It is well established that PRT can produce significant and marked improvements in muscle strength, mass and size (17). More recently, there has been an increased interest into the effect of PRT on cognitive function due to a possible link between muscle and cognitive function (15, 16, 19, 20). This section will briefly discuss the
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current evidence for the effects of PRT on cognitive function, followed by potential mechanisms which may explain any beneficial effects.
In a large cross-sectional analysis using data from 2157 adults aged 65-85 years from the NHANES study, Loprinzi et al. found that after adjusting for a number of factors including age, sex, ethnicity, CRP, smoking and physical activity, muscle strengthening activities were significantly and positively associated with cognitive function (βadjusted=3.4; 95% confidence interval [CI]: 1.7–5.1; P<0.001) (344).
Further, those doing aerobic exercise or muscle strengthening activities or both, were found to have higher executive function scores than those not doing aerobic exercise or muscle strengthening activities or both (344). Although not directly examining the effects of PRT on cognition, one prospective study with a mean follow-up of 3.6 years found that greater muscle strength at baseline was associated with a 43% reduced risk of developing AD in adults aged 54-100 years (15). It was also found that a high level of muscle strength (90th percentile) was associated with a 48% decrease in the risk of developing MCI compared to a low level of muscle strength (10th percentile) (15). These results suggest that improvements in muscle strength which are consistently reported with PRT may result in a lowered risk for cognitive decline.
As summarised in Table 2.8, there are a number of RCTs which have investigated the effects of PRT on cognitive function (345-351).
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Table 2.8 Summary of key studies which have examined the effect of PRT on cognitive function in older adults
Author, Year Subjects Duration and
design Groups Key Findings
Domain PRT> Control Effect of PRT Dose†
de Camargo Smolarek et al. 2016 (346) N= 66 healthy women with a mean age of 66 years 12- week RCT.
1) Three times weekly
moderate-intensity (60-75% of 1-RM) resistance training
2) Controls
Global cognitive function + NA
Ikudome et al. 2016 (345) N= 170 healthy older adults aged 52-81 years 12-week non- randomised trial.
1) body mass-based home exercise program (intensity not defined) 2) controls Information processing Inhibitory control Attention Working memory Timing ability O + (NS) O + O NA Suo et al. 2016 (351) N=100 with dementia prodome MCI with an average age of 70.1 years
6 month RCT 1) twice weekly high-intensity (80-92% of 1-RM) PRT
2) Computerised cognitive training (CCT)
3) Twice weekly high-intensity PRT+ CCT
4) Control
Global cognitive function Memory + (PRT) O NA Best et al. 2015 (349) N= 155 healthy women aged 2 year follow- up of 52-week RCT.
1) once weekly high-intensity resistance training Verbal memory Executive function O + + (frequency)* O
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65-75 years 2) twice weekly high-intensity resistance training *
3) twice weekly balance and tone training Bolandzadeh et al. 2015 (352) N= 42 healthy community- dwelling women aged 65-75 years with white matter lesions
52-week RCT. 1) once weekly PRT (no intensity defined)
2) twice weekly PRT* (no intensity defined)
3) twice weekly balance and toning
White matter lesions Executive function + *only NR + (frequency)* NR Ruiz et al. 2015 (350) N= 20 older adults aged 90 years and over living in a nursing home
8-week RCT. 1) light-moderate intensity (10- 12 on 20 point BORG scale) aerobic and PRT three times a week
2) control
Global cognitive function O NA
Liu-Ambrose et al. 2012 (353) N=52 community- dwelling women aged 65-75 years 12 month single-blind RCT.
1) once weekly resistance training (no intensity defined)
2) twice weekly resistance training * (no intensity defined)
3) twice weekly balance and tone training
Selective attention and conflict resolution + * only + (frequency)* Anderson- Hanley et al. 2010 (347) N= 32 community dwelling
4-week RCT. 1) Two-three times weekly resistance training (intensity not defined) Executive function Information processing + O NA
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adults aged between 55 and 85 years
2) exercise waiting list (controls) Kimura et al. 2010 (354) N=119 aged over 65 years 12-week single blind RCT.
1) twice weekly 1.5 hour strength training sessions (60% of 1-RM)
2) health education classes twice a month Reaction time O NA Liu-Ambrose et al. 2010 (348) N=155 community- dwelling men and women aged 65-75 years 12-month single-blind RCT.
1) once weekly resistance training (intensity not defined)
2) twice weekly (intensity not defined)
3) twice weekly balance and tone training
Selective attention and conflict resolution Set shifting Working memory + O O NR O O Cassilhas et al. 2007 (73) N=62 sedentary males aged 65-75 years 24-week RCT. 1) Control 2) moderate intensity (50% of 1-RM) PRT 3) high intensity PRT (80% of 1-RM)
Short term memory Attention
Long term memory
+ + + O O O
+ significant positive association between PRT and cognitive function; - significant negative association between PRT and cognitive function; O no association between PRT and cognitive domains. NA: not assessed; NS: non-significant; NR: not reported. † dose includes frequency, duration and intensity of exercise.
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A 3-month non-randomised trial conducted in 170 older adults aged between 52 and 81 years found that performance on the Go/No-Go reaction and serial subtraction tasks (measures of inhibition and memory) improved following a body mass based home strength exercise program performed six days a week, although the only significant between group difference was for memory when compared to a non- exercise control group (345). There were no improvements on measures of processing speed, attention or reaction time (345). A limitation of this study is the large difference in the numbers of participants in the intervention versus control group (144 versus 26) due to participants being recruited separately for each group (345). Further, participant characteristics such as education which may influence cognitive function, were not taken into account in this study and the intensity of the training may not have been sufficient to induce cognitive benefits (345). In contrast, one 12-week RCT conducted in 66 healthy women with a mean age of 66 years found that moderate-intensity (60-75% of 1-repitition maximum [RM]) resistance training performed three times a week improved cognitive capacity by 19% as measured by the MoCA, compared to controls (346). These findings are supported by another 4-week study in 32 community-dwelling older adults aged between 55 and 85 years which found that performance on the Digit Span Backward test and Stroop colour C (executive function) test improved following a resistance training program performed two to three times a week compared to those on an exercise waiting list; there were no improvements in other cognitive tests of executive function (Color Trails 2 test, Digit Span Forwards) or information processing (Digit Span Forward, Stroop A & B, Color Trails 1 and Letter Digit Substitution Test [LDST]) (347). It was suggested that the lack of findings in these tests may have been due to subtle effects of the exercise across multiple cognitive domains and the tests used may not have been sensitive enough to detect these subtle changes (347). For instance, a limitation of this study noted by the authors was the lack of consistency between the three tests used which were designed to assess executive function (347).
Despite this, other studies have found benefits for PRT on cognitive function with less frequent training. One 12-month RCT in 155 community-dwelling adults aged 65-75 years found that once weekly and twice weekly high-intensity PRT (increased using the 7-RM method) improved selective attention and conflict resolution as measured by the Stroop test (12.6 % and 10.9% improvements respectively)
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compared to a twice-weekly balance/tone training control (0.5% decline) (348). More recently, a follow-up study (two year follow-up post training) of these participants to investigate the long term effects of high-intensity resistance training on cognitive function reported that the benefits were maintained (349). In this study, it was found that both once and twice weekly high-intensity resistance training improved executive function (as measured by the Stroop test, Trail Making test, Backward digit span and DSST) two years after the intervention (standardized difference [d]=.31–.48) and twice weekly resistance training improved memory as measured by the RAVLT (d=.45), when compared to balance and toning exercises (349). While this suggests that PRT may have the potential to have a long-term influence on cognitive function even after training cessation, the mechanism(s) underlying these long-term benefits remains unknown. In contrast to this study, one 8-week RCT conducted in 20 men and women aged 90 years and over living in a nursing home, found no changes in cognitive function as measured by the MMSE following light-moderate intensity (increasing from 30% of 1-RM to 70% of 1-RM) PRT (mainly leg press) performed three times a week compared to the control group (350). However, limitations of this study include the short duration and the lack of sensitivity of the measure (MMSE) used to assess cognitive function. Given the age of the participants, it would be expected that they would have a high level of age- related decline at baseline, and thus would be more sensitive to the effects of the program with more scope to improve. Thus the lack of effect observed in this study may be related to the use of the MMSE as this may not have been sensitive enough to pick up on subtle changes over a short duration.
Consistent with the mixed findings reported above, several reviews of RCTs have also reported contrasting results with regard to the effects of PRT on cognitive function (355, 356). One review of the effects of resistance training on mental health which included depression, anxiety, self-esteem, chronic pain, fatigue, cognitive function and sleep, found that there were seven RCTs which had specifically investigated the effects on cognitive function in healthy older adults (355). All of these studies reported small to moderate positive effects on cognitive function with the largest effects found for memory, although in three of these studies the changes were not significant (355). These studies however, had the limitation of small sample sizes (8-17 per group). More recently, a review of 10 studies investigating the effects of PRT on cognitive function in healthy older adults reported mixed findings when
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comparing the exercise to no exercise groups or other exercise modalities (356). This was suggested to be due to differences in participant characteristics, exercise designs and tests of cognitive function among studies (356).
There is evidence to suggest that PRT has beneficial effects on cognitive function in those who are already cognitively impaired. One meta-analysis of 41 RCTs (21 conducted in older adults with cognitive impairment and 20 in those without) found moderate to large effects sizes (ES=0.49 to 0.51) for resistance training in cognitively impaired individuals (357). Further, there was no significant difference in terms of the effect sizes for resistance training on cognitive function in cognitively impaired or cognitively normal older adults, suggesting that baseline cognitive status does not appear to influence the effects of PRT on cognitive function (357).
Although there are guidelines outlined by the American College of Sports Medicine (ACSM) for PRT with regard to improving muscle strength and hypertrophy in older adults (356), the dose of PRT which is the most beneficial for cognitive function is still a topic for debate. As discussed above, there is some evidence for beneficial effects of once weekly PRT on cognitive function although other studies have found no benefits following training three times a week (350). There is also some evidence to suggest that high-intensity PRT is more beneficial for cognitive function compared to lower intensities (348-350). This is further supported by other studies which have reported that PRT can have acute effects on different cognitive domains based on the intensity of the training (358). For instance, one RCT conducted over two days in 68 young men and women (mean age 26 years) found that a 30 minute bout of PRT resulted in a linear relationship between exercise intensity and processing speed and a quadratic relationship between intensity and executive function (358). This acute study indicates that high-intensity exercise (100% of 10-RM) was more beneficial for processing speed, while moderate-intensity (70% of 10-RM) was more beneficial for executive function (358). The reason(s) for the varying effects is not clear although it has been suggested that the dose-response relationship between exercise and cognitive performance may be dependent on the cognitive demands of the task (359). Similarly, a RCT conducted in 210 community-dwelling older adults with a mean age of 75.3 years, found that while there were no differences in memory between controls and a group undertaking six months of theraband resistance training three days a week, changes in resistance throughout the intervention were a significant
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predictor of change in memory performance (360). Taken together, the current findings suggest that dosage of PRT is important for predicting exercise-induced changes in cognitive function, but questions still remain as to what represents the optimal dose.