Assistant Professor Terese Liu-Ambrose from the Brain Research Center at the University of British Columbia recently published a study examining whether there were any benefits to be gained in brain function from resistance & aerobic training in people who exhibited a mild degree of cognitive impairment. It is known that people who show a decline in memory or other brain function have a greater risk of developing dementia over the next five years. The areas to show the most significant deficits are memory but also the executive components i.e. a person’s ability to make decisions well and to also plan and multi-task.
By Teresa Liu-Ambrose, PhD, PT
Cognitive decline is one of the most pressing health care issues of the 21st century. Worldwide, one new case of dementia is detected every seven seconds 1. The number of people affected is projected to be over 80 million by 2040 1. Thus, the societal value of developing effective intervention strategies cannot be overstated 2. Indeed, if the onset and progression of dementia could be delayed by a modest one year, there would be nearly 9.2 million fewer cases of disease in 2050 2.
Physical activity has been widely promoted as a strategy for healthy aging as it can reduce the incidence of cancer, diabetes, and heart disease 3. Critically, evidence now suggests that exercise is a promising strategy for the prevention of cognitive decline and dementia in older adults. Broadly, there are two distinct forms of exercise training: 1) aerobic training (e.g., running, biking), aimed at improving cardiovascular health, and 2) resistance training (e.g., lifting weights), aimed at improving muscle strength. Both types of exercise training have a broad range of systemic benefits for older adults.
In the field of exercise neuroscience, much of the focus has been on the cognitive benefits of aerobic training – both in animals 4-7 and humans 8-12. These studies highlight that aerobic training enhances both brain structure and function. In rats, aerobic training increases brain-derived neurotrophic factors 13, 14 as well as other neurochemicals 14 that increase neuronal survival 15, synaptic development, and plasticity 16. In humans, research using both structural and functional magnetic resonance imaging (fMRI) revealed similar physiological changes among older adults who carried out six months of aerobic training 8, 9.
These beneficial effects were greatest in the frontal, prefrontal, and parietal cortices 8, 9 – regions of the brain that show the greatest age-related declines in humans and are thought to support executive functions. Executive functions are higher order cognitive processes that control, integrate, organize, and maintain other cognitive abilities 17. These cognitive processes are critical to the person’s ability to carry out health-promoting behaviours 18, such as medication management, dietary and lifestyle changes, self-monitoring of responses, and follow-up with health care professionals.
However, emerging evidence is also now suggesting that resistance training also has neurocognitive benefits 19-22. Resistance training is an attractive alternative to aerobic training to promote brain structure and function as impaired mobility is prevalent in older adults. In addition, resistance training moderates the development of sarcopenia (the degenerative loss of skeletal muscle mass and strength associated with ageing) – something that aerobic training does not do. The damaging effects of sarcopenia include increased falls and fracture risk as well as physical disability.
At first glance, the evidence regarding whether or not resistance training has neurocognitive benefit for older adults may appear equivocal. However, it should be noted that the most studies with negative results had small sample sizes (i.e., 13 to 23 participants per experimental group), short intervention periods (i.e., 8 to 16 weeks), or the training protocol did not require progression of loading (i.e., progressive resistance training) 23-26. We highlight the results of three recent randomized controlled trials of progressive resistance training in older adults.
Cassilhas and colleagues 22 demonstrated six months of either thrice-weekly moderate or high intensity resistance training improved memory performance and verbal concept formation in 62 community-dwelling senior men ages 65 to 75 years. The work of Cassilhas and colleagues 22 provides valuable insight into the possible mechanisms underlying the benefit of resistance training on cognitive performance. They found serum insulin-like growth factor-1 (IGF-1) levels were higher in the resistance training groups than in the control group. IGF-1 promotes neuronal growth, survival, and differentiation and improves cognitive performance.
Liu-Ambrose and colleagues 19 also demonstrated that 12 months of either once-weekly or twice-weekly progressive resistance training improved executive functions in 155 community-dwelling senior women ages 65 to 75 years. In addition, they 20 demonstrated that twice-weekly progressive resistance training also increased activation in brain regions that support executive functions. Furthermore, the cognitive benefits associated with resistance training were sustained for one year after the intervention has ended 27. Similar to the Cassilhas and colleagues 22, Liu-Ambrose and colleagues 19 used a progressive and high intensity protocol. Both a Keiser® Pressurized Air system and free weights were used to provide the training stimulus. The Keiser-based exercises consisted of biceps curls, triceps extension, seated row, latissmus dorsi pull downs, leg press, hamstring curls, and calf raises. The intensity of the training stimulus was at a work range of six to eight repetitions (two sets). The training stimulus was subsequently increased using the 7RM method – when two sets of six to eight repetitions were completed with proper form and without discomfort. Other key strength exercises included mini-squats, mini-lunges, and lunge walks.
Most recently, Nagamatsu and colleagues 21 demonstrated that twice-weekly progressive resistance training improved both executive functions and associative memory in 86 community-dwelling senior women ages 70 to 80 years with probable mild cognitive impairment (MCI). Mild cognitive impairment – a well recognized risk factor for dementia 3 – represents a critical window of opportunity for intervening and altering the trajectory of cognitive decline in older adults. Critically, both impaired executive functions and associative memory are robust predictors of conversion from MCI to dementia. Furthermore, twice-weekly progressive resistance training also increased activation in brain regions that support associative memory.
In summary, recent work in the area of exercise neuroscience provide an optimistic outlook to our future in dementia prevention. It really may be as simple as keeping the ageing population as active for as long as possible! Some may still argue the evidence is still not quite there yet – that we need larger and longer trials with hard outcomes (e.g., a 5-year exercise trial aimed to assess whether an exercise intervention reduced the number of individual who develop dementia). However, can we afford to keep waiting given the impending crisis that both our health care system and society will face? Furthermore, is there any other intervention strategy that could be feasibly implemented at the population level with equal benefits as exercise?
In closing, exercise neuroscience is an exciting area of research, providing new insight to how exercise may influence the nervous system across the life span. However, it would appear that the benefits of physical activity were well observed long ago.
Dr. Teresa Liu-Ambrose, PhD, PT, is an Assistant Professor in the Department of Physical Therapy, University of British Columbia , Vancouver, Canada and Director the Ageing, Mobility and Cognitive Function Laboratory. Dr. Liu-Ambrose is a member of the UBC Brain Research Centre and a principal investigator of the Centre for Hip Health and Mobility.
Source: Fitness Australia