Respiratory Exchange Ratio Values Research Articles

Effects of short-term continuous Montmorency tart cherry juice supplementation in participants with metabolic syndrome.

Metabolic Syndrome (MetS) augments the incidence of cardiovascular disease by two-fold and type II diabetes mellitus by five-fold. Montmorency tart cherries are rich in phytochemicals shown to improve biomarkers related to cardio-metabolic health in humans. This study aimed to examine cardio-metabolic responses after 7-days Montmorency tart cherry juice (MTCJ) supplementation and also acute on short-term supplementation responses to a single bolus, in humans with MetS. In a randomised, single-blind, placebo-controlled, crossover trial, 12 participants with MetS (50 ± 10years; 6M/6F), consumed MTCJ or placebo (PLA) for 7days. Blood-based and functional cardio-metabolic biomarkers were measured pre- and post-supplementation, and acute responses measured pre-bolus and up to 5h post-bolus on the 7th day. 24-h ambulatory systolic (P = 0.016), diastolic (P = 0.009) blood pressure and mean arterial pressure (P = 0.041) were significantly lower after 7-days MTCJ supplementation compared to PLA. Glucose (P = 0.038), total cholesterol (P = 0.036), LDL (P = 0.023) concentrations, total cholesterol:HDL ratio (P = 0.004) and respiratory exchange ratio values (P = 0.009) were significantly lower after 6-days MTCJ consumption compared to PLA. This study revealed for the first time in humans that MTCJ significantly improved 24-h BP, fasting glucose, total cholesterol and total cholesterol:HDL ratio, and also lowered resting respiratory exchange ratio compared to a control group. Responses demonstrated clinically relevant improvements on aspects of cardio-metabolic function, emphasising the potential efficacy of MTCJ in preventing further cardio-metabolic dysregulation in participants with MetS. Registered at clinicaltrials.gov (NCT03619941).

Effects Of Short-term Continuous Montmorency Tart Cherry Juice Supplementation In Participants With Metabolic Syndrome

PURPOSE: The prevention of cardiovascular disease (CVD) and type II diabetes mellitus (T2D) would be a major step in retarding rising global prevalence and incidence rates. Metabolic Syndrome (MetS) augments the incidence of CVD by 2-fold and T2D by 5-fold. Montmorency tart cherries are rich in phytochemicals and have previously been shown to improve cardio-metabolic biomarkers in humans. This study aimed to examine cardio-metabolic responses after 7 days Montmorency tart cherry juice (MTCJ) supplementation and also acute responses to a single-bolus, in humans with MetS. METHODS: In a randomised, single-blind, placebo-controlled, crossover trial, twelve participants with MetS (50 ±10 y; 6M/6F), consumed MTCJ or placebo (PLA) for 7 days. Blood-based (serum glucose, insulin, lipid profile) and functional (cardiac haemodynamics, arterial stiffness and resting metabolic rate) cardio-metabolic biomarkers were measured pre- and post-supplementation, and acute responses measured pre-bolus and up to 5 hours post-bolus on the 7th day. Comparisons were made by two-way, repeated measures ANOVA design. RESULTS: 24-hour ambulatory systolic (PLA vs. MTCJ, 2±1 vs. -5±1 mmHg, P = 0.016), diastolic (2±1 vs. -2±1 mmHg , P = 0.009) blood pressure and mean arterial pressure (3±1 vs. -2±0 mmHg, P = 0.041) were significantly lower after 7 days MTCJ supplementation compared to PLA. Findings also showed a significant reduction in glucose (0.03±0.07 vs. -0.50±0.00 mmol.L-1, P = 0.038), total cholesterol (0.04±0.06 vs. -0.40±0.07 mmol.L-1, P = 0.036), LDL (0.26±0.09 vs. -0.36±0.14 mmol.L-1, P = 0.023) concentrations and total cholesterol:HDL ratio (0.13±0.00 vs. 0.02±0.00, P = 0.004) with concomitant lower resting respiratory exchange ratio values (0.01±0.02 vs. -0.03±0.00, P = 0.009) after 6 days MTCJ consumption compared to PLA. CONCLUSIONS: This study revealed for the first time MTCJ to significantly improve 24-hour BP, fasting glucose, total cholesterol and total cholesterol:HDL ratio, and also lower resting respiratory exchange ratio compared to a control in any human population. Responses demonstrated clinically relevant improvements on aspects of cardio-metabolic function, emphasising the potential efficacy of MTCJ in preventing further cardio-metabolic dysregulation in an ‘at risk’ population.

Effects of body weight support and gait velocity via antigravity treadmill on cardiovascular responses early after total knee arthroplasty.

To investigate the effects of body weight support (BWS) and gait velocity on cardiovascular responses during walking on an antigravity treadmill early after unilateral and bilateral total knee arthroplasty (TKA).This study was a cross-sectional study design. Fifty patients (7 males and 43 females; average age, 72.0 ± 5.1 years) at 4 weeks after unilateral (n = 25) and bilateral (n = 25) primary TKA were enrolled in the study. Subjects walked on an antigravity treadmill at speeds of 2.5 km/hour and 3.5 km/hour with 3 levels (50%, 25%, and 0%) of BWS. Cardiovascular responses were monitored by measuring oxygen consumption (VO2), heart rate (HR), systolic and diastolic blood pressure (SBP/DBP), the respiratory exchange ratio (RER), and rate pressure product (RPP). Borg rating of perceived exertion (RPE) and a visual analog scale (VAS) of knee pain were recorded immediately after each trial.There were no significant differences in cardiovascular responses between the unilateral and bilateral TKA groups. In the repeated measures Analysis of Variance, VO2 levels, HR, RPP, RPE, RER, and VAS were significantly increased in proportion to 3 levels (50%, 25%, and 0%) of BWS for unilateral and bilateral TKA groups, respectively. Meanwhile, SBP and DBP were unaffected by differences in BWS. At 3.5 km/hour, VO2, RPE, and RER values were statistically greater than those at 2.5 km/hour under the same BWS conditions.We found that the reduction in the metabolic demand of activity, coupled with positive pressure on the lower extremities, reduced VO2 and HR values as BWS increased.Cardiovascular responses vary according to BWS and gait velocity during antigravity treadmill walking. BWS rather than gait velocity had the greatest effect on cardiovascular responses and knee pain.

Accuracy of the Cosmed K5 portable calorimeter.

PurposeThe purpose of this study was to assess the accuracy of the Cosmed K5 portable metabolic system dynamic mixing chamber (MC) and breath-by-breath (BxB) modes against the criterion Douglas bag (DB) method.MethodsFifteen participants (mean age±SD, 30.6±7.4 yrs) had their metabolic variables measured at rest and during cycling at 50, 100, 150, 200, and 250W. During each stage, participants were connected to the first respiratory gas collection method (randomized) for the first four minutes to reach steady state, followed by 3-min (or 5-min for DB) collection periods for the resting condition, and 2-min collection periods for all cycling intensities. Collection periods for the second and third methods were preceded by a washout of 1–3 min. Repeated measures ANOVAs were used to compare metabolic variables measured by each method, for seated rest and each cycling work rate.ResultsFor ventilation (VE) and oxygen uptake (VO2), the K5 MC and BxB modes were within 2.1 l/min (VE) and 0.08 l/min (VO2) of the DB (p≥0.05). Compared to DB values, carbon dioxide production (VCO2) was significantly underestimated by the K5 BxB mode at work rates ≥150W by 0.12–0.31 l/min (p<0.05). K5 MC and BxB respiratory exchange ratio values were significantly lower than DB at cycling work rates ≥100W by 0.03–0.08 (p<0.05).ConclusionCompared to the DB method, the K5 MC and BxB modes are acceptable for measuring VE and VO2 across a wide range of cycling intensities. Both K5 modes provided comparable values to each other.

Effects of Citrulline Malate and Beetroot Juice Supplementation on Energy Metabolism and Blood Flow During Submaximal Resistance Exercise

The ergogenic effects of citrulline malate (CitMal) and beetroot juice (BEET) have been widely studied, but their effects on physiological outcomes related to resistance exercise are not fully understood. The purpose of this randomized, double-blind, crossover study was to investigate the effects of CitMal (8 g) and BEET (400 mg nitrate) on blood pressure (BP), blood flow, and energy efficiency during submaximal leg extension. Recreationally active males (n = 27; age: 22 ± 4 yrs) completed familiarization, followed by three testing visits. Supine and standing BP were measured upon arrival, followed by supplement ingestion, a 2-h rest period, postsupplement BP measurement, and a bout of repeated submaximal isotonic leg extensions at 25% of maximal voluntary contraction torque. Diameter (aDIAM) and blood flow (aBF) of the superficial femoral artery, and cross-sectional area (CSA) and echo intensity (EI) of the vastus lateralis, were measured before and after exercise via ultrasonography. Muscle blood flow (mBF) and oxygen consumption (mVO2), along with whole-body energy expenditure (EE) and respiratory exchange ratio (RER), were measured before and during exercise via indirect calorimetry and near-infrared spectroscopy. Baseline RER values differed among treatments (p = 0.01); BEET was higher than CitMal (p = 0.01) but not PLA (p = 0.58); CitMal and PLA were not significantly different (p = 0.12). No other measurements were significantly affected by treatment (all p > 0.05). Results suggest that neither CitMal nor BEET significantly influence resting BP, blood flow, or metabolic efficiency during submaximal leg extension in recreationally active males.

Influence of the ACTN3 Genotype and the Exercise Intensity on the Respiratory Exchange Ratio and Excess Oxygen Consumption After Exercise.

de L. Corrêa, H, Ribeiro, HS, Maya, ÁTD, Neves, RP, de Moraes, MR, Lima, RM, Nóbrega, OT, and Ferreira, AP. Influence of the ACTN3 genotype and the exercise intensity on the respiratory exchange ratio and excess oxygen consumption after exercise. J Strength Cond Res 35(5): 1380-1388, 2021-This study aimed to assess the respiratory exchange ratio (RER) and excess postexercise oxygen consumption (EPOC) after high-intensity interval training and continuous moderate-intensity aerobic training in accordance with the ACTN3 genotype. A cross-sectional study with 30 physically active individuals who participated in 3 experimental sessions, as follows: a high-intensity interval aerobic exercise, for 3 minutes at 115% anaerobic threshold, with 90 seconds of passive recovery; a continuous moderate-intensity aerobic exercise at 85% anaerobic threshold; and a control session. Respiratory exchange ratio and V̇o2 were obtained through an indirect, calorimetry-based gas analysis method, using a breath-by-breath approach, assessed at baseline, during the trials, and at 1, 2, 3, and 4 hours after exercise. We found that lower postexercise RER values were observed only in subjects with the X allele, in both the high- and the moderate-intensity training protocols. Homozygous RR subjects showed no differences in postexercise RER compared with the scores at the control day. After both sessions of exercise, EPOC levels were higher compared with scores at the control day for 2 hours among X allele carriers, and only in the first hour among RR homozygous. Thus, the RER and EPOC presented different responses after moderate and intense exercise according to the ACTN3 genotype. Moreover, individuals with the X allele of the ACTN3 gene show a higher oxidation of fats in the postexercise period.

Normalizing glucocorticoid levels attenuates metabolic and neuropathological symptoms in the R6/2 mouse model of huntington's disease

Huntington's disease (HD) is a fatal genetic neurological disorder caused by a mutation in the human Huntingtin (HTT) gene. This mutation confers a toxic gain of function of the encoded mutant huntingtin (mHTT) protein, leading to widespread neuropathology including the formation of mHTT-positive inclusion bodies, gene dysregulation, reduced levels of adult dentate gyrus neurogenesis and neuron loss throughout many regions of the brain. Additionally, because HTT is ubiquitously expressed, several peripheral tissues are also affected. HD patients suffer from progressive motor, cognitive, psychiatric, and metabolic symptoms, including weight loss and skeletal muscle wasting. HD patients also show neuroendocrine changes including a robust, significant elevation in circulating levels of the glucocorticoid, cortisol. Previously, we confirmed that the R6/2 mouse model of HD exhibits elevated corticosterone (the rodent homolog of cortisol) levels and demonstrated that experimentally elevated corticosterone exacerbates R6/2 HD symptomology, resulting in severe and rapid weight loss and a shorter latency to death. Given that efficacious therapeutics are lacking for HD, here we investigated whether normalizing glucocorticoid levels could serve as a viable therapeutic approach for this disease. We tested the hypothesis that normalizing glucocorticoids to wild-type levels would ameliorate HD symptomology. Wild-type (WT) and transgenic R6/2 mice were allocated to three treatment groups: 1) adrenalectomy with normalized, WT-level corticosterone replacement (10 μg/ml), 2) adrenalectomy with high HD-level corticosterone replacement (35 μg/ml), or 3) sham surgery with no corticosterone replacement. Normalizing corticosterone to WT levels led to an improvement in metabolic rate in male R6/2 mice, as indicated by indirect calorimetry, including a reduction in oxygen consumption and normalization of respiratory exchange ratio values (p < .05 for both). Normalizing corticosterone also ameliorated brain atrophy in female R6/2 mice and skeletal muscle wasting in both male and female R6/2 mice (p < .05 for all). Female R6/2 mice given WT-level corticosterone replacement also showed a reduction in HD neuropathological markers, including a reduction in mHTT inclusion burden in the striatum, cortex, and hippocampus (p < .05 for all). This data illustrates that ameliorating glucocorticoid dysregulation leads to a significant improvement in HD symptomology in the R6/2 mouse model and suggests that cortisol-reducing therapeutics may be of value in improving HD patient quality of life.

Cardiorespiratory response according to weight support and velocity using a lower-body positive pressure treadmill early after bilateral total knee arthroplasty

This study was undertaken to investigate cardiorespiratory response according to weight support and velocity using a lower-body positive pressure (LBPP) treadmill and to find specific velocity and weight support combinations after bilateral TKA. Twenty-five patients who underwent a primary TKA were enrolled. Subjects walked with 2.5 km/h and 3.5 km/h on a LBPP treadmill at 3 levels (50%, 75%, 100%) of body weight (BW). Each trial was performed for 2 minutes. Oxygen consumption (VO 2 ), heart rate, systolic (SBP) and diastolic blood pressure (DBP), respiratory exchange ratio (RER) and rate pulse product (RPP) were measured continuously with average values. Borg's rating of perceived exertion scale (RPE) and Visual Analog Scale (VAS) of knee pain were recorded immediately after each condition. In the two-way repeated measures Anova, VO 2 levels ( P < 0.01) were increased in proportion to BW. HR ( P < 0.01), RPP ( P < 0.01), RPE ( P < 0.01), RER ( P < 0.01) and VAS ( P < 0.01) were also higher at 100% of BW compared with 50% and 75% of BW. However, SBP ( P = 0.65) and DBP ( P = 0.39) were not influenced by difference of BW levels. While walking with a speed of 3.5 m/s at same BW level, only RPE ( P < 0.01) and RER ( P = 0.01) values were statistically greater than 2.5 m/s. Based on BW and gait velocity settings of the LBPP treadmill, the equations were VO 2 = 1.46 v + 0.081 BW + 3.13 ( r 2 = 0.34). This study demonstrated that cardiorespiratory responses during LBPP treadmill were determined by combination of weight support and velocity, and it was more influenced by change of weight support than velocity. These findings suggest that factors such as body weight support and speed should be considered for gait training to improve aerobic capacity early after bilateral total knee arthroplasty.

Metabolic characteristics of Appalachian children

The purpose of this investigation is to assess the physiological characteristics and the resting metabolic rates of a representative population of children in Buchanan County in order to identify those factors that may be contributing to the predisposition for being overweight or obese and provide nutritional and physical activity guidance for prevention. Twenty-three volunteers from grades 5, 6 and 7 from Buchannan County, VA underwent parametric and metabolic testing over three consecutive years in order to determine their height, weight, BMI, percent body fat, resting oxygen consumption (VO2), resting energy expenditure (REE), respiratory exchange ratio (RER) and daily energy expenditure (DEE) and consumption. Over the 3 year study period, subjects' BMI increased significantly over time (p=0.001) while there were no changes in their, REE, RER, VO2, percent fat and DEE. However, there was a moderate negative correlation between VO2 and BMI in grade 5 (r=-0.578, p=0.002), grade 6 (r=-0.477, p=0.015) and grade 7 (r=-0.438, p=0.023). Gender specific differences in percent body fat were evident among subjects during the last two measurement cycles and were strongly correlated with BMI (r=0.907, r=0.959, p=0.000). The use of resting VO2, REE, and RER values as a screening tool for identifying those children or adolescents at risk for becoming overweight or obese is most likely cost and time prohibitive due to the need for several repeated measures to ensure accurate results. However increased VO2 is correlated with decreased BMI.

Effectiveness of Neuromuscular Electrical Stimulation During Rest and Exercise

PURPOSE: To determine the effectiveness of neuromuscular electrical stimulation (NMES) as an aid to enhance venous blood return during rest and submaximal exercise. METHODS: Twenty apparently healthy males (Age = 35.0 ± 15.0 yrs; Height = 179.9 ± 8.5 cm; Body Mass = 85.4 ± 12.0 kg) provided informed consent prior to participation. In Session 1, participants were familiarized with all equipment. Sessions 2-4 were randomly selected and included the following 5-min trials: a) Rest and Rest + NMES, b) Rest, Arms-Only, Arms + NMES, and c) Rest, Arms + Legs, Arms + Legs + NMES. Physiological variables collected during rest and submaximal exercise were volume of oxygen (VO2), heart rate (HR), systolic and diastolic blood pressure (SBP and DBP), respiratory exchange ratio (RER), and rate pressure product (RPP). Paired sample t-test was used to determine if there were significant mean differences between the NMES and non-NMES trials. The Bonferroni correction established the alpha level at 0.008. RESULTS: From the 18 paired t-tests, the only observed significant mean difference [t(19) = -6.4, p<0.001] was RER values between the Arms-Only trial compared to the Arms + NMES trial (0.94 and 1.00, respectively). CONCLUSION: While RER displayed a significant difference, collectively, NMES did not elicit any physiological alterations during rest and submaximal exercises within an apparently healthy population. Supported and funded by UNCW Undergraduate Research Fellowship Award.

Treadmill vs. Cycle Ergometry Graded Exercise Test Responses in Multiple Sclerosis Patients

INTRODUCTION: Cardiorespiratory fitness is measured by peak oxygen consumption (VO2max) and is one of the strongest predictors of all-cause and cardiovascular disease mortality. In a healthy adult population, VO2max values obtained on a treadmill are approximately 10-15% higher than those yielded by cycle ergometry. VO2max testing in those with multiple sclerosis (MS) is typically performed on a cycle ergometer, as loss of walking mobility or balance issues may limit treadmill walking. Therefore, potential mode-specific differences in VO2max may result in the inability to accurately assess MS patients’ risk and lead to inaccurate exercise prescriptions in this cohort. PURPOSE: To compare hemodynamic, ventilatory, and cardiorespiratory responses between graded exercise tests performed on both a treadmill and cycle ergometer in individuals with relapsing-remitting MS. METHODS: Twenty persons with MS (42±11 years, 11±10 years since Dx, 26.9±6.5 kg[BULLET OPERATOR]m-2) completed two VO2max tests approximately 1 week apart, with random order of testing. Treadmill tests consisted of a constant, self-determined speed with an increase in grade of 2% every two minutes. Cycle ergometry tests increased wattage by 15 watts per minute. A repeated measures ANOVA was used to investigate differences in testing response to both treadmill and cycle ergometry. RESULTS: Treadmill testing resulted in VO2max values that were 11% higher and respiratory exchange ratio (RER) values that were 8% lower than those obtained via cycle ergometry. See Table 1. DISCUSSION: Relapsing-remitting MS patients exhibit a mode-related difference in VO2max similar to healthy adults. Therefore, exercise prescriptions or study designs cannot directly calculate submaximal workloads for one mode based on maximal data obtained from the other. Additionally, while HRpeak values are within normal limits, they’re bordering chronotropic incompetence.Table 1: Mean ± SD. *p<0.05 between Treadmill and Cycle Ergometer

VO2, RER, And Heart Rate During Recovery Following A Whole-body High-Intensity And Moderate-Intensity Workout

Whole-body high-intensity interval training (WB HIIT), including CrossFit®, has gained wide popularity, partly because HIIT benefits can be achieved in less time than moderate-intensity exercise. Most HIIT research, however, has used bicycle ergometer or treadmill-based exercises that emphasize only the lower body. PURPOSE: To compare heart rate (HR), respiratory exchange ratio (RER), and VO2 following a 10-minute functional, WB HIIT CrossFit® workout and a 20-minute steady-state, moderate-intensity workout. METHODS: Fourteen CrossFit® athletes (11 F/3 M) aged 36.6±9.2y performed a 20-minute rowing ergometer exercise at 70% +5 bpm of age-predicted max and a 10-minute WB HIIT workout consisting of as many continuous reps as possible of 10 barbell thrusters (men 75lbs/women 55 lbs) and 10 burpees over the barbell, on separate days. VO2 and RER were measured using indirect calorimetry immediately following each exercise and throughout recovery until VO2 and RER returned to pre-workout levels. Heart rate was continuously monitored. Differences in time to return to baseline for VO2 and RER between the two modalities were determined using dependent t-tests (p<0.05). RESULTS: Participants achieved 96.4+4.4% of age-predicted max HR during the WB HIIT workout, classifying it as a max-effort exercise. Time to return to resting RER values between the two workouts was significantly different (19.1+3.8 ml/kg/min after rowing vs. 32.5+5.4 min after WB HIIT, p<0.001). Peak VO2 levels immediately after exercise also differed (19.5+4.8 ml/kg/min after rowing vs. 32.9+6.0 ml/kg/min after WB HIIT, p<0.001), as did the time for VO2 recovery (8.2+1.6 min after rowing vs. 22.3+7.7 min after WB HIIT, p<0.001). CONCLUSION: RER and VO2 remained elevated over 11 and 14 min longer, respectively, following WB HIIT, despite half the workout time. This is likely due to a longer time to restore ATP-PC stores, recycle lactate, and reduce body temperature. Heart rate remained elevated following the observed recovery period after WB HIIT suggesting a higher EPOC and caloric expenditure compared to moderate-intensity exercise. Our equipment prevented the measurement of VO2 during the workout, so future research should use equipment that would allow for testing VO2 during WB HIIT exercise so that EPOC can be accurately calculated.

Stable isotope analysis of CO2 in breath indicates metabolic fuel shifts in torpid arctic ground squirrels

Stable carbon isotope ratios (δ13C) in breath show promise as an indicator of immediate metabolic fuel utilization in animals because tissue lipids have a lower δ13C value than carbohydrates and proteins. Metabolic fuel consumption is often estimated using the respiratory exchange ratio (RER), which has lipid and carbohydrate boundaries, but does not differentiate between protein and mixed fuel catabolism at intermediate values. Because lipids have relatively low δ13C values, measurements of stable carbon isotopes in breath may help distinguish between catabolism of protein and mixed fuel that includes lipid. We measured breath δ13C and RER concurrently in arctic ground squirrels (Urocitellus parryii) during steady-state torpor at ambient temperatures from −2 to −26°C. As predicted, we found a correlation between RER and breath δ13C values; however, the range of RER in this study did not reach intermediate levels to allow further resolution of metabolic substrate use with the addition of breath δ13C measurements. These data suggest that breath δ13C values are 1.1‰ lower than lipid tissue during pure lipid metabolism. From RER, we determined that arctic ground squirrels rely on nonlipid fuel sources for a significant portion of energy during torpor (up to 37%). The shift toward nonlipid fuel sources may be influenced by adiposity of the animals in addition to thermal challenge.

Caffeine effects on velocity selection and physiological responses during RPE production.

Caffeine (CAF) blunts estimated ratings of perceived exertion (RPE) but the effects on RPE production are unclear. This study examined effects of acute caffeine ingestion during treadmill exercise where participants exercised at prescribed RPE 4 and 7. Recreational runners (maximal oxygen consumption = 51.4 ± 9.8 mL·kg-1·min-1) (n = 16) completed a maximal treadmill test followed by trials where they selected treadmill velocity (VEL) (1% grade) to produce RPE 4 and RPE 7 (10 min each). RPE production trials followed CAF (6 mg·kg-1) or placebo (PLA) (counterbalanced) ingestion. Participants were blinded to treadmill VEL but the Omni RPE scale was in full view. Repeated-measures ANOVA showed a main effect (trial) for VEL (CAF ∼5 m·min-1 faster) for RPE 4 (p = 0.07) and RPE 7 (p = 0.03). Mean heart rate and oxygen consumption responses were consistently higher for CAF but failed to reach statistical significance. Individual responses to CAF were labeled positive using a criterion of 13.4 m·min-1 faster for CAF (vs. PLA). Ten of 32 trials (31%) were positive responses. In these, systematic increases were observed for heart rate (∼12 beats·min-1) and oxygen consumption (∼5.7 mL·kg-1·min-1). Blunted/stable respiratory exchange ratio values at higher VEL for positive responders suggest increased free fatty acid reliance during CAF. In conlusion, mean results show a mild effect of CAF during RPE production. However, individual responses more clearly indicate whether a true effect is possible. Trainers and individuals should consider individual responses to ensure effectively intensity regulation.

The Pilates method and cardiorespiratory adaptation to training

ABSTRACTAlthough all authors report beneficial health changes following training based on the Pilates method, no explicit analysis has been performed of its cardiorespiratory effects. The objective of this study was to evaluate possible changes in cardiorespiratory parameters with the Pilates method. A total of 45 university students aged 18–35 years (77.8% female and 22.2% male), who did not routinely practice physical exercise or sports, volunteered for the study and signed informed consent. The Pilates training was conducted over 10 weeks, with three 1-hour sessions per week. Physiological cardiorespiratory responses were assessed using a MasterScreen CPX apparatus. After the 10-week training, statistically significant improvements were observed in mean heart rate (135.4–124.2 beats/min), respiratory exchange ratio (1.1–0.9) and oxygen equivalent (30.7–27.6) values, among other spirometric parameters, in submaximal aerobic testing. These findings indicate that practice of the Pilates method has a positive influence on cardiorespiratory parameters in healthy adults who do not routinely practice physical exercise activities.

Are gait characteristics and ground reaction forces related to energy cost of running in elite Kenyan runners?

ABSTRACTThe aim of this study was to determine whether gait cycle characteristics are associated with running economy in elite Kenyan runners. Fifteen elite Kenyan male runners completed two constant-speed running sets on a treadmill (12 km ·h−1 and 20 km ·h−1). VO2 and respiratory exchange ratio values were measured to calculate steady-state oxygen and energy cost of running. Gait cycle characteristics and ground contact forces were measured at each speed. Oxygen cost of running at different velocities was 192.2 ± 14.7 ml· kg−1· km−1 at 12 km· h−1 and 184.8 ± 9.9 ml· kg−1· km−1 at 20 km· h−1, which corresponded to a caloric cost of running of 0.94 ± 0.07 kcal ·kg−1·km−1 and 0.93 ± 0.07 kcal· kg−1· km−1. We found no significant correlations between oxygen and energy cost of running and biomechanical variables and ground reaction forces at either 12 or 20 km· h−1. However, ground contact times were ~10.0% shorter (very large effect) than in previously published literature in elite runners at similar speeds, alongside an 8.9% lower oxygen cost (very large effect). These results provide evidence to hypothesise that the short ground contact times may contribute to the exceptional running economy of Kenyan runners.

Dietary macronutrient distribution influences postexercise substrate utilization in women: a cross-sectional evaluation of metabolic flexibility.

Metabolic flexibility is the ability to alter substrate utilization in response to substrate availability, which may influence health and performance. The current study evaluated the effects of habitual macronutrient distribution on energy expenditure (EE) and metabolic flexibility in physically active women. Participants (N.=20) completed a 3-day food log and a standardized bout of high-intensity interval training to determine EE and respiratory exchange ratio (RER). EE and RER were measured via indirect calorimetry at rest (PRE) and immediately (IP), 30 minutes (30 min), and 60 minutes postexercise (60 min). To evaluate metabolic flexibility, RER changes were calculated from PRE to IP, IP to 30 min, and IP to 60 min. For each macronutrient, participants were categorized into high- and low-intake groups using a median split. No significant correlations were observed between macronutrient distribution and EE when covaried for lean mass (all P≥0.232), and ANCOVAs revealed no significant group × time interactions (all P≥0.241). Fat intake was not associated with ∆RER (all P≥0.477). Correlations between PRO intake and ∆RER approached significance (r=0.373-0.411; P=0.079-0.115), as did inverse associations between CHO and ∆RER (r=-0.404 - -0.409; P=0.084-0.087). Lower RER values were observed in the low-CHO group at 30 min and 60 min (P=0.030) compared to high-CHO. Higher RER values were observed in the high-PRO group at IP (P=0.042) compared to low-PRO. Estradiol was not correlated with RER at any time point, or different between diet groups (all P≥0.401). Results suggest that high PRO and low CHO intakes are associated with greater metabolic flexibility in women.

Gas analyzer's drift leads to systematic error in maximal oxygen uptake and maximal respiratory exchange ratio determination.

The aim was to examine the drift in the measurements of fractional concentration of oxygen (FO2) and carbon dioxide (FCO2) of a Nafion-using metabolic cart during incremental maximal exercise in 18 young and 12 elderly males, and to propose a way in which the drift can be corrected. The drift was verified by comparing the pre-test calibration values with the immediate post-test verification values of the calibration gases. The system demonstrated an average downscale drift (P < 0.001) in FO2 and FCO2 of −0.18% and −0.05%, respectively. Compared with measured values, corrected average maximal oxygen uptakevalues were 5–6% lower (P < 0.001) whereas corrected maximal respiratory exchange ratio values were 8–9% higher (P < 0.001). The drift was not due to an electronic instability in the analyzers because it was reverted after 20 min of recovery from the end of the exercise. The drift may be related to an incomplete removal of water vapor from the expired gas during transit through the Nafion conducting tube. These data demonstrate the importance of checking FO2 and FCO2 values by regular pre-test calibrations and post-test verifications, and also the importance of correcting a possible shift immediately after exercise.

Closed system respirometry may underestimate tissue gas exchange and bias the respiratory exchange ratio (RER)

Closed respirometry is a commonly used method to measure gas exchange in animals due to its apparent simplicity. Typically, the rates of O2 uptake and CO2 excretion (V˙O2 and V˙CO2, respectively) are assumed to be in steady state, such that the measured rates of gas exchange equal those at tissue level. In other words, the respiratory gas exchange ratio (RER) is assumed to equal the respiratory quotient (RQ). However, because the gas concentrations change progressively during closure, the animal inspires air with a progressively increasing CO2 concentration and decreasing O2 concentration. These changes will eventually affect gas exchange causing the O2 and CO2 stores within the animal to change. Because of the higher solubility/capacitance of CO2 in the tissues of the body, V˙CO2 will be more affected than V˙O2, and we hypothesize therefore that RER will become progressively underestimated as closure time is prolonged. This hypothesis was addressed by a combination of experimental studies involving closed respirometry on ball pythons (Python regius) as well as mathematical models of gas exchange. We show that increased closed duration of the respirometer reduces RER by up to 13%, and these findings may explain previous reports of RER values being below 0.7. Our model reveals that the maximally possible reduction in RER is determined by the storage capacity of the body for CO2 (product of size and specific capacitance) relative to the respirometer storage capacity. Furthermore, modeling also shows that pronounced ventilatory and circulatory response to hypercapnia can alleviate the reduction in RER.

FDWI Evaluation of Hypothalamic Appetite Regulation Pathways in Mice Genetically Deficient in Leptin or Neuropeptide Y

We evaluate the contribution of leptin-dependent anorexigenic pathways and neuropeptide Y (NPY)-dependent orexigenic pathways to the changes in hypothalamic water diffusion parameters observed in vivo by functional diffusion weighted MRI (fDWI). Mice genetically deficient in leptin (B6.V-Lep (ob) /J) or NPY (129S-Npy (tm1Rpa) /J) and the corresponding wild-type controls, were subjected to sequential isocaloric feeding, fasting and recovery regimes. Non-invasive fDWI measurements were performed under these conditions, and complemented with parallel determinations of food and water consumption, respiratory exchange ratio (RER), locomotor activity and endocrine profiles. Control mice showed significant increases in hypothalamic water diffusion parameters upon fasting, returning to normal values in the recovery period. Leptin deficient mice depicted permanently increased water diffusion parameters under all feeding conditions as compared to wild type controls, without important changes upon fasting or recovery. These results paralleled sustained increases in food and water intake, significantly augmented body weight, and decreased RER values or locomotor activity, thus configuring an obese phenotype. NPY-deficient mice showed significantly reduced increases (or even slight decreases) in the water diffusion parameters upon fasting as compared to wild type controls, paralleled by decreased food and water intake during the recovery period. In conclusion, leptin deficiency results in sustained orexigenic stimulation, leading to increased water diffusion parameters, while NPY deficiency lead to reduced orexigenic stimulation and water diffusion parameters. Diffusion changes are proposed to reflect net astrocytic volume changes induced by the balance between the orexigenic and anorexigenic firings of AgRP/NPY and POMC/CART neurons, respectively. Together, our results suggest that fDWI provides an adequate tool to investigate hypothalamic appetite disorders.