bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Hyperhydration on the Cardiovascular Responses to an LBNP Presyncopal Challenge
Authors: Pawluk Cristyn , Payne Taylor , Gibson Morgan , Davis John E 
Published: November 2023

PURPOSETo determine the effects of hyperhydration on heart rate, blood pressure, leg blood volume and forearm blood flow during a lower body negative challenge to presyncope.METHODSNine subjects (Age = 20.2 ± 1.3 yrs, Weight = 75.3 ± 21.1 kgs) participated in two graded LBNP (Lower Body Negative Pressure) tests to pre‐syncope while forearm blood flow (FBF), heart rate (HR), blood pressure (BP), and leg blood volume were measured. Each subject was tested in a control trial (with no fluid ingestion), and after consumption of a hypervolemia‐inducing beverage (NaCl solution of 4.9g per kg of body weight in 10mL of grape flavored Propel). Treatment order was randomized for all subjects. A cumulative stress index (CSI) was subsequently calculated (minutes completed x box pressure) to assess changes in orthostatic tolerance between the control and fluid ingestion LBNP. For all trials in the LBNP chamber, subjects were tested at LBNP levels of −20 mmHg, −40 mmHg, and −60 mmHg for three minutes at each trial, and then an additional increase of −10 mmHg every three minutes until pre‐syncopal symptoms appeared. Forearm blood flow was measured using venous occlusion plethysmography. Near‐infrared spectroscopy (Portamon, Artinis, Inc.) in the right calf muscle was used to determine lower leg blood volume.RESULTSThere were no significant differences in CSI between the hyperhydration (619.8 ± 55.2mmHg.min) and control conditions (640.0 ± 70.3 mmHg.min). Furthermore, the change in forearm blood flow, lower leg blood volume, and heart rate during the LBNP hyperhydration trial were not different from the control trial.CONCLUSIONIngestion of a hypervolemia‐inducing beverage did not alter orthostatic tolerance or the cardiovascular responses to an orthostatic challenge. This suggests that either a larger volume of fluid or a fluid with a different composition needs to be ingested to improve orthostatic tolerance.
The Impact of Caloric Restriction and Resistance Training on Bone Mineral Density and Bone Strength in Growing Male Rats
Authors: Slater Brady , Lee Kassandra , Folta Haley , Wong Quinton , Gettleman Brandon , Hernandez John , Prakash Anu , Jaque S Victoria , Sumida Ken D 
Published: November 2023

The purpose of this study was to examine the impact of caloric restriction and resistance training on bone mineral density (BMD, in g/cm2, measured via DXA) and bone strength (Fmax, in Newtons, measured via 3 pt bending rig) of the tibia in growing male rats. 32 male rats (initially 8 wks old) were randomly divided into: a non‐exercised ad libitum fed Control group (C, n=8) pair fed with a non‐exercised group fed a 20% caloric restrictive diet (D, n=8), and an exercised ad libitum fed group (RT, n=8) pair fed with an exercised group fed a 20% caloric restrictive diet (DT, n=8). The exercise groups were conditioned to climb a 1 meter vertical ladder 4X per session with weights appended to their tail 3 days/wk for 6 wks. All exercised animals initially carried 30% of their body weight (BW) and progressed to 150% BW by week 6. After 6 wks, the body weight was significantly lower for diet fed animals (383.8 ± 6.8 g) compared to ad libitum fed animals (459.9 ± 9.3 g). There were no interaction effects (exercise x diet) for BMD or bone strength. The main effect of exercise on BMD was significantly greater (P = 0.047) for trained groups (RT and DT = 0.215 ± 0.002) compared to non‐exercised groups (C and D = 0.206 ± 0.002) whereas the main effect of diet on BMD was not statistically significant (P = 0.086) for ad libitum fed groups (C and RT = 0.214 ± 0.004) compared to diet fed groups (D and DT = 0.207 ± 0.002). The main effect of exercise on Fmax was significantly greater (P = 0.001) for exercised groups (RT and DT = 139.5 ± 5.1) compared to non‐exercised groups (C and D = 118.7 ± 3.8) and the main effect of diet on Fmax was significantly greater (P = 0.001) for ad libitum fed groups (C and RT = 138.8 ± 5.3) compared to diet fed groups (D and DT = 119.4 ± 3.8). The results indicate that during growth, resistance training elevated BMD and bone strength whereas a 20% caloric restrictive diet lowered bone strength in the absence of a decline in BMD.Support or Funding InformationChapman University Faculty Research Grant
Does Local Heating of the Carotid Body Chemoreceptors Modulate Ventilation or Hemodynamics?
Authors: Johnson Blair D , Sackett James R , Sarker Suman , Coleman Gregory L , Chapman Christopher L , Schlader Zachary J 
Published: November 2023

BackgroundActivation of the carotid body chemoreceptors is sympathoexcitatory and causes increases in ventilation, heart rate, and blood pressure. In vitro evidence indicates that heat stressed carotid body chemoreceptors are activated and cause an increase in carotid sinus nerve activity. However, the role that the carotid body chemoreceptors play in the physiological responses to whole body heat stress is not clear. We developed an experimental model to isolate heat stress to the carotid body chemoreceptors. This model will allow us to determine if local heating of the carotid body chemoreceptors influences ventilation and hemodynamics.PurposeWe tested the hypothesis that local heating of the carotid body chemoreceptors modulates ventilation and hemodynamics.MethodsFive healthy men (age: 25 ± 2) participated in two local heating protocols. In the CB heat protocol, local heaters (surface area: 7.9 cm2) were adhered to the skin at the bifurcation of the left and right carotid artery and set to 44°C. In the ARM heat protocol, local heaters were adhered to the ventral side of both forearms and set to 44°C. Heat was applied for 45 minutes in both protocols. The protocols were randomized and separated by a minimum of 30 minutes or until skin blood flow returned to baseline values. We measured ventilation (heated pneumotach), heart rate (ECG), blood pressure (Finometer), and forearm skin blood flow (laser Doppler) throughout each protocol. Skin blood flow was also normalized to mean arterial pressure (MAP) and expressed as a percentage of the local heating induced maximal cutaneous vascular conductance (%CVCmax).ResultsFour of the five participants had an increase in ventilation from baseline ranging from 5–16% during CB heat. However, the change in ventilation from baseline was not statistically distinguishable between CB heat (0.5 ± 0.7 L/min) and ARM heat (−0.6 ± 1.2 L/min) (P = 0.14). The change in heart rate from baseline tended to be greater in CB heat vs. ARM heat (4 ± 4 vs. −3 ± 5 bpm; P < 0.08). The change in MAP was not different between protocols (CB heat: 3 ± 4 mmHg vs. ARM heat: 3 ± 3 mmHg; P = 0.45). When compared to baseline, skin blood flow (20 ± 9 vs. 13 ± 3 PU; P < 0.10) and %CVCmax tended to be lower during CB heat (7.2 ± 0.6 vs. 5.2 ± 1.8%; P < 0.07).ConclusionsThese preliminary data indicate that the carotid body chemoreceptors appear to play an independent role in the ventilatory and hemodynamic responses to heat stress.Support or Funding InformationThis project was supported by the University at Buffalo Innovative Micro‐Programs Accelerating Collaboration in Themes (IMPACT) program.
Effects of exercise‐induced increases in body temperatures on local skin thermal sensitivity in Multiple Sclerosis patients
Authors: Filingeri Davide , Chaseling Georgia K , Hoang Phu , Barnett Michael , Davis Scott L , Jay Ollie 
Published: November 2023

Exercise and concomitant increases in body temperature reduces local skin thermal sensitivity via hypothesized analgesic‐effects. Abnormal thresholds for thermal sensations and heat‐sensitivity are well‐established symptoms and modulatory factors, respectively, of Multiple Sclerosis. However, it is unknown whether increases in body temperature modulate sensory abnormalities in MS. We therefore investigated the hypothesis that changes in local skin thermal sensitivity are reduced in relapsing‐remitting MS patients during cycling in the heat (30°C; 35%RH). Seven MS patients (age 54±7 y; body mass 76.1±10.9 kg; body surface area 1.9±0.2 m2), with increased warmth thresholds (0.61±0.58°C) compared to 4 age‐, mass‐ and body surface area‐matched healthy controls (CTR) (53±9 y; 75.6±14.0 kg; 1.9±0.2 m2; warmth threshold: 0.38±0.25°C); were asked to perform 30‐min cycling at an intensity of 3.3 W/kg of total body mass. A quantitative thermo‐sensory test, consisting of reporting (visual analogue scale) perceived magnitude of local warm (38°C) and cold (22°C) thermal stimuli (25 cm2‐thermal probe) applied to the dorsum of the hand, was performed before and after every 10 min of cycling. Rectal temperature increased similarly between MS (+0.20±0.17°C) and CTR (+0.15±0.09°C) (p=0.619), whereas changes in mean skin temperature were greater in MS (1.41±0.38°C) than CTR (0.96±0.28°C) (p=0.077). 30 min of cycling reduced CTR thermo‐sensitivity to warm (−10.5±10.0%) and cold (−14.1±8.5%) thermal stimuli. MS patients also experienced exercise‐induced reductions in local thermo‐sensitivity, however these were of smaller magnitude, both for warm (−2.7±16.4%) and cold (−10.4±8.6%) thermal stimuli. In line with previous research, exercise‐induced increases in body temperature reduce skin thermo‐sensitivity providing an analgesic effect in healthy controls. However, MS diminishes the magnitude of such effect.Support or Funding InformationThis study was supported by a MS Research Australia Incubator Grant (Holders: Jay, Barnett, Hoang and Davis) and a University of Sydney International Collaboration research Award (IRCA) (Holders: Davis and Jay). Dr Filingeri was supported by a Government of Australia Endeavour Fellowship
Steady State Skeletal Muscle Temperature during Moderate Intensity Single Leg Dynamic Knee Extension Exercise
Authors: Mangum Joshua Earl , Luttrell Meredith , Ely Matthew , Abdala Pedro , Sieck Dylan , Halliwill John 
Published: November 2023

In resting skeletal muscle, there is a temperature gradient with deeper tissue typically having higher temperatures than more superficial tissue. During exercise, skeletal muscle temperature increases with the rise in metabolism. Our lab has previously used a model of dynamic knee extension exercise which consists of single‐leg kicking for 60 minutes at 60% of peak power output. The rate of skeletal muscle temperature rise, maximal temperature attained, and range of intramuscular temperatures with this mode of exercise is unknown. Therefore, the purpose of this study was to examine the changes in skeletal muscle temperature at three different depths during exercise using this model. It was hypothesized that the three depths within skeletal muscle would have different temperatures at rest, and these would rapidly increase, converging at some point during exercise. Five young (ages 21–38) healthy male subjects completed the exercise protocol and intramuscular temperature was measured via a percutaneous intramuscular thermocouple that measured temperature at three different depths within the vastus lateralis. Individual temperatures from each depth were measured and also averaged to express a mean intramuscular temperature. Within 10 minutes of exercise, mean intramuscular temperature increased from 34.59 ± 0.44°C to 37.06 ± 0.10°C (mean ± SE, p < 0.01). By 30 minutes, mean intramuscular temperature reached a plateau of 39.15 ± 0.11°C. The variability of temperature in muscle, expressed as the range of the three different intramuscular temperatures, decreased from 1.40 ± 0.39°C to 0.60 ± 0.21°C by 30 minutes (p = 0.08), and did not further decrease to the end of exercise. These data suggest that skeletal muscle temperature increases rapidly during exercise, and the heterogeneity in temperatures typically associated with depth is reduced. As well, these data suggest that there is a steady intramuscular temperature reached within 30 minutes of steady state exercise at 60% of peak power output.Support or Funding InformationSupport provided by NIH grant HL115027
A Lower Heat Activated Sweat Gland Density in Larger Individuals Does Not Impair Local Sweat Rates During Hot and Humid Heat Stress
Authors: Ravanelli Nicholas , Imbeault Pascal , Jay Ollie 
Published: November 2023

While the absolute number of sweat glands is primarily determined in utero, a larger body surface area (BSA) will naturally reduce the density of sweat glands per surface area which may compromise sweat rate per unit BSA, and consequently the maximal skin surface sweat coverage (i.e. skin wettedness: ωmax) during exercise in a hot/humid environment. The purpose of the present study was to compare the heat activated sweat gland density (HASGD), sweat gland output (SGO), local sweat rate (LSR) and ωmax between groups differing greatly in BSA during hot and humid active heat stress. Twelve participants separated into two groups based on body size (Small (SM): n=6, 65±6 kg, 1.8±0.1 m2; Large (LG): n=6, 102±13 kg, 2.3±0.1 m2) exercised on an upright cycle ergometer at an evaporative heat balance requirement (Ereq) of 240 W/m2 and 290 W/m2 for up to 75 min at 36°C, 70% RH. LSR of the upper back was measured throughout and expressed relative to surface area (mg/cm2/min). HASGD in number of sweat glands per cm2 (glands/cm2) was measured medially to LSR using the starch iodine technique every 15 minutes and averaged throughout the trial. Mean SGO was derived from the division of LSR and mean HASGD, and expressed as μg/gland/min. On a separate occasion ωmax was measured using a humidity‐ramp protocol (increase of 0.3 kPa from 2.3 kPa every 7.5‐min) during exercise at a fixed external workload of 100W at 36°C until an inflection of esophageal temperature was observed. LSR was similar at 240 W/m2 (SM: 1.24±0.24; LG: 1.40±0.47 mg/cm2/min, P=0.25) and 290 W/m2 (SM: 1.36±0.18; LG: 1.36±0.36 mg/cm2/min, P=0.48). HASGD was greater in SM compared to LG group at 240 W/m2 (SM: 67±12; LG: 55±6 glands/cm2, P=0.03) and 290 W/m2 (SM: 73±9; LG: 57±11 glands/cm2, P<0.01). SGO was trending to be greater in the LG group at 240 W/m2 (SM: 18.6±5.0; LG: 25.2±10.2 μg/gland/min, P=0.10) while significantly greater in the LG group at 290 W/m2 (SM: 17.3±1.6; LG: 21.2±5.7 μg/gland/min, P=0.03). On the other hand, ωmax was not different between groups (SM: 0.82±0.16; LG: 0.72±0.07, P=0.13). In conclusion, a lower HASGD in people with a greater BSA is compensated by a greater SGO to yield a similar LSR up to an Ereq of 290 W/m2 and a similar ωmax. Future research should attempt to assess how even greater reductions in HASGD due to disproportionally larger differences in BSA (ie morbid obesity) compromise LSR, ωmax, and therefore the level of heat stress that can be physiologically compensated.Support or Funding InformationSupported by a NSERC Discovery Grant (P. Imbeault & O. Jay)
Does Body Surface Area Independently Alter Whole‐body Sweat Loss during Exercise at a Fixed Absolute Evaporative Requirement for Heat Balance?
Authors: Cramer Matthew N , Coombs Geoffrey B , Ravanelli Nicholas M , Jay Ollie 
Published: November 2023

The absolute evaporative requirement for heat balance (Ereq) is the principal determinant of whole‐body sweat loss (WBSL) during fixed‐duration exercise in ambient conditions that permit complete sweat evaporation, regardless of body size. However, exercise at a fixed absolute Ereq in hot/humid conditions may lead to disproportionately greater WBSL among individuals of smaller body surface area (BSA) due to a lower absolute maximum evaporative capacity and thus higher skin wettedness required for heat balance (ωreq) and lower sweating efficiency (Seff). To test this hypothesis, young adult males of small (SM: 1.81±0.07 m2; n=4) or large (LG: 2.28±0.15 m2; n=3) BSA cycled for 70 min at 34±0.3°C, 71.8±1.3% RH at an exercise intensity set to elicit a fixed VO2 of 1.5 L/min, and therefore a metabolic heat production of ~450 W and an Ereq of ~430 W (indirect calorimetry). Body mass was measured at 0, 45, and 70 min to estimate WBSL during non‐steady‐state (0–45 min) and steady‐state (45–70 min) exercise. Seff was calculated as the quotient of the WBSL required to attain Ereq with complete evaporation and the observed WBSL during the steady‐state period, and expressed as a percentage. The attainment of a steady state (i.e., the actual rate of evaporation equaled the required rate of evaporation) from 45 to 70 min was confirmed by stable esophageal and skin temperatures (±0.1°C throughout steady state). During non‐steady‐state exercise, ωreq was not different between groups (SM: 0.81±0.05 g; LG: 0.73±0.08 g; P=0.17), and no between‐group difference in WBSL was observed (SM: 522±81 g; LG: 476±115 g; P=0.56). In contrast, steady‐state ωreq was greater in SM (SM: 0.81±0.03; LG: 0.71±0.04; P=0.02), leading to significantly higher WBSL (SM: 361±49 g; LG: 260±54 g; P<0.05) and diminished Seff (SM: 74.1±12.7%; LG: 96.3±6.4%; P=0.04) in the SM group. In summary, our preliminary data suggest that in hot/humid ambient conditions, a large between‐group difference in BSA may lead to disproportionately greater steady‐state WBSL in smaller individuals despite exercising at the same absolute Ereq due to an independent effect of BSA on Seff.Support or Funding InformationSupported by an NSERC Discovery Grant (O. Jay)
Leucine Modulates mTORC1 Signaling by Acting Specifically to Alter the Phosphorylation Status of Sestrin2
Authors: Kimball Scot R , Gordon Bradley S , Moyer Jenna E , Dennis Michael D , Jefferson Leonard S 
Published: November 2023

Studies performed more than 35 years ago showed that the branched‐chain amino acids, and in particular leucine, were as effective as a complete mixture of amino acids in stimulating protein synthesis in skeletal muscle, heart, and diaphragm. Subsequent studies showed that the leucine‐induced stimulation of protein synthesis occurred through activation of the initiation phase of mRNA translation, and that in turn was due to activation of the protein kinase referred to as the mechanistic target of rapamycin in complex 1 (mTORC1). Over the past decade studies performed primarily using cells in culture exposed to either complete amino acid depletion or repletion conditions have yielded the identification of a molecular pathway through which amino acids signal to mTORC1. However, despite these advances in our knowledge, we still do not know how leucine acts selectively to activate mTORC1 or how its availability is recognized. In the present study, we assessed the role of Sestrin2 in mediating the leucine‐specific activation of mTORC1. We found that in cells in culture exposed to medium lacking leucine, Sestrin2 phosphorylation was enhanced, and that leucine repletion rapidly (within 10 min) reversed the phosphorylation. Moreover, leucine‐induced dephosphorylation occurred over physiological concentrations of the amino acid, and was inversely proportional to changes in phosphorylation of the mTORC1 substrate, p70S6K1. The effect was specific for leucine, as neither glutamine nor arginine had any effect on Sestrin2 phosphorylation, even though arginine was as potent as leucine in activating mTORC1. Interestingly, phosphorylation of Sestrin2 correlated with enhanced interaction with the GATOR2 complex, a key upstream regulator of mTORC1 activity. Finally, three Sestrin2 phosphorylation sites were identified by mass spectrometry, and site‐directed mutagenesis is currently being used to assess their role in mediating leucine‐specific modulation of mTORC1 activity. Overall, the results support a model in which leucine selectively promotes dephosphorylation of Sestrin2, causing it to dissociate from GATOR2 to allow activation of mTORC1.Support or Funding InformationSupported by NIH grant DK15658
Contractile Properties of the Rat Extensor Digitorum Longus Muscle in Relation to Regional Variation in Fibre Type Composition
Authors: Kissane Roger , Egginton Stuart , Askew Graham N 
Published: November 2023

Muscle contractile characteristics are commonly investigated in relation to global phenotype. The extensor digitorum longus (EDL) muscle has frequently been used in physiological studies as an example of a typical fast muscle. However, the fibre type composition is not homogeneous. In the rat, the EDL contains a mixture of oxidative and glycolytic fibres, heterogeneously distributed across the muscle cross section to produce a gradient of aerobic capacity. The aim of this study was to characterize the contractile characteristics of this mixed muscle in relation to the regional variation in fibre type composition. It was hypothesized that isometric twitch characteristics and optimal frequency for power generation would not differ regionally, while the fatigability will correlate with aerobic capacity.The EDL muscle from male Wistar rats comprises four segments which insert on to phalanges 2–5; we used the medial and lateral segments, which insert on to phalanges 2 and 5, respectively. The contractile characteristics of each segment were determined under isometric conditions, in order to quantify twitch kinetics and tetanic stress. Power output of the muscle was measured at a range of cycle frequencies during cyclical contractions, using the work loop technique. The ability to sustain power was quantified using a series of repeated cyclical contractions. A range of monoclonal antibodies was used to determine fibre type composition.The two muscle segments had significantly different fibre type composition; the medial segment containing 41% Type IIb, 49% Type IIa and 10% Type I while the lateral segment contained 95% Type IIb and 5% Type IIa. The medial segment had slower twitch kinetics than the lateral segment, consistent with the presence of Type 1 fibres and lower proportion of Type 2 fibres. Isometric stress was lower in the medial segment producing 155.3 kN m−2 compared to 194.6 kN m−2 in the lateral segment; this may be related to the higher proportion of non‐contractile elements such as mitochondria in the medial segment, i.e. a lower proportion of myofibrils, compared with the lateral segment. Peak net power output and the frequency at which this was attained were similar between both muscle segments.Variation in the physiological properties of the lateral and medial segments of the rat EDL are consistent with the decrease in oxidative capacity and a decrease in the proportion of fast‐twitch fibres from medial to lateral sides. This suggests that there may be regional variation in mechanical function, with a shift from the medial segment providing work for ankle flexion at relatively low speeds, to the lateral segment increasingly fulfilling the role at higher speeds.