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1.
Plasma norepinephrine and heart rate dynamics during recovery from submaximal exercise in man 总被引:2,自引:0,他引:2
Renza Perini Claudio Orizio Alessandro Comandè Maurizio Castellano Marina Beschi Arsenio Veicsteinas 《European journal of applied physiology》1989,58(8):879-883
Summary The time course of heart rate (HR) and venous blood norepinephrine concentration [NE], as an expression of the sympathetic
nervous activity (SNA), was studied in six sedentary young men during recovery from three periods of cycle ergometer exercise
at 21%±2.8%, 43%±2.1% and 65%±2.3% of
respectively (mean±SE). The HR decreased mono-exponentially withτ values of 13.6±1.6 s, 32.7±5.6 s and 55.8±8.1s respectively in the three periods of exercise. At the low exercise level no
change in [NE] was found. At medium and high exercise intensity: (a) [NE] increased significantly at the 5th min of exercise
(Δ[NE]=207.7±22.5 pg·ml−1 and 521.3±58.3 pg·ml−1 respectively); (b) after a time lag of 1 min [NE] decreased exponentially (τ=87 s and 101 s respectively); (c) in the 1st min HR decreased about 35 beats · min−1; (d) from the 2nd to 5th min of recovery HR and [NE] were linearly related (100 pg·ml−1
Δ[NE]5 beats ·min−1). In the 1st min of recovery, independent of the exercise intensity, the adjustment of HR appears to have been due mainly
to the prompt restoration of vagal tone. The further decrease in HR toward the resting value could then be attributed to the
return of SNA to the pre-exercise level. 相似文献
2.
Carole A. Williams J. G. Mudd Alexander R. Lind 《European journal of applied physiology》1985,54(2):156-162
Summary Experiments were performed to assess the possible neurally mediated constriction in active skeletal muscle during isometric
hand-grip contractions. Forearm blood flow was measured by venous occlusion plethysmography on 5 volunteers who exerted a
series of repeated contractions of 4 s duration every 12 s at 60% of their maximum strength of fatigue. The blood flows increased
initially, but then remained constant at 20–24 ml·min−1·100 ml−1 throughout the exercise even though mean arterial blood pressure reached 21–23 kPa (160–170 mm Hg). When the same exercise
was performed after arterial infusion of phentolamine, forearm blood flow increased steadily to near maximal levels of 38.7±1.4
ml·min−1·100 ml−1.
Venous catecholamines, principally norepinephrine, increased throughout exercise, reaching peak values of 983±258 pg·ml−1 at fatigue. Of the vasoactive substances measured, the concentration of K+ and osmolarity in venous plasma also increased initially and reached a steady-state during the exercise but ATP increased
steadily throughout the exercise. These data indicate a continually increasing α-adrenergic constriction to the vascular beds
in active muscles in the human forearm during isometric exercise, that is only partially counteracted by vasoactive metabolites. 相似文献
3.
The purpose of the present study was to examine comprehensively the kinetics of oxygen uptake (
) during treadmill running across the moderate, heavy and severe exercise intensity domains. Nine subjects [mean (SD age,
27 (7) years; mass, 69.8 (9.0) kg; maximum
,
, 4,137 (697) ml·min–1] performed a series of "square-wave" rest-to-exercise transitions of 6 min duration at running speeds equivalent to 80% and
100% of the
at lactate threshold (LT; moderate exercise); and at 20%, 40%, 60%, 80% and 100% of the difference between the
at LT and
(Δ, heavy and severe exercise). Critical velocity (CV) was also determined using four maximal treadmill runs designed to result
in exhaustion in 2–15 min. The
response was modelled using non-linear regression techniques. As expected, the amplitude of the
primary component increased with exercise intensity [from 1,868 (136) ml·min–1 at 80% LT to 3,296 (218) ml·min–1 at 100% Δ, P<0.05]. However, there was a non-significant trend for the "gain" of the primary component to decrease as exercise intensity
increased [181 (7) ml·kg–1·km–1 at 80% LT to 160 (6) ml·kg–1·km–1 at 100% Δ]. The time constant of the primary component was not different between supra-LT running speeds (mean value range
= 17.9–19.1 s), but was significantly shorter during the 80% LT trial [12.7 (1.4) s, P<0.05]. The
slow component increased with exercise intensity from 139 (39) ml·min–1 at 20% Δ to 487 (57) ml·min–1 at 80% Δ (P<0.05), but decreased to 317 (84) ml·min–1 during the 100% Δ trial (P<0.05). During both the 80% Δ and 100% Δ trials, the
at the end of exercise reached
[4,152 (242) ml·min–1 and 4,154 (114) ml·min–1, respectively]. Our results suggest that the "gain" of the primary component is not constant as exercise intensity increases
across the moderate, heavy and severe domains of treadmill running. These intensity-dependent changes in the amplitudes and
kinetics of the
response profiles may be associated with the changing patterns of muscle fibre recruitment that occur as exercise intensity
increases.
Electronic Publication 相似文献
4.
Theodore J. Angelopoulos Bart G. Denys Cathy Weikart Sergio G. Dasilva Timothy J. Michael Robert J. Robertson 《European journal of applied physiology》1995,70(3):195-199
To determine the effect of endogenous opioids on catecholamine response during intense exercise [80% maximal oxygen uptake (
O2max)], nine fit men [mean (SE) (
O2max, 63.9 (1.7) ml · kg–1 · min–1; age 27.6 (1.6) years] were studied during two treadmill exercise trials. A double-blind experimental design was used with subjects undertaking the two exercise trials in counterbalanced order. Exercise trials were 20 min in duration and were conducted 7 days apart. One exercise trial was undertaken following administration of naloxone (N; 1.2 mmol · l–1; 3 ml) and the other after receiving a placebo (P; 0.9% saline; 3 ml). Prior to each experimental trial a flexible catheter was placed into an antecubital vein and baseline blood samples were collected. Immediately afterwards, each subject received bolus injection of either N or P. Blood samples were also collected after 20 min of continuous exercise while running. Epinephrine and norepinephrine were higher (P < 0.05) in the N than P exercise trial with mean (SE) values of 1679 (196) versus 1196 (155) pmol · l–1 and 24 (2.2) versus 20 (1.7) nmol · · l–1 respectively. Glucose and lactate were higher (P < 0.05) in the N than P exercise trial with values of 7 (0.37) versus 5.9 (0.31) mmol · l–1 and 6.9 (1.1) versus 5.3 (0.9) mmol · l–1 respectively. These data suggest an opioid inhibition in the release of catecholamines during intense exercise. 相似文献
5.
S. V. Gein K. G. Gorshkova S. P. Tendryakova 《Neuroscience and behavioral physiology》2009,39(6):591-595
The studies reported here showed that β-endorphin at concentrations of 10−7–10−11 M increased interleukin-1β (IL-1β) production in unfractionated leukocyte suspensions both in the presence of 0.1 μg/ml lipopolysaccharide
(LPS) and in cultures not stimulated with LPS. Interleukin-8 (IL-8) production by leukocytes was inhibited by β-endorphin
at concentrations of 10−7 and 10−11 M in the presence of LPS. The stimulatory effect of β-endorphin on IL-1β production was not blocked by naloxone or naltrindole.
Suppression of IL-8 production was blocked by naloxone and naltrindole. In the mononuclear cell and neutrophil fractions,
β-endorphin and the δ agonist DADLE increased IL-1β synthesis in both the spontaneous and stimulated versions of the test,
while β-endorphin and the δ agonist DADLE inhibited IL-8 production in the mononuclear cell and neutrophil fractions only
in LPS-stimulated cultures. The μ agonist DAGO had no effect on IL-1β production by mononuclear cells or neutrophils, though
it suppressed LPS-induced secretion of IL-8 by neutrophils.
Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 94, No. 7, pp. 814–821, July, 2008. 相似文献
6.
Takeshi Harada Takeshi Yamauchi Atsuko Tsukanaka Yoshinori Matsumura Masashi Kurono Akiko Honda Nobuo Matsui 《European journal of applied physiology》2000,83(4-5):268-273
The purpose of this study was to examine the role of muscarinic cholinergic and α2-adrenergic mechanisms in growth hormone (GH) secretion during exercise in humans. The GH responses induced during moderate-intensity
exercise (using a cycle ergometer at 60% maximal oxygen uptake, V˙O2max, for 30 min) without treatment (control) and after the administration of a muscarinic cholinergic antagonist (atropine 1 mg)
or after an α2-adrenergic antagonist (yohimbine 15 mg) were compared in seven healthy men. Although, serum GH concentration had increased
significantly after exercise in the control experiment [mean peak GH concentration 52.64 (SEM 18.60) ng · ml−1], the increase was suppressed by the administration of either atropine [mean peak GH concentration 8.64 (SEM 7.47) ng ·
ml−1] or yohimbine [mean peak GH concentration 17.50 (SEM 7.89) ng · ml−1]. The area under the curve of serum GH concentration against time was significantly lower in the experiment using these drugs
[with atropine, mean area 458 (SEM 409) ng · ml−1 · min], with yohimbine mean area 946 (SEM 435) ng · ml−1 · min] than in the control experiment [mean area 3135 (SEM 1098) ng · ml−1 · min]. These results suggest that muscarinic cholinergic and α2-adrenergic mechanisms are involved in GH secretion during exercise in humans.
Accepted: 9 March 2000 相似文献
7.
This study investigated the possible influence of oral caffeine administration on endogenous glucose production and energy
substrate metabolism during prolonged endurance exercise. Twelve trained endurance athletes [seven male, five female; peak
oxygen consumption (
) = 65.5 ml·kg–1·min–1] performed 60 min of cycle ergometry at 65%
twice, once after oral caffeine administration (6 mg·kg–1) (CAF) and once following consumption of a placebo (PLA). CAF and PLA were administered in a randomized double-blind manner
75 min prior to exercise. Plasma glucose kinetics were determined with a primed-continuous infusion of [6,6-2H]glucose. No differences in oxygen consumption (
), and carbon dioxide production (
) were observed between CAF and PLA, at rest or during exercise. Blood glucose concentrations were similar between the two
conditions at rest and also during exercise. Exercise did lead to an increase in serum free fatty acid (FFA) concentrations
for both conditions; however, no differences were observed between CAF and PLA. Both the plasma glucose rate of appearance
(
) and disappearance (
) increased at the onset of exercise (P<0.05), but were not affected by CAF, as compared to PLA. CAF did lead to a higher plasma lactate concentration during exercise
(P<0.05). It was concluded that an acute oral dose of caffeine does not influence plasma glucose kinetics or energy substrate
oxidation during prolonged exercise in trained endurance athletes. However, CAF did lead to elevated plasma lactate concentrations.
The exact mechanism of the increase in plasma lactate concentrations remains to be determined.
Electronic Publication 相似文献
8.
Mobilization and oxidative burst of neutrophils are influenced by carbohydrate supplementation during prolonged cycling in humans 总被引:1,自引:0,他引:1
Scharhag J Meyer T Gabriel HH Auracher M Kindermann W 《European journal of applied physiology》2002,87(6):584-587
Prolonged, strenuous exercise may lead to suppressive effects on the immune system, which might be responsible for a greater
susceptibility to opportunistic infections. The aim of this study was to examine the influence of carbohydrate substitution
(CHS) during prolonged, strenuous exercise on neutrophil granulocytes and their oxidative burst (intracellular oxidation of
dihydrorhodamine123 to rhodamine123 after induction by formylized 1-methionyl-1-leucyl-1-phenylalanin) using flow cytometry. In three trials different concentrations
of CHS (placebo compared to 6% and 12% CHS; 50 ml·kg–1) were given randomly to 14 endurance trained cyclists [mean (SD) age 25 (5) years, maximal oxygen uptake 67 (6) ml·min–1·kg–1] cycling for 4 h in a steady state at 70% of their individual anaerobic threshold. Blood samples were taken before, immediately
after cessation, 1 h and 19 h after exercise. A significant rise in neutrophil counts was observed immediately after cessation
and 1 h after exercise with a return to normal rest values 19 h after exercise for all three conditions (P<0.001). The relative proportions of rhodamine123+ neutrophils were significantly diminished in all three conditions 1 h after exercise (P<0.01), while the mean fluorescence intensity was lowest in the placebo trial and differed significantly to the 12% CHS trial
(P=0.024) and almost significantly to the 6% CHS trial (P=0.052). In conclusion, these data suggest a beneficial effect of CHS on the neutrophil oxidative burst and a possible attenuation
of the susceptibility to infections, presumably due to the reduction of metabolic stress in prolonged, strenuous exercise.
Electronic Publication 相似文献
9.
Effects of high-altitude exposure on vascular endothelial growth factor levels in man 总被引:3,自引:0,他引:3
Walter R Maggiorini M Scherrer U Contesse J Reinhart WH 《European journal of applied physiology》2001,85(1-2):113-117
Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen and permeability factor that is inducible by hypoxia.
Its contribution to high-altitude illness in man is unknown. We measured VEGF levels in 14 mountaineers at low altitude (490 m)
and 24 h after their arrival at high altitude (4,559 m). At high altitude, VEGF increased from [mean (SEM)] 32.5 (9.2) to
60.9 (18.5) pg·ml–1 (P<0.004) in the arterial blood, and from 15.9 (2.9) to 49.3 (15.9) pg·ml–1 (P=0.0001) in the mixed venous blood. Whereas at low altitude venous and arterial VEGF levels were not statistically different
from each other (P=0.065), the VEGF concentration was significantly lower in venous than in arterial blood samples at high altitude (P=0.004). The pulmonary capillary VEGF concentration remained unchanged at high altitude [14.8 (2.5) vs 17.1 (5.4) pg·ml–1, P=0.85]. VEGF levels in the nine mountaineers who developed symptoms of acute mountain sickness (AMS), and in the six subjects
who had radiographic evidence of high-altitude pulmonary edema were similar to those in subjects without symptoms. VEGF was
not correlated with either AMS scores, mean pulmonary arterial pressures, arterial partial pressure of O2, or alveolar-arterial O2 gradients. We conclude that VEGF release is stimulated at high altitude, but that VEGF is probably not related to high-altitude
illness.
Electronic Publication 相似文献
10.
Theodore J. Angelopoulos Robert J. Robertson F. L. Goss Allan Utter 《European journal of applied physiology》1997,75(2):132-135
Eight fit men [maximum oxygen consumption ( O2max) 64.6 (1.9) ml?·?kg?1?·?min?1, aged 28.3 (1.7) years (SE in parentheses) were studied during two treadmill exercise trials to determine the effect of endogenous opioids on insulin and glucagon immunoreactivity during intense exercise (80% O2max). A double-blind experimental design was used with subjects undertaking the two exercise trials in counterbalanced order. Exercise trials were 20 min in duration and were conducted 7 days apart. One exercise trial was undertaken following administration of naloxone (N; 1.2 mg; 3?ml) and the other after receiving a placebo (P; 0.9% NaCl saline; 3?ml). Prior to each experimental trial a flexible catheter was placed into an antecubital vein and baseline blood samples were collected. Immediately after, each subject received either a N or P bolus injection. Blood samples were also collected after 20?min of continuous exercise (running). Glucagon was higher (P?0.05), while insulin was lower (P?0.05), during exercise compared with pre-exercise values in both trials. However, glucagon was higher (P?0.05) in the P than in the N exercise trial [141.4 (8.3) ng?·?l?1 vs 127.2 (7.6) ng?·?l?1]. There were no differences in insulin during exercise between the P and N trials [50.2 (4.3) pmol?·?l?1 vs 43.8 (5) pmol?·?l?1]. These data suggest that endogenous opioids may augment the glucagon response during intense exercise. 相似文献
11.
Plasma vasopressin,renin activity,and aldosterone responses to maximal exercise in active college females 总被引:1,自引:0,他引:1
Summary The effect of maximal treadmill exercise on plasma concentrations of vasopressin (AVP); renin activity (PRA); and aldosterone
(ALDO) was studied in nine female college basketball players before and after a 5-month basketball season. Pre-season plasma
AVP increased (p<0.05) from a pre-exercise concentration of 3.8±0.5 to 15.8±4.8 pg · ml−1 following exercise. Post-season, the pre-exercise plasma AVP level averaged 1.5±0.5 pg · ml−1 and increased to 16.7±5.9 pg · ml−1 after the exercise test. PRA increased (p<0.05) from a pre-exercise value of 1.6±0.6 to 6.8±1.7 ngAI · ml−1 · hr−1 5 min after the end of exercise during the pre-season test. In the post-season, the pre-exercise PRA was comparable (2.4±0.6
ngAI · ml−1 · hr−1), as was the elevation found after maximal exercise (8.3±1.9 ngAI · ml−1 · hr−1). Pre-season plasma ALDO increased (p<0.05) from 102.9±30.8 pg · ml−1 in the pre-exercise period to 453.8±54.8 pg · ml−1 after the exercise test. In the post-season the values were 108.9±19.4 and 365.9±64.4 pg · ml−1, respectively. Thus, maximal exercise in females produced significant increases in plasma AVP, renin activity, and ALDO that
are comparable to those reported previously for male subjects. Moreover, this response is remarkably reproducible as demonstrated
by the results of the two tests performed 5 months apart. 相似文献
12.
Comparison of the effects of pre-exercise feeding of glucose,glycerol and placebo on endurance and fuel homeostasis in man 总被引:1,自引:0,他引:1
Summary Six men were studied during exercise to exhaustion on a cycle ergometer at 73% of
following ingestion of glycerol, glucose or placebo. Five of the subjects exercised for longer on the glucose trial compared to the placebo trial (p<0.1; 108.8 vs 95.9 min). Exercise time to exhaustion on the glucose trial was longer (p<0.01) than on the glycerol trial (86.0 min). No difference in performance was found between the glycerol and placebo trials. The ingestion of glucose (lg · kg–1 body weight) 45 min before exercise produced a 50% rise in blood glucose and a 3-fold rise in plasma insulin at zero min of exercise. Total carbohydrate oxidation was increased by 26% compared to placebo and none of the subjects exhibited a fall in blood glucose below 4 mmol · l–1 during the exercise. The ingestion of glycerol (lg · kg–1 body weight) 45 min before exercise produced a 340-fold increase in blood glycerol concentration at zero min of exercise, but did not affect resting blood glucose or plasma insulin levels; blood glucose levels were up to 14% higher (p<0.05) in the later stages of exercise and at exhaustion compared to the placebo or glucose trials. Both glycerol and glucose feedings lowered the magnitude of the rise in plasma FFA during exercise compared to placebo. Levels of blood lactate and alanine during exercise were not different on the 3 dietary treatments. These data contrast with previous reports that have indicated glucose feeding pre-exercise produces hypoglycaemia during strenuous submaximal exercise and reduces endurance performance. It appears that man cannot use glycerol as a gluconeogenic substrate rapidly enough to serve as a major energy source during this type of exercise. 相似文献
13.
M. A. Oleshansky J. M. Zoltick R. H. Herman E. H. Mougey J. L. Meyerhoff 《European journal of applied physiology》1990,59(6):405-410
Summary Neuroendocrine and sympathoadrenal responses to exhaustive graded treadmill exercise were examined in 17 male subjects of
varying degrees of fitness. The mean duration of exercise to exhaustion was 15.2±0.7 (±SE) min. Exercise duration was inversely
correlated with baseline heart rate (P<0.05). Compared to standing baseline values, mean plasma norepinephrine and epinephrine levels increased 339% and 301%, respectively,
in an integrated 2-min blood sample collected immediately after completion of exercise. Mean adrenocorticotrophic hormone
(ACTH),β-endorphin (β-EP),β-lipotropin (β-LPH), and prolactin levels increased 282%, 720%, 372%, and 211%, respectively, in an integrated 4-min blood sample beginning
2 min after completion of exercise. Cortisol levels increased 183% in the sample collected 17–21 min after exercise. The magnitude
of these neuroendocrine responses to exercise was similar among individuals at the same relative intensity of exhaustive exercise,
regardless of the duration of exercise. The exercise-induced increases of the pro-opiomelanocortin (POMC)-derived peptides,
ACTH,β-EP, andβ-LPH, were highly correlated with each other (P values <0.001), and were correlated with prolactin increases, (P values <0.05). During a 20-min recovery period after exercise, changes in heart rate, ACTH, andβ-LPH levels were correlated with duration of exercise, (P<0.01,P<0.03, andP<0.03, respectively). Assuming that the duration of exercise reflects fitness, these data suggest that the pattern of POMC-derived
peptide responses during recovery from exhaustive exercise is dependent on fitness.
The views of the author(s) do not purport to reflect the position of the Department of the Army or the Department of Defense,
(para 4-3, AR 360-5). Human subjects participated in these studies after giving their free and informed consent. Investigators
adhered to AR 70-25 相似文献
14.
Bernard Geny Jocelyn Saini Bertrand Mettauer Eliane Lampert François Piquard Marguerite Follenius Eric Epailly Blandine Schnedecker Bernard Eisenmann Pascal Haberey Jean Lonsdorfer 《European journal of applied physiology》1996,73(3-4):259-266
Exercise tolerance of heart transplant patients is often limited. Central and peripheral factors have been proposed to explain
such exercise limitation but, to date, the leading factors remain to be determined. We examined how a short-term endurance
exercise training programme may improve exercise capacity after heart transplantation, and whether atrial natriuretic peptide
(ANP) release may contribute to the beneficial effects of exercise training by minimizing ischaemia and/or cardiac and circulatory
congestion through its vasodilatation and haemoconcentration properties. Seven heart transplant recipients performed a square-wave
endurance exercise test before and after 6 weeks of supervised training, while monitoring haemodynamic parameters, ANP and
catecholamine concentrations. After training, the maximal tolerated power and the total mechanical work load increased from
130.4 (SEM 6.5) to 150.0 (SEM 6.0) W (P < 0.05) and from 2.05 (SEM 0.1) to 3.58 (SEM 0.14) kJ · kg−1 (P < 0.001). Resting heart rate decreased from 100.0 (SEM 3.4) to 92.4 (SEM 3.5) beats · min−1 (P < 0.05) but resting and exercise induced increases in cardiac output, stroke volume, right atrial, pulmonary capillary wedge,
systemic and pulmonary artery pressures were not significantly changed by training. Exercise-induced decrease of systemic
vascular resistance was similar before and after training. After training arterio-venous differences in oxygen content were
similar but maximal lactate concentrations decreased from 6.20 (SEM 0.55) to 4.88 (SEM 0.6) mmol · 1−1 (P < 0.05) during exercise. Similarly, maximal exercise noradrenaline concentration tended to decrease from 2060 (SEM 327) to
1168 (SEM 227) pg · ml−1. A significant correlation was observed between lactate and catecholamines concentrations. The ANP concentration at rest
and the exercise-induced ANP concentration did not change throughout the experiment [104.8 (SEM 13.1) pg · ml−1 vs 116.0 (SEM 13.5) pg · ml−1 and 200.0 (SEM 23.0) pg · ml−1 vs 206.5 (SEM 25.9) pg · ml−1 respectively]. The results of this study suggested that the significant improvement in exercise capacity observed after this
short-term endurance training period may have arisen mainly through peripheral mechanisms, associated with the possible decrease
in plasma catecholamine concentrations and reversal of muscle deconditioning and/or prednisone-induced myopathy. 相似文献
15.
Merati G Negrini S Sarchi P Mauro F Veicsteinas A 《European journal of applied physiology》2001,85(1-2):41-48
The use of a school backpack is one of the possible causes of back pain in children. Oxygen consumption (
), pulmonary ventilation, and heart rate (f
c) were measured in 35 pre-pubertal subjects [17 girls and 18 boys, mean (SD) age 11.3 (0.6) years]. They took part in a four-step
experiment: (1) standing for 5 min, (2) walking at 3 km·h–1 for 7 min, (3) walking at 3 km·h–1 for 7 min carrying a school backpack weighing 8 kg, and (4) walking at 7 km·h–1 for 5 min with no load. The occurrence of back pain in the last 2–3 years and during the last 15 days was assessed for the
subjects by means of a questionnaire. Mean (SD) standing
was 215 (45) ml.min–1 during walking at 3 km·h–1, 503 (101) ml.min–1 during walking without a load, and increased to 541 (98) ml.min–1 during walking with a load (P<0.01). Carrying a backpack increased f
c only minimally. The energy cost of walking at 3 km.h–1 without the backpack was 10.0 (2.0) ml O2
.m–1, and with the backpack was 10.8 (1.9) ml O2
.m–1 (P<0.01). The net energy cost of locomotion was 0.129 (0.032) ml.kg body mass–1.m–1 for the unloaded condition and slightly lower, at 0.123 (0.025) ml.kg body mass–1.m–1 during loaded walking (P<0.05). Ventilation did not change significantly between unloaded and loaded conditions. When the data were assessed according
to the occurrence of back pain, the f
c/
slope was significantly lower in children without back pain, even though the net energy cost of locomotion was similar. Overall,
these data suggest that the cardiovascular effortrequired for locomotion while carrying a backpack is minimal. However, fatigability
and back pain are more likely to take place in less physical performing subjects. Thus, the occurrence of back pain in schoolchildren
during locomotion while carrying a backpack may improve with an improvement in their level of fitness.
Electronic Publication 相似文献
16.
A number of training adaptations in skeletal muscle might be expected to enhance lactate extraction during hyperlactataemia.
The aim of the present study was to determine whether resting endurance-trained forearms exhibit an increased net lactate
removal during hyperlactataemia. Six racquet-sport players attended the laboratory for two experiments, separated by 2 weeks.
In the first experiment incremental handgrip exercise to fatigue was performed to identify trained (TRFA, n=6) and untrained (UTFA, n=5) forearms. In the second experiment net forearm lactate exchange was compared between TRFA and UTFA during an incremental
infusion of sodium lactate. TRFA performed more work than UTFA during handgrip exercise [mean (SE) TRFA, 66.1 (9.5) J·100 ml–1; UTFA, 35.1 (2.3) J·100 ml–1; P=0.02] and UTFA exhibited a greater increase in net lactate output relative to work load (P=0.003). During lactate infusion net lactate uptake across the resting forearms increased linearly with the arterial lactate
concentration in both groups (TRFA, r=–0.95 (0.03); UTFA, r=–0.92 (0.04); P<0.02], with no difference in the regression slopes [TRFA, –1.06 (0.13); UTFA, –1.07 (0.27); P=0.97] or y-intercepts [TRFA, 0.67 (0.20); UTFA, 1.36 (0.67); P=0.37] between groups. Almost all of the lactate taken up was disposed of by both groups of forearms [TRFA, 99.6 (0.2)%; UTFA,
98.5 (1.0)%; P=0.37]. It was concluded that the net uptake and removal of lactate by resting skeletal muscle is a function of the concentration
of lactate in the blood perfusing the muscle rather than the muscle training status.
Electronic Publication 相似文献
17.
Effects of pre-exercise ingestion of carbohydrate on glycaemic and insulinaemic responses during subsequent exercise at differing intensities 总被引:1,自引:0,他引:1
The development of rebound hypoglycaemia has been reported after pre-exercise carbohydrate (CHO) ingestion in some studies
but not in others. Differences in the experimental design and factors such as the exercise intensity are likely to be responsible
for the discrepancies between these studies. Exercise intensity might be a crucial factor since it affects both insulinaemia
and glucose uptake. Therefore the aim of the present study was to compare the glycaemic and insulinaemic responses to exercise
at different intensities after ingestion of a standardized pre-exercise CHO load. Eight moderately trained subjects consumed
75 g of glucose 45 min prior to 20 min of exercise at 40%, 65% or 80% maximal power output. Blood samples were collected before
glucose ingestion, at 15 min intervals at rest and 5 min intervals during exercise. During exercise, measurements of heart
rate and breath-by-breath analysis of expired gas were performed continuously. The trials were performed at [mean (SEM)] 55 (1),
77 (1) and 90 (1) percentages maximal oxygen uptake . At the onset of exercise, plasma glucose concentration returned to pre-ingestion
levels, while the insulin concentration was more than three times higher than at rest [on average 57 (7) compared to 16 (1) μU·ml–1). During exercise, plasma glucose concentrations decreased during the first 5 min of exercise and then stabilized in all
trials at concentrations that would not be considered to be hypoglycaemic. There were no significant differences in glucose
or insulin concentrations between the three trials during exercise. These data suggest that the glycaemic response to ingestion
of 75 g of CHO 45 min pre-exercise is similar during exercise of different intensities.
Electronic Publication 相似文献
18.
In this study we examined the oxygenation trend of the vastus medialis muscle during sustained high-intensity exercise. Ten
cyclists performed an incremental cycle ergometer test to voluntary exhaustion [mean (SD) maximum oxygen uptake 4.29 (0.63) l·min–1; relative to body mass 60.8 (2.4) ml·kg–1·min–1] and a simulated 20-km time trial (20TT) on a wind-loaded roller system using their own bicycle (group time = 23–31 min)
in two separate sessions. Cardiorespiratory responses were monitored using an automated metabolic cart and a wireless heart
rate monitor. Tissue absorbency, which was used as an index of muscle oxygenation, was recorded simultaneously from the vastus
medialis using near-infrared spectroscopy. Group mean values for oxygen uptake, ventilation, heart rate, respiratory exchange
ratio, power output, and rating of perceived exhaustion were significantly (P≤0.05) higher during the incremental test compared to the 20TT [4.29 (0.63) l·min–1 vs 4.01 (0.55) l·min–1, 120.4 (26) l·min–1 vs 97.6 (16.1) l·min–1, 195 (8) beats·min–1 vs 177 (9) beats·min–1, 1.15 (0.06) vs 0.93 (0.06), 330.1 (31) W vs 307.2 (24.5) W, and 19 (1.5) vs 16 (1.7), respectively]. Oxygen uptake and heart
rate during the 20TT corresponded to 93.5% and 90.7%, respectively, of the maximal values observed during the incremental
test. Comparison of the muscle oxygenation trends between the two tests indicated a significantly greater degree of deoxygenation
during the 20TT [–699 (250) mV vs –439 (273) mV; P≤0.05] and a significant delay in the recovery oxygenation from the 20TT. The mismatching of whole-body oxygen uptake and
localised tissue oxygenation between the two tests could be due to differences in muscle temperature, pH, localised blood
flow and motor unit recruitment patterns between the two tests.
Electronic Publication 相似文献
19.
M. C. Riddell O. Bar-Or H. P. Schwarcz G. J. F. Heigenhauser 《European journal of applied physiology》2000,83(4-5):441-448
The influence of glucose ingestion on substrate utilization during prolonged exercise in children and adolescents is currently
unknown. In the present study we determined the effect of intermittent exogenous glucose (GLUexo) ingestion on substrate utilization during prolonged exercise, in adolescent boys ages 13–17 years. Healthy untrained volunteers
performed four 30-min exercise bouts on a cycle ergometer, separated by 5-min rest periods (≅60% maximum O2 consumption), on two occasions spaced 1–4 weeks apart. Two trials were performed, a control trial (CT), in which subjects
ingested water intermittently during the exercise, and a glucose trial (GT), in which subjects ingested a 13C-enriched GLUexo drink (≅3 g glucose · kg body mass−1), also intermittently during the exercise. Total free fatty acids (FATtotal), glucose (GLUtotal) and carbohydrate (CHOtotal) oxidation was determined from indirect calorimetry, while GLUexo oxidation was calculated from the 13C/12C ratio in expired air after 5–10 min and 25–30 min of exercise in each bout. Heart rate and rating of perceived exertion
(RPE) were determined at the same time intervals. The oxidation of CHOtotal was 169.1 (12.9) g · 120 min−1 and 203.1 (15.9) g · 120 min−1 (P < 0.01) and that of FATtotal was 31.0 (4.2) g · 120 min−1 and 17.1 (2.5) g · 120 min−1 (P < 0.01) in CT and GT, respectively. GLUexo oxidation in GT was 57.8 (4.3) g · 120 min−1, or 34.2 (2.2)% of that ingested. Endogenous glucose oxidation was 169.1 (12.9) g · 120 min−1 and 145.3 (11.9) g · 120 min−1 (P < 0.01) in CT and GT, respectively. Insulin and glucose concentrations were higher in GT than in CT by 226% and 37%, respectively
(both P < 0.05). Free fatty acids and glycerol concentrations were lower in GT than in CT, by 27% and 79%, respectively (both P < 0.05). Heart rate was similar between trials, but RPE was lower in GT vs CT at both 115 and 135 min. Thus, under these
experimental conditions, GLUexo intake spares endogenous carbohydrate and fat by 16% and 45%, respectively, contributes to approximately 25% of the total
energy demand of exercise, and lowers the RPE.
Accepted: 21 May 2000 相似文献
20.
The aim of this investigation was to examine the effect of water ingestion on physiological responses to prolonged cycling
(CYC) and running (RUN). A group of 11 men with mean (SEM) maximal oxygen uptake (V˙O2max) 48.5 (1.8) ml·kg–1·min–1 on a cycle-ergometer and 52.1 (2.2) ml·kg–1·min–1 on a treadmill (P<0.01) exercised for 90 min on four occasions, twice on each ergometer, at 60% of mode specific V˙O2max. No fluid was taken (D) in one trial on each ergometer, whereas 60% of fluid losses were replaced by drinking water in the
other trial (W). In CYC, water ingestion attenuated the change in cardiac output (
) and the reduction in stroke volume (ΔSV) [ΔSV: –22.7 (3.8) in D, –10.7 (2.9) ml·beat–1 in W, P<0.01;
: –1.9 (0.5) in D, –0.2 (0.4) l·min–1 in W at 85 min, P<0.01], but did not affect rectal temperature [T
re at 90 min: 38.8 (0.1)°C in D, 38.7 (0.1)°C in W]. In contrast, fluid replacement reduced hyperthermia in RUN [T
re at 90 min: 39.6 (0.2) in D, 39.1 (0.2)°C in W, P<0.01], and this was linked with a higher skin blood flow [RUN-W 88.9 (8.5), RUN-D 70.7 (8.4)%, P<0.05]. The
and ΔSV were also attenuated with water ingestion in this mode of exercise (P<0.05). It is concluded that water ingestion improves physiological function in both cycling and running, but that the underlying
mechanism is different in the two modes of exercise.
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