Biomedical subjects

Kirk J Cureton

Publications and source records attributed to Kirk J Cureton.

12 recordsLinked to original sources

PubMed2006

Body cooling attenuates the decrease in maximal oxygen uptake associated with cardiovascular drift during heat stress.

Previous research suggests cardiovascular drift (CV drift) is associated with decreased maximal oxygen uptake (VO(2)(max)) during heat stress, but more research manipulating CV drift with subsequent measurement of VO(2)(max) is needed to assess whether this relationship is causal. To assess causation, VO(2)(max) was measured during the same time interval that CV drift occurred (between 15 and 45 min of submaximal exercise under different conditions of body cooling intended to manipulate CV drift). Ten men completed a control graded exercise test (GXT) in 22 degrees C to measure VO(2)(max) then on separate occasions they cycled in 35 degrees C at 60% VO(2)(max) for 15 min (15 max), 45 min with no cooling (NC), and 45 min with fan airflow (FAN) beginning at approximately 18 min into exercise, and each bout was immediately followed by a GXT to measure VO(2)(max) In NC, VO(2)(max) decreased 18%, heart rate (HR) increased 16%, and stroke volume (SV) fell 12% (P < 0.05) from min 15 to min 45. In FAN, VO(2)(max) fell less (5.7%, P < 0.05) , HR rose less (4%, P < 0.05) and SV decreased less (3%, P < 0.05) from 15 to 45 min. The fall in VO(2)(max) associated with CV drift during exercise in a hot environment is attenuated with body cooling via fan airflow. The findings support the notion that a causal link exists between CV drift that occurs during prolonged exercise in a hot environment and a decrease in VO(2)(max).

Adaptation, Physiological↗

PubMed2006

Fluid ingestion attenuates the decline in VO2peak associated with cardiovascular drift.

INTRODUCTION/PURPOSE: This study investigated whether manipulation of cardiovascular drift (CV drift) by changing exercise duration or by fluid ingestion is associated with altered peak oxygen uptake VO(2peak). METHODS: VO(2peak) was measured in 11 trained men immediately after they cycled at 60% control VO(2max) in 30 degrees C, 40% relative humidity for 15, 60, and 120 min with no fluid (15 NF, 60 NF, 120 NF) or 120 min with fluid (120 F). Stroke volume (SV), heart rate (HR), and related measures were measured in 120 NF and 120 F at 15, 60, and 120 min. RESULTS: Body mass decreased 0.7, 2.3, and 3.7% in 120 F, 60 NF, and 120 NF. SV at the end of submaximal exercise and VO(2peak) measured immediately thereafter were reduced significantly (P < 0.05) from 15-min values in 120 NF (13.8 and 8.7%) but not in 60 NF (4.6 and 1.2%) or 120 F (2.1 and 1.9%). CONCLUSIONS: The progressive decline in SV during prolonged, constant-rate submaximal exercise in a warm environment, reflective of increased cardiovascular strain associated with hyperthermia, dehydration, and other changes that occur over time, reduces VO(2peak). Fluid ingestion improves performance in prolonged exercise, in part, by mitigating the decline in SV and its determinants, and preserving VO(2peak).

Adult↗

PubMed2006

Maximal oxygen uptake after attenuation of cardiovascular drift during heat stress.

INTRODUCTION: Exercise intensity is often regulated in hot conditions by maintaining a constant target heart rate (HR) to counteract increased physiological strain and thereby avoid premature fatigue. It is unknown, however, whether the HR-percent maximal oxygen uptake (%VO2max) relationship is maintained during prolonged exercise in the heat when the rise in HR concomitant with cardiovascular drift (CV drift) is eliminated by lowering exercise intensity. The purpose of this study was to determine if VO2max is reduced when exercise intensity and absolute VO2 are lowered by a magnitude sufficient to reduce CV drift and maintain constant HR during prolonged exercise in the heat, and thereby examine if the HR-%VO2max relationship is preserved. METHODS: Seven men cycled at 60% VO2max in 35 degrees C for 15 min (one trial) and 45 min (two trials) while HR rose over time (HRvar) or remained constant (HRcon). VO2max was measured immediately after the 15 and 45 min trials to correspond with the same time interval in which CV drift occurred. RESULTS: Power output decreased 37%, VO2 decreased 24%, and VO2max decreased 7.5% from 15 to 45 min in HRcon, while HR remained the same. In HRvar, HR increased 13%, SV decreased 10%, and VO2max decreased 15%. DISCUSSION: %VO2max was decreased from approximately 60% to 50% to hold HR constant in these conditions, so the HR-%VO2max relationship was not preserved in the absence of CV drift. Attenuating CV drift by lowering exercise intensity only partially eliminated the reduction in VO2max after prolonged exercise in the heat.

Acclimatization↗

PubMed2005

Cardiovascular drift is related to reduced maximal oxygen uptake during heat stress.

INTRODUCTION/PURPOSE: This study investigated whether the progressive rise in heart rate (HR) and fall in stroke volume (SV) during prolonged, constant-rate, moderate-intensity exercise (cardiovascular drift, CVdrift) in a hot environment is associated with a reduction in VO(2max). METHODS: CVdrift was measured in nine male cyclists between 15 and 45 min of cycling at 60% VO(2max) in 35 degrees C that was immediately followed by measurement of VO(2max). VO(2max) also was measured after 15 min of cycling on a separate day, so that any change in VO(2max) between 15 and 45 min could be associated with the CVdrift that occurred during that time interval. This protocol was performed under one condition in which fluid was ingested and there was no significant body weight change (0.3 +/- 0.4%), and under another in which no fluid was ingested and dehydration occurred (2.5 +/- 1%, P < 0.05). RESULTS: Fluid ingestion did not affect CVdrift or change in VO(2max). A 12% increase in HR (151 +/- 9 vs 169 +/- 10 bpm, P < 0.05) and 16% decrease in SV (120 +/- 12 vs 101 +/- 10 mL.beat(-1), P < 0.05) between 15 and 45 min was accompanied by a 19% decrease in VO(2max) (4.4 +/- 0.6 vs 3.6 +/- 0.4 L.min(-1), P < 0.05) despite attainment of a higher maximal HR (P < 0.05) at 45 min (194 +/- 5 bpm) vs 15 min (191 +/- 5 bpm). Submaximal VO(2) increased only slightly over time, but VO(2max) increased from 63 +/- 5% at 15 min to 78 +/- 8% at 45 min (P < 0.05). CONCLUSION: We conclude CVdrift during 45 min of exercise in the heat is associated with decreased VO(2max) and increased relative metabolic intensity. The results support the validity of using changes in HR to reflect changes in relative metabolic intensity during prolonged exercise in a hot environment in which CVdrift occurs.

Adult↗

PubMed2004

Hyperthermia and maximal oxygen uptake in men and women.

To compare the effect of hyperthermia on maximal oxygen uptake (VO2max) in men and women, VO2max was measured in 11 male and 11 female runners under seven conditions involving various ambient temperatures (Ta at 50% RH) and preheating designed to manipulate the esophageal (Tes) and mean skin (Tsk) temperatures at VO2max. The conditions were: 25 degrees C, no preheating (control); 25, 35, 40, and 45 degrees C, with exercise-induced preheating by a 20-min walk at approximately 33% of control VO2max; 45 degrees C, no preheating; and 45 degrees C, with passive preheating during which Tes and Tsk were increased to the same degree as at the end of the 20-min walk at 45 degrees C. Compared to VO2max (l x min(-1)) in the control condition (4.52+/-0.46 in men, 3.01+/-0.45 in women), VO2max in men and women was reduced with exercise-induced or passive preheating and increased Ta, approximately 4% at 35 degrees C, approximately 9% at 40 degrees C and approximately 18% at 45 degrees C. Percentage reductions (7-36%) in physical performance (treadmill test time to exhaustion) were strongly related to reductions in VO2max (r=0.82-0.84). The effects of hyperthermia on VO2max and physical performance in men and women were almost identical. We conclude that men and women do not differ in their thermal responses to maximal exercise, or in the relationship of hyperthermia to reductions in VO2max and physical performance at high temperature. Data are reported as mean (SD) unless otherwise stated.

Adult↗

PubMed2004

Effect of race and musculoskeletal development on the accuracy of air plethysmography.

PURPOSE: The purpose of this study was to determine the effect of race and musculoskeletal development on the accuracy of estimates of body fatness (%fat) via air displacement plethysmography (AP). METHODS: Estimates of %fat were made via AP, hydrostatic weighing (HW), dual-energy x-ray absorptiometry (DXA), and the criterion, a four-component model (4C) in 64 black (B) and white (W) men, who were either resistance trained (RT) or served as controls (C). RESULTS: Based on a three-way ANOVA, there were no statistically significant three-way or race x musculoskeletal development interactions. There was no main effect of race on the validity of estimating %fat by AP; the mean bias between %FatAP and %Fat4C was similar for B (3.6% body fat) and W (3.7%). In addition, the density of the fat-free mass (Dffm) for B (1.098 +/- 0.002 g x mL) was not different than 1.10 g x mL. There was a significant effect of musculoskeletal development on the validity of the estimation of %fat from AP; the mean difference in %fat between %FatAP and %Fat4C was less in RT (1.5% body fat) than in C (5.3%), but a large SEE of 5.5% was observed for RT. A significant (P < 0.05) correlation was found between the mean bias between methods and body volume (-0.44) and mesomorphy (-0.55). CONCLUSIONS: Race does not affect the accuracy of estimating %fat by AP. Race-specific equations estimating %fat via densitometry (e.g., AP, HW) such as the Schutte are not justified, because Dffm is not greater than 1.10 g x mL. Estimation of %fat via AP is more accurate in larger individuals with high musculoskeletal development as a group, but individual results are highly variable.

Absorptiometry, Photon↗

PubMed2003

Cooling vest worn during active warm-up improves 5-km run performance in the heat.

We investigated whether a cooling vest worn during an active warm-up enhances 5-km run time in the heat. Seventeen competitive runners (9 men, maximal oxygen uptake = 66.7 +/- 5.9 ml x kg(-1) x min(-1); 8 women, maximal oxygen uptake = 58.0 +/- 3.2 ml x kg(-1) x min(-1)) completed two simulated 5-km runs on a treadmill after a 38-min active warm-up during which they wore either a T-shirt (C) or a vest filled with ice (V) in a hot, humid environment (32 degrees C, 50% relative humidity). Wearing the cooling vest during warm-up significantly (P < 0.05) blunted increases in body temperature, heart rate (HR), and perception of thermal discomfort during warm-up compared with control. At the start of the 5-km run, esophageal, rectal, mean skin, and mean body temperatures averaged 0.3, 0.2, 1.8, and 0.4 degrees C lower; HR averaged 11 beats/min lower; and perception of thermal discomfort (5-point scale) averaged 0.6 point lower in V than C. Most of these differences were eliminated during the first 3.2 km of the run, and these variables were not different at the end. The 5-km run time was significantly lower (P < 0.05) by 13 s in V than C, with a faster pace most evident during the last two-thirds of the run. We conclude that a cooling vest worn during active warm-up by track athletes enhances 5-km run performance in the heat. Reduced thermal and cardiovascular strain and perception of thermal discomfort in the early portion of the run appear to permit a faster pace later in the run.

Body Temperature↗

PubMed2003

Assessment of skeletal muscle mass in men with spinal cord injury using dual-energy X-ray absorptiometry and magnetic resonance imaging.

The purpose of this study was to determine whether the proportion of skeletal muscle in the fat-free soft tissue mass (FFST) is the same in men with spinal cord injury (SCI) and able-bodied controls. Skeletal muscle mass and FFST of the midthigh were determined by using magnetic resonance imaging and dual-energy X-ray absorptiometry, respectively, in men with long-term (>2 yr) complete SCI (n = 8) and able-bodied controls of similar age, height, and weight (n = 8). Muscle mass (1.36 +/- 0.77 vs. 2.44 +/- 0.47 kg) and FFST (1.70 +/- 0.94 vs. 2.73 +/- 0.80 kg) were lower in the SCI group than in the controls (P < 0.05), but the lower ratio of muscle to FFST in the SCI group (0.80 +/- 0.09 vs. 0.91 +/- 0.10, P < 0.05) suggested that they had a lower proportion of muscle in the FFST than in controls. This notion was supported by analysis of covariance, in that the mean muscle adjusted to the mean FFST of the groups combined was lower in the SCI group. Despite the lower proportion of muscle in the FFST of the SCI group, the relation between muscle and FFST was strong in the SCI group (r = 0.99) and controls (r = 0.96). The findings suggest a disproportionate loss of muscle in the paralyzed thighs after SCI relative to other nonfat constituents, which may be accurately estimated in men with long-term SCI by dual-energy X-ray absorptiometry if the lower proportion of muscle in the FFST (approximately 15%) is taken into account.

Absorptiometry, Photon↗

PubMed2003

Effects of prior exercise on postprandial lipemia: a quantitative review.

The purpose of this report is to synthesize the results from studies examining the effect of exercise on postprandial lipemia to summarize the existing data and provide direction for future research. A quantitative review of the literature was performed using meta-analytic methods to quantify the effect sizes. Moderator analyses were performed to examine features of the studies that could potentially influence the effect of exercise on postprandial lipemia. Thirty-eight effects from 555 people were retrieved from 29 studies. The mean weighted effect was moderate as indicated by Cohen's d (d = -0.57; 95% confidence interval [CI], -0.71 to -0.43), indicating that people who perform exercise before meal ingestion exhibit a 0.5 standard deviation reduction in the postprandial triglyceride (TG) response relative to persons in comparison groups. There was no significant effect of study design, gender, age, type of meal ingested, exercise intensity, exercise duration, or timing of exercise on the postprandial response (P >.05). There was, however, significant variation in the effect sizes, for women for exercise performed within 24 hours of meal ingestion, and for exercise performed more than 24 hours before meal ingestion (P <.01). For studies that reported the energy expenditure of exercise, there was a significant relationship between effect size and energy expenditure (r = -.62, P =.02). Results from this quantitative review of the literature suggest that exercise has a moderate effect on the postprandial lipemic response and that the energy expenditure of prior exercise may play a role in the magnitude of this effect. Other factors that may affect the response remain to be clarified.

Aging↗

PubMed2003

Endurance training reduces end-exercise VO2 and muscle use during submaximal cycling.

INTRODUCTION: End-exercise VO2 during heavy, constant-load exercise is reduced after endurance training, due to an attenuated VO2 slow component. PURPOSE/METHODS: To determine whether the training-induced reduction in end-exercise VO2 was associated with reduced muscle use, we measured VO2 and T2 changes in magnetic resonance images in the final minute of two 15-min constant-load cycle rides, one above lactate threshold and the other below lactate threshold. These measures were repeated after a 4-wk period in eight subjects who trained on a cycle ergometer and seven controls. RESULTS: There were no changes in end-exercise VO2 or active muscle after training in either group during low-intensity cycling, in which no VO2 slow component was present. During high-intensity cycling, in which there was a slow component before training, the training group experienced a significant reduction (P < 0.05) in end-exercise VO2 (2625 +/- 673; 2567 +/- 605 mL.min (-1) and the T2 of the vastus lateralis (35.6 +/- 1.4; 34.5 +/- 0.9 ms). CONCLUSION: These results support the hypothesis that reduction in end-exercise VO2 (and the VO2 slow component) after training is due to reduced muscle use during heavy, constant load cycling.

Adult↗

PubMed2002

Effect of resistance exercise on postprandial lipemia.

The purpose of this study was to examine the effect of resistance exercise on postprandial lipemia. Fourteen young men and women participated in each of three treatments: 1) control (Con), 2) resistance exercise (RE), and 3) aerobic exercise (AE) estimated to have an energy expenditure (EE) equal that for RE. Each trial consisted of performing a treatment on day 1 and ingesting a fat-tolerance test meal 16 h later (day 2). Resting metabolic rate and fat oxidation were measured at baseline and at 3 and 6 h postprandial on day 2. Blood was collected at baseline and at 0.5, 1, 2, 3, 4, 5, and 6 h after meal ingestion. RE and AE were similar in EE [1.7 +/- 0.1 vs. 1.6 +/- 0.1 (SE) MJ, respectively], as measured by using the Cosmed K4b(2). Baseline triglycerides (TG) were significantly lower after RE than after Con (19%) and AE (21%). Furthermore, the area under the postprandial response curve for TG, adjusted for baseline differences, was significantly lower after RE than after Con (14%) and AE (18%). Resting fat oxidation was significantly greater after RE than after Con (21%) and AE (28%). These results indicate that resistance exercise lowers baseline and postprandial TG, and increases resting fat oxidation, 16 h after exercise.

Adult↗

PubMed2002

Relation of heart rate to percent VO2 peak during submaximal exercise in the heat.

We tested the hypothesis that elevation in heart rate (HR) during submaximal exercise in the heat is related, in part, to increased percentage of maximal O(2) uptake (%Vo(2 max)) utilized due to reduced maximal O(2) uptake (Vo(2 max)) measured after exercise under the same thermal conditions. Peak O(2) uptake (Vo(2 peak)), O(2) uptake, and HR during submaximal exercise were measured in 22 male and female runners under four environmental conditions designed to manipulate HR during submaximal exercise and Vo(2 peak). The conditions involved walking for 20 min at approximately 33% of control Vo(2 max) in 25, 35, 40, and 45 degrees C followed immediately by measurement of Vo(2 peak) in the same thermal environment. Vo(2 peak) decreased progressively (3.77 +/- 0.19, 3.61 +/- 0.18, 3.44 +/- 0.17, and 3.13 +/- 0.16 l/min) and HR at the end of the submaximal exercise increased progressively (107 +/- 2, 112 +/- 2, 120 +/- 2, and 137 +/- 2 beats/min) with increasing ambient temperature (T(a)). HR and %Vo(2 peak) increased in an identical fashion with increasing T(a). We conclude that elevation in HR during submaximal exercise in the heat is related, in part, to the increase in %Vo(2 peak) utilized, which is caused by reduced Vo(2 peak) measured during exercise in the heat. At high T(a), the dissociation of HR from %Vo(2 peak) measured after sustained submaximal exercise is less than if Vo(2 max) is assumed to be unchanged during exercise in the heat.

Adult↗