EX Trial Research Articles

Cardiovascular and Hematological Responses to Simulated Dynamic Apnea in Breath Hold Divers

The mammalian dive reflex, characterized by bradycardia and peripheral vasoconstriction, occurs in all mammals, including humans, in response to apnea or facial submersion in water. However, the dive reflex to a single, maximal effort dynamic apnea (DYN), and how it compares to a time-matched exercise control trial (EX), has not been studied. We examined the hypotheses that, when compared to EX, (a) the magnitude of the cardiovascular response, including reduced heart rate (HR), increased systolic-, diastolic-, and mean arterial- pressure (SBP, DBP, and MAP, respectively) would be greater during DYN, and; (b) red blood cells (RBCs), hemoglobin (Hb), and hematocrit (Hct) would also all be elevated following DYN. Twenty-three (F=6) apnea divers performed a maximal DYN and time-matched EX on a swimming ergometer without facial submersion. For the DYN protocol, participants were instructed to exercise maximally while holding their breath which the EX trial was then time and distance matched. Trial duration was similar between DYN (126±7s [mean±SE]) and EX (126±7s;P>0.3), however the change in venous lactate (DYN 1.8±0.3mmol/l, EX: 0.2±0.2mmol/l) and peripheral oxygen saturation (DYN: -15±3%, EX: -1.8±0.5%;p<0.05, both comparisons) were greater during DYN compared to EX. During DYN ΔSBP (DYN: 107±6mmHg, EX: 45±6 mmHg), ΔDBP (DYN: 46±3mmHg, EX: 17±3mmHg) and ΔMAP (DYN: 66±3mmHg EX: 26±3mmHg) were increased compared to EX, while ΔHR was greater during EX (DYN: -24±5bpm, EX: 36±5bpm;p<0.0001, all comparisons). Similarly, the change in estimated stroke volume was further reduced in DYN (DYN: -15.2±3.3mL, EX: -1.0±3.3m;p<0.005) while Δcardiac output was reduced during DYN (-2.9±0.4l/min) and elevated during EX (2.9±0.4l/min;p<0.0001). The change in RBCs (DYN: 0.20±0.04x106 cells/μL, EX: 0.06±0.04x106 cells/μL) and Hct (DYN:1.7±0.3%, EX:0.5±0.3%) were greater during DYN than EX (p<0.02, both comparisons), whereas ΔHb (DYN: 4.0±0.9g/dL, EX: 1.9±0.8g/dL) and spleen volume (DYN: -9.1±7.4cm3, EX:-8.3±6.4cm3;P>0.1, both comparisons) was comparable between the two trials. There was a main effect of sex for ΔDBP (Female: 36±3mmHg, Male: 27±2mmHg), and ΔMAP (Female: 52±5mmHg, Male: 40±3mmHg) indicating that females overall had a greater blood pressure response to both DYN and EX (p<0.05, both comparisons). Together, these data indicate that DYN elicits a greater cardiovascular and hematological response than EX alone, likely due to the combined activation of the metabo- and chemo-reflex during DYN. The mechanism(s) that may elicit greater changes in blood pressure response to DYN and EX in females when compared to males warrant future investigation. NSERC, University Research Chair. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A Single Bout of Exercise Reduces Postprandial Lipemia but Has No Delayed Effect on Hemorheological Variables.

High plasma triglyceride (TG) concentration in fasting state could cause hemorheological abnormality, thus increasing the incidence of metabolic diseases. Exercise has been reported to effectively reduce postprandial TG response. This study aimed to investigate whether a single bout of pre-prandial exercise can affect lipemia and hemorheological variables after a high-fat meal. Nine healthy young male subjects completed two experimental trials. The subjects walked for 1 h at 50% maximal oxygen uptake (V̇O₂max) (the exercise, EX trial), or rested (the control, CON trial). In the next morning, the subjects consumed a high-fat meal, and the postprandial lipemia and hemorheological responses were monitored for 6 h. The results showed that postprandial plasma TG concentrations were significantly lower in the EX trial compared to the CON trial. The postprandial low-density lipoproteins (LDL) concentration declined in the first 2 h and then gradually returned to the baseline level in both trials. The postprandial blood viscosity also decreased in the CON trial. There was no significant difference in postprandial blood viscosity, red blood cell (RBC) deformation index and aggregation degree between the trials. There was no significant correlation between plasma TG concentration and blood viscosity. In conclusion, brisk walking effectively reduced postprandial TG concentration, but has no significant impact on postprandial blood viscosity, RBC deformation index and RBC aggregation index.

Functional Changes in Motor Cortical Brain Regions following Passive and Exertional Heat Stress

Endurance performance is impaired when exercising in the heat. Hyperthermia-induced fatigue cannot be entirely explained by alterations in peripheral mechanisms. The central nervous system may have key roles in hyperthermia-induced fatigue and thus warrant further investigations. PURPOSE: To evaluate functional changes in the brain following passive or exertional heat stress. METHODS: Five moderately-trained athletes (mean ± SD: age 23.6 ± 1.7 years; body fat 9.3±2.0%; VO2max 58±6 ml kg-1 min-1) underwent a motor task-based blood-oxygen-level dependent (BOLD) fMRI scan while donning a water-perfused thermal suit in a familiarization and four randomized, counterbalanced trials. fMRI scans were conducted after (a) running on a motorized treadmill at 70% VO2max with ingestion of ambient water (EX) or (b) ice slurry (ICE), (c) passive heating via warm water immersion at 41°C (PAH), or (d) rest (CON). Serum osmolality was evaluated from blood samples collected at the start and end of each trial. Rectal temperature (Tre) and heart rate (HR) were assessed using two-way ANOVA with p < 0.05 considered as significant. RESULTS: Participants started all trials euhydrated (mean serum osmolality: 292 ± 1 mOsmol/kg; p= 0.719), with similar baseline HR (66 ± 2 beats/min; p=0.908) and Tre (36.9 ± 0.1°C; p=0.431). Post-intervention percent body mass change were similar across trials (-0.7 ± 0.2%; p= 0.110). Post-intervention Tre for EX (39.4 ± 0.2°C) was similar to PAH trial (39.3 ± 0.2°C; p = 0.59) but higher than ICE (39.0 ± 0.2°C; p = 0.01) and CON trials (36.5 ± 0.2°C; p < 0.01). Mean Tre achieved during post-intervention fMRI scan were 38.5 ± 0.1°C for both EX and PAH trials, 37.7 ± 0.1°C for ICE trial and 36.3 ± 0.1°C for CON trial. Task-based fMRI detected lower BOLD signals from primary motor cortex in PAH (fold changes from baseline: 0.46 ± 0.35) compared to EX trials (1.03 ± 0.21, p = 0.01). BOLD signals were also lower in primary somatosensory cortex for PAH (0.39 ± 0.23) compared to EX (1.04 ± 0.18, p < 0.01) and CON trials (0.98 ± 0.10, p = 0.02). CONCLUSION: Preliminary results from task-based BOLD analysis showed that passive heating led to functional suppression in the sensorimotor areas in the brain. Supported by DIRP Grant, PA No. 9015102335.

The Effect Of 5-hydroxytryptophan (5-htp) And Intense Exercise On Plasma And Salivary Cortisol

Background: Oral administration of 5-hydroxytryptophan (5-HTP), the precursor of serotonin, has been reported to stimulate the Hypothalamic-Adrenal Axis resulting in increased cortisol in healthy volunteers and clinical populations. Exercise is known to stimulate the cortisol secretion, whether pre-exercise 5-HTP enhances the cortisol response to intense exercise is not yet known. PURPOSE: The purpose of this study was to examine the effect of 5-HTP and a graded exercise test to maximal effort (EX) on plasma (PL) and salivary(SA) cortisol in 9 healthy young volunteers (7M/2F). METHODS: Each subject completed an EX trial in the evening spaced at least 5 days apart, one under placebo and another under 5-HTP (200mg capsule 90-120 min prior to testing). The study was randomized double-blinded trial. Capillary and SA samples were obtained at rest before exercise (EX0), at 5 (Post-EX5) and at 20 (Post-EX20) minutes post-exercise. An ANOVA for crossover experimental design and t-tests were used to determine differences in PL and SA cortisol concentrations between placebo vs 5-HTP trials, and to determine if plasma and salivary cortisol increased over time, respectively. Cortisol was analyzed by enzyme immunoassays. RESULTS: There was a significant increase in plasma cortisol in the placebo (EX0: 265 ± 67 nM vs Post-EX20: 664 ± 78 nM; p<0.001) and in the 5-HTP trial (EX0: 349 ± 58 nM vs Post-EX20: 567 ± 81 nM, p< 0.001). Similarly, there was a significant increase in SA cortisol in the placebo (EX0: 1.26 ± 0.20 nM, Post-EX20: 8.63 ± 1.96 nM; p<0.01) and in the 5-HTP trial (EX0: 3.96 ± 1.73 nM vs Post-EX20: 9.57 ± 2.96 nM, p< 0.01). However, there was no treatment effect for cortisol in either media nor was there a treatment effect at baseline (p>0.05). CONCLUSIONS: Under the present experimental conditions, there was no difference between placebo and 5-HTP. There was an increase from EX0 to Post-EX20 for both placebo and 5-HTP. Increasing sample size, and examining higher 5-HTP dosage regimen are warranted.

Metformin does not attenuate the acute insulin-sensitizing effect of a single bout of exercise in individuals with insulin resistance

Combining metformin and exercise is recommended for the treatment of insulin resistance. However, it has been suggested that metformin blunts the insulin-sensitizing effects of exercise. We evaluated in a group of insulin-resistant patients the interactions between exercise and their daily dose of metformin. Ten insulin-resistant patients underwent insulin sensitivity assessment using intravenous glucose tolerance test after an overnight fast in the following conditions: (1) after taking their habitual morning dose of metformin (MET), (2) after 45min of high intensity interval exercise having withheld metformin during 24h (EX), and (3) after their habitual metformin dose plus an identical exercise bout (MET+EX). During the exercise trials (EX and MET+EX), energy expenditure and substrate oxidation were assessed by indirect calorimetry. In addition, 12-h postprandial blood glucose was measured in all three trials. Insulin sensitivity was similar between MET and EX [4.0±0.8 and 4.1±0.7×10(-4)min(-1)(μUmL)(-1); P=0.953] but was 43% higher than both MET and EX after MET+EX (NS; P=0.081). Blood glucose disappearance rate was higher after MET+EX than after MET or EX trials (1.7±0.2, 1.0±0.1, and 1.2±0.1%min(-1), respectively; P=0.020). There was no difference in postprandial blood glucose concentration after the three meals that followed the trials (P=0.446). Exercise energy expenditure was 9% higher during MET+EX than during EX (P=0.015) partly due to increased carbohydrate oxidation. Our data suggest that habitual metformin treatment in insulin-resistant patients does not blunt the acute insulin-sensitizing effects of a single bout of exercise that on the contrary, tends to enhance it.

Acute aerobic exercise differentially alters acylated ghrelin and perceived fullness in normal-weight and obese individuals

Adiposity alters acylated ghrelin concentrations, but it is unknown whether adiposity alters the effect of exercise and feeding on acylated ghrelin responses. Therefore, the purpose of this study was to determine whether adiposity [normal-weight (NW) vs. obese (Ob)] influences the effect of exercise and feeding on acylated ghrelin, hunger, and fullness. Fourteen NW and 14 Ob individuals completed two trials in a randomized counterbalanced fashion, including a prior exercise trial (EX) and a no exercise trial (NoEX). During the EX trial, the participants performed 1 h of treadmill walking (55-60% peak O2 uptake) during the evening, 12 h before a 4-h standardized mixed meal test. Frequent blood samples were taken and analyzed for acylated ghrelin, and a visual analog scale was used to assess perceived hunger and fullness. In NW individuals, EX, compared with NoEX, reduced fasting acylated ghrelin concentrations by 18% (P = 0.03), and, in response to feeding, the change in acylated ghrelin (P = 0.02) was attenuated by 39%, but perceived hunger and fullness were unaltered. In Ob individuals, despite no changes in fasting or postprandial acylated ghrelin concentrations with EX, postprandial fullness was attenuated by 46% compared with NoEX (P = 0.05). In summary, exercise performed the night before a meal suppresses acylated ghrelin concentrations in NW individuals without altering perceived hunger or fullness. In Ob individuals, despite no changes in acylated ghrelin concentrations, EX reduced the fullness response to the test meal. Acylated ghrelin and perceived fullness responses are differently altered by acute aerobic exercise in NW and Ob individuals.

Muscle afferent activation causes ventilatory and cardiovascular responses during concurrent hypercapnia in humans

Respiratory and cardiovascular responses to muscle mechanoreflex (passive calf stretch) and metaboreflex activation (local circulatory occlusion) were examined during inhalation of a hypercapnic gas mixture in four trials. These controlled for the effects of central command, metabolite sensitization of muscle afferents and hypercapnia-induced elevation of central respiratory drive. In an isokinetic dynamometer, with circulation through the right leg occluded by inflation of a thigh cuff, 13 participants either rested (control trial; CON) or plantarflexed their ankle at 50% maximal force for 1.5 min (voluntary exercise trial; EX). Thereafter, circulatory occlusion was maintained and the calf passively stretched before return to the resting position. Both trials were performed while breathing air, as well as while breathing a normoxic, hypercapnic (5% CO(2)) gas mixture (CO(2) trial and CO(2)+EX trial). Hypercapnic gas inhalation increased baseline minute ventilation (V), heart rate and mean arterial pressure (+27.67 ± 1.74 l min(-1), +7 ± 0.85 beats min(-1) and +13 ± 3.41 mmHg, respectively; means ± SEM) above control values (9.78 ± 0.86 l min(-1), 62 ± 2.3 beats min(-1) and 88 ± 2.6 mmHg, respectively). Voluntary exercise further increased these variables from baseline during both trials (P < 0.05). During the continued circulatory occlusion after voluntary exercise, mean arterial pressure remained significantly elevated (P < 0.05). Minute ventilation returned to baseline during circulatory occlusion following exercise in the EX trial, but in the CO(2)+EX trial the V remained elevated at end-exercise levels during this period (+7.12 ± 1.13 l min(-1)). Passive stretch caused further increases in V during CO(2)+EX and CO(2) trials but not in CON and EX. These results indicate that in the absence of central command, either muscle metaboreflex and/or mechanoreflex activation stimulates ventilation during concurrent hypercapnia.

Use of Salivary Osmolality to Assess Dehydration

Objective. To investigate the ability of salivary osmolality to assess dehydration while subjects perform alternating work/rest cycles in personal protective equipment (PPE). Methods. Eight healthy men (mean ± standard deviation age: 23.5 ± 4.9 years; body fat: 17.8% ± 5.0%; maximum volume of oxygen consumption [VO2max]: 57.2 ± 5.5 mL·kg−1·min−1) performed two exercise trials: one while wearing shorts and a T-shirt (EX) and one while wearing firefighting PPE (EX+PPE). Saliva samples were taken before exercise, at minutes 40, 80, and 120 of the exercise trial, and during recovery. Results. Percent body mass loss (BML) was significantly greater while the subjects were wearing PPE (2.18% ± 0.54% vs. control 0.81% ± 0.30%). Salivary osmolality increased significantly in both trials (73.4 ± 12.4 to 125.1 ± 30.3 mOsm·kg−1 and 70.1 ± 12.5 to 83.6 ± 17.7 mOsm·kg−1); however, the increase in the EX+PPE trial was significantly greater than the increase in the EX trial. Plasma osmolality did not change significantly in either trial, whereas urinary osmolality increased significantly in both trials. Changes in salivary osmolality were strongly correlated with percent BML (r = 0.80; p < 0.01). Conclusion. Salivary osmolality may be a sensitive indicator of moderate dehydration under carefully controlled conditions. Key words: exercise; heat; dehydration; osmolality; saliva; personal protective equipment

The endothelial microparticle response to a high fat meal is not attenuated by prior exercise

Triglyceride-rich postprandial lipoproteins are known to activate endothelial cells in vitro, contributing to atherosclerosis. Endothelial microparticles (EMP) are membranous vesicles released into the circulation from vascular endothelial cells that permit cell activation to be monitored in vivo. The objective of the study was to examine changes in EMP following a high fat meal, consumed with and without prior exercise. Eight recreationally active young men underwent two oral fat tolerance tests following either 100 min exercise at 70% VO(2)peak (EX trial) or no exercise (CON trial) on the previous evening. Postprandial triglycerides were reduced (1.97 +/- 0.31 vs. 1.17 +/- 0.13 mmol L(-1), p < 0.05) and HDL-cholesterol (HDL-C) increased (1.20 +/- 0.07 vs. 1.30 +/- 0.08 mmol L(-1), p < 0.05) in the EX compared to CON trial. EMP (CD31+/42b-) increased postprandially (p < 0.05). However, counts were not different between trials (postprandial CON and EX trial counts x 10(3 )microL(-1), 3.10 +/- 0.14 vs. 3.26 +/- 0.37). There were no changes in sICAM-1 or sVCAM-1 postprandially and no differences between trials. Interleukin-6 (IL-6) and leukocytes increased postprandially (p < 0.05). IL-6 values were not different between trials. Leukocytes were higher at 0 h in the EX trial with CON and EX trial values similar at 6 h. EMP, but not sICAM-1 or sVCAM-1, increase in response to a high fat meal. However, EMP are not attenuated by acute exercise, despite a considerable reduction in postprandial lipemia and an increase in HDL-C.

Associations of plasma ghrelin, leptin and cholecystokinin (CCK) with sensations of hunger and fullness during manipulations of energy balance by meal size, exercise and intravenous nutrient replacement.

Role for ghrelin, leptin and CCK in ratings of hunger or fullness was examined in 12 healthy volunteers in five 11-h long trials. A 500 kcal meal at 6 h in a sedentary trial (SF) served as a control. A total of 400 kcal were either withhheld from breakfast (SR) or expended through exercise (between 10 and 12 h) In each experimental arm (SRR and EXR trials), 400 kcal were also replaced intravenously between 6 and 11 h. Ratings of hunger and fullness and plasma concentrations of total ghrelin, leptin (Linco Research) and CCK (ALPCO) were measured throughout. Results Dietary restriction increased hunger, decreased fullness, and increased ghrelin and decreased leptin and CCK concentrations Exercise decreased hunger and increased fullness and ghrelin and CCK concentrations. Intravenous nutrient replacement in SR trial blunted hunger and increased CCK concentration but had no effect on ratings of fullness or other hormones. IV nutrients during exercise did not affect hunger or fullness, increased CCK concentration as in EX trial, and increased leptin concentration above the EX trial. Conclusions Conscious tracking of energy balance was more accurate when calories were withheld from meals than when they were restored intravenously. Changes in plasma ghrelin, leptin, and CCK appropriately reflected hunger and fullness during sedentary trials. Calories lost during exercise were registered as being added. Increased leptin and CCK concentrations may have contributed to inappropriate reduction in hunger ratings and increased ratings of fullness during exercise-induced negative energy balance. Support: NIDDK 1R15DK066286-01A2 and Tanita Healthy Weight Community Trust grants.

Effect of Acute Exercise on Postprandial Triglycerides and Cellular Microparticles

Microparticles (MP) are membranous vesicles shed from formed elements such as circulating platelets, leukocytes, and vascular endothelial cells. They have been shown to play an important role in atherosclerotic and inflammatory vascular disease. PURPOSE: To examine changes in endothelial microparticles (EMP) and platelet microparticles (PMP) following a high fat meal, with and without prior exercise. METHODS: Eight recreationally active young men (26.9±4.1 yr, VO2peak 46.8±4.9 ml.kg-1.min-1, BMI 26.0±3.6 kg.m-2, % body fat 15.2±5.0%) underwent two oral fat tolerance tests (test meal per 2m2 BSA; 97g fat, 124g carbohydrate, 1450 kcal) following either 100 min cycle ergometry exercise at 70%VO2peak (EX trial), or no exercise (CON trial) on the previous evening. RESULTS: Postprandial triglycerides (AUC) were reduced (11.8±1.84 vs 7.0±0.81mmol. L-1.h, p<0.05) and fasting HDL-C increased (1.20±0.07vs 1.30±0.08 mmol.L-1, p<0.05) in the EX compared to CON trial. There was no difference in postprandial insulin (117. 1±25.0 vs 87.6±11.0 uU.L-1.h, p=0.12) between the two trials. EMP (CD31+/42b-) increased postprandially (mean 0 and 4hr counts. uL-1, 1433±236vs 3592±262, p<0.01). However, counts were not different between trials (mean CON and EX trial counts. uL-1, 2505±137 vs 2519±310, p=0.97). PMP (CD42b) decreased postprandially (mean 0 and 4hr counts. μL-1, 15915±2219vs 7819±1722, p<0.05) and were higher in the EX trial (mean CON and EX trial counts.μL-1, 8426±1504vs 15308±2131,p<0.05). There were no changes in soluble adhesion molecules postprandially or between trials (mean CON and EX trial values for sVCAM-1 and sICAM-1, 738±69 vs 750±76 ng.mL-1, p=0.59; 214±15 vs 207±15 ng.mL-1, p=0.63). Total leukocyte counts (p<0.05) and IL-6 (p<0.05) increased postprandially with no differences between trials. There were no changes in platelet counts postprandially or between trials. CONCLUSIONS: Despite favourable changes in blood lipids, endothelial function appears to be unchanged, and platelet activation increased 12 h following an acute bout of exercise.

Exercise-induced alterations in plasma concentrations of ghrelin, adiponectin, leptin, glucose, insulin, and cortisol in horses

Six Standardbred (STB) mares (11 ± 2 years, 521 ± 77 kg; means ± SD) performed an exercise trial (EX) where they underwent an incremental exercise test (GXT) as well as a parallel control trial (CON) to test the hypothesis that short-term, high intensity exercise would alter plasma concentrations of glucose, leptin, adiponectin, ghrelin, insulin and cortisol. Plasma samples were taken before (0 min), during (last 10 s at 6, 8 m/s, and the velocity eliciting VO 2max), and after exercise (2, 10, 30, 60 min; 12 and 24 h post-GXT). A second set of blood samples was collected before and after an afternoon meal given at 1515 h (at 1500, 1514, 1530, and 1545 h). Data were analyzed using ANOVA for repeated measures and Tukey’s test. During the GXT, there were no changes ( P > 0.05) in the plasma concentrations of glucose, leptin, adiponectin or ghrelin. However, there was a 29% increase ( P < 0.05) in mean plasma cortisol concentration and a 35% decrease ( P < 0.05) in mean plasma insulin concentration. Substantial increases ( P < 0.05) in the mean plasma concentrations of glucose and cortisol of 36% and 102%, respectively, were seen in the EX trial during the first 60 min post-GXT. Plasma leptin concentration, measured at the 24 h post-GXT time point, was 20% lower ( P < 0.05) during the EX trial compared with the parallel time point in the standing control (CON) trial. Plasma ghrelin concentration was 37% lower ( P < 0.05) in the EX trial compared with CON before and after the afternoon meal, but was 43% higher ( P < 0.05) 12 h post-GXT. There were no differences between EX and CON for plasma concentrations of insulin or adiponectin during recovery. It was concluded that short-term high intensity exercise alters plasma leptin and ghrelin concentrations in STB mares post-exercise, which may signal the exercised animals to alter energy intake.

Exercise-Induced Alterations in Plasma Insulin, Cortisol, Leptin, and Ghrelin Concentrations in Horses

0995 It is critical that an athletic horse maintain proper energy balance to ensure adequate substrate supply for the production of energy to fuel exercise. To that end, several hormones have been shown respond to challenges involving the integrative control of appetite and energy homeostasis. PURPOSE: To test the hypothesis that shortterm, high intensity exercise would alter plasma concentrations of ghrelin, leptin, adiponectin, glucose, insulin and cortisol. METHODS: Six Standardbred (STB) mares (9–14 yrs; ∼525 kg) underwent an incremental exercise test (GXT) as well as a parallel control trial where samples were obtained at the same time points while standing quietly for 24 hrs. A crossover design was used with mares assigned to either a control (CON) or exercise trial (EX) during week one and the other treatment 1 wk later. Testing commenced at 1200 each day. Plasma samples (30 mL) were taken before (0 min), during (last 10 s at 4m/s, 8m/s, and the velocity eliciting VO2max), and after exercise (2, 10, 30, 60 min; 12 h and 24 h post-GXT). A secondary set of blood samples were collected before and after an afternoon meal given at 1515 (at 1500, 1514, 1530, and 1545). Data were analyzed using ANOVA for repeated measures and Tukeys. RESULTS: During the GXT, there were no changes (p > 0.05) in the plasma concentrations of glucose, leptin, adiponectin, or ghrelin. However, there were increases (p < 0.05) in plasma cortisol concentration and decreases (p < 0.05) in plasma insulin concentration. Substantial increases (p < 0.05) in the plasma concentrations of glucose and cortisol were seen in the EX trial compared to the CON trial during the first 60 min post-GXT. Interestingly, plasma leptin concentrations, measured 24 hr post-GXT, were significantly lower (p < 0.05) during the EX trial compared to CON. Furthermore, plasma ghrelin concentrations were significantly lower (p < 0.05) in the EX trial compared to CON before and after the afternoon meal, but were higher (p < 0.05) 12 h post-GXT. Finally, there were no differences between EX and CON for plasma concentrations of insulin or adiponectin during recovery. CONCLUSION: It was concluded that short-term high intensity exercise alters plasma leptin and ghrelin concentrations in STB mares post exercise, which may signal the exercised animals to alter energy intake.

CHARACTERISTICS OF BONE DENSITY RESPONDERS AND NON-RESPONDERS TO EXERCISE TRAINING

The purpose of this study was to identify bone density (BMD) responders (R) and non-responders (NR) to exercise training (EX) in postmenopausal women either taking or not taking hormone therapy (HRT) and to determine differences in body composition, hormone levels, muscular strength, and exercise volume between R and NR. This is a secondary analysis of a larger randomized 1 year EX trial that determined the effects of exercise on BMD. BMD and body composition were measured using a Lunar dual-energy x-ray absorptiometer. Supervised EX was performed 3 days per week and included high intensity resistance training and aerobic weight bearing exercise. Osteocalcin (OC) and deoxypyridinoline crosslinks (DPD), markers of bone formation and resorption, respectively, and estrogen levels were measured at baseline, 6 months and 1 year. R and NR were identified from women who lifted > 1 million pounds for 1 year and who gained or lost > 0.025g/cm2 of spine, femoral neck or trochanter BMD over 1 year. For spine, neck and trochanter BMD, 17, 29, and 28 R and 13, 15, and 6 NR, respectively, were identified with 12, 17, and 18 R on HRT and 3, 4, and 3 NR on HRT. The HRT group (n = 70) was 54.3 ± 4.4 years old and 5.3 ± 4.2 years past menopause. The nonHRT group was 55.2 ± 4.8 years old and 6.1 ± 2.9 years past menopause. The following differences were significant at p < 0.05. For HRT users, spine R had higher serum estrogen levels than spine NR. Spine R not on HRT lifted 33742 and 95427 lbs more on the seated row and leg press than spine NR not on HRT. For the neck, R lifted more on the rotary torso (mean difference = 44586 lbs, HRT users) and less on the seated row (mean difference = −23922 lbs, nonHRT users) than NR. For the trochanter, R lifted more than NR on the squat (mean difference = 142116 lbs, HRT users) and the rotary torso (mean difference = 59161 lbs, nonHRT users). No differences existed between R and NR in body composition, bone turnover, or changes in muscular strength. We conclude that in this sample of women, R and NR differed in the loads lifted for specific exercises rather than body composition, strength, or bone turnover markers. Supported by NIH AR39559 and Mission Pharmacal.