Heart Rate Variability Responses to Exercise in Mid-Spectrum Chronic Kidney Disease

Heart rate variability (HRV) is a measure of autonomic nervous system (ANS) activity, and decreased HRV is associated with many cardiovascular conditions. Chronic kidney disease (CKD) is characterized by a decrease in renal function and may be associated with ANS imbalances in the renal vasculature. Low HRV is associated with CKD incidence. Exercise is able to alter HRV by modulating the ANS. The effect of exercise on HRV in mid-spectrum CKD patients remains understudied. PURPOSE: To determine the effect of steady-state exercise (SSE) and high-intensity interval exercise (HIIE) on post-exercise HRV in patients with stage 3 or 4 CKD. METHODS: Twenty participants with stage 3 or 4 CKD (n = 6 men; n = 14 women; age 62.0 ± 9.9 yr; weight 80.9 ± 16.2 kg; body fat 37.3 ± 8.5% of weight; VO2max 19.4 ± 4.7 ml/kg/min, eGFR 51.5 ± 6.82). On separate days, each participant completed 30 minutes of aerobic exercise on the treadmill with exercise intensities set at 65% VO2reserve for SSE and 90% and 20% of VO2reserve in 3:2 min ratio for HIIE in a randomized crossover design. Both conditions averaged ~ 65% VO2reserve. HRV was measured at baseline, immediately post-exercise (IPE), 1-hr post-exercise, and 24-hr post-exercise. HRV was measured for 5 mins in the supine position using an elastic belt and Bluetooth monitor (Polar H7). CardioMood software was used to process HRV variables high frequency (HF), low frequency (LF), and standard deviation of all NN intervals (SDNN). Data were analyzed using 2 (condition) by 4 (time) repeated-measures ANOVAs. Data violated normality and were natural log (ln) transformed prior to analysis. Significant main effects were followed up using pairwise comparisons using a Bonferroni adjustment for multiple comparisons. All analyses were performed using SPSS (v.26). RESULTS: For ln LF/HF there were no significant main effects for exercise condition, time, or their interaction (p \u3e 0.05). For ln HF (F = 3.507, p \u3c 0.05, ηp2 = 0.156), ln LF (F = 3.093, p \u3c 0.05, ηp2 = 0.140), and ln SDNN (F = 3.761, p \u3c 0.05, ηp2 = 0.165) there was a significant main effect for time. Post-hoc comparisons revealed that HF, LF, and SDNN were lower IPE than for all other time points. CONCLUSION: Thirty minutes of aerobic exercise transiently decreases HRV in mid-spectrum CKD patients. This response was not modified by exercise condition

A Dietary Assessment of Mid-Spectrum Chronic Kidney Disease

Diets of adult individuals with mid-spectrum (stages III and IV) Chronic Kidney Disease (CKD) remain understudied. The 2015-2020 Dietary Guidelines for Americans food patterns based on the Recommended Dietary Allowances (RDA) in concert with the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF KDOQI) guidelines are advised to individuals with CKD. Estimated glomerular filtration rate (eGFR) remains the best method for tracking CKD progression, yet relationships between self-reported dietary intake and eGFR are understudied. PURPOSE: To assess the self-reported dietary pattern in patients with stage III or IV CKD in contrast to the RDA and NKF KDOQI dietary guidelines and to identify correlates of eGFR. METHODS: Twenty participants with stage III or IV CKD [n = 6 male (M); n = 14 female (F)]; age 62.0 ± 9.9 years; weight 80.9 ± 16.2 kg; body fat 37.3 ± 8.5% of weight; eGFR 51.5 ± 6.82 mL/min/1.73m2) completed self-reported dietary assessments for an average of 5 days. Diet was assessed using the ESHA Food Processor Software, Version 11.1. Micro- and macronutrient analyses for males and females were compared to the RDA and NKF KDOQI guidelines to identify malnutrition. T-tests were used to test the difference in eGFR between genders and bivariate correlation analyses were used to identify correlates of eGFR, p-values were considered significant at the α = 0.05 level. RESULTS: On average, all subjects met the RDA and NKF KDOQI guidelines for caloric intake. Average consumption of saturated fat (F = 24.3 ± 10.8g, M = 34.1 ± 6.0g), sodium (F = 3780 ± 2510mg, M = 4210 ± 386mg) and protein (F = 65.0 ± 23.5g, M = 107.3 ± 27.3g) was higher than the recommendations while the average consumption of fiber (F = 13.6 ± 4.1g, M = 14.8 ± 7.3g), calcium (F = 573 ± 325mg, M = 720 ± 224mg), potassium (F = 240 ± 1800mg, M = 940 ± 492mg) and phosphorous (F = 628 ± 1320mg, M = 425 ± 314mg) was low. On average, males had a higher eGFR than females (t = -2.40, p = 0.03). Age, body fat percentage, weight, cholesterol, calcium intake, protein intake, and daily caloric intake were not found to be significantly correlated with eGFR. CONCLUSION: When compared to the RDA and NKF KDOQI guidelines, individuals with mid-spectrum CKD had poor nutritional quality. Female gender was correlated with reduced eGFR. Future interventions in individuals with mid-spectrum CKD should look to improve diet quality to align with clinical guidelines and prevent progression to end-stage renal disease

Impact of Acute Dietary Manipulations on Dual-Energy X-ray Absorptiometry Estimates of Visceral Adipose Tissue

Dual-energy x-ray absorptiometry (DXA) is viewed as a superior method of body composition assessment, but whole-body DXA scans are impacted by variation in pre-assessment activities, such as eating and drinking. DXA software now allows for estimation of visceral adipose tissue (VAT), which has been implicated in a number of diseases. It is unknown to what extent food and fluid intake affect VAT estimates. PURPOSE: determine the effects of acute high-carbohydrate (HC) and very low-carbohydrate (VLC) diets on DXA estimates of VAT. METHODS: Male and female adults completed two one-day dietary conditions in random order: a VLC diet (1 – 1.5 g CHO/kg) and a HC diet (9 g CHO/kg). The diets were isocaloric to each other, and all food items were provided to participants. DXA scans were conducted in the morning after an overnight fast and in the afternoon soon after the third standardized meal. VAT volume, mass, and area were obtained, and paired samples t-tests were performed to compare the changes in VAT measures between diets. RESULTS: Fifteen males (age 22 ± 3, BF% 21 ± 5%) and eighteen females (age 21 ± 2, BF% 31 ± 5%) were included in the analysis. The change in VAT volume between the fasted and fed visits was different between diets (HC: +1.6%; VLC: -9.2%, p= 0.047). There were also trends for differences in VAT mass (p= 0.089) and area (p= 0.096) changes between diets. CONCLUSIONS: Within a single day, VAT estimates are differentially affected by isocaloric HC and VLC diets, with VLC consumption leading to reductions in VAT estimates. The content of the diet on the day of a DXA scan can affect estimates of VAT, which could spuriously influence the categorization of an individual’s health risk by DXA VAT estimates. Standardization of food intake prior to scans, preferably in the form of an overnight fast, should be employed to eliminate this important source of error

Mental Health Best Practices in NCAA: The Bidirectional Relationship between Mental Toughness and Self-Compassion

Based on National Collegiate Athletic Association (NCAA) reports, student-athletes’ well-being is compromised by sub-clinical issues of mental health (MH) disorders, such as depression and anxiety. Preliminary data have shown a positive relationship between mental toughness (MT) and MH, self-compassion (SC) and MH, and SC and MT. To date, possible indirect causal relationships between these three constructs have not been investigated. PURPOSE: To confirm the three aforementioned relationships in NCAA athletes and explore the mediation role of MT and SC on the SC-MH and MT-MH relationships, respectively. Hypotheses: (1) MT will correlate positively with MH, (2) SC will correlate positively with MH, (3) MT will correlate positively with SC, (4) MT will mediate the SC-MH relationship, and (5) SC will mediate the MT-MH relationship. METHODS: The Mental Toughness Index, the Self-Compassion Scale, and the Mental Health Continuum-Short Form were uploaded on Qualtrics. NCAA athletes were invited to participate via email. The sample (n=466) was predominantly Division III, White, female, freshmen, soccer players, and in-season (Mage=19.8, SD=1.8). The analysis consisted of two parts. In the first, bivariate correlations were computed among MT, SC, and MH. In the second, a structural equation model was constructed to test the bidirectional relationship between MT and SC, where MT and SC also had direct effects on MH. All analyses were completed in R. RESULTS: The findings showed a positive relationship between MT and MH (r=0.371, pr=0.461, pr=0.533, pCONCLUSION: Our positive correlation results are in accordance with Gucciardi, Hanton, and Fleming (2017), Neff, Rude, and Kirkpatrick (2007), Wilson, Bennett, Mosewich, Faulkner, and Crocker (2018), and Ales, Kurzum, Deal, and Stamatis (2018). The full bidirectional model analysis revealed that MT is associated with increases in SC and increases in both MT and SC are associated with increases in MH. Therefore and concerning updating mental health best practices, both MT and SC psychological skill training can potentially increase MH levels. However, to most appropriately increase athletes’ MH, stakeholders should prioritize MT, over and above SC, but not to its detriment. Possible limitations include self-assessment and athletes representing three institutions only. Similar, larger-scale research projects are needed in the future

Renal Function Responses to Steady-State Moderate-Intensity and High-Intensity Interval Exercise in Mid-Spectrum Chronic Kidney Disease

Efficacy of exercise to improve renal function remains understudied in adults with mid-spectrum chronic kidney disease (CKD). In addition, a comparison of steady-state exercise (SSE) and high-intensity interval exercise (HIIE) may contribute clinically-relevant information for exercise-related augmentation of renal function in mid-spectrum CKD. PURPOSE: To determine the influence of SSE and a comparable amount of HIIE on indicators of post-exercise renal function in patients diagnosed with secondary Stage 3 or 4 CKD. METHODS: Twenty participants (n = 6 men; n = 14 women; age 62.0 + 9.9 yr; weight 80.9 + 16.2 kg; body fat 37.3 + 8.5% of weight; VO2max 19.4 + 4.7 ml/kg/min) completed 30 min of SSE at 65% VO2reserve or HIIE by treadmill walking (90% and 20% of VO2reserve in 3:2 min ratio) in a randomized crossover design. Both exercise conditions averaged ~ 65% VO2reserve. Blood and urine samples were obtained by the same technician under standardized conditions just before, 1hr and 24hrs after exercise. Serum creatinine (sCR), urine epidermal growth factor ratio (uEGFr), cystatin C and estimates of glomerular filtration rate - modification of diet in renal disease (MDRD) and the CKD-EPI - responses were analyzed using 2 (condition) by 3 (sample point) repeated measures ANOVAs. RESULTS: sCR decreased from 1.45 + 0.05 pre-exercise to 1.26 + 0.05 mg/dl (-13%) 1hr after exercise and returned to pre-exercise levels by 24hr (p = 0.009). Both MDRD and CKD-EPI estimates of glomerular filtration rate were 16 to 19% higher at 1hr, returning to pre-exercise values by 24hrs after exercise. The MDRD estimate increased from 43.1 + 1.9 pre-exercise to 50.3 + 2.1 ml/min/1.73m2 1hr after exercise (p = 0.007) and CKD-EPI from 45.2 + 2.1 to 53.8 + 2.4 ml/min/1.73m2 at 1hr post-exercise (p = 0.009). Relative to pre-exercise measures, uEGFr remained stable with SSE but was 5.4% greater 24hr after HIIE (p = 0.052). Cystatin C remained stable in the hours after exercise (p \u3e 0.05). CONCLUSION: By clinical estimates, renal function was not normalized but transiently improved with SSE and HIIE in mid-spectrum CKD

Brachial Artery FMD and Endothelial Responses to High-Intensity Interval and Steady-State Moderate-Intensity Exercise

Brachial artery flow-mediated dilation (FMD) is a nitric oxide-dependent measure of conduit artery endothelial function that is potentiated by moderate- and high-intensity steady state exercise (SSE) for up to an hour after exercise; however, it is unclear whether high-intensity interval exercise (HIIE) provides a longer-lasting stimulus for enhancing FMD or greater oxidative and nitrative stress on the vascular endothelium than a comparable or greater amount of SSE. PURPOSE: Determine the influence of HIIE on post-exercise brachial artery FMD and the relationship between FMD and markers of endothelial function relative to a comparable amount of moderate-intensity SSE and a dose that is half that of SSE. METHODS: Seventeen male participants (age 27.8 + 6.4 yr; weight 80.6 + 9.0 kg; BMI 25.1 + 2.4 kg/m2; VO2max 52.1 + 7.5 ml/kg/min) underwent HIIE by treadmill running (90% and 40% of VO2reserve in 3:2 min ratio) to expend 500 kcals; HIIE to expend 250 kcals, and; SSE at 70% VO2reserve to expend 500 kcals in a randomized crossover design. All exercise conditions averaged 70% VO2reserve. Ultrasound measurements of brachial artery FMD and blood measures of total antioxidant capacity (TAC) in copper reducing equivalents, apolipoprotein A-1 (ApoA1: g/L), PON1 concentration (PON1c: mg/mL), arylesterase activity (PON1a: kU/L), soluble vascular adhesion molecule-1 (sVCAM-1: ng/mL) and nitrotyrosine (NT: nM) were obtained just before and 2 hr after exercise. FMD responses to exercise were analyzed using 3 (condition) by 2 (sample point) repeated measures ANOVAs. Pearson product-moment correlations of change variables (2 hr post-exercise – pre-exercise values) were calculated to determine relationships between FMD responses and blood variable responses to exercise. RESULTS: Brachial artery FMD responses were unaltered 2 hr after exercise in all three conditions (p \u3e 0.05). FMD responses were correlated with changes in PON1c (r = 0.221, p \u3c 0.0001) and inversely with changes TAC (r = -0.170, p \u3c 0.0001). Changes in s-VCAM1 were correlated with change in NT (r = 0.423, p \u3c 0.0001) and inversely with changes in PON1c (r = -0.177, p \u3c 0.0001). SUMMARY: Brachial artery FMD is unaltered 2 hr after HIIE or SSE of moderate duration in young fit men and does not appear to be related to responses in other markers of endothelial function

Impacts of Varying Blood Flow Restriction Cuff Size and Material on Arterial, Venous and Calf Muscle Pump-Mediated Blood Flow

Blood flow restriction (BFR) may become ineffective or potentially dangerous without sufficient standardization. The purpose of this investigation was therefore to (1) assess the viability of multiple sizes of a novel BFR cuff to determine arterial occlusion pressure (AOP) and (2) compare resting arterial, venous and calf muscle pump (cMP)-mediated blood flow between the aforementioned conditions and a commonly employed wide-rigid, tourniquet-style cuff. In randomized, counter-balanced, and crossover fashion, 20 apparently healthy males (18–40 years) donned a widely employed wide-rigid (WR) cuff, along with the largest (NE) and manufacturer-recommended sizes (NER) of a novel narrow-elastic cuff. Participants subsequently assessed AOP, as well as (at 80%AOP) arterial, venous, and venous cMP flow relative to baseline values via ultrasound. All analyses were performed at a significance level of p \u3c 0.05. Analyses revealed a significant condition effect for AOP (p \u3c 0.001; ηp2 = 0.907) whereby WR was significantly lower than both NE and NER; in addition, the latter two did not differ. Compared with baseline, there were no statistically significant differences between cuffs for either arterial or cMP-mediated blood flow. Unsurprisingly, no participants demonstrated venous blood flow at 80% AOP. These findings support the viability of a novel narrow-elastic BFR product, evidenced by consistent AOP acquisition and equivocal blood flow parameters

Comprehensive Analysis of Mental Toughness Predictors Using Machine Learning Techniques

Mental toughness (MT) is a critical determinant of success in various high-pressure environments. Traditional methods of assessing MT often rely on subjective metrics only (self-assessed questionnaire scores), which may lack the precision and objectivity necessary for a thorough understanding. PURPOSE: To develop an objective, quantitatively robust model to predict MT, by integrating physiological and psychological variables using machine learning (ML) techniques. METHODS: The study involved a sample of 50 participants, encompassing diverse demographic backgrounds and physiological (e.g., DEXA, complete metabolic and lipid panel, and complete blood count) and psychological (e.g., Mental Toughness and Self-compassion surveys) characteristics. The analysis began with descriptive statistics to understand the dataset’s structure, followed by handling missing values through imputation methods. Key variables identified included self-compassion (SC), white blood cell count (WBC), total protein, Android/Gynoid Ratio, and Trunk/Leg Fat Ratio. Principal Component Analysis (PCA) was employed for dimensionality reduction, ensuring the model’s efficiency, and addressing multicollinearity. A Random Forest Regression model was chosen for its ability to handle complex, non-linear relationships. The model underwent iterative tuning, adjusting parameters like the number of trees (300), tree depth (no limit), and minimum samples for node splitting (2) and leaf nodes (1). The process also included evaluating and comparing linear and non-linear approaches, cross-validation for robustness, and detailed performance metrics analysis. RESULTS: The final model (R2 = 0.74) indicates a high degree of variance explanation in MT scores. Key predictive factors included both physiological measures and psychological aspects, along with body fat distribution metrics. The Mean Squared Error was 0.29, reflecting the model’s accuracy and precision in prediction. CONCLUSION: This study illustrates the effective use of ML in integrating diverse physiological and psychological factors to predict MT with high accuracy. The findings provide a nuanced understanding of MT, suggesting that it is influenced by a complex interplay of mental and physiological health aspects. This model serves as a valuable tool for identifying key factors in MT, aiding in targeted interventions for performance enhancement and resilience training

The Ability of Cardiac Autonomic Modulations Stress Index to Independently Predict VO2max in Cardiometabolically Healthy Individuals

Cardiac autonomic modulation (CAM) is crucial for heart health, mediated by the sympathetic and autonomic systems (SAS). The link between CAM and aerobic exercise underscores the importance of aerobic fitness assessments in optimizing training to enhance performance. Heart rate variability (HRV) assesses CAM in various healthy populations, with the Stress Index (SI) identified as key in determining the SAS regulation involvement in performance and recovery outcomes. The SI may provide a quick and non-invasive metric to assess aerobic performance. PURPOSE: To determine if the SI can accurately predict aerobic performance via VO2max in healthy individuals free of metabolic diseases. METHODS: fifty cardiometabolically healthy individuals (n = 30 males, n = 20 females; Age 37.8 + 12.7 years, %BF 24.9 + 4.0) completed a single maximal treadmill exercise protocol to determine VO2max. HRV was measured for 5 minutes in the supine position prior to performing the exercise protocol using an elastic belt and Bluetooth monitor (Polar H7). CardioMood software was used to process HRV indices; SI, high frequency (HF), low frequency (LF), and total power (TP) were assessed for the frequency domain, and standard deviation of all NN intervals (SDNN) and the square root of the mean of the squares of successive R-R interval differences (RMSSD) for the time domain. The data was analyzed using a multiple correlation and linear regression between HRV indices and VO2max to determine the relationship between the two. All analyses were performed using SAS (v. 28.0.1.1). RESULTS: HRV indices SI was not significantly correlated to VO2max (r = -0.118, p = 0.414). Additionally, SI and all other HRV indices were not able to independently or combined predict VO2max (R2 = 0.014, p = 0.414). CONCLUSION: The utilization of HRV to assess CAM has proven beneficial in multiple clinical and athletic settings. However, the utilization of the SI to predict aerobic performance via VO2max does not appear to be significant. Thus, there are potential limitations to HRV to non-invasively assess aerobic performance

Variation in Individual Responses to Time-Restricted Feeding and Resistance Training

Time-restricted feeding (TRF) is a form of intermittent fasting which limits all caloric intake to a certain period of time each day in an attempt to reduce daily energy intake, promote weight loss, and improve health. Resistance training (RT) has been reported to increase muscular strength and improve body composition. Very limited information is available on the combination of TRF and RT. The purpose of this study was to examine the variation in individual body composition, dietary intake, and muscular performance responses to an 8-wk TRF and RT program. Healthy males (n = 20; age = 22 ± 3 y; BMI = 27 ± 6 kg/m2; % fat = 22 ± 6 % wt) were randomized to TRF + RT or RT alone for 8 wks. RT was performed 3 dys/wk and consisted of alternate workouts of upper and lower body using a resistance progression scheme. TRF limited energy intake to a 4-hr period on the 4 dys/wk when RT was not performed. Energy intake was not restricted in either group, and eating times were not specified in the RT alone group. Body composition, muscular performance, and dietary records were assessed at 0, 4, and 8 wks. Inter- and intra-individual variations in outcome measures were estimated by hierarchical linear growth modeling. The amount of variability attributable to characteristics between or within participants was evaluated from variance estimates. For TRF + RT, percent changes ranged from -5.5 to +2.6% for body weight, -22.1 to +9.4% for fat mass, -7.7 to +4.6% for lean body mass, +3.4 to +30.4% for bench press 1-RM, and +10.1 to +67.6% for leg press 1-RM. For RT alone, percent changes ranged from -6.6 to +2.1% for body weight, -14.4 to +12.6% for fat mass, -4.1 to +3.9% for lean body mass, +4.9 to +12.9% for bench press 1-RM, and +14.3 to +37.7% for leg press 1-RM. Percentages of total variability attributed to inter-individual factors ranged from 3.3 to 49.2% for dietary measures, 59.0 to 93.9% for muscular performance, and 97.0 to 99.6% for body composition. Remaining variability was attributed to intra-individual factors. Individual responses to the study interventions varied widely. Differences between individuals were an important source of variability, indicating participant samples should be homogenous and/or quite large to examine changes in body composition or muscular performance using nutrition and exercise interventions