Regulating anaerobic metabolism and promoting myocardial ischemia-hypoxia injury by diesel particulate matter and its key component benzoapyrene via targeting oxygen sensors / 环境与职业医学

Background The exposure to diesel particulate matter (DPM) and its polycyclic aromatic hydrocarbons (PAH) is closely related to the morbidity and mortality of ischemic heart disease (IHD). However, it is unclear what key components and targets of DPM exposure involve in myocardial ischemia-hypoxia injury and associated mechanisms. Objective To identify key PAH components of DPM that act on myocardial hypoxic injury, andclarify the role of oxygen sensors-regulated anaerobic metabolism in DPM and key components-induced hypoxic injury and the targets of the key PAH components. Methods Human cardiomyocyte cell line AC16 cells were exposed to 0, 1, 5, and 10 μg·mL−1 DPM in a high glucose DMEM medium with 10% fetal bovine serum (FBS) (HGM) or low FBS (0.5%) in high glucose DMEM medium (LFM), for 12 h under 2% O2, and expression of hypoxia-inducible factor-1α (HIF-1α), Bax, and Cleaved-caspase3 was determined by Western blotting. Under normal condition, the cell viability was detected after PAH exposure for 12 h. Under the condition of ischemia-hypoxia model, cells were exposed to 0, 0.005, 0.5, and 5 µg·mL−1 PAH for 12 h, and the protein expression of HIF-1α, Bax, and Cleaved-caspase3 was determined. After exposure to DPM or PAH for 12 h, the contents of pyruvate and lactate in cells were detected. Pretreatment with glycolysis inhibitor GSK2837808A was used to explore the role of glycolysis in DPM and benzo[a]pyrene (BaP)-induced hypoxia injury. A molecular docking technique was used to analyze the binding affinity between PAH and oxygen sensors (prolyl hydroxylase domain-containing protein 2, PHD2, and factor-inhibiting hypoxia-inducible factor 1, FIH1), and the protein levels of PHD2, FIH1, and hydroxyl-HIF-1-alpha (OH-HIF-1α) after the DPM or BaP treatment were further determined. Results Under hypoxia, DPM exposure in the LFM induced the expression of HIF-1α, Bax, and Cleaved-caspase3 (P<0.01). Therefore, hypoxia and LFM were selected as the basic ischemia and hypoxia condition. Except for anthracene (Ant) (P>0.05), other PAH decreased cell viability when the concentration was above 1 μg·mL−1 (P<0.05). All concentrations of BaP induced the expression of HIF-1α protein (P<0.05), and the protein levels of Bax and Cleaved-caspase3 were up-regulated after the 0.5 and 5 µg·mL−1 BaP exposure (P<0.01). After exposure to DPM (1, 5 and 10 μg·mL−1) or BaP (0.5 and 5 μg·mL−1), the intracellular pyruvate and lactate contents increased (P<0.05). The glycolysis inhibitor co-treatment decreased the levels of HIF-1α, Bax, and Cleaved-caspase3 proteins compared with the DPM or BaP exposure group for 12 h (P＜0.05). The binding abilities of the five PAHs to the oxygen sensors PHD2 and FIH1 were strong, and BaP was the strongest. Although the DPM or BaP exposure had no effects on the protein levels of PHD2 and FIH1 in AC16 cells (P＜0.05), the protein level of OH-HIF-1α was decreased (P＜0.01). Conclusion BaP exposure can promote hypoxia and injury of myocardial cells and is the key PAH component of DPM that induces myocardial ischemia and hypoxia injury. BaP exposure inhibits the hydroxylation function of PHD2 on HIF-1α by combining with PHD2, decreases the level of OH-HIF-1α and induces HIF-1α accumulation. And then HIF-1α promotes anaerobic metabolism and accelerates ischemia and hypoxia injury of myocardial cells.

Comparação da proporção entre pressão venosa central menos arterial de dióxido de carbono e conteúdo de oxigênio arterial menos venoso central e níveis de lactato como preditores de mortalidade em pacientes críticos: uma revisão sistemática e metanálise / Comparison of central venous minus arterial carbon dioxide pressure to arterial minus central venous oxygen content ratio and lactate levels as predictors of mortality in critically ill patients: a systematic review and meta-analysis

RESUMO Objetivo: A proporção entre pressão venosa central menos arterial de dióxido de carbono e conteúdo de oxigênio arterial menos venoso central (Pcv-aCO2/Ca-cvO2) é frequentemente usada como substituta para a oxigenação tecidual. O objetivo deste estudo foi identificar e sintetizar a literatura e a qualidade das evidências que suportam a Pcv-aCO2/Ca-cvO2 como um preditor de mortalidade em comparação com o lactato em pacientes críticos. Métodos: Pesquisamos vários bancos de dados procurando estudos que tivessem medido a Pcv-aCO2/Ca-cvO2 em pacientes críticos. Pesquisadores independentes realizaram a triagem dos artigos e a extração de dados. Uma metanálise de efeitos aleatórios foi realizada. Diferenças médias padronizadas agrupadas foram usadas para comparar a capacidade prognóstica da Pcv-aCO2/Ca-cvO2 e do lactato. Resultados: Inicialmente, obtivemos 172 estudos; 17 foram incluídos para descrição qualitativa, e dez foram incluídos para síntese quantitativa. A média de Pcv-aCO2/Ca-cvO2 foi maior nos não sobreviventes do que nos sobreviventes (diferença média padronizada agrupada de 0,75; IC95% 0,34 - 1,17; I2 = 83%), assim como os níveis de lactato (diferença média padronizada agrupada = 0,94; IC95% 0,34 - 1,54; I2 = 92%). Ambos os testes foram preditores estatisticamente significativos de mortalidade, embora com sobreposição de IC95% entre eles. Conclusão: Evidências de qualidade moderada mostraram pouca ou nenhuma diferença na capacidade da Pcv-aCO2/Ca-cvO2, em comparação com o lactato, em predizer mortalidade. No entanto, nossas conclusões são limitadas pela considerável heterogeneidade entre os estudos. Registro no PROSPERO:CRD42019130387

ABSTRACT Objective: The central venousarterial carbon dioxide pressure to arterial-central venous oxygen content ratio (Pcv-aCO2/Ca-cvO2) is frequently used as a surrogate for tissue oxygenation. We aimed to identify and synthesize literature and quality of evidence supporting Pcv-aCO2/Ca-cvO2 as a predictor of mortality in critically ill patients compared with lactate. Methods: We searched several databases for studies measuring Pcv-aCO2/Ca-cvO2 in critically ill patients. Independent investigators performed the article screening and data extraction. A random-effects metaanalysis was performed. Pooled standardized mean differences (SMD) were used to compare the prognostic ability of Pcv-aCO2/Ca-cvO2 and lactate. Results: We initially retrieved 172 studies; 17 were included for qualitative description, and 10 were included for quantitative synthesis. The mean Pcv-aCO2/Ca-cvO2 was higher in nonsurvivors than in survivors (pooled SMD = 0.75; 95%CI 0.34 - 1.17; I2 = 83%), as was the case with lactate levels (pooled SMD = 0.94; 95%CI 0.34 - 1.54; I2 = 92%). Both tests were statistically significant predictors of mortality, albeit with overlapping 95%CIs between them. Conclusion: Moderate-quality evidence showed little or no difference in the ability of Pcv-aCO2/Ca-cvO2, compared with lactate, to predict mortality. Nevertheless, our conclusions are limited by the considerable heterogeneity among the studies. PROSPERO registration:CRD42019130387

El índice de anaerobiosis predice mortalidad en neumonía grave por SARS-CoV-2 / The anaerobiosis index predicts mortality in patients with severe pneumonia due to SARS-CoV-2 / O índice de anaerobiose prevê a mortalidade em pneumonia grave devido a SARS-CoV-2

Resumen: Introducción: Detectar y corregir el metabolismo anaerobio es indispensable en el paciente críticamente enfermo; desafortunadamente, no existe un estándar de oro. Los pacientes con neumonía grave por SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) presentan hipoxemia severa, aumentando el metabolismo anaerobio. El lactato y la diferencia de presión venoarterial de dióxido de carbono/diferencia del contenido arteriovenoso de oxígeno (Δp(v-a)CO2/ΔC(a-v)O2) son útiles en este contexto. Material y métodos: Estudio de cohorte, prospectivo, descriptivo y analítico, que incluyó pacientes ingresados a la Unidad de Cuidados Intensivos (UCI) en el periodo comprendido entre el 18 de abril de 2020 al 18 de enero de 2021 con neumonía grave (definida por el inicio de ventilación mecánica invasiva) por SARS-CoV-2 confirmados. Resultados: En el periodo comprendido se incluyeron 91 pacientes que cumplieron con los criterios de inclusión. Del total, 39 pacientes se incluyeron en el grupo de supervivientes y 52 en el grupo de no supervivientes. Se puede observar que la Δp(v-a)CO2/ΔC(a-v)O2, o índice de anaerobiosis, tiene OR de 4.4, IC de 95% 1.51-13.04, p = 0.006 en el análisis multivariable. Conclusión: El incremento de la Δp(v-a)CO2/ΔC(a-v)O2, o índice de anaerobiosis, > 1.4 mmHg/mL está relacionado con 4.44 veces más riesgo de muerte en los pacientes con neumonía grave (intubados) por SARS-CoV-2.

Abstract: Introduction: Detecting and correcting anaerobic metabolism is essential in the critically ill patient, unfortunately, there is no gold standard. Patients with severe pneumonia due to SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) present severe hypoxemia, increasing anaerobic metabolism. Lactate and the venoarterial carbon dioxide pressure difference/arteriovenous oxygen content difference (Δp(v-a)CO2/ΔC(a-v)O2) are useful in this context. Material and methods: Prospective, descriptive and analytical cohort study that included patients admitted to the Intensive Care Unit (ICU) in the period from April 18, 2020 to January 18, 2021 with severe pneumonia (defined by the start of invasive mechanical ventilation) by SARS-CoV-2 confirmed. Results: In the period covered, 91 patients who met the inclusion criteria were included. Of the total, 39 patients were included in the survivors group and 52 in the non-survivors group. It can be seen that the Δp(v-a)CO2/ΔC(a-v)O2 also called anaerobiosis index has OR 4.4, 95% CI 1.51-13.04, p = 0.006 in the multivariate analysis. Conclusion: The increase in the Δp(v-a)CO2/ΔC(a-v)O2 also called anaerobiosis index > 1.4 mmHg/mL is associated with a 4.44 times higher risk of death in patients with severe pneumonia (intubated) due to SARS-CoV-2.

Resumo: Introdução: Detectar e corrigir o metabolismo anaeróbio é essencial no paciente crítico, infelizmente, não existe um «padrão ouro¼. Pacientes com pneumonia grave por SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) apresentam hipoxemia grave, aumentando o metabolismo anaeróbio. O lactato e a diferença de pressão venoarterial de dióxido de carbono/diferença do conteúdo arteriovenoso de oxigênio (Δp(v-a)CO2/ΔC(a-v)O2) são úteis neste cenário. Material e métodos: Estudo de coorte, prospectivo, descritivo e analítico que incluiu pacientes internados na Unidade de Terapia Intensiva (UTI) no período de 18 de abril de 2020 a 18 de janeiro de 2021 com pneumonia grave (definida pelo início da ventilação mecânica invasiva) por SARS-CoV-2 confirmados. Resultados: No período compreendido, foram incluídos 91 pacientes que atenderam aos critérios de inclusão. Do total, 39 pacientes foram incluídos no grupo sobrevivente e 52 no grupo não sobrevivente. Pode-se observar que o Δp(v-a)CO2/ΔC(a-v)O2 ou índice de anaerobiose tem OR 4.4, IC 95% 1.51-13.04, p = 0.006 na análise multivariada. Conclusão: Um aumento em Δp(v-a)CO2/ΔC(a-v)O2 ou índice de anaerobiose > 1.4 mmHg/mL está associado a um aumento de 4.44 vezes no risco de morte em pacientes com pneumonia grave (entubados) por SARS-CoV-2.

Energy system contribution in a maximal incremental test: correlations with pacing and overall performance in a 10-km running trial

This study aimed to verify the association between the contribution of energy systems during an incremental exercise test (IET), pacing, and performance during a 10-km running time trial. Thirteen male recreational runners completed an incremental exercise test on a treadmill to determine the respiratory compensation point (RCP), maximal oxygen uptake (V˙O2max), peak treadmill speed (PTS), and energy systems contribution; and a 10-km running time trial (T10-km) to determine endurance performance. The fractions of the aerobic (WAER) and glycolytic (WGLYCOL) contributions were calculated for each stage based on the oxygen uptake and the oxygen energy equivalents derived by blood lactate accumulation, respectively. Total metabolic demand (WTOTAL) was the sum of these two energy systems. Endurance performance during the T10-km was moderately correlated with RCP, V˙O2maxand PTS (P<@0.05), and moderate-to-highly correlated with WAER, WGLYCOL, and WTOTAL (P<0.05). In addition, WAER, WGLYCOL, and WTOTAL were also significantly correlated with running speed in the middle (P<0.01) and final (P<0.01) sections of the T10-km. These findings suggest that the assessment of energy contribution during IET is potentially useful as an alternative variable in the evaluation of endurance runners, especially because of its relationship with specific parts of a long-distance race.

Efecto del anegamiento en la actividad de la enzima alcohol deshidrogenasa en raíces de maracuyá amarillo Passiflora Edulis var. Flavicarpa / Effect of waterlogging on the alcohol dehydrogenase activity in yellow passion fruit roots Passiflora Edulis var. Flavicarpa

Bajo entornos naturales, las plantas de maracuyá amarillo frecuentemente se enfrentan a condiciones de anegamiento, un factor limitante para la producción generalizada de su cultivo, especialmente en tierras bajas inundables. El presente estudio se encargó de identificar la activación de la enzima alcohol deshidrogenasa (ADH) durante la inundación, como un posible mecanismo de sobrevivencia de plántulas de maracuyá amarillo. Se evaluó la actividad de la enzima ADH durante 0, 1, 3, 7, 9 y 14 días de tratamiento con inundación y sin inundación, en raíces de plántulas de maracuyá amarillo de tres meses y medio de germinadas. En las raíces de plántulas de maracuyá amarillo en condiciones de inundación, la actividad de la enzima ADH presentó un aumento significativo respecto a las plántulas en condiciones normales de riego (sin inundación). Esto sugiere que la actividad de la enzima alcohol deshidrogenasa, implicada en el metabolismo anaeróbico, es un posible mecanismo de supervivencia al anegamiento de plántulas de maracuyá amarillo en periodos cortos de inundación.

Under natural environments, yellow passion fruit plants often face flooded conditions as a limiting factor for the widespread production of the crop, especially in flood-prone lowlands. This study was carried out to identify the activation of the enzyme alcohol dehydrogenase (ADH) during the flood, as a possible mechanism for the survival of yellow passion fruit seedlings. The activity of the ADH enzyme was assessed on days 0, 1, 3, 7, 9 and 14, with and without flooding, on rooted yellow passion fruit seedlings germinated during three and a half months. In the roots of the yellow passion fruit seedlings in flood conditions, the activity of the ADH enzyme showed a significant increase compared to seedlings under normal irrigation (no flooding). These results suggest that the activity of the alcohol dehydrogenase enzyme involved in anaerobic metabolism, is a possible mechanism for survival of yellow passion fruit seedlings waterlogged in short periods of flooding.

Association between anaerobic components of the maximal accumulated oxygen deficit and 30-second Wingate test

The purpose of this study was to analyze the relationship between the anaerobic components of the maximal accumulated oxygen deficit (MAOD) and of the 30-second Wingate anaerobic test (30-WAnT). Nine male physical education students performed: a) a maximal incremental exercise test; b) a supramaximal constant workload test to determine the anaerobic components of the MAOD; and c) a 30-WAnT to measure the peak power (PP) and mean power (MP). The fast component of the excess post-exercise oxygen consumption and blood lactate accumulation were measured after the supramaximal constant workload test in order to determine the contributions made by alactic (ALMET) and lactic (LAMET) metabolism. Significant correlations were found between PP and ALMET (r=0.71; P=0.033) and between MP and LAMET (r=0.72; P=0.030). The study results suggested that the anaerobic components of the MAOD and of the 30-WAnT are similarly applicable in the assessment of ALMET and LAMET during high-intensity exercise.

Atividade de enzimas fermentativas em raízes e nódulos de soja sob condições de hipóxia e pós-hipóxia / Fermentative enzymes activity in soybean roots and nodules under hypoxia and post-hypoxia conditions

O objetivo deste trabalho foi avaliar a atividade de enzimas fermentativas em raízes e nódulos de soja (Glycine max) sob condições de hipóxia e pós-hipóxia. Os genótipos Fundacep 53 RR e BRS Macota foram cultivados em vasos de 3L contendo vermiculita como substrato em associação com Bradyrhizobium elkanii em casa de vegetação. No estádio R2, o sistema radicular das plantas foi submetido à hipóxia pelo encaixe de um segundo vaso sem perfurações e inundado com solução nutritiva diluída a 1/3 da concentração original, por 8 dias. Posteriormente, foram retirados os vasos sem perfurações para avaliação da recuperação. O material vegetal foi coletado no 2º, 4º, 6º e 8º dias após a inundação ou recuperação, juntamente com os controles para a dosagem da atividade das enzimas álcool desidrogenase (ADH), piruvato descarboxilase (PDC) e lactato desidrogenase (LDH) em raízes e nódulos. Os dados foram submetidos à ANOVA e comparados pelo teste de Tukey a 5% de probabilidade. As atividades da ADH, PDC e LDH foram fortemente estimuladas com a inundação, especialmente em nódulos, e diminuíram com a recuperação, em ambos os genótipos. Fundacep 53 RR respondeu de forma mais efetiva aos efeitos dos tratamentos.

This study aimed to evaluate the activity of fermentative enzymes in soybean (Glycine max) roots and nodules under hypoxia and post-hypoxia conditions. The soybean genotypes Fundacep 53 RR and BRS Macota associated with Bradyrhizobium elkanii were grown in 3L pots containing vermiculite as substrate under greenhouse conditions. Root system of plants at the R2 stage was subjected to hypoxia by blocking drainage of the pot, by fitting a second one without holes and flooded with nutrient solution diluted one-third of the original. The flooding of the plants was carried out for eight days and after, the pot without drilling was removed for recovery assessment. Non-waterlogged plants were kept as control. Activities of the fermentation enzymes alcohol dehydrogenase (ADH), pyruvate decarboxylase (PDC) and lactate dehydrogenase (LDH) were quantified in roots and nodules collected at 2, 4, 6 and 8 days after flooding or recovery. Data were analyzed by ANOVA and compared by the Tukey test (P ≤ 0,05). Activities of ADH, PDC and LDH were hardly stimulated during flooding, especially in nodules, in both genotypes and decreased with recovery. Fundacep 53 RR responded more effectively to treatment effects.

Response of antioxidative and ethanolic fermentation enzymes in maize seedlings of tolerant and sensitive genotypes under short term waterlogging.

Fifteen days old seedlings of waterlogging tolerant (Parkash) and sensitive (Paras) maize genotypes were subjected to short term waterlogging (18 h) under field conditions. Activities of various antioxidative and anaerobic metabolism enzymes were investigated in leaf and root tissues. Superoxide dismutase (SOD) activity increased in leaf tissue while glutathione reductase (GR) activity was enhanced in leaf as well as root in both the genotypes. However, tolerant genotype had better induction capability of SOD and GR in roots in comparison with sensitive genotype. Catalase activity increased in roots of both genotypes. Waterlogging caused strong induction in alcohol dehydrogenase activity in the roots of Paras and Parkash under stress conditions. Aldehyde dehydrogenase activity was significantly increased only in roots of Parkash in response to waterlogging. In comparison with sensitive genotype, the tolerant genotype had low H2O2 and malondialdehyde content in roots under stress conditions. The present studies suggested that tolerant genotype had a greater protective ability due to higher induced activities of antioxidant and ethanolic fermentation systems than Paras.

Aerobic and anaerobic metabolism for the zebrafish, Danio rerio, reared under normoxic and hypoxic conditions and exposed to acute hypoxia during development / Metabolismo aeróbico e anaeróbico do paulistinha Danio rerio, mantidos sob normóxia e hipóxia moderada e expostos a hipóxia aguda durante diferentes estágios de desenvolvimento

In order to verify the influence of chronic and acute ambient oxygen levels from egg to adult stage of the zebrafish, in vivo oxygen consumption (MO2), critical tensions of oxygen (Pcrit), heart rate (fH) and total body lactate concentration (Lc) were determined for Danio rerio (Hamilton, 1822) raised at 28 °C under normoxic (7.5 mgO2.L-1 or 80 mm.Hg-1) and hypoxic conditions (4.3 mgO2.L-1) and exposed to acute hypoxia during different developmental stages. Our findings confirmed that very early stages do not respond effectively to ambient acute hypoxia. However, after the stage corresponding to the age of 30 days, D. rerio was able to respond to acute hypoxia through effective physiological mechanisms involving aerobic and anaerobic metabolism. Such responses were more efficient for the fishes reared under hypoxia which showed that D. rerio survival capability increased during acclimation to mild hypoxia. Measurements of body mass and length showed that moderate hypoxia did not affect growth significantly until the fish reached the stage of 60 days. Moreover, a growth delay was verified for the hypoxic-reared animals. Also, the D. rerio eggs-to-larvae survival varied from 87.7 to 62.4 percent in animals reared under normoxia and mild hypoxia, respectively. However, the surviving animals raised under moderated hypoxia showed a better aptitude to regulate aerobic and anaerobic capacities when exposed to acute hypoxia.

A influência de diferentes níveis de oxigênio no desenvolvimento (ovos a adulto) do peixe paulistinha Danio rerio (Hamilton, 1822) foi verificada por meio de medidas experimentais de consumo de oxigênio (MO2), tensões críticas de oxigênio (Pcrit), taxa de batimentos cardíacos (fH) e concentração total de lactato nos tecidos (Lc), para os animais mantidos a 28 ºC sob níveis normóxicos de oxigênio (7.5 mgO2.L-1 ou 80 mmHg) e hipóxicos (4.3 mgO2.L-1) e submetidos a hipóxia ambiental aguda, em diferentes estágios de desenvolvimento. Os resultados obtidos indicam que os peixes em estágios iniciais do desenvolvimento não variam suas respostas fisiológicas em função das oscilações ambientais nos níveis de oxigênio, visto que tais respostas iniciaram-se somente no estágio de 30 dias de vida. A partir deste estágio D. rerio apresentou capacidade em responder à hipóxia aguda por meio de mecanismos fisiológicos efetivos envolvendo metabolismo aeróbico e anaeróbico. Tais respostas foram mais efetivas para os peixes mantidos sob hipóxia, o que mostrou que a capacidade de sobrevivência de D. rerio aumentou durante o período de aclimatação à hipóxia moderada. As medidas de massa e comprimento corpóreos mostraram que a permanência dos peixes em hipóxia durante o desenvolvimento não afetou esses parâmetro até os peixes atingirem o estágio de 60 dias. A partir deste estágio foi observado ligeiro atraso no crescimento dos espécimes mantidos sob hipóxia. A taxa de sobrevivência de D.rerio variou de 87,7 a 62,4 por cento para os animais mantidos respectivamente sob níveis normóxicos e hipóxicos. No entanto, os animais mantidos sob hipóxia moderada, que sobreviveram, mostraram maior capacidade em regular seu metabolismo aeróbico e anaeróbico quando expostos à hipóxia ambiental aguda.

The relationship between exercise diuresis and running load / 体力科学

This study was designed to examine the relationship between exercise diuresis and running load, following seven types of running events by five male athletes, aged 19 to 25 years. None had a history of renal disease.<BR>Informed written consent was obtained from all subjects prior to the study.<BR>1. Compared to the resting levels, significant increases in the urinary volume were observed thirty minutes after performing a 400-meter dash, but not after the other exercises.<BR>2. The changes in creatinine concentration (30 min after exercise/after warm-up) were inversely proportional to the changes in urinary volume, indicating that exercise diuresis depends on the depressed reabsorption of water in the renal tubules.<BR>3. The absence of diuresis after 60 and 100-meter sprints, indicates that the phosphagen system is mainly employed for energy supply.<BR>4. The urinary volumes after 200, 300 and 400-meter dashs highly correlated with the changes in the excretion rate of pyruvate. This suggests that exercise diuresis is related to the lactic system in energy metabolism.<BR>5. The decreased excretion rate of creatinine after 800 and 1, 500-meter runs indicates that GFR is reduced by these exercises. Furthermore, the lactic energy system caused the diuretic effect. Thus, even though secretion of antidiuretic hormones is increased following exercise, their effectiveness is reduced by lactic oxygen deficit.