. Physical activity and brain plasticity in late adulthood. Dialogues Clin Neurosci 2013; 15: 99–108.
- Abbott RD, White LR, Ross GW, et al. Walking and dementia in physically capable elderly men. JAMA 2004; 292: 1447–53.
- Rasmussen P, Brassard P, Adser H, et al. Evidence for a release of brain-derived neurotrophic factor from the brain during exercise. Exp Physiol 2009; 94: 1062–9.
- Colcombe S, Kramer AF. Fitness effects on the cognitive function of older adults: a meta-analytic study. Psychol Sci 2003; 14: 125–30.
- Gates N, Fiatarone Singh MA, Sachdev PS, et al. The effect of exercise training on cognitive function in older adults with mild cognitive impairment: a meta-analysis of randomized controlled trials. Am J Geriatr Psychiatry 2013; 21: 1086–97.
- Moher D, Liberati A, Tetzlaff J, et al; PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. BMJ 2009; 339: b2535.
- ACSM. ACSM's guidelines for exercise testing and prescription: Lippincott Williams & Wilkins, 2013.
- Smith PJ, Blumenthal JA, Hoffman BM, et al. Aerobic exercise and neurocognitive performance: a meta-analytic review of randomized controlled trials. Psychosom Med 2010; 72: 239–52.
- Higgins J, Green S, The Cochrane Collaboration. Cochrane handbook for systematic reviews of interventions. NY: John Wiley & Sons, 2011.