Research Review By Demetry Assimakopoulos©

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Date Posted:

November 2011

Study Title:

Resistance Training and Functional Plasticity of the Aging Brain: A 12-month Randomized Control Trial

Authors:

Liu-Ambrose T, Nagamatsu LS, Voss MW et al.

Author's Affiliations:

University of British Columbia, Canada

Publication Information:

Neurobiology of Aging 2012; 33(8): 1690-8. doi: 10.1016/j.neurobiolaging.2011.05.010. Epub 2011 Jul 7.

Background Information:

A current and promising approach for maintaining one`s functional brain plasticity during aging is exercise. Exercise, as we all know, comes in two, very broad forms: aerobic training and resistance training. Evidence has shown that aerobic exercise in particular is an admirable practice for geriatrics, because it has the power to preserve and even increase levels of brain-derived neurotrophic factors, which can lead to increased neuron survival rates, synaptic development and plasticity. It has also been shown that these cognitive changes stemming from aerobic exercise occur in areas of the brain that typically show the greatest age-related decline (1,2). However, aerobic exercise can often be difficult for seniors, because it typically requires relatively healthy joints and some existing cardiovascular fitness.

Resistance training, on the other hand, is a form of exercise that is within reach of the elderly community, despite their potential for limited mobility and decreased fitness level. There have been two studies within the last decade, which have suggested that moderate-to-high intensity resistance training can be beneficial for seniors, because it has the power to improve memory, verbal concept formation, selective attention and conflict resolution in elderly populations (3,4). However, there is currently little information regarding resistance training’s affect on functional plasticity. It is the hypothesis of the authors of this study that resistance training will increase activation in the frontal and parietal cortices, specifically the superior and middle frontal giri, and the superior parietal lobe. Additionally, the authors will strive to prove that resistance exercise will reduce activation of the anterior cingulate cortex.

Pertinent Results:

Fifty-two older adult women participated in the study. There were no significant differences in exercise compliance between groups at the end of the study. The group who trained twice weekly (RT2) demonstrated a significant reduction in interference, when compared to the group who partook in balance and tone training (BAT) (p < 0.05). The group who only trained once per week (RT1) did not show a significant reduction in interference when compared to the BAT group. No significant difference was found between the RT1 and the RT2 group. The RT2 group showed an 8.48% decrease in interference, followed by the RT1 and BAT who lessened their interference by 2.29% and 1.47%, respectively. There were no significant differences between groups in the congruent and incongruent reaction times.

The researchers were successful in identifying cortical areas which showed significant changes in hemodynamic activity for incongruent vs. congruent trials at trial completion compared to baseline. When compared to the BAT group, the RT2 group showed a significantly greater percent signal change in the left anterior insular cortex, extending into the lateral orbital frontal cortex and anterior portion of the left middle temporal gyrus (p < 0.03). These signal changes RT2 group occurred due to an increase in activation for incongruent trials and a decrease in congruent trials. The RT2 group also showed a decrease in activation for congruent trials in the anterior portion of the left middle temporal gyrus at trial completion. No differences were found between the RT1 group and the BAT group.

Clinical Application & Conclusions:

Senior women who engage in resistance training twice weekly significantly improved their performance on the Flanker Task (see below). This improvement occurred concurrently with positive functional changes in hemodynamic activity in the left anterior insular cortex, extending into the lateral orbital frontal cortex and the anterior portion of the left middle temporal gyrus. Other research has shown that these areas are associated with response inhibition processing in tasks like the Flanker task.

At the start of the study, the participants grouped to the RT2 group were engaging in a response inhibition process regardless of the trial type; this infers that the subjects were set to a default state of preparing for a response conflict. At the time of study completion, these subjects demonstrated more adaptable response inhibition process, meaning they had an enhanced ability to avoid making automatic and unwanted responses. The bottom-line is that two days a week of resistance training has a positive effect on the functional plasticity of the cerebral cortex and a more efficient recruitment of the response inhibition process. A progressive resistance training program is important for maintaining functional independence in older adults.

These cognitive benefits as a result of resistance training are thought to be mediated by a reduction of serum homocysteine (5) and increased levels of IGF-1 (6). Increased levels of homocysteine are said to produce negative cognitive and brain structure outcomes. When IGF-1 is stimulated to release, it actually improves cognitive performance, and promotes the growth of neurons, prolongs their survival times and allows for greater neuronal differentiation.

Study Methods:

This study took place over the course of 12-months. The participants included were women aged 65-75 years, living independently in their own home, who scored greater than or equal to 24 on the Mini Mental State Examination (MMSE) and had a visual acuity of 20/40 with or without corrective lenses. Subjects were excluded if they had a current medical condition which necessitates avoiding exercise, had participated in resistance training within the last 6 months, had a neurodegenerative disease or stroke, were diagnosed with depression, did not speak the English language fluently, were taking cholinesterase inhibitors, were using estrogen replacement therapy and were using testosterone therapy.

Subjects were randomized to one of three groups, which differentiated themselves based on the frequency of resistance exercise per week and the type of resistance training: once weekly (RT1); twice weekly (RT2); balance and tone training (BAT).

The RT1 and RT2 groups participated in progressive resistance training programs, which utilized both free weights and a Keiser Pressurized Air system. Each participant performed 2 sets of 6-8 repetitions. When a subject could complete 2 sets of 6-8 repetitions with proper form and without discomfort, the intensity of the training stimulus increased. The BAT experimental group performed stretching, range of motion and basic core strength exercises (kegals, balance exercises and relaxation techniques), and served as control for confounding variables.

Prior to the trial, each participant underwent a baseline physician’s assessment to confirm their health status and eligibility for the study. In addition, each subject answered the 15-item Geriatric Depression Scale (GDS) to screen for depression and the Physical Activities Scale for the Elderly (PASE). Also, the timed up and go test (TUG) was used to judge general mobility.

Functional MRI (fMRI) was used to gain images of the brain. During the scanning process, each participant performed a modified Eriksen Flanker task, which is designed to engage both selective attention and conflict resolution. In this task, the participants are asked to signal when the outer chevrons, in a line of 5 chevrons (<<<<< - or the congruent direction), turn to the opposite direction (>><>> - or the incongruent direction). This task was used in the study’s behavioural analysis, where the percentage increase or decrease in reaction time to the incongruent stimuli was computed using the formula [(incongruent reaction time – congruent reaction time)/congruent reaction time]. This formula was used to calculate differences between the 2 experimental groups and the control group. The main change that the researchers sought to keep track of over time was the percentage increase or decrease in the amount of time to complete the Eriksen Flanker task trial; this measurement was used to reflect interference which was unbiased by differences in groups in base reaction time (**It is assumed here, that bias can be introduced due to inherent difference in responses between groups and that this needed to be corrected by using the formula described above**). Specifically, they compared the magnitude of the change in task performance time (or percent signal change on the fMRI) in each cortical area between groups.

Study Strengths / Weaknesses:

Weaknesses
  • The RT1 group had an average compliance of 75.1%, while the RT2 and the BAT groups had a compliance of 79.2% and 71.8%, respectively. While these are non-significant differences, the threshold for the volume or compliance of resistance training over time is unknown and could have been at play in this study.
  • The population sample was limited to healthy 65-75 year old women, thus rendering the results of the study possibly un-generalizable to older adults or the elderly on mass.
  • The researchers did not measure homocysteine and IGF-1.
  • The authors only suggested that in their study, resistance training did affect the anterior cingulate cortex. However, they did address this later on in the paper when they spoke about a past study, where aerobic training decreased activity in the anterior cingulate cortex, while increasing activity in the frontal and superior parietal regions (7).
  • The researchers did not specifically describe what they mean by “interference.” This had to be assumed.
Strengths
  • A dose response, quantifying the resistance training volume required to create plastic cortical changes was established.

Additional References:

  1. Colcombe, SJ, Erickson KI, Raz N, Webb AG, Cohen NJ, McAuley E, et al. Aerobic fitness reduces brain tissue loss in aging Humans. J Gerontol A Biol Sci Med 2003; 58: 176–180.
  2. Colcombe SJ, Kramer AF, Erickson KI, Scalf P, McAuley E, Cohen NJ, et al. Cardiovascular fitness, cortical plasticity, and aging. Proc Natl Acad Sci USA 2004; 101: 3316–3321.
  3. Cassilhas RC, Viana VA, Grassmann V, Santos RT, Santos RF, Tufik S, et al. The impact of resistance exercise on the cognitive function of the elderly. Med Sci Sports Exerc 2007; 39: 1401–1407.
  4. Liu-Ambrose T, Nagamatsu LS, Graf P, Beattie BL, Ashe MC, Handy TC. Resistance training and executive functions: a 12-month randomized controlled trial. Arch Intern Med 2010; 170: 170–178.
  5. Vincent KR, Braith RW, Bottiglieri T, Vincent HK, Lowenthal DT. Homocysteine and lipoprotein levels following resistance training in older adults. Prev Cardiol 2003; 6: 197–203.
  6. Colcombe SJ, Kramer AF, Erickson KI, Scalf P, McAuley E, Cohen NJ, et al. Cardiovascular fitness, cortical plasticity, and aging. Proc Natl Acad Sci USA 2004; 101: 3316–3321.