Blood Lactate Production Research Articles

Correlation Between Blood Lactate and Salivary Biomarkers During Exercise in Women with Hypothyroidism Treated With L-Thyroxine

Background: Hypothyroidism reduces circulating levels of thyroid hormones metabolic enzymatic activities, and the skeletal muscle's work capacity and lactatemia increase during exertion. Objectives: To analyze salivary biomarkers and blood lactate obtained in exercise stages through exhaustion and investigate their correlation. Methods: Eight females attended the University Clinical Hospital who showed a condition of subclinical hypothyroidism. Before they began replacing with L-thyroxine, they were submitted to an ergometric test to check their tolerance to effort. Eight weeks after treatment, all volunteers were again submitted to lab and ergometric tests. Saliva and blood were collected to determine total protein, nitric oxide, IgA, lactate, and lipid profile. Results: The present study identified a correlation (0.8), so the behavior of the blood lactate could explain the behavior of the salivary of total proteins by 74.22% (R2 = 0.7422). Lactate production was minimized when women underwent L-thyroxine treatment in the first six stages of exercise. Still, total salivary proteins increased for pharmacotherapy between stages 1 and 8. While salivary nitric oxide had a percentage variation between pre- and post-exercise times of 96% before the start of treatment when the same exercise was performed after eight weeks of treatment with L-Thyroxine, this variation was 150%. Conclusion: The measurement of STP is an essential marker of stress, and it is highly correlated with the most used blood marker, lactate. Regarding treatment with L-Thyroxine in women with subclinical hypothyroidism, after eight weeks of this therapy, it was possible to observe a reduction in blood lactate production after the incremental load test on a cycle ergometer, accompanied by a reduction in the concentration of SA. SNO and SIgA tended to increase in women undergoing treatment, and this treatment should be considered in subsequent studies as causing a different effect on these markers.

Probiotic Strains Isolated from an Olympic Woman's Weightlifting Gold Medalist Increase Weight Loss and Exercise Performance in a Mouse Model.

Obesity is a worldwide health problem. Calorie-restricted diets constitute a common intervention for treating obesity. However, an improper calorie-restricted diet can lead to malnutrition, fatigue, poor concretion, muscle loss, and reduced exercise performance. Probiotics have been introduced as an alternative treatment for obesity. In the present study, we tested the weight loss and exercise performance enhancement effectiveness of probiotic strains of different origins, including four isolated from an Olympic weightlifting gold medalist (Bifidobacterium longum subsp. longum OLP-01, Lactobacillus plantarum PL-02, Lactobacillus salivarius subsp. salicinius SA-03, and Lactococcus lactis subsp. lactis LY-66). A high-fat diet (HFD) was used to induce obesity in 16 groups of mice (n = 8/group). The mice were administered probiotic supplements at a dosage of 4.1 × 109 CFU/kg/day for 10 weeks. All probiotic supplementation groups showed a significant reduction in body weight and fat mass compared with the HFD group. TYCA06, CS-773, BLI-02, PL-02, bv-77, and OLP-01 were the most effective in facilitating weight loss and fat reduction, which may be due to fatty-acid absorbing activity. PL-02, LY-66, TYCA06, CS-773, and OLP-01 elevated the animals’ grip strength and exhaustive running duration. PL-02, LY-66, and OLP-01 increased tissue glycogen (liver and muscle) levels and muscle capillary density and reduced blood lactate production levels after exercise. In conclusion, OLP-01, PL-02, LY-66, TYCA06, and CS-773 were highly effective in enhancing weight loss and exercise performance. This study should be repeated on humans in the future to further confirm the findings.

Determinants Of Metabolic Cost During Four Styles Of 30-second Sprint Rope Skipping

Rope jumping has been a major training tool for many sports. However, no study has been conducted as yet to determine energy expenditure with incremental skipping rate per jump (difficulty) from single under to quad under. PURPOSE: To determine and compare 30-seconds all-out effort energy expenditure between four incremental rope skipping difficulties. METHOD: Ten skilled rope-jumpers (height=169.3±4.7cm, body mass=65.5±9.2kg, age=23.2±2.1yrs, years of training=3.8±1.3yrs) volunteered to participate this study. Participants conducted rope skipping as many repetitions as possible at 1 skip.jump-1 (single under, SU), 2 skips.jump-1 (double under, DU), 3 skips.jump-1 (triple under, TU) and 4 skips.jump-1 (quad under, QU) during 30-second test with 24 hours between trials. Kinematic and kinetic data were collected to calculate flight time (FT) and vertical center of mass displacement (vCOM). Each style was assessed in three trials and then averaged. Net energy expenditure (Wtot) was calculated from VO2 during exercise, the fast component of the EPOC above resting and net blood lactate production. RESULT: SU exhibited significantly lower VO2peak (28.01±4.62 ml.kg-1.min-1, p<0.05) compared to TU (34.96±3.45) and QU (36.12±6.38). Wtot (J.jump-1) in QU (7975.1±3265.66 J.jump-1) was significantly higher than these values of the other three styles (SU 474.9±108.80, DU 1086.4±183.17, TU 1769.3±540.46, p<0.05). FT (ms) and vCOM (cm) increased significantly with increase in difficulty (SU: 125.0±19.6 and 1.95±0.66, DU: 276.6±36.1 and 9.53±2.24, TU: 473.6±32.1 and 27.64±3.76, QU: 544.4±60.5 and 36.76±8.15, p<0.01). 30s skip repetitions in QU (46.0±19.34) was significantly lower than the other styles (SU 105.2±12.08, DU 128.2±15.12, TU 126.9±20.39, p<0.01). Standard Wtot (J.kg-1.jump-1) was exponentially related to skipping difficulty from 1 skip.jump-1 to 4 skips.jump-1 (R2=0.89, p<0.001). CONCLUSION: Skipping difficulty (skip per jump) is one of the main determinants of metabolic cost, whereas skip repetition does not significantly contribute to metabolic cost during 30 seconds all-out rope skipping.

Cognitive Function in Simulated Paragliding Flight.

INTRODUCTION: Paragliding is an emerging discipline of aviation, with recreational pilots flying distances over 100 km. It remains risky. Accidents typically relate to pilot error rather than equipment failure. We measured cognition and physiological responses during simulated flight, to investigate whether errors might be due to pilot impairment, rather than misjudgment.METHODS: There were 10 male paraglider pilots (aged 19-58 yr) who undertook a simulated flight in an environmental chamber from sea level (0.209 FIo₂) to 1524 m (0.174 FIo₂), 2438 m (0.156 FIo₂), and 3658 m (0.133 FIo₂), over approximately 2 h. They experienced normobaric hypoxia, environmental cooling and headwind, completing logical reasoning, mannikin, mathematical processing, Stroop Color-Word and Tower Puzzle tasks; as well as measures of risk-taking (BART), mood (POMS), and subjective experience.RESULTS: Results were compared to ten controls, matched by age, sex, and flying experience. Physiological measures were oxygen consumption, carbon dioxide production, ventilation, heart rate, oxygen saturation, rectal and skin temperatures, blood glucose, blood lactate, and urine production. There were no significant differences between pilots and controls at any altitude. Results were heterogenous within and between individuals. As altitude increased, oxygen consumption and minute volume increased significantly, while oxygen saturations fell (98.3% [baseline] to 88.5% [peak]). Rectal temperatures fell by a statistically (but not clinically) significant amount (37.6°C to 37.3°C), while finger skin temperatures dropped steeply (32.2°C to 13.9°C).DISCUSSION: Results suggest cognitive impairment is unlikely to be a primary cause of pilot error during paragliding flights (of less than 2 h, below 3658 m), though hand protection requires improvement.Wilkes M, Long G, Massey H, Eglin C, Tipton MJ. Cognitive function in simulated paragliding flight. Aerosp Med Hum Perform. 2019; 90(10):851-859.

Various exercise intensities differentially regulate GAP-43 and CAP-1 expression in the rat hippocampus

Exercise intensity is known to affect neuroplasticity. Although corticosterone and lactate levels have been linked to neuroplasticity, the effect of different endurance exercise intensity-dependent production of these biochemicals on the behaviour of hippocampal growth cone markers remains incompletely explored. Here, we investigated the effects of three different endurance treadmill training episodes for six weeks on GAP-43 and CAP-1 expression in the hippocampus of adult male Wistar rats. Our findings showed that mild exercise intensity (MEI) with a lactate production slightly higher than the lactate threshold (LT) is the optimal form of physical activity for elevating GAP-43 without changing CAP-1 expression. It was further observed that high exercise intensity (HEI) with the highest level of corticosterone and lactate production, reduced GAP-43 expression, yet increased CAP-1 expression in the hippocampus. Like HEI, we further identified similar expression patterns for these markers in low exercise intensity (LEI) with blood lactate production below LT and corticosterone level similar to MEI. The findings suggested that in high-intensity exercise, the negative pattern of hippocampal neuroplasticity depends on both corticosterone and lactate levels, whereas in low-intensity exercise, the most important factor determining this negative pattern is the lactate level. Generally, MEI with a lactate production of slightly higher than LT is the most optimal intensity for improving hippocampal neuroplasticity.

Effect of self-paced active recovery and passive recovery on blood lactate removal following a 200 m freestyle swimming trial.

PurposeThe aim of this study was to investigate the effect of self-paced active recovery (AR) and passive recovery (PR) on blood lactate removal following a 200 m freestyle swimming trial.Patients and methodsFourteen young swimmers (with a training frequency of 6–8 sessions per week) performed two maximal 200 m freestyle trials followed by 15 minutes of different recovery methods, on separate days. Recovery was performed with 15 minutes of passive rest or 5 minutes of passive rest and 10 minutes of self-paced AR. Performance variables (trial velocity and time), recovery variables (distance covered and AR velocity), and physiological variables (blood lactate production, blood lactate removal, and removal velocity) were assessed and compared.ResultsThere was no difference between trial times in both conditions (PR: 125.86±7.92 s; AR: 125.71±8.21 s; p=0.752). AR velocity was 69.10±3.02% of 200 m freestyle trial velocity in AR. Blood lactate production was not different between conditions (PR: 8.82±2.47 mmol L−1; AR: 7.85±2.05 mmol L−1; p=0.069). However, blood lactate removal was higher in AR (PR: 1.76±1.70 mmol L−1; AR: 4.30±1.74 mmol L−1; p<0.001). The velocity of blood lactate removal was significantly higher in AR (PR: 0.18±0.17 mmol L−1 min−1; AR: 0.43±0.17 mmol L−1 min−1; p<0.001).ConclusionSelf-paced AR shows a higher velocity of blood lactate removal than PR. These data suggest that athletes may be able to choose the best recovery intensity themselves.

RESPUESTAS Y ADAPTACIONES FISIOLÓGICAS AL ENTRENAMIENTO DE TAEKWONDO. UNA REVISIÓN SISTEMÁTICA

El objetivo de analizar las principales respuestas y adaptaciones fisiológicas que se asocian a la práctica del taekwondo se plantea para evaluar el desarrollo del conocimiento en esta área y orientar a entrenadores y deportistas acerca de los procesos de entrenamientos más apropiados. Por lo tanto, se realiza una búsqueda sistemática en las bases de datos: "Academic Search Complete, ERIC, Medline, SportDiscus, Proquest, y Ovid". De las cuales se toman en cuenta solo investigaciones publicadas en revistas científicas y se incluyen únicamente las variables que fueron analizadas en un mínimo de cinco estudios. Dicho requisito se cumplió para la fuerza (independientemente de su manifestación), la capacidad aeróbica, la frecuencia cardíaca y la producción de lactato sanguíneo. Veintiocho publicaciones aportaron sus hallazgos a la presente revisión bibliográfica. No existe suficiente congruencia en la evidencia desarrollada que permita establecer tendencias sobre el volumen e intensidad de cargas de trabajo más adecuadas para guiar el proceso de entrenamiento de un practicante de taekwondo, ya sea con fines competitivos o de salud. El diseño metodológico de las investigaciones realizadas en el área debe ser mejorado.

Atrial supply–demand balance in healthy adult pigs: coronary blood flow, oxygen extraction, and lactate production during acute atrial fibrillation

Little is known about how atrial oxygen supply responds to increased demand, and under which conditions it falls short (supply-demand mismatch). Here, we have investigated the vasodilator response, oxygen extraction, and lactate production of the left atrium (LA) and left ventricle (LV) in response to atrial pacing and atrial fibrillation (AF). Series A (n = 9 Dutch landrace pigs) was instrumented to measure LA and LV vascular conductance in branches of the circumflex artery. Coronary conductance reserve (CCR) was calculated as the ratio between conductance during adenosine infusion and baseline. Series B (n = 7) was instrumented with sampling catheters in LA and LV veins for determination of blood gases and lactate levels. LA CCR (1.76 ± 0.14) was significantly lower than LV CCR (3.16 ± 0.27, P = 0.002). However, basal oxygen extraction was lower in LA (27 ± 3%) than that in the LV (58 ± 6%, P = 0.0006), indicating a larger extraction reserve in the LA than that in the LV (4.68 ± 0.84 vs. 1.88 ± 0.26, P = 0.01). Atrial pacing caused an increase in LA conductance (Series A) and oxygen extraction (Series B). AF increased LA vascular conductance to 177 ± 14% at 1 min, 168 ± 14 at 5 min, and 164 ± 31% at 10 min of AF (P < 0.05 vs. baseline). Atrial oxygen extraction also increased from 26 ± 3% at baseline to 63 ± 5% (P < 0.01) at 5 min and 60 ± 11% (P < 0.01) at 10 min of AF. Arterio-venous lactate difference increased significantly (P = 0.02) during AF. In healthy pigs, the LA has a lower CCR, but a higher extraction reserve compared with the LV. Although both reserves were recruited during AF, atrial lactate production increased significantly.

The Effect of Continuous Positive Airway Pressure on Stair-Climbing Performance in Severe COPD Patients

Stair climbing is associated with dynamic pulmonary hyperinflation and the development of severe dyspnea in patients with chronic obstructive pulmonary disease (COPD). This study aimed to assess whether (i) continuous positive airway pressure (CPAP) applied during stair climbing prevents dynamic hyperinflation and thereby reduces exercise-induced dyspnea in oxygen-dependent COPD-patients, and (ii) the CPAP-device and oxygen tank can be carried in a hip belt. In a randomised cross-over design, oxygen-dependent COPD patients performed two stair-climbing tests (44 steps): with supplemental oxygen only, then with the addition of CPAP (7 mbar). The oxygen tank and CPAP-device were carried in a hip belt during both trials.Eighteen COPD patients were included in the study. Although all patients could tolerate stair climbing with oxygen alone, 4 patients were unable to perform stair climbing while using CPAP. Fourteen COPD patients (mean FEV1 36 ± 14% pred.) completed the trial and were analyzed. The mean flow rate of supplemental oxygen was 3 ± 2 l/min during stair climbing. Lung hyperinflation, deoxygenation, hypoventilation, blood lactate production, dyspnea and the time needed to manage stair climbing were not improved by the application of CPAP (all p > 0.05). However, in comparison to climbing with oxygen alone, limb discomfort was reduced when oxygen was supplemented with CPAP (p = 0.008).In conclusion, very severe COPD patients are able to carry supporting devices such as oxygen tanks or CPAP-devices in a hip belt during stair climbing. However, the application of CPAP in addition to supplemental oxygen during stair climbing prevents neither exercise-induced dynamic hyperinflation, nor dyspnea.

Target blood pressure for hypotensive resuscitation

BackgroundGood outcomes have resulted from hypotensive resuscitation of hemorrhagic shock patients. We hypothesized that mean arterial pressure (MAP) 60mmHg is the target blood pressure for hypotensive resuscitation during uncontrolled hemorrhagic shock in trauma. MethodsTo determine the effective target MAP for hypotensive resuscitation during uncontrolled hemorrhagic shock, we randomly assigned 80 rats to one of 8 treatment groups (n=10 for each group). We then observed the effects of different target MAPs (control, 40, 50, 60, 70, 80, 90mmHg, and sham) on fluid resuscitation of uncontrolled hemorrhagic shock. Blood pressure, serum lactate, hematocrit, fluid therapy, blood loss, and plasma cytokine levels were measured at 0, 30, 90, 120, 180, 240, 300min after the start of the surgical procedure. ResultsA target MAP of 90, 80 and 70mmHg had increased blood loss and decreased hematocrit and IL-6 and TNF-α production. A target MAP of 60, 50 and 40mmHg had lower blood loss, good hematocrit, higher IL-6 and TNF-α production, and decreased animal survival. Only target MAPs of 40 and 50 had and decreased animal survival. The differences in blood loss, hematocrit, lactate, post-resuscitation MAP, survival, IL-6, IL-10, and TNF-α production between rats with a target MAP of 60mmHg and those with a target MAP of 70mmHg were not significant. The amount of fluid therapy in the BP 60 groups was less than in the BP 70 groups (P<0.001). ConclusionA MAP of 60mmHg should be considered for evaluation in human studies as a target for hypotensive resuscitation.

Ergogenic effects of quercetin supplementation in trained rats

BackgroundQuercetin is a natural polyphenolic compound currently under study for its ergogenic capacity to improve mitochondrial biogenesis. Sedentary mice have exhibited increased endurance performance, but results are contradictory in human models.MethodsWe examined the effects of six weeks of endurance training and quercetin supplementation on markers of endurance performance and training in a rodent model. Rats were randomly assigned to one of the following groups: placebo+sedentary (PS), quercetin+sedentary (QS), placebo+endurance training (PT) and quercetin+endurance training (QT). Quercetin was administered at a dose of 25 mg/kg on alternate days. During six weeks of treatment volume parameters of training were recorded, and after six weeks all groups performed a maximal graded VO2 max test and a low-intensity endurance run-to-fatigue test.ResultsNo effects were found in VO2 peak (p>0.999), nor in distance run during low-intensity test, although it was 14% greater in QT when compared with PT (P = 0.097). Post-exercise blood lactate was increased in QT when compared with PT (p=0.023) and also in QS compared with PS (p=0.024).ConclusionsThis study showed no effects in VO2 peak, speed at VO2 peak or endurance time to exhaustion after six weeks of quercetin supplementation compared with placebo in trained rats. Quercetin was show to increase blood lactate production after high-intensity exercise.

Exertional Fatigue in Patients With CKD

Fatigue is one of the most prevalent symptoms in chronic kidney disease (CKD). However, fatigue mechanisms are poorly understood due in part to nonspecific definitions. This study investigates exertional fatigue during simulated activities of daily living, focusing on oxygen delivery and utilization. "Explanatory" matched-cohort study. 13 patients with CKD (stages 3b-4; mean age, 62 ± 13 [SD] years) and 13 healthy controls, mean matched for age, height, body mass and composition, and physical activity level. Participants completed an incremental cycle ergometer test to simulate energy expenditure of typical activities of daily living. 4 exercise intensities: 1, 1.8, 2.4, and 3.1 metabolic equivalent tasks (METs). The primary outcome was exertional fatigue by rating of perceived exertion (RPE) on a 6-20 scale. Other multidimensional measures of fatigue: UK Short Form Health Survey 36 (UK SF-36) Vitality and Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue) subscales. Physiologic measures of the oxygen transport and utilization chain (expired gas analysis, cardiac output, and arterial oxygen content) and blood lactate. RPE was increased in patients compared with controls at 2.4 (10.5 [ie, light] ± 2.7 vs 8.7 [very light] ± 1.7 units) and 3.1 (12.5 [somewhat hard] ± 2.6 vs 10.2 [light] ± 1.7 units) METs (interaction P = 0.03), which was consistent with higher chronic fatigue in patients by both the UK SF-36 Vitality (P = 0.01) and FACIT-Fatigue (P = 0.004) subscales. Arterial oxygen content was decreased in patients (P = 0.001), but cardiac output and oxygen extraction ratio were unchanged, decreasing oxygen delivery (P = 0.04). Respiratory exchange ratio (P = 0.004) and blood lactate production (P = 0.002) were increased. Those inherent to a matched-cohort study. Using a novel application of the outcome measure RPE, patients with non-dialysis-dependent CKD reported considerable exertional fatigue during simulated activities of daily living. Poor compensation for mild anemia contributed to this symptom. In addition to anemia, the entire oxygen transport chain needs to be targeted to treat fatigue in patients with CKD.

Time to Exhaustion at the VO2max Velocity in Swimming: A Review

The aim of this study was to present a review on the time to exhaustion at the minimum swimming velocity corresponding to maximal oxygen consumption (TLim-vVO2max). This parameter is critical both for the aerobic power and the lactate tolerance bioenergetical training intensity zones, being fundamental to characterize it, and to point out its main determinants. The few number of studies conducted in this topic observed that swimmers were able to maintain an exercise intensity corresponding to maximal aerobic power during 215 to 260 s (elite swimmers), 230 to 260 s (high level swimmers) and 310 to 325 s (low level swimmers), and no differences between genders were reported. TLim-vVO2max main bioenergetic and functional determinants were swimming economy and VO2 slow component (direct relationship), and vVO2max, velocity at anaerobic threshold and blood lactate production (inverse relationship); when more homogeneous groups of swimmers were analysed, the inverse correlation value between TLim-vVO2max and vVO2max was not so evident. In general, TLim-vVO2max was not related to VO2max. TLim-vVO2max seems also to be influenced by stroking parameters, with a direct relationship to stroke length and stroke index, and an inverse correlation with stroke rate. Assessing TLim-vVO2max, together with the anaerobic threshold and the biomechanical general parameters, will allow a larger spectrum of testing protocols application, helping to build more objective and efficient training programs.

The kinetics of lactate production and removal during whole-body exercise.

BackgroundBased on a literature review, the current study aimed to construct mathematical models of lactate production and removal in both muscles and blood during steady state and at varying intensities during whole-body exercise. In order to experimentally test the models in dynamic situations, a cross-country skier performed laboratory tests while treadmill roller skiing, from where work rate, aerobic power and blood lactate concentration were measured. A two-compartment simulation model for blood lactate production and removal was constructed.ResultsThe simulated and experimental data differed less than 0.5 mmol/L both during steady state and varying sub-maximal intensities. However, the simulation model for lactate removal after high exercise intensities seems to require further examination.ConclusionsOverall, the simulation models of lactate production and removal provide useful insight into the parameters that affect blood lactate response, and specifically how blood lactate concentration during practical training and testing in dynamical situations should be interpreted.

Exercise in severe COPD: Is walking different from stair-climbing?

It remains unclear whether the 6-min walking test can predict performance during stair-climbing in severe COPD patients. The present study aimed to assess different pathophysiological changes between walking and stair-climbing in these patients. Sixteen COPD patients (mean FEV1 33+/-13% predicted) underwent a 6-min walking test and performed stair-climbing (44 steps) in a randomized, cross-over design. Blood gases, blood lactate, lung function parameters, maximal inspiratory mouth, sniff nasal and twitch mouth pressures, blood pressure, heart rate, and Borg Dyspnea Scale (BDS) were measured before and after exercise. The median drop of PaO2 during walking (2.6 mmHg) and stair-climbing (2.4 mmHg) was comparable (p=0.93). However, stair-climbing caused more dyspnea (median BDS 6.5 vs. 5.5, p=0.01), a higher median blood lactate (1.1 vs. 0.3 mmol/l p<0.001), a more pronounced drop in mean pH (-0.05+/-0.02 vs. -0.03+/-0.03, p=0.02) and a higher increase in mean systolic blood pressure (27+/-11 vs. 13+/-16 mmHg; p=0.009). Stair-climbing, but not walking, caused prolonged lung hyperinflation (mean TLC difference 4.4+/-4.7% predicted, p=0.003). There was no relationship between the 6-min walking distance (314+/-104 m) and the time needed for stair-climbing (55+/-33 s), nor were there any differences in inspiratory muscle strength and heart rate. Although the drop of PaO2 was comparable, stair-climbing resulted in more prolonged hyperinflation of the lungs, higher blood lactate production and more dyspnea than walking. The walking distance was not related to the time needed to manage stair-climbing. Therefore, pathophysiological changes during the 6-min walking test do not anticipate those during stair-climbing in patients with severe COPD.

Velocidade crítica como um método não invasivo para estimar a velocidade de lactato mínimo no ciclismo

A velocidade de lactato mínimo (VLM) representa o ponto de equilíbrio entre produção e remoção do lactato sanguíneo (lac). Com objetivo de analisar a validade da velocidade crítica (VC) como método não invasivo de estimar a VLM no ciclismo outdoor, 15 ciclistas (67,9 ± 5,7kg; 1,70 ± 0,1m; 26,7 ± 4,2 anos) percorreram as distâncias de 2, 4 e 6km em velódromo no menor tempo possível. A VC foi identificada pelo modelo distância-tempo a partir das combinações de séries preditivas de 2 e 4km (VC2/4), 2 e 6km (VC2/6), 4 e 6km (VC4/6) e 2, 4 e 6km (VC2/4/6). Para identificação da VLM foi realizada uma série de 2km à máxima velocidade, seguida de seis séries incrementais de 2km com 1 minuto de pausa para dosagem de lac. A VLM foi identificada visualmente (VLMv) e aplicando-se função polinomial (VLMp). Não foram observadas diferenças entre VLMv (33,3 ± 2,5km.h¹) e VLMp (33,1 ± 2,6km.h¹). Com exceção da VC4/6 (34,6 ± 3,5km.h¹), os valores de VC2/4 (38,0 ± 2,2km.h¹), VC2/6 (36,1 ± 2,4km.h¹) e VC2/4/6 (36,1 ± 2,5km.h¹) diferiram da VLMp e VLMv. Os autores concluem que, apesar de ser ~1km/h acima da VLM, a VC identificada a partir de séries preditivas de maior duração (4 e 6km - aproximadamente 6 e 10 min) não diferem estatisticamente e apresentam alta correlação e concordância com a VLM. No entanto, é necessário investigar se a VC representa um equilíbrio entre remoção e produção de lac durante exercícios de longa duração no ciclismo outdoor.

Haematopoietic stem cells and endothelial progenitor cells in healthy men: effect of aging and training

The number of hematopoietic stem cells (HSC) and endothelial progenitor cells (EPC) is thought to be a marker for neovascularization and vascular repair. Because physical inactivity and aging are risk factors for cardiovascular diseases, these factors may influence the numbers of HSCs and EPCs. Therefore, we examined baseline and exercise-induced levels of HSCs and EPCs in sedentary and trained young and older men. To study the role of aging in eight sedentary young (19-28 years) and eight sedentary older men (67-76 years), baseline and acute exercise-induced numbers of HSCs (CD34+-cells) and EPCs (CD34+/VEGFR-2+-cells) were quantified by fluorescence-activated cell sorter (FACS) analysis. To examine the effect of chronic training, eight age-matched trained young men (18-28 years) were compared with sedentary young men, whereas older men performed an 8-week endurance training. Older men showed significantly lower baseline and exercise-induced levels of HSCs/EPCs than the young men (P < 0.05). In young and older men, acute exercise significantly increased HSCs (P < 0.01), but not EPCs. The absolute increase in numbers of HSCs was attenuated in older men (P = 0.03). Apart from the lower baseline numbers of EPCs after chronic training in older men, training status did not alter baseline or exercise-induced levels of HSCs/EPCs in young and older men. We concluded that advancing age results in lower circulating numbers of HSCs and EPCs and attenuates the acute exercise-induced increase in HSCs. Interestingly, in young as well as in older men chronic endurance training does not affect baseline and exercise-induced numbers of HSCs and EPCs.

Is impairment similar between arm and leg cranking exercise in COPD patients?

Impaired skeletal muscle function has been reported in patients with chronic obstructive disease (COPD), but such impairment is not homogenous and its distribution between the upper and the lower limbs is still unclear. The present study was designed to assess and compare upper and lower limb capacities in patients with moderate to severe COPD during incremental and constant-load exercises. Thirteen COPD patients of similar age with moderate to severe air flow limitation (FEV(1): 35%+/-5% predicted) and 19 healthy subjects were studied. Four sessions were organized: two incremental and two constant-load cycling exercises with arm or leg in randomized order. As observed in a previous study involving incremental and constant tests, power, VO(2), RER, VE, and HR were all significantly lower in the upper and lower limbs of patients with COPD than in healthy controls. In the healthy population, aerobic capacity and mechanical efficiency (ME) were lower in the course of arm exercises than in leg exercises. For the same relative workload, dyspnea and blood lactate production were higher during arm exercise. In contrast, no significant difference was observed between arm and leg capacities for any of these parameters in COPD patients. Although aerobic capacity is impaired in COPD patients, arm aerobic capacity is relatively preserved. Given the lack of significant difference between arm and leg capacities in COPD, we hypothesize that upper limb muscles are less compromised than lower limb muscles in this patient population.

The metabolic costs of ‘bent-hip, bent-knee’ walking in humans

The costs of different modes of bipedalism are a key issue in reconstructing the likely gait of early human ancestors such as Australopithecus afarensis. Some workers, on the basis of morphological differences between the locomotor skeleton of A. afarensis and modern humans, have proposed that this hominid would have walked in a ‘bent-hip, bent-knee’ (BHBK) posture like that seen in the voluntary bipedalism of untrained chimpanzees. Computer modelling studies using inverse dynamics indicate that on the basis of segment proportions AL-288-1 should have been capable of mechanically effective upright walking, but in contrast predicted that BHBK walking would have been highly ineffective. The measure most pertinent to natural selection, however, is more likely to be the complete, physiological, or metabolic energy cost. We cannot measure this parameter in a fossil. This paper presents the most complete investigation yet of the metabolic and thermoregulatory costs of BHBK walking in humans. Data show that metabolic costs including the basal metabolic rate (BMR) increase by around 50% while the energy costs of locomotion and blood lactate production nearly double, heat load is increased, and core temperature does not return to normal within 20 minutes rest. Net effects imply that a resting period of 150% activity time would be necessary to prevent physiologically intolerable heat load. Preliminary data for children suggest that scaling effects would not significantly reduce relative costs for hominids of AL-288-1's size. Data from recent studies using forwards dynamic modelling confirm that similar total (including BMR) and locomotor metabolic costs would have applied to BHBK walking by AL-288-1. We explore some of the ecological consequences of our findings.

PHYSIOLOGICAL RESPONSES TO FITNESS ACTIVITIES

This study compared the heart rate (HR) and blood lactate (BL) responses in young healthy women performing the same routine of aerobics exercise in 3 different conditions: on land, in shallow water (0.8 m), and in deep water (1.4 m). The average age and body mass index (BMI) of the group were 27.4 years and 22.6 kg·m−2, respectively. The highest HR and BL values were reached during land aerobics (median HR values were 138.0 and 161.5 b·min−1, and lactate values were 3.10 and 5.65 mmol·L−1 at slow and at faster pace, respectively). These parameters were progressively reduced going from shallow water (121.5 and 154.0 b·min−1, 1.75 and 3.15 mmol·L−1) to deep water (97.5 and 113.5 b·min−1, 1.70 and 1.75 mmol·L−1). The HR measured as percentage of maximum HR varied from 48.43% to 77.53% depending on the water depth and the pace. These data indicate that exercise in water significantly reduces HR and BL production compared with the same exercise performed on land.