The dissociation of (a+c) misfit dislocations at the InGaN/GaN interface.

In hexagonal materials, (a+c) dislocations are typically observed to dissociate into partial dislocations. Edge (a+c) dislocations are introduced into (0001) nitride semiconductor layers by the process of plastic relaxation. As there is an increasing interest in obtaining relaxed InGaN buffer layers for the deposition of high In content structures, the study of the dissociation mechanism of misfit (a+c) dislocations laying at the InGaN/GaN interface is then crucial for understanding their nucleation and glide mechanisms. In the case of the presented plastically relaxed InGaN layers deposited on GaN substrates, we observe a trigonal network of (a+c) dislocations extending at the interface with a rotation of 3° from <1 1 ¯ $\bar 1$ 00> directions. High-resolution microscopy studies show that these dislocations are dissociated into two Frank-Shockley 1/6<2 2 ¯ $\bar 2$ 03> partial dislocations with the I1 BSF spreading between them. Atomistic simulations of a dissociated edge (a+c) dislocation revealed a 3/5-atom ring structure for the cores of both partial dislocations. The observed separation between two partial dislocations must result from the climb of at least one of the dislocations during the dissociation process, possibly induced by the mismatch stress in the InGaN layer.

The heterogeneous nucleation of threading dislocations on partial dislocations in III-nitride epilayers.

III-nitride compound semiconductors are breakthrough materials regarding device applications. However, their heterostructures suffer from very high threading dislocation (TD) densities that impair several aspects of their performance. The physical mechanisms leading to TD nucleation in these materials are still not fully elucidated. An overlooked but apparently important mechanism is their heterogeneous nucleation on domains of basal stacking faults (BSFs). Based on experimental observations by transmission electron microscopy, we present a concise model of this phenomenon occurring in III-nitride alloy heterostructures. Such domains comprise overlapping intrinsic I1 BSFs with parallel translation vectors. Overlapping of two BSFs annihilates most of the local elastic strain of their delimiting partial dislocations. What remains combines to yield partial dislocations that are always of screw character. As a result, TD nucleation becomes geometrically necessary, as well as energetically favorable, due to the coexistence of crystallographically equivalent prismatic facets surrounding the BSF domain. The presented model explains all observed BSF domain morphologies, and constitutes a physical mechanism that provides insight regarding dislocation nucleation in wurtzite-structured alloy epilayers.

Stack of two III-nitride laser diodes interconnected by a tunnel junction.

We demonstrate a stack of two III-nitride laser diodes (LDs) interconnected by a tunnel junction grown by plasma-assisted molecular beam epitaxy. Hydrogen-free growth is used to obtain as-grown p-type conductivity essential for buried tunnel junctions (TJ). We show the impact of the design of tunnel junction. In particular, we show that, apart from the beneficial piezoelectric polarization inside the TJ, heavy doping reduces the differential resistivity even further. The device starts to lase at a wavelength of 459 nm with a slope efficiency (SE) of 0.7 W/A followed by lasing at 456 nm from the second active region doubling the total SE to 1.4 W/A. This demonstration opens new possibilities for the fabrication of stacks of ultraviolet and visible high power pulsed III-nitride LD.

Early effects of short-term endurance training on hormonal responses to graded exercise.

Twelve male, sedentary volunteers (22.0 +/-) were submitted to three weeks of a bicycle ergometer training, consisting of 45 min exercise (at 70% VO2max), 4 times in the first week and 3 times in the next 2 weeks. They performed four incremental exercise tests with the power output increased by 50 W every 3 min until volitional exhaustion: two before training (C1 and C2), and after one (T1) and three (T3) weeks of training. Before and after each load the plasma noradrenaline (NA), adrenaline (A) and blood lactate (LA) concentrations were determined in venous blood samples as well as plasma growth hormone (HGH) and cortisol concentrations before and at the end of exercise. A decrease in NA concentration was found already after 1 week of training at power output of 100 W (p<0.01) and 200 W (p<0.05). Similar decline was maintained after 3 weeks of training. No significant training-induced differences in plasma A concentration were found, however, the thresholds for both catecholamines were significantly shifted towards higher values after 3 weeks of training. One week of training caused a decrease in the pre-exercise (p<0.01), as well as post-exercise (p<0.05) plasma cortisol and HGH concentrations. It was concluded that endurance training induced a decrease in HGH, cortisol and NA concentration already after one week of training. A decline of pre-exercise plasma HGH and cortisol levels with time of experiment may, in part, indicate familiarization to exercise protocol.

Early effects of short-term aerobic training. Physiological responses to graded exercise.

AIM: The aim of this study was to find out how early the moderate training effects appear and to check the hypothesis that familiarization with exercise protocol may contribute to an early physiological responses to training in previously sedentary subjects. METHODS: Twelve male, sedentary volunteers (22.0+/-0.7 yrs) were submitted to 3 weeks of a bicycle ergometer training, consisting of 45 min of exercise (at 70% VO(2)max), 3-4 times a week. The subjects performed 4 incremental exercise tests until volitional exhaustion: 2 before training (C1 and C2), and then after 1 (T1) and 3 (T3) weeks of training. During exercise HR, VO(2), electrical activity (EMG) of rectus femoris, biceps femoris, soleus and trapezius muscles were recorded and blood samples were taken for blood lactate (LA) determination. RESULTS: Already after 1 week of training HR decreased (p<0.05) with a further decline after 3 weeks the training (p<0.01). Maximal work load after 3 weeks of training increased to 277+/-10.4 W vs 250+/-9.5 W (p<0.05), VO(2)max achieved higher values than in C1 and C2 tests (p<0.05) and LA and EMG thresholds were elevated (p<0.05). CONCLUSION: A decrease in the resting and submaximal heart rate is the earliest effect of increased physical activity. Familiarization to exercise protocol decreased EMG of biceps femoris and soleus muscles during exercise, but did not influence that of rectus femoris muscle the most engaged during cycling.

[Patient's preferences concerning the course of labor]. / Preferencje kobiet dotyczace przebiegu porodu.

OBJECTIVE: Much concern is being focused on the improvement of perinatal care standards in recent time. Not only the safety of woman and newborn, but also the comfort and individual preferences should to be considered. The aim of this study was to assess of expectations and requirements of the delivering women in relation to the course of labor and usage of the most common procedures in clinical practice. MATERIAL AND METHODS: 47 women who delivered in Obstetrical Word in Puck were questionnaire. Mean gestational age was 39 +/- 1.5 hbd. 47% of women were nulliparous, 53% were multiparous. The following variables were analyzed: the presence of medical staff and family at delivery, possibility of the delivery position choice, use of auxiliary devices, a friendly atmosphere during delivery, use of analgesia and labor induction, episiotomy and ante-partum preparation, cesarean section on request, attendance to labor school. Mann-Whitney, Pearson and Yule tests were used for statistical analysis. RESULTS: 25% of women, mainly younger gravidae, attended the labor school. The midwife was considered the most important person at delivery. The presence of family member(s) was important for highly-educated women. The possibility to choose the delivery position and to walk during the 1st stage of labor was important for 73% of respondents. The majority of women who had attended the labor school avoided the horizontal position. Over 60% of patients accepted the usage of labor induction. A vast majority of women were against antepartum perineal shaving and episiotomy. Better-educated women preferred water delivery. 69% of the studied women would like to listen to the music at the delivery room. Cesarean section on request was supported by 11% of women. CONCLUSIONS: The tendency to promote modern delivery methods and active participation in labor leading is noticed. The significant influence of labor school on women's knowledge and their preferences was found.

[The influence of water immersion on the course of labor]. / Wplyw immersji wodnej na przebieg porodu.

OBJECTIVE: The aim of this study was to examine the influence of water immersion on the course of labor. MATERIAL AND METHODS: The study group consisted of 109 women, who have delivered in water in Obstetrical Ward in Puck from 1998 to 2000. 110 women composed control group. Mean patients' age in study and control group was respectively 26.40 +/- 4.33 and 26.72 +/- 5.82 years (ns). Gestational age was 40.69 +/- 5.91 and 39.71 +/- 2.03 weeks (ns). The duration of labor stages, time from membranes rupture to delivery, birthweight and newborns condition, frequency of episiotomy and perineum injuries as well as necessity of labor stimulants use were analyzed. Particular parameters were also assessed regarding to parity. The differences were determined using T-test. RESULTS: Mean duration of 1st labor stage was 319 min in study group and 375 min in control group (p < 0.02). The 2nd and 3rd labor stages did not differ significantly. II labor stage in nulliparous and I stage in multiparous were shorter in study group (respectively 34.41 vs. 45.5 min; p < 0.02 and 258.23 vs. 329.83 min; p < 0.02). The episiotomy was less frequent in study group (p < 0.01), whereas perineum injuries in control one (p < 0.05). Use of oxytocin was comparable between both groups. 97% of newborns from study group and 93% from control group, they were in good condition (ns). CONCLUSIONS: The profitable influence of water immersion to short 1st labor stage was noted. There were no differences in newborns' condition. The water birth is a safe method of labor in patients with physiological pregnancy.

[Feto-maternal immunization and fetal hemolytic disease: invasive diagnostics and therapy in the Warsaw center of serological collision in years 1992-1999]. / Immunizacja matczyno-plodowa i choroba hemolityczna plodu--inwazyjna diagnostyka i terapia w stolecznym osrodku konfliktu serologicznego w latach 1992-1999.

OBJECTIVE: The objective of this study was the assessment of intrauterine procedures, which are performed during the diagnostic phase and therapy of fetal hemolytic disease in the Warsaw Center of Serological Collision. MATERIALS AND METHODS: The study covered 146 women, who were patients of the Center from 1992 to 1999. Analyzed were the time of commencement of diagnostic and treatment, type of operations, duration of therapy, time and manner of delivery after the past intrauterine procedures, the medical condition of infants born as a result of these deliveries and the necessity for blood treatment in the early neonatal stage. RESULTS: 451 intrauterine procedures were carried out, of which 159 were diagnostic punctures of the umbilical vessel and 292 were fetal transfusions. The diagnostics and treatment was performed between the 19 and 38 week of pregnancy. The number of punctures for each patient ranged from 1 to 4, and 1 to 10 for intrauterine transfusions. The therapy, which on average lasted 42 days, significantly improved the fetal blood morphology results. During the therapy 5 intrauterine demises were noted--3 as a result of advanced fetal hemolytic disease and 2 related to operation complications. The average pregnancy duration in the analyzed group was 36.4 for treated women and 37.4 weeks for diagnosed women. 52.7% of deliveries were vaginal, 47.3% were performed by cesarean section. The general condition of 87% of infants was good. However, 77% of infants required blood treatment during the early neonatal period. CONCLUSIONS: Invasive methods of fetal hemolytic disease diagnostics and intrauterine therapy assure high efficiency in the guiding of serological collision and fetal hemolytic disease conflicted pregnancies. At the same time, these methods are safe and carry a low risk of complications.

Relationship between EMG blood lactate, and plasma catecholamine thresholds during graded exercise in men.

The aim of this study was to follow up the electromyographic activity (EMG) of dynamically working muscles with simultaneous determinations of blood lactate and plasma catecholamine concentrations during progressive exercise. Twenty eight male soccer players aged 20.6 +/- 0.8 yrs performed incremental bicycle ergometer exercise test. The test consisted of 3-min stages exercise separated by 1-min rest intervals. Work load at each stage increased by 50 W until volitional exhaustion. The root mean square (rms)-EMG activity of the rectus femoris and soleus muscles were recorded continuously during exercise. Venous blood samples were taken after each exercise stage for determination of blood lactate (LA). Additionally in seven subjects adrenaline (A) and noradrenaline (NA) concentrations were determined. The EMG activity increased negligibly during exercise of low to moderate intensities revealing an abrupt rise at the load corresponding to thresholds of blood lactate and plasma catecholamine accumulation (LA-T, A-T, NA-T). Close correlations (P < 0.001) were found between blood LA concentration and EMG derived from rectus f. (r = 0.72) and soleus (r = 0.68) muscles. The mean threshold exercise intensities for m. rectus f. and m. soleus EMG (176 +/- 9 W and 172 +/- 9 W, respectively) did not differ significantly from lactate (164 +/- 7 W), noradrenaline (178 +/- 6 W) and adrenaline (180 +/- 5 W) thresholds, all of them detected by log-log transformation. The results indicate that threshold character of EMG changes in dynamically working muscles reflects to some extend the patterns of blood lactate and plasma catecholamine changes during incremental exercise.

Substrate availability limits human skeletal muscle oxidative ATP regeneration at the onset of ischemic exercise.

We have demonstrated previously that dichloroacetate can attenuate skeletal muscle fatigue by up to 35% in a canine model of peripheral ischemia (Timmons, J.A., S.M. Poucher, D. Constantin-Teodosiu, V. Worrall, I.A. Macdonald, and P.L. Greenhaff. 1996. J. Clin. Invest. 97:879-883). This was thought to be a consequence of dichloroacetate increasing acetyl group availability early during contraction. In this study we characterized the metabolic effects of dichloroacetate in a human model of peripheral muscle ischemia. On two separate occasions (control-saline or dichloroacetate infusion), nine subjects performed 8 min of single-leg knee extension exercise at an intensity aimed at achieving volitional exhaustion in approximately 8 min. During exercise each subject's lower limbs were exposed to 50 mmHg of positive pressure, which reduces blood flow by approximately 20%. Dichloroacetate increased resting muscle pyruvate dehydrogenase complex activation status by threefold and elevated acetylcarnitine concentration by fivefold. After 3 min of exercise, phosphocreatine degradation and lactate accumulation were both reduced by approximately 50% after dichloroacetate pretreatment, when compared with control conditions. However, after 8 min of exercise no differences existed between treatments. Therefore, it would appear that dichloroacetate can delay the accumulation of metabolites which lead to the development of skeletal muscle fatigue during ischemia but does not alter the metabolic profile when a maximal effort is approached.

Physiological characteristics and hormonal profile of young normotensive men with exaggerated blood pressure response to exercise.

Exaggerated blood pressure (BP) response to exercise in normotensive subjects is considered as a predictor of future hypertension. The aim of the study was to find out whether elevated BP response to exercise is associated with any other haemodynamic, metabolic or hormonal abnormalities. Abnormal BP response to exercise, i.e. systolic BP (SBP) > 200 mmHg at 150 W or lower workload, was found in 37 out of 180 normotensive, male students, aged 20-24 years. Fifteen students with elevated exercise BP (group E) volunteered for further examinations. Their resting and ambulatory BP showed high normal values. Eight of them had a family history of hypertension. Four subjects met the criteria of cardiac hypertrophy. Significant correlations were found between exercise SBP and left ventricular mass index, average 24 h and daytime SBP recordings. In comparison with normal subjects of the same age (group N, n = 13), those from group E did not differ in body mass index, plasma lipid profile, fasting glucose, insulin and catecholamine (CA) concentrations, but had increased erythrocyte sodium content, slightly elevated plasma renin activity and cortisol level. During exercise, E subjects showed greater cardiac output (CO) increases with normal heart rate, total peripheral resistance (TPR) and plasma CA. There were no significant differences between groups in haemodynamic and plasma CA responses to posture change from supine to standing. Glucose ingestion (75 g) caused smaller increases in CO and smaller decreases in TPR in E than in N subjects without differences in BP, blood glucose plasma insulin and CA. It is concluded that young normotensive men with exaggerated BP response to exercise show some other characteristics that may be considered as markers of predisposition to hypertension or factors promoting the development of hypertension.

Phosphate supplementation prevents a decrease of triiodothyronine and increases resting metabolic rate during low energy diet.

Thirty overweight women participated in 8 week slimming program consisting of a self-controlled low-energy diet (4.2 MJ/day) supplemented with highly viscous fibres and mineral tablets containing calcium, potassium and sodium phosphates (Redusan Combi, Biokraft Pharma AB, Sweden). Half of the patients received in double blind manner mineral tablets during first 4 weeks and placebo (without phosphates) during next 4 weeks (group 1) while the remaining patients were treated (cross-over) with placebo first and mineral tablets in the final period (group 2). The rate of weight loss was similar in groups 1 and 2 (4.7 vs 5.2 kg during the first 4 weeks and 2.7 vs 3.0 kg in the further 4 weeks). During periods of phosphate supplementation, the resting metabolic rate (RMR) increased by approx. 12% (p < 0.05) in group 1 and 19% (p < 0.05) in group 2. Phosphate supplementation ameliorated also a decrease in plasma triiodothyronine level and a decrease in thyroxine to triiodothyronine ratio. There were no differences between groups in the plasma insulin, catecholamine, growth hormone, cortisol and testosterone levels. Phosphate supplementation did not affect plasma lipids or blood glucose concentration. It is concluded that phosphate supplementation in obese patients on a low-energy diet enhances RMR irrespectively of the rate of weight loss. This effect seems to be, at least partly, due to an influence of phosphates on peripheral metabolism of thyroid hormones.

Threshold increases in plasma growth hormone in relation to plasma catecholamine and blood lactate concentrations during progressive exercise in endurance-trained athletes.

Plasma human growth hormone ([HGH]), adrenaline ([A]), noradrenaline ([NA]) and blood lactate ([La-](b)) concentrations were measured during progressive, multistage exercise on a cycle ergometer in 12 endurance-trained athletes [aged 32.0 (SEM 2.0) years]. Exercise intensities (3 min each) were increased by 50 W until the subjects felt exhausted. Venous blood samples were taken after each intensity. The [HGH] and catecholamine concentrations increased negligibly during exercise of low to moderate intensities revealing an abrupt rise at the load corresponding to the lactate threshold ([La-]-T). Close correlations (P <0.001) were found between [La-]b and plasma [HGH] (r = 0.64), [A] (r = 0.71) and [NA] (r = 0.81). The mean threshold exercise intensities for [HGH], [A] and [NA], detected by log-log transformation, [154 (SEM 19) W, 162 (SEM 15) W and 160 (SEM 17) W, respectively] were not significantly different from the [La-]-T [161 (SEM 12) W]. The results indicated that the threshold rise in plasma [HGH] followed the patterns of plasma catecholamine and blood lactate accumulation during progressive exercise in the endurance-trained athletes.

Effect of mild psychological stress on physiological responses to exercise in men.

UNLABELLED: To find out whether a negative shift in subject's mood alters cardio-respiratory and endocrine responses to exercise, 20 young men performed a graded bicycle ergometer test (50, 100, 150 W): 1) when they experienced a mixed emotional and cognitive stress before exercise (1st session), 2) when they were familiarized with the laboratory and rested quietly before exercise (2nd session). The subjects' mood was assessed by the Profile of Mood State (POMS) questionnaire. In the 1st session the subjects started exercise with significantly higher scores of tension, anger, depression, confusion and global mood in comparison with the 2-nd session. They also had slightly elevated systolic blood pressure, blood lactate, plasma cortisol and noradrenaline concentrations. During exercise performed in the 1st session only plasma free and total noradrenaline and cortisol levels were higher than those in the 2nd session. IN CONCLUSION: a mild psychological stress, causing the mood worsening before standard exercise test, does not evoke pronounced alterations in cardio-respiratory responses to exercise in healthy men, but it does affect the magnitude of exercise-induced changes in both plasma free and total noradrenaline concentrations.

Effect of phosphate supplementation on metabolic and neuroendocrine responses to exercise and oral glucose load in obese women during weight reduction.

Thirty six obese women (BMI 29.5 to 44.0 kg m-2, aged 27 to 45 yrs) participated in the 4- week weight reducing program. All of them have prescribed low fat diet of approx. 4.2 MJ (1000 kcal per day) with high viscous fibre capsules as a basic supplement. In addition 18 women (group 1) received Redusan mineral tablets containing mainly calcium and potassium phosphates while the remaining subjects (group 2) were given Placebo instead of mineral tablets. Before energy restriction and after 4 weeks on the diet, half of the women from each group performed 30 min--bicycle ergometer exercise (30-50 W; HR approx. 110 beats.min-1). The remaining subjects were submitted to oral glucose (75 g) tolerance test (OGTT). Weight loss during energy restriction was not affected by phosphate supplementation (4.6 +/- 0.4 and 5.2 +/- 0.5 kg in group 1 and 2, respectively). Phosphates caused a significant increase (p < 0.05) in the resting metabolic rate (RMR). Net energy cost of work, resting and post-exercise blood glucose, lactate, plasma FFA, adrenalin, cortisol, growth hormone, insulin and testosterone did not differ between the groups receiving phosphates and placebo while respiratory exchange ratio was slightly higher (p < 0.05), and the plasma beta-hydroxybutyrate concentration lower (p < 0.05) than without phosphate supplementation. Post-exercise plasma noradrenaline was significantly lowered after 4 weeks of energy restriction in group 2 (on Placebo). Neither blood glucose, plasma insulin and noradrenaline responses to oral glucose ingestion nor the glucose induced thermogenesis were significantly affected by phosphate supplementation, whilst blood pressure increases following glucose load were reduced (p < 0.05). In conclusion, the present study confirmed a potential usefulness of phosphate supplementation during energy restriction in obese patients due to its effect on resting metabolic rate. The results did not, however, reveal any major alterations in the metabolic and hormonal responses to exercise or to glucose ingestion in comparison with placebo treatment.

Effects of warm-up on muscle glycogenolysis during intense exercise.

This study investigated the effects of preliminary exercise (warm-up) on glycogen degradation and energy metabolism during intense cycle ergometer exercise. After determination of VO2max, six male subjects were randomly assigned to perform warm-up (WU) and no warm-up (NWU) trials incorporating a 2 min standardized sprint ride (SR) at 120% of the power output attained at VO2max (POmax). Muscle biopsies and temperature (Tm) recordings were obtained from the vastus lateralis muscle. Tm was elevated above the resting level prior to the SR during the WU trial (37.7 +/- 0.1 vs 35.4 +/- 0.4 degrees C; P less than 0.05) and remained higher than the NWU trial after the SR (38.6 +/- 0.2 vs 37.1 +/- 0.4 degrees C; P less than 0.05). Similar trends existed for rectal temperature (Tr). The increases in Tm and Tr during the SR were both greater in the NWU trial (P less than 0.05). Muscle glycogen degradation was similar for the WU and NWU trials (30.8 +/- 3.7 vs 25.6 +/- 3.7 mmol.kg-1, respectively). When blood and muscle lactate concentrations after the SR were expressed relative to values before the SR, the WU trial resulted in a lower accumulation of blood lactate (6.5 +/- 0.9 vs 10.7 +/- 0.8 mEq.l-1; P less than 0.01) and muscle lactate (20.1 +/- 0.1 vs 23.4 +/- 2.2 mEq.kg-1 wet wt.; P less than 0.05). Furthermore, oxygen consumption during the 1st min of the SR was higher in the WU trial (2.3 +/- 0.2 vs 1.9 +/- 0.2 l.min-1; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood lactate threshold differences between arterialized and venous blood.

The purpose of this study was to investigate the differences between lactate thresholds determined from venous and arterialized blood. Seven endurance-trained college males performed an incremental bicycle ergometer exercise test until exhaustion. At the end of each 3 min stage, blood was sampled simultaneously from a hyperemized ear-lobe and an antecubital vein for the measurement of blood lactate (La-). Two-minute rest intervals separated each stage. Arterialized blood La-concentrations ([La-]) were significantly higher than venous blood at 350 W (14.5 and 9.7 mmol.l-1), maximal exercise (15.5 and 11.39 mmol.l-1), and throughout recovery. Arterialized [La-] was significantly higher than venous blood at the onset of blood La- accumulation (OBLA) (4.0 and 2.8 +/- 0.1 mmol.l-1), the individual anaerobic threshold (IAT) (3.4 +/- 0.3 and 2.1 +/- 0.1 mmol.l-1), and the ventilatory threshold (VT) (4.7 +/- 0.9 and 3.2 +/- 0.6 mmol.l-1). No significant differences were found between either La-threshold for arterialized or venous blood. The oxygen consumption (VO2) at OBLA was significantly lower when determined from arterialized blood La (2.3 +/- 0.2 and 2.8 +/- 0.2 l.min-1). No significant differences existed between the LT, OBLA, and IAT threshold-VO2 determinations from arterialized blood; however, significant differences were found between IAT-OBLA (2.1 +/- 0.2 and 2.8 +/- 0.2 l.min-1) and LT (2.2 +/- 0.2 l.min-1)-OBLA from venous blood. These results indicate that differences between venous and arterialized blood [La-] need to be considered when comparing different anaerobic threshold determinations.

Effects of warm-up on blood gases, lactate and acid-base status during sprint swimming.

A standardized 200-m front crawl sprint swim (SpS) was used to evaluate the effects of warm-up on pH, blood gases, and the concentrations of lactate ([La-]) and bicarbonate ([HCO3-]) in arterialized and venous blood. Eight trained male swimmers performed two randomly assigned 200-m front crawl swims at previously determined intensities corresponding to 120% VO2max. One swim was preceded by a warm-up (WU trial) which consisted of a 400-m front crawl swim (82% VO2max), 400-m flutter kicking (45% VO2max), and 4 x 50-m front crawl sprints (111% VO2max). The second was performed without warm-up (NWU trial). Blood was sampled from a hyperemized earlobe and an antecubital vein before the warm-up, 9 min after the warm-up (1 min before the swim), immediately following the SpS, and at 2, 5, 10, and 20 min after the SpS. The warm-up exercise resulted in a higher pre-SpS [La-] in arterialized blood (3.1 +/- 0.4 and 1.7 +/- 0.4 mmol x l-1, p less than 0.05), a higher hydrogen ion concentration ([H+]) in venous blood (45.9 +/- 0.9 and 42.2 +/- 0.8 nmol x l-1, p less than 0.001), and a lower arterialized blood [HCO3-] (25.1 +/- 0.9 and 22.2 +/- 0.8 mmol x l-1, p less than 0.05). The SpS was accompanied with higher heart rates during the WU trial (178 +/- 3 and 169 +/- 3 bpm; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Threshold for muscle lactate accumulation during progressive exercise.

The purpose of this study was to investigate the relationship between muscle and blood lactate concentrations during progressive exercise. Seven endurance-trained male college students performed three incremental bicycle ergometer exercise tests. The first two tests (tests I and II) were identical and consisted of 3-min stage durations with 2-min rest intervals and increased by 50-W increments until exhaustion. During these tests, blood was sampled from a hyperemized earlobe for lactate and pH measurement (and from an antecubital vein during test I), and the exercise intensities corresponding to the lactate threshold (LT), individual anaerobic threshold (IAT), and onset of blood lactate accumulation (OBLA) were determined. The test III was performed at predetermined work loads (50 W below OBLA, at OBLA, and 50 W above OBLA), with the same stage and rest interval durations of tests I and II. Muscle biopsies for lactate and pH determination were taken at rest and immediately after the completion of the three exercise intensities. Blood samples were drawn simultaneously with each biopsy. Muscle lactate concentrations increased abruptly at exercise intensities greater than the "below-OBLA" stage [50.5% maximal O2 uptake (VO2 max)] and resembled a threshold. An increase in blood lactate and [H+] also occurred at the below-OBLA stage; however, no significant change in muscle [H+] was observed. Muscle lactate concentrations were highly correlated to blood lactate (r = 0.91), and muscle-to-blood lactate ratios at below-OBLA, at-OBLA, and above-OBLA stages were 0.74, 0.63, 0.96, and 0.95, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of active warming-up on thermoregulatory, circulatory, and metabolic responses to incremental exercise in endurance-trained athletes.

The influence of 10 min warming-up at 40% VO2 max on thermal, circulatory, and metabolic responses to an incremental exercise to exhaustion as well as on the anaerobic threshold at the blood lactate level of 4 mmol.l-1 (AT) and the individual anaerobic threshold (IAT) was investigated in eight cross-country skiers. During exercise preceded by warming-up, the mean skin temperature (T sk) and external auditory canal temperature (Tac) did not change significantly in contrast to exercise without warming-up, producing a rise in both T sk and Tac (by approx. 1.2 degrees C and 1.1 degrees C, respectively). Warming-up did not alter the course of the rectal temperature changes during exercise. With warming-up skin humidity rose immediately after the beginning of exercise, whereas the onset of sweating without warming-up appeared much later at higher work intensities. Warming-up did not change the circulatory and ventilatory responses to incremental exercise and the oxygen uptake (VO2) either at submaximal or maximal work loads. With warming-up a significant increase was found in the threshold work load both at the AT and the IAT. The data demonstrated that warming-up has an advantageous effect on the efficiency of thermoregulation in endurance-trained athletes producing an early sweating response to the incremental exercise that results in attenuation of hyperthermia. An increase in the anaerobic threshold during incremental exercise preceded by warming-up may indicate an enhancement of the endurance capacity subsequent to warming-up.