<p dir="ltr">Past research has extensively explored the benefits of acute aerobic exercise (AE) on memory and executive functions. Additionally, the cross-sectional relationship between muscle strength – a direct outcome of RE – and cognition is unknown, despite the simultaneous onset of muscle and cognitive decline in one’s thirties. However, the effects of acute resistance exercise (RE) on cognition remain understudied, despite the growing popularity of RE and evidence that RE may have distinct effects on cognition.. Therefore, the present study aimed to broaden our understanding of the connection between muscle strength and hippocampal-dependent memory and to investigate the influence of RE on memory and executive function.</p><p dir="ltr">A sample of 125 healthy young adults (18-50 years old) completed this study. On the first day of testing, subjects completed a cognitive battery testing aspects of hippocampal dependent memory, spatial abilities, and working memory, a maximal muscle strength testing session including handgrip strength and one-rep-max testing, and maximal aerobic capacity testing. Subjects completed a bioelectrical impedance assessment (BIA) body scan to measure body composition on Day 2. Day 3 consisted of a randomized controlled trial (RCT), where subjects completed either 42 minute moderate intensity RE (n = 62) or a seated rest (n = 61). Cognitive testing including a memory recognition task, an inhibitory control task, and a working memory task were performed both before and after the intervention. Subjects also completed lactate, blood pressure, and blood draw (only a subset of subjects (n = 59)) before and after intervention.</p><p dir="ltr">The results first revealed that after controlling for known covariates, those with greater handgrip strength performed better on mental rotation tasks (t = 2.14, p = 0.04, Δr2= 0.04), while those with higher upper-body relative strength did better on recognition (t = 2.78, p = 0.01, Δr2 = 0.06) and pattern separation (t = 2.03, p = 0.04, Δr2= 0.04) tasks. Further, while there was no acute effect of RE on memory performance, response times during measures of inhibitory control (t = 4.15, p < 0.01, d = 0.40) and working memory decreased after exercise (t = 7.01, p < 0.01, d = 0.46), along with decreases in P3 latency during the inhibitory control task (t =-5.99, p < 0.01, d = 0.58). Additionally, blood lactate (t =-17.18, p < 0.01, d = 2.06), serum brain derived neurotropic factor (BDNF) (t = -4.17, p < 0.01, d = 0.66), and systolic blood pressure (t = -10.58, p < 0.01, d = 0.99) all increased following RE, while diastolic blood pressure (t = 4.90, p < 0.01,d = 0.50) decreased. Notably, the change in systolic blood pressure (t = -2.83, p = 0.01, Δr2 = 0.06) was associated with improvements in behavioral measures of inhibitory control, changes in lactate (t = -2.26, p = 0.03, Δr2 = 0.04) and systolic blood pressure (t = -3.30, p < 0.01, Δr2 = 0.08) were also related to improved behavioral changes in working memory, and changes in lactate (t = -3.31, p < 0.01, Δr2= 0.08) and BDNF (t = -2.12, p = 0.04, Δr2= 0.08) related to faster P3 latency during inhibitory control. Importantly, these associations between physiological and cognitive changes were consistent across both exercise and rest groups, suggesting that physiological changes were linked to improved cognitive performance regardless of group assignment.</p><p dir="ltr">In conclusion, this study highlights the positive relationships between cross-sectional muscle strength and aspects of memory and spatial abilities, with distinct contributions from handgrip and upper body strength. Furthermore, acute RE was shown to enhance executive functions, particularly in terms of processing speed during inhibitory control (response time and P3 latency) and working memory (response time). This study suggests that RE can be a valid way to garner exercise-induced benefits on executive functions potentially through its influence on lactate, BDNF, and blood pressure, however, since these effects were evident regardless of intervention, more work is needed to determine if RE-induced changes have the same mechanisms. Overall, these findings underscore the potential benefits of muscle strength and RE on enhancing executive function in young and middle-aged adults.</p>

Background: Knee osteoarthritis is a degenerative disease characterized by damaged joint tissues (e.g., cartilage) that leads to joint pain, and reduced mobility and quality of life. Various factors are involved in disease progression, including biomechanical, patient-reported outcome and mobility measures. This thesis provides important longitudinal data on the role of these factors in disease progression, and the trajectory of biomechanical factors in persons with knee osteoarthritis. Objectives: (1) Determine the extent to which changes over 2.5 years in knee cartilage thickness and volume in persons with knee osteoarthritis were predicted by the knee adduction and flexion moment peaks, and knee adduction moment impulse and loading frequency. (2) Determine the extent to which changes over 2 years in walking and stair-climbing mobility in women with knee osteoarthritis were predicted by quadriceps strength and power, pain and self-efficacy. (3) Estimate the relative and absolute test-retest reliabilities of biomechanical risk factors for knee osteoarthritis progression. Methods: Data were collected at 3-month intervals during a longitudinal (3-year), observational study of persons with clinical knee osteoarthritis (n=64). Magnetic resonance imaging of the study knee was acquired at the first and last assessments, and used to determine cartilage thickness and volume. Accelerometry and dynamometry data were acquired every 3 months, and used to determine knee loading frequency and knee muscle strength and power, respectively. Walking and stair-climbing mobility, as well as pain and self-efficacy data, were also collected every 3 months. Gait analyses were performed every 6 months, and used to calculate lower-extremity kinematics and kinetics. Results: (1) The knee adduction moment peak and impulse each interacted with body mass index to predict loss of medial tibial cartilage volume over 2.5 years. These interactions suggested that larger joint loads in those with a higher body mass index were associated with greater loss of cartilage volume. (2) In women, lower baseline self-efficacy predicted decreased walking and stair ascent performances over 2 years. Higher baseline pain intensity/frequency also predicted decreased walking performance. Quadriceps strength and power each interacted with self-efficacy to predict worsening stair ascent times. These interactions suggested that the impact of lesser quadriceps strength and power on worsening stair ascent performance was more important among women with lower self-efficacy. (3) Relative reliabilities were high for the knee adduction moment peak and impulse, quadriceps strength and power, and body mass index (i.e., intraclass correlation coefficients >0.80). Absolute reliabilities were high for quadriceps strength and body mass index (standard errors of measurement <15% of the mean). Data supported the use of interventions effective in reducing the knee adduction moment and body mass index, and increasing quadriceps strength, in persons with knee osteoarthritis. Conclusion: Findings from this thesis suggest that biomechanical factors play a modest independent role in the progression of knee osteoarthritis. However, in the presence of other circumstances (e.g., obesity, low self-efficacy, high pain intensity/frequency), biomechanical factors can vastly worsen the disease. Strategies aiming to curb structural progression and improve clinical outcomes in knee osteoarthritis should target biomechanical and clinical outcomes simultaneously. / Thesis / Doctor of Philosophy (PhD) / Knee osteoarthritis is a multifactorial disease whose progression involves worsening joint structure, symptoms, and mobility. Various factors are linked to the progression of this disease, including biomechanical, patient-reported outcome and mobility measures. This thesis provides important information on how these factors, separately and collectively, are involved in worsening disease over time, as well as benchmarks that are useful to clinicians and researchers in interpreting results from interventional or longitudinal research. First, we examined how different elements of knee loading were associated with changes in knee cartilage quantity over time in persons with knee osteoarthritis. Second, we examined how different elements of knee muscle capacity and patient-reported outcomes were related to changes in mobility over time in persons with knee osteoarthritis. Third, we examined the stability over time of various biomechanical risk factors for the progression of knee osteoarthritis. Novel results from this thesis showed that: (1) larger knee loads predicted cartilage loss over 2.5 years in obese individuals with knee osteoarthritis but not in persons of normal weight or overweight; (2) among women with knee osteoarthritis with lower self-efficacy (or confidence), lesser knee muscle capacity (strength, power) was an important predictor of declining stair-climbing performance over 2 years; and (3) clinical interventions that can positively alter knee biomechanics include weight loss, knee muscle strengthening, as well as specific knee surgery and alterations during walking to reduce knee loads. Interventions for knee osteoarthritis should target biomechanical and clinical outcomes simultaneously.