Meghan K. Edwards

Potential Avenues for Exercise to Activate Episodic Memory-Related Pathways: A Narrative Review

Memory function plays an important role in activities of daily living, and consequently, quality and quantity of life. In this narrative review, we discuss the anatomical components of episodic memory, including the structure of the hippocampus and the routes of communication to and from this structure. We also highlight cellular traces of memory, such as the engram cell and pathway. To provide etiological insight, the biological mechanisms of episodic memory are discussed, including factors subserving memory encoding (e.g., cognitive attention, neuroelectrical indices), consolidation (i.e., synaptic and brain systems level), and retrieval (e.g., availability of cues, context‐dependent, state‐dependent, and cognitive processing). Central to this manuscript, we highlight how exercise may influence each of these aforementioned parameters (e.g., exercise‐induced hippocampal growth, synaptic plasticity, and cue retrieval) and then discuss the implications of these findings to enhance and preserve memory function. Collectively, this narrative review briefly summarizes potential mechanisms of episodic memory, and how exercise may activate these mechanistic pathways.

Experimentally increasing sedentary behavior results in increased anxiety in an active young adult population

INTRODUCTION Knowledge regarding the effects of sedentary behavior on anxiety has resulted mainly from observational studies. The purpose of this study was to examine the effects of a free-living, sedentary behavior-inducing randomized controlled intervention on anxiety symptoms. METHODS Participants confirmed to be active (i.e., acquiring 150min/week of physical activity) via self-report and accelerometry were randomly assigned into a sedentary behavior intervention group (n=26) or a control group (n=13). For one week, the intervention group eliminated exercise and minimized steps to ≤5000 steps/day whereas the control group continued their normal physical activity levels. Both groups completed the Overall Anxiety Severity Impairment Scale (OASIS) pre- and post-intervention, with higher OASIS scores indicating worse overall anxiety. The intervention group resumed normal physical activity levels for one week post-intervention and then completed the survey once more. RESULTS A significant group x time interaction effect was observed (F(1,37)=11.13; P=.002), with post-hoc contrast tests indicating increased OASIS scores in the intervention group in Visit 2 compared with Visit 1. That is, we observed an increase in anxiety levels when participants increased their sedentary behavior. OASIS scores significantly decreased from Visit 2 to Visit 3 (P=.001) in the intervention group. CONCLUSION A one-week sedentary behavior-inducing intervention has deleterious effects on anxiety in an active, young adult population. To prevent elevated anxiety levels among active individuals, consistent regular physical activity may be necessary. Clinicians treating inactive patients who have anxiety may recommend a physical activity program in addition to any other prescribed treatment.

The Effects of Exercise on Memory Function Among Young to Middle-Aged Adults: Systematic Review and Recommendations for Future Research

Objective: To systematically summarize the experimental effects of exercise on cognitive-related memory function among young to middle-aged adults, which has yet to be done in the literature. Data Source: PubMed. Study Inclusion and Exclusion Criteria: Studies were included if they were published in the English language, indexed in PubMed, employed an experimental study design (eg, traditional parallel group randomized controlled trial: either acute intervention or chronic/training intervention study), and conducted among human adults. Studies were excluded if nonhumans (ie, animal models) were studied, if children/adolescents (<18 years) or older adults (>50 years) were evaluated, and if select chronic diseases (eg, diabetes and dementia) were present. Data Extraction: A systematic review approach was employed. Data Synthesis: An extraction table was created synthesizing the key results, and recommendations for future research are emphasized. Results: Among the 17 evaluated studies, 2 were published before the year 2000 (ie, 1998 and 1999), 2 were published in 2007, and the remaining 13 were published in the years 2011 and beyond. This highlights the emergence of this research topic within this age-group (young to middle-aged adults). Among the 17 evaluated studies, 14 were conducted among healthy samples, with 3 conducted among those with a diagnosis of depression. Among the 17 studies, 4 employed a chronic training protocol, with 13 utilizing an acute exercise protocol. Among the 3 experimental studies in the depressed population, all demonstrated a favorable effect of exercise on memory function. Among the 14 trials in the nondepressed population, 10 (71%) demonstrated a favorable effect of exercise on some aspect of memory function. Conclusion: Acute and chronic exercise appears to play a pronounced effect on memory function among young to middle-aged adults. Implications and recommendations for future research are outlined in this systematic review.

The Association Between Sedentary Behavior and Cognitive Function Among Older Adults May Be Attenuated With Adequate Physical Activity

OBJECTIVE Examine the independent association of sedentary behavior and cognitive function in older adults, as well as whether physical activity attenuates this potential association. METHODS Data from the 1999-2002 National Health and Nutrition Examination Survey were used (N = 2472 adults 60 to 85 yrs). Sedentary behavior was subjectively assessed and the Digit Symbol Substitution Test (DSST) was employed to assess cognitive function. RESULTS Among an unadjusted and an adjusted model not accounting for physical activity, only 5+ hrs/day (vs. < 1 hr) of sedentary time was independently associated with lower DSST scores (β = -3.1; 95% CI: -5.8 to -0.4; P= .02). However, a fully adjusted model (adding in moderate-to-vigorous physical activity as a covariate) did not yield a statistically significant association between 5+ hrs/day of sedentary time and DSST scores (β = -2.5; 95% CI: -5.1 to 0.2; P = .07). CONCLUSION Accumulated daily sedentary behavior of 5+ hrs is associated with lower cognitive function in an older adult population when physical activity is not taken into account. However, physical activity may account for 19% of the total association between sedentary behavior and cognitive function, thus attenuating the sedentary-cognitive function association. Efforts should be made to promote physical activity in the aging population.

All-cause mortality risk as a function of sedentary behavior, moderate-to-vigorous physical activity and cardiorespiratory fitness

ABSTRACT Objective: Emerging work demonstrates individual associations of sedentary behavior, moderate-to-vigorous physical activity (MVPA) and cardiorespiratory fitness (CRF) on mortality risk. Limited research has evaluated all three of these parameters in a model when considering mortality risk, and their potential additive association on mortality risk has not been fully evaluated, which was the purpose of this study. Methods: Data from the 2003–2006 National Health and Nutrition Examination Survey were used (N = 2,295 adults 20–85 yrs), with follow-up through 2011. Sedentary behavior and MVPA were objectively assessed (accelerometry) with cardiorespiratory estimated from a prediction equation taking into consideration participant demographic, anthropometric and behavioral characteristics. Using the median values, a PACS (Physical Activity Cardiorespiratory Sedentary) score was created that ranged from 0–3, indicating the number of these three positive characteristics. Results: Those with below median sedentary behavior did not have a reduced all-cause mortality risk (HR = 0.59; 95% CI: 0.34–1.04; P = 0.07), but those with above median MVPA (HR = 0.35; 95% CI: 0.15–0.82; P = 0.02) and above median CRF did (HR = 0.20; 95% CI: 0.09–0.43; P < 0.001). Compared to those with a PACS score of 0, those with a PACS score of 1, 2, and 3, respectively, had a 67% (HR = 0.33; 95% CI: 0.17–0.63, P = 0.002), 82% (HR = 0.12; 95% CI: 0.05–0.30; P < 0.001) and 96% (HR = 0.04; 95% CI: 0.02–0.11; P < 0.001) reduced risk of all-cause mortality. Conclusion: Cardiorespiratory fitness and MVPA, but not sedentary behavior, were independently associated with reduced mortality risk. Adults with all three characteristics (below median sedentary and above median MVPA and CRF), however, had the lowest mortality risk.

Sedentary behavior & health-related quality of life among congestive heart failure patients

BACKGROUND Previous research demonstrates that participation in light-intensity physical activity (LIPA) and moderate-to-vigorous physical activity (MVPA) are favorably associated with health-related quality of life (HRQOL). Emerging work demonstrates that sedentary behavior (SB) is detrimentally associated with various cardiometabolic biomarkers, with few studies exploring the association of SB on HRQOL, and no studies examining this among congestive heart failure patients. Therefore, the purpose of this study was to examine the potential independent associations of SB on HRQOL among congestive heart failure patients. METHODS Data from the 2003-2006 National Health and Nutrition Examination Survey were used. Physical activity was assessed over 7days during all waking hours using the ActiGraph 7164 accelerometer. HRQOL was assessed using the Centers for Disease Control HRQOL index survey. RESULTS 190 participants self-reported a physician-diagnosis of congestive heart failure. After adjustments, SB behavior (1-min/day increase) was associated with worse HRQOL (β=0.004; 95% CI: 0.0004-0.007; P=0.03). When MVPA was added as a covariate to this model, SB remained significantly associated with worse HRQOL (β=0.003; 95% CI: 0.0001-0.007; P=0.04). However, when adding LIPA to this model that also included MVPA as a covariate, SB was no longer associated with HRQOL (β=0.0001; 95% CI: -0.003-0.004; P=0.92). CONCLUSIONS If confirmed by prospective/experimental work, this suggests that SB may not have detrimental HRQOL effects among congestive heart failure patients.

Associations between accelerometer-assessed sedentary behavior, physical activity and objectively-measured cardiorespiratory fitness with red blood cell distribution width

BACKGROUND Emerging work identifies red blood cell distribution width (RDW) as a unique biomarker independently associated with cardiovascular disease and mortality. Encouragingly, recent research demonstrates individual associations of sedentary behavior, physical activity and cardiorespiratory fitness with RDW. However, no study has evaluated their independent and combined associations on RDW, which was this studys purpose. METHODS Data from the 2003-2004 National Health and Nutrition Examination Survey were used (N=627 adults 20-49yrs). Sedentary behavior and MVPA were objectively assessed (accelerometry) with cardiorespiratory fitness determined from a submaximal treadmill-based test. Participants were classified as above or below the median values for each of these three parameters, with a PACS (Physical Activity Cardiorespiratory Sedentary) score ranging from 0 to 3, indicating the participant number of these three positive characteristics. A blood sample was obtained from each participant to assess RDW. RESULTS Only above median MVPA (OR=0.47; 95% CI: 0.32-0.68) was independently associated with a reduced odds of having an elevated RDW. With regard to the additive model, and after adjustment, the odds ratio (95% CI) for the PACS score of 1 (vs. 0), 2 (vs. 0), and 3 (vs. 0), respectively, were 0.81 (0.45-1.45; P=0.46), 0.66 (0.44-0.99; P=0.04) and 0.35 (0.18-0.68; P=0.004). CONCLUSION When considering sedentary behavior, MVPA, and cardiorespiratory fitness, only MVPA was associated with reduced odds of elevated RDW, but those with all three characteristics had the lowest odds of elevated RDW.

Sedentary behavior, physical activity and cardiorespiratory fitness on leukocyte telomere length

Background: Emerging work is starting to investigate the cumulative effects of moderate-to-vigorous physical activity (MVPA), sedentary behavior and cardiorespiratory fitness on health. The objective of this study was to examine the cumulative and independent associations of MVPA, sedentary behavior and cardiorespiratory fitness on leukocyte telomere length (LTL). Methods: Data from the 1999-2002 National Health and Nutrition Examination Survey (NHANES) were used (N = 1868 adults 20+ years); analyzed in 2016. Sedentary behavior and MVPA were subjectively assessed with cardiorespiratory fitness determined from a submaximal treadmill-based test; participants were classified as above or below the median values for each of these three parameters. A blood sample was obtained from each participant to assess LTL via quantitative polymerase chain reaction, with participants grouped into LTL tertiles. Results: Participants who engaged in higher MVPA, sat less and had higher cardiorespiratory fitness had an increased odds (ranging from 85% to 105%) of being in LTL tertile 3 (vs. 1). In an extended adjusted multinomial logistic regression model, only MVPA was positively associated with LTL (odds ration [OR] = 1.37; 95% CI: 0.99-1.90; P = 0.05). Conclusion: All three behavior characteristics, but particularly MVPA, may be important in preserving LTLs.

Exercise and Implicit Memory: A Brief Systematic Review

Background Emerging work demonstrates that acute exercise may enhance explicit memory function. No published systematic reviews have evaluated the totality of research examining the effects of exercise on implicit memory function, which was the purpose of this systematic review. Methods Databases (PubMed, PsychInfo, and Sports Discus) were searched to evaluate animal and human experimental studies evaluating the effects of exercise on implicit memory function. Results Among the 10 evaluated studies that met inclusionary criteria for this systematic review, 7 were conducted in animal models (rats or mice), with 3 utilizing human samples. Among the seven animal model studies, all employed a fear conditioning paradigm to evaluate implicit memory performance. All six animal studies employing a chronic exercise paradigm demonstrated evidence for associations between chronic exercise and enhanced fear conditioning. The one animal study evaluating a high-intensity acute bout of exercise showed that high-intensity acute exercise worsened implicit memory retrieval. Among the three human studies, one demonstrated a beneficial effect of acute exercise on implicit memory function. Discussion There is consistent evidence in animal models that chronic exercise enhances implicit memory, as assessed by fear conditioning. However, there have been too few human studies investigating this topic to render any meaningful conclusions regarding the relationship between exercise and cognitive-based implicit memory among humans.

Combined associations of sedentary behavior and cardiorespiratory fitness on cognitive function among older adults

BACKGROUND Sedentary behavior, cardiorespiratory fitness, cognition and age are interrelated and associated with cardiovascular function. No study, however, has specifically evaluated the independent and combined associations of cardiorespiratory fitness and sedentary behavior on cognition, which was this studys purpose. METHODS Data from the 1999-2002 NHANES were used (N=2451; 60-85yrs). Sedentary behavior was assessed via self-report; cardiorespiratory fitness was assessed from a medical-related algorithm; and cognition function was assessed from the Digit Symbol Substitution Test (DSST). RESULTS Being in the bottom quartile for sedentary behavior (β=2.13; 95% CI: 0.49-3.77; P=0.01) and the top quartile for cardiorespiratory fitness (β=7.48; 95% CI: 5.4-9.5; P<0.001) were independently associated with higher cognitive function. In the additive model, those with an index score of 1 (vs. 0) and 2 (vs. 0), respectively, had a 3.87 (β=3.87; 95% CI: 1.76-5.98; P=0.001) and 10.40 (β=10.4; 95% CI: 7.31-13.5; P<0.001) higher DSST score. CONCLUSION High cardiorespiratory fitness and low sedentary behavior were jointly associated with the highest cognitive function. This has important cardiovascular implications as a progression of neurocognitive impairment is associated with increasingly severe manifestations of cardiovascular disease.