Preventing cognitive decline through resistance training

The foundations for later-life cognitive health are often laid decades prior to the first symptoms of cognitive decline, therefore preventative strategies should be implemented early in life. Structured resistance training shows promise at reducing dementia risk and has been associated with enhanced cognitive function and biomarker profiles. More specifically, intense acute resistance exercise and chronic resistance training may increase levels of growth factors, such as brain-derived neurotrophic factor (BDNF), insulin-like growth factor (IGF-1) and vascular endothelial growth factor (VEGF), which influence the proliferation and maintenance of neural and vascular tissue. Furthermore, biomarkers associated with suboptimal cognitive health (e.g., homocysteine) are decreased following longer-term resistance training. Although promising, the current literature is inconsistent, with varying resistance exercise regimens implemented, contributing to conflicting reported effects on cognition and biomarkers. The aim of the current thesis was to evaluate the impact of different strength training protocols on cognitive health. Four studies were conducted to examine acute response in growth factors following resistance exercise in young and older adults, and the chronic response in neurotrophic growth factors and cognitive function following resistance training in older adults. Chapters Four and Five explored the acute response in neurotrophic growth factors to intense resistance exercise in young or late middle-aged adults. Sixteen young adults were recruited (Chapter Four) to perform to-fatigue (i.e., maximal), high-volume acute resistance exercise bouts: i) traditional hypertrophy-based resistance exercise (i.e., three sets, 10 repetitions at 100% of 10 repetition maximum [RM]), or ii) traditional strength-based resistance exercise (i.e., five sets, five repetitions at 100% of 5RM). Levels of serum BDNF and blood lactate concentration (i.e., physiological marker of session intensity) were measured prior to and following exercise. Serum BDNF was increased (p<0.01; d=0.52) immediately post-hypertrophy resistance exercise when compared to strength resistance exercise. Change in serum BDNF levels were positively correlated (r=0.70; p<0.01) with change in blood lactate concentration immediately following hypertrophy-based resistance exercise only. The acute BDNF response to resistance exercise may not be consistent across the lifespan, and to-fatigue and high-volume resistance exercise is not practical in ageing adults. For this reason, Chapter Five explored the acute growth factor response to intense, yet pragmatic resistance exercise (i.e., submaximal and lower-volume) in 29 late middle-aged adults. Two resistance exercise sessions i) moderate-load (i.e., three sets, 10 repetitions at 70% of 1RM), or ii) high-load (i.e., five sets, five repetitions at 85% of 1RM) were performed in parallel groups (Chapter Six and Seven). Session intensity was determined by change in blood lactate concentration, and session rating of perceived exertion (sRPE). Serum samples were taken prior to and following exercise for later BDNF, IGF-1, and VEGF analysis. No acute changes in BDNF, IGF-1 or VEGF were observed. Changes in BDNF, IGF-1 or VEGF were not associated with changes in blood lactate concentration or sRPE. My findings provide evidence that to-fatigue, high-volume resistance exercise can increase acute levels of BDNF; however, under more practical resistance training scenarios (e.g., moderate volume, submaximal resistance exercise) this outcome is less likely to occur. Resting levels of BDNF, IGF-1, VEGF and homocysteine are important predictors for later life cognitive function in ageing adults; thus, Chapter Six explored changes in resting blood markers following a 12-week period of intense, lower-volume resistance training twice per week in 45 late middle-aged adults. Participants were randomised into one of three groups; i) moderate-load (i.e., three sets, 10 repetitions at 70% of 1RM), ii) high-load (i.e., five sets, five repetitions at 85% of 1RM), or iii) a non-exercising (i.e., no intervention) control group for comparison. Fasted levels of serum BDNF, IGF-1, VEGF, and plasma homocysteine were quantified from blood samples collected before and after the 12-week intervention. No differences were observed in BDNF, IGF-1, VEGF, or plasma homocysteine from pre- to post- intervention between groups. Despite an intense training stimulus, it is possible that the protocols implemented here were not of high enough volume to enhance growth factors. However, high-intensity and high-volume resistance exercise is not a practical training model in ageing adults. Chapters Four-Six placed a strong emphasis on the importance of physiology, and the levels of certain biomarkers, in regards to cognitive health. Therefore, it is essential to evaluate the functional outcomes of resistance training on cognitive health. As part of the randomised controlled trial introduced in Chapter Six, Chapter Seven explored the response in cognitive function following 12 weeks of intense resistance training in 45 late middle-aged adults. Participants were randomised into either i) moderate-load resistance training, ii) high-load resistance training, or iii) a non-exercising control group. Cognitive function was assessed using the CogState computerised cognitive battery, which evaluates performance within several cognitive domains. Greater delayed short-term memory (p=0.02) was observed in high-load and moderate-load groups when compared to the control, with no difference observed between resistance training groups. No other differences for changes in cognitive function between groups were observed. In cognitively healthy adults, 12 weeks of intense resistance training enhances short-term memory, a finding supporting the use of structured resistance training to promote physical and cognitive health. In conclusion, the findings presented in this thesis provide evidence that resistance exercise needs to be to-fatigue and high in volume to enhance BDNF levels. Intense resistance exercise in late middle-aged adults influences neither the acute nor chronic response in neurotrophic growth factors or homocysteine when resistance exercise is reduced in total volume. However, 12 weeks of intense resistance training enhances short-term memory in cognitively healthy adults, a relevant outcome that supports the hypothesis that resistance training can contribute to reducing dementia risk. These findings support the use of structured resistance training to promote full body health inclusive of physical and cognitive health.