Cross-validation of a Prediction Equation for Energy Expenditure of an Acute Resistance Exercise Bout

Previously, our laboratory introduced a regression equation for predicting net kcal consumption of a resistance exercise (RE) bout: Total net kcal = 0.874(height, cm) - 0.596(age, years) - 1.016(fat mass, kg) + 1.638(lean mass, kg) + 2.461(total volume x 10-3) - 110.742 (R2 = 0.773, SEE=28.5 kcal). PURPOSE: The purpose of this study was to validate this regression equation using the same variables as predictors. METHODS: Forty-seven healthy, active subjects (23 men, 24 women, 20-58 yrs, 173.5 ± 10.5 cm, 85.5 ± 19.0 kg, VO2max 36.0 ± 8.4 ml/kg/min) were randomly divided into validation and cross-validation groups (nv = 24, ncv = 23). The validation group’s data was used to develop an equation to predict net kcal consumption, which was applied to the cross-validation group’s data to estimate net kcal consumption. Similarly, a prediction equation was derived from the cross-validation group’s raw data and applied to that of the validation group. The strength of the relationship between each group’s measured and estimated net kcal consumption was assessed via correlational analysis. RESULTS: Multiple linear regression yielded the following estimates of net kcal consumption: validation net kcal = 1.125(height, cm) – 0.662(age, years) – 0.800(fat mass, kg) + 1.344(lean mass, kg) + 2.278(total volume x 10-3) – 144.846 (R2 = 0.751, p \u3c 0.0001, SEE=29.7 kcal); cross-validation net kcal = 0.515(height, cm) - 0.520(age, years) - 1.220(fat mass, kg) + 1.995(lean mass, kg) + 2.620(total volume x 10-3) – 59.988 (R2 = 0.823, p \u3c 0.0001, SEE=29.2 kcal). These equations had a cross-validation coefficient of 0.902 and a double cross-validation coefficient of 0.863. CONCLUSION: The strong relationship between the measured and estimated net kcal consumption of both the cross-validation and validation group lead us to conclude that the regression equation derived by this laboratory is valid for estimating net energy expenditure for a total RE bout

Significant Predictors of Nonalcoholic Fatty Liver Disease in Texas Firefighters

Risk factors for Nonalcoholic Fatty Liver Disease (NAFLD) include obesity, hypertension, dyslipidemia, and diabetes mellitus. Not only are these prevalent in the general US population, but they are also present at high rates in a specific subset responsible for public safety – firefighters. PURPOSE: The aim of the present study is to use logistic regression to predict the likelihood of occurrence of NAFLD in firefighters using a subset of health-related factors associated with common cardiometabolic risk factors. METHODS: Data were collected on 136 firefighters (128 males, 8 females; 36.3 ± 9.0 yrs; 95.7 ± 17.0 kg; 178.9 ± 7.4 cm; 29.8 ± 4.2 kg/m2) participating in FITLIFE, a university-based fitness program at Texas A&M University. Nominal logistic regression with stepwise removal was used to estimate the best model to predict fatty liver disease. Stepwise removal identified resting systolic blood pressure (RSBP, mm HG), Body Mass Index (BMI, kg/m2), visceral adipose tissue (VAT, cm2), whether or not has hypertension or is on medication (HTNMED; 0=No,1=Yes), and plasma triglyceride concentrations (TG, mg/dL) as independent predictors (p\u3c0.05). Odds ratios (OR) were calculated to determine the change in the odds of NAFLD per unit increase in each predictor. RESULTS: Logistic regression yielded the following equation to predict the probability of developing NAFLD: Logit = -22.5176 + 0.0918(RSBP) + 0.2154(BMI) + 0.0065(TG) + 0.0161(VAT) + 1.830(HTNMED) (R2 = 0.4655, p \u3c 0.001). Of the predictors, the ORs from largest to smallest were 6.235, 1.240, 1.096, 1.016, and 1.002 for HTNMED, BMI, RSBP, VAT, and TG, respectively. CONCLUSION: Using RSBP, BMI, VAT, TG, and HTNMED as predictors, this study demonstrates that the probability of developing NAFLD in Texas firefighters can be reasonably predicted. This regression model and individual predictors may be used by health practitioners as a cost-effective screening tool to identify those at higher risk for NAFLD

Insulin-induced Increase in Anabolic Capacity is Blunted by Autophagic Inhibition in L6 Myotubes

Insulin is an anabolic hormone that acts on skeletal muscle cells to stimulate protein synthesis, an effect that is enhanced by the availability of amino acids. While autophagy within the cell provides an intracellular source of amino acids to support anabolism, little is known about how this pathway impacts the insulin-induced increase in anabolic capacity within skeletal muscle cells. PURPOSE: The purpose of this study was to determine the impact of autophagic inhibition in cultured L6 myotubes in conjunction with insulin stimulation in vitro. METHODS: Differentiated, cultured L6 myotubes were treated for 24 hours with or without insulin (100 nM) and NSC 185058 (100 μM), a specialized inhibitor of the autophagic catabolic pathway, in media enriched with 4% deuterium. Cells were harvested from each treatment group (n=3/group) 24 hours post-deuterium enrichment and were processed for protein synthesis and western blot protein analysis. A one-way ANOVA was used to compare groups, and when significant F ratios were present, a Student’s Newman-Keuls post hoc procedure was used to test differences among group means. Alpha was set at p≤0.05 for all analyses. RESULTS: Cells treated with insulin (INS) had a higher ratio of phosphorylated to total P70S6K compared to untreated (CON) cells and those incubated with both insulin and NSC 185058 (INS+NSC; 1694% and 327%, respectively; p\u3c0.05). INS+NSC also decreased the ratio of phosphorylated to total 4EBP1 relative to CON (-51%) and INS (-49%), although these differences were not significant (p\u3e0.05). Myofibrillar protein synthesis was stimulated with INS compared to CON and INS+NSC (30.3% and 70.1% respectively; p\u3c0.05) but was lower in INS+NSC relative to CON (-23.4%; p\u3c0.05). CONCLUSION: Results from our study indicate that insulin (100 nM) stimulates anabolism in skeletal muscle cells, but that addition of the autophagic inhibitor NSC 185058 (100 μM) blunts this effect to a level similar to or less than control. Further, our data suggest that the reduction of protein synthesis is mediated through the downregulation of the mTORC1 signaling pathway. While it is widely recognized that insulin promotes anabolic activity through both the direct stimulation of mTOR signaling and extracellular amino acid uptake, our data strongly indicate that autophagic processes are necessary for full anabolic responses in muscle. This decrease in anabolic capacity supports previous literature indicating that the amino acid availability impacts the stimulatory impact of insulin on protein synthesis

Autophagy, but Not Proteolysis, May Aid in Muscle Protein Synthesis

For muscle growth to occur, protein synthesis must be greater than protein degradation. However, up to this point, anabolic pathways have garnered the brunt of investigations examining anabolic capacity with little investigation into the connectedness of catabolic signaling on these anabolic targets. PURPOSE: The purpose of this study was to elucidate the contributions of proteasomal-dependent and autophagic-dependent catabolic pathways on anabolism via analysis of fractional synthetic rates (FSR) in L6 myotubes. METHODS: Differentiated, cultured L6 myoblasts were treated with media containing 4% deuterium oxide (stable isotope label) and a corresponding pharmacological treatment (NSC 185058 [autophagic inhibitor; 100 μM], MG-262 [proteasomal inhibitor; 0.01 μM] or DMSO control; n=3/group) during the final 24-hours of the differentiation period prior to harvest. The myofibrillar pellet of the processed samples was used to determine FSR via mass-spectrometry analysis. DMSO-treated myotubes served as controls, with a one-way analysis of variance and Tukey’s post-hoc test used to test for any differences among groups. RESULTS: Our results indicate that MG-262 had no impact on myofibrillar FSR when compared to DMSO control (MG-262 1.0993 %/day vs. control 1.239 %/day). However, NSC 185058 lowered myofibrillar FSR (NSC 185058 0.9009 %/day vs. control 1.239 %/day; P=0.0282). CONCLUSION: These data suggest that inhibition of autophagic machinery can impair anabolism. This may be due to autophagy’s role in increasing the amino acid pool within the cell. Further, the lack of inhibition seen from MG-262 suggests that there is a delineation of roles within the catabolic pathways in regard to their influence on anabolism in healthy, metabolically unchallenged myotubes

Autophagy is Required for the Anabolic Response to Muscle Contraction

Exercise is a key stimulus in regulating the behavior and metabolism of skeletal muscle, with exercise inducing muscular growth through activation of the anabolic mechanistic target of rapamycin kinase (mTOR). Separately, there is mounting evidence that exercise increases autophagy (one of the main routes by which intracellular proteins are degraded) and that the autophagic process may indeed be required for adaptations to exercise training. PURPOSE: To investigate the effects of autophagy inhibition on mTOR signaling and cellular anabolism after muscular contraction. METHODS: Cultured L6 myotubes were to exposed to electrical pulse stimulation using a stimulator set to deliver bipolar pulses of 30V at 100 Hz for 200 ms every fifth second for 60 minutes. Subsequently, cells received either vehicle control, or 100 μM NSC-185058, an antagonist of the key autophagy protein ATG4B and known inhibitor of autophagy. All groups were also exposed to 4% deuterium oxide, a stable isotopic tracer for measurements of protein synthesis. 24 hours post “exercise” bout, cells were lysed in ice-cold Norris buffer, and prepared for Western immunoblot of protein expression, or determination of protein fractional synthesis rate (FSR) of the myofibrillar fraction via mass-spectrometry analysis. Non-stimulated cells receiving vehicle control treatment served as controls, with a one-way analysis of variance and Tukey’s post-hoc test used to test for any differences between groups. RESULTS: We found that phosphorylation of a key downstream target of mTOR, P70S6 kinase, was roughly seven times greater in cells subjected to EPS and vehicle control (710.3%) relative to control (p0.05). While there was a trend for EPS treatment to increase expression of ATG4B, along with a reduction of ATG4B content as a result of NSC-185058 treatment, this finding did not rise to the level of statistical significance. There were no differences in FSR between cells exposed to EPS; however, NSC-185058 treatment significantly reduced FSR in EPS treated cells relative to controls (0.8712 %/hr vs 1.193 %/hr). CONCLUSION: These findings present two conclusions: high-intensity EPS as an in vitro model of exercise elevates mTOR signaling through P70S6K 24 hours post exercise, and mTOR activation as a result of muscular contraction is reliant upon autophagy in skeletal muscle. Further work will be required to elucidate the dynamics of this relationship, and the interplay between skeletal muscle autophagy and anabolism

High Fat Relative to Low Fat Ground Beef Consumption Lowers Blood Pressure and Does Not Negatively Alter Arterial Stiffness

Beef consumption has been stigmatized as an unhealthy dietary choice. However, randomized control trials to support this claim are lacking. PURPOSE: To examine the effect of low-fat (5%) and high-fat (25%) ground beef consumption on blood pressure (BP) and carotid-femoral pulse wave velocity (PWV).METHODS: Twenty-three male subjects (age 40±11 yrs, height 177.4±6.7 cm, weight 97.3±25.0 kg, lean mass 64.5±9.5 kg, fat mass 30.6±19.1 kg) volunteered to participate in this cross-over design study. Each participant completed two, 5-week ground beef interventions in a randomized order with a 4-week washout period in-between. All participants visited the lab four times after an overnight fast. Each visit to the lab consisted of supine BP, dual energy x-ray absorptiometry (DXA) scan to assess body composition, and PWV analysis. The PWV recording was assessed on the right carotid and femoral arteries. The distance used for the PWV calculation was 80% of the actual distance between carotid and femoral sites. All PWV measures were completed according to previously published procedures (Van Bortel, 2011). BP and PWV results were analyzed separately via 2x2 repeated measures ANOVA. RESULTS: Our results indicate there was a significant decrease in systolic BP (p=0.01) following the high-fat ground beef intervention compared to the low-fat. The BP values for low-fat beef and high-fat beef are 120/74 and 116/73 mmHg, respectively. Further, there were no significant differences between the PWV measures. CONCLUSION: Based on our results, high fat ground beef favorably alters systolic BP and does not negatively affect PWV measures

Blood Pressure, Body Composition, and Plasma Lipids Are Not Related to Indices of Vascular Health

Blood pressure, body composition and plasma lipoprotein concentrations are important markers for cardiovascular disease (CVD) risk. PURPOSE: To examine potential relationships between blood pressure, body composition, plasma lipoprotein concentrations and indices of vascular health as assessed with carotid-femoral pulse wave velocity (PWV) and flow mediated dilation (FMD). METHODS: Fourteen male subjects (age 32 ± 13 yrs, height 177.6 ± 6.6 cm, weight 83.3 ± 9.0 kg, lean mass 61.7 ± 6.3 kg, fat mass 18.4 ± 6.8 kg) volunteered for lab testing as part of a health assessment program, which included resting blood pressure, dual energy x-ray absorptiometry (DXA), FMD, PWV, and blood analysis. All testing was completed on the same day after an overnight fast. The vascular measures were taken via ultrasound, in a temperature controlled room with dim lighting. Each subject would lay supine for 10 minutes prior to the vascular measures. FMD was assessed in the brachial artery in response to a 5-minute distal occlusion. FMD results are given as a percent change from baseline. The PWV measure was assessed on the carotid and femoral arteries using 80% of the total distance between measure sites. PWV results are given in meter per second. All PWV and FMD measures were completed according to previously published procedures (Bortel, 2011; Corretti, 2002.). Body composition was assessed via DXA. Relationships among the data were analyzed with Pearson’s r (a = 0.05). RESULTS: No significant relationships were found with PWV or FMD and any of the CVD risk factors measured. CONCLUSION: Based on our results, accepted risk factors for CVD, including blood pressure, plasma lipoproteins, and body composition, are not related to indices of vascular health as assessed with PWV and FMD. Reference lists are not generally included

Effects of an Acute Strength and Conditioning Training Session on Dual Energy X-ray Absorptiometry Results

In the use of dual x-ray absorptiometry (DXA) scans to obtain reliable measures of body composition, athletic staff must be aware of acute factors that may alter scan estimates. Although factors such as hydration status and food intake have been shown to alter DXA results (Tinsley, MSSE 2016), it is unknown whether an acute strength and conditioning (S&C) session will alter DXA scan estimates. PURPOSE: To determine if a strength and conditioning (S&C) training session, based upon what athletes regularly engage in, will alter body composition estimates (lean mass, fat mass, and bone mineral content) of a DXA scan. METHODS: The S&C session lasted ~ 90 minutes and consisted of upper and lower body resistance exercises and interval running. Twenty-two strength-trained subjects (15 men, 7 women, age 24 ± 2 yrs, height 174.2 ± 8.5 cm, weight 83.5 ± 15.0 kg) volunteered to participate in the study. A food log was distributed during the informed consent process, which participants maintained for 24 hours prior to the DXA scans. Each subject completed two standard DXA scans on the same day, before and within 45 minutes of completing the S&C session. Participants were instructed to consume a normal, free-living breakfast prior to the first scan, and to then avoid all food intake until completing the second scan. Throughout the S&C session, subjects were encouraged to drink water ad libitum. RESULTS: No significant difference was found on any of the total body measures between pre and post DXA body composition measurements except for total mass, which was found to be lower after the S&C session (pre to post: 83.8-83.5 kg). Compartmental results showed significant differences between pre and post scans in the arms, legs, and trunk. Arm and leg % fat were found to be lower (pre to post: arm % fat 20.5-19.9, leg % fat 23.2-22.6); arm total and lean mass, and leg lean mass were found to be higher (pre to post: arm total mass 10.8-11.0 kg, arm lean mass 8.3-8.5 kg, leg lean mass 21.5-21.8 kg); and trunk lean mass was found to be lower (pre to post: 28.7-28.2 kg) after the S&C session. CONCLUSION: Based on the results of the present study, the acute physiological effects of a S&C session alter body composition measures obtained by DXA scan. Thus, athletic staff should consider the timing of DXA scans in relation to S&C sessions