Comparação das intensidades correspondentes ao lactato mínimo, limiar de lactato e limiar anaeróbio durante o ciclismo em atletas de endurance

O objetivo deste estudo foi comparar a intensidade de exercício no lactato mínimo (LACmin), com a intensidade correspondente ao limiar de lactato (LL) e limiar anaeróbio (LAn). Participaram do estudo, 11 atletas do sexo masculino (idade, 22,5 + 3,17 anos; altura, 172,3 + 8,2 cm; peso, 66,9 + 8,2kg; e gordura corporal, 9,8 + 3,4%). Os indivíduos foram submetidos, em uma bicicleta eletromagnética (Quinton - Corival 400), a dois testes: 1) exercício contínuo de cargas crescentes - carga inicial de 100W, com incrementos de 25W a cada três min. até a exaustão voluntária; e 2) teste de lactato mínimo - inicialmente os indivíduos pedalaram duas vezes 425W (+ 120%max) durante 30 segundos, com um min. de intervalo, com o objetivo de induzir o acúmulo de lactato. Após oito min. de recuperação passiva, os indivíduos iniciaram um teste contínuo de cargas progressivas, idêntico ao descrito anteriormente. O LL e o LAn foram identificados como sendo o menor valor entre a razão - lactato sanguíneo (mM) / intensidade de exercício (W), e a intensidade correspondente a 3,5mM de lactato sanguíneo, respectivamente. O LACmin foi identificado como sendo a intensidade correspondente a menor concentração de lactato durante o teste de cargas progressivas. Não foi observada diferença significante entre a potência do LL (197,7 + 20,7W) e do LACmin (201,6 + 13,0W), sendo ambas significantemente menores do que do LAn (256,7 + 33,3W). Não foram encontradas também diferenças significantes para o (ml.kg-1.min-1) e a FC (bpm) obtidos no LL (43,2 + 5,01; 152,0 + 13,0) e no LACmin (42,1 + 3,9; 159,0 + 10,0), sendo entretanto significantemente menores do que os obtidos para o LAn (52,2 + 8,2; 174,0 + 13,0, respectivamente). Pode-se concluir que o teste de LACmin, nas condições experimentais deste estudo, pode subestimar a intensidade de MSSLAC (estimada indiretamente pelo LAn), o que concordacom outros estudos que determinaram a MSSLAC diretamente. Assim, são necessários mais estudos que analisem o possível componente tempo-dependente (intensidade inicial) que pode existir no protocolo do LACmin.

Índices fisiológicos associados com a performance aeróbia em corredores de endurance: efeitos da duração da prova

O objetivo deste estudo foi analisar a validade do consumo máximo de oxigênio (VO2max), da velocidade correspondente ao VO2max (vVO2max), do tempo de exaustão na vVO2max (Tlim), da economia de corrida (EC) e do limiar anaeróbio (LAn) para a predição da performance de atletas de endurance. Quatorze corredores de endurance (33,4 ± 4,4 anos; 62,7 ± 4,3kg; 166,1 ± 5,0cm; VO2max = 60,4 ± 5,9ml.kg-1.min-1) realizaram os seguintes testes: a) competição simulada nas distâncias de 1.500 e 5.000m. e; b) testes de laboratório para a determinação do VO2max, vVO2max, EC, LAn e Tlim na intensidades de 100% vVO2max. As velocidades (km/h) da vVO2max (18,7 ± 0,8), LAn (17,3 ± 1,1) v1.500m (19,9 ± 0,8) e v5.000m (17,9 ± 0,9) foram significantemente diferentes. A regressão múltipla stepwise revelou que o LAn foi o único preditor da performance da v5.000m, explicando 50% da variação desta performance. Para a v1.500m, o Tlim e a vVO2max explicaram 88% da variação da performance. Com base em nossos resultados, pode-se concluir que a validade dos índices fisiológicos (VO2max, vVO2max, Tlim, EC e LAn), para a predição da performance aeróbia de atletas de endurance, é dependente da distância da prova (1.500 x 5.000m) analisada.

Effect of the passive recovery period on the lactate minimum speed in sprinters and endurance runners

The objective of this study was to verify the effect of the passive recovery time following a supramaximal sprint exercise and the incremental exercise test on the lactate minimum speed (LMS). Thirteen sprinters and 12 endurance runners performed the following tests: 1) a maximal 500 m sprint followed by a passive recovery to determine the time to reach the peak blood lactate concentration; 2) after the maximal 500 m sprint, the athletes rested eight mins, and then performed 6 x 800 m incremental test, in order to determine the speed corresponding to the lower blood lactate concentration (LMS1) and; 3) identical procedures of the LMS1, differing only in the passive rest time, that was performed in accordance with the time to peak lactate (LMS2). The time (min) to reach the peak blood lactate concentration was significantly higher in the sprinters (12.76+/-2.83) than in the endurance runners (10.25+/-3.01). There was no significant difference between LMS1 and LMS2, for both endurance (285.7+/-19.9; 283.9+/-17.8 m/min; r= 0.96) and sprint runners (238.0+/-14.1; 239.4+/-13.9 m/min; r= 0.93), respectively. We can conclude that the LMS is not influenced by a passive recovery period longer than eight mins (adjusted according with the time to peak blood lactate), although blood lactate concentration may differ at this speed. The predominant type of training (aerobic or anaerobic) of the athletes does not seem to influence the phenomenon previously described.

Effects of aerobic endurance training status and specificity on oxygen uptake kinetics during maximal exercise

The main purpose of this study was to analyze the effects of exercise mode, training status and specificity on the oxygen uptake ((V)over dot O-2) kinetics during maximal exercise performed in treadmill running and cycle ergometry. Seven runners (R), nine cyclists (C), nine triathletes (T) and eleven untrained subjects (U), performed the following tests on different days on a motorized treadmill and on a cycle ergometer: (1) incremental tests in order to determine the maximal oxygen uptake ((V)over dot O-2max) and the intensity associated with the achievement of (V)over dot O-2max (I(V)over dot O-2max); and (2) constant work-rate running and cycling exercises to exhaustion at I(V)over dot O-2max to determine the effective time constant of the (V)over dot O-2 response (tau(V)over dot O-2). Values for (V)over dotO(2max) obtained on the treadmill and cycle ergometer [R=68.8 (6.3) and 62.0 (5.0); C=60.5 (8.0) and 67.6 (7.6); T=64.5 (4.8) and 61.0 (4.1); U=43.5 (7.0) and 36.7 (5.6); respectively] were higher for the group with specific training in the modality. The U group showed the lowest values for VO2max, regardless of exercise mode. Differences in tau(V)over dot O-2 (seconds) were found only for the U group in relation to the trained groups [R=31.6 (10.5) and 40.9 (13.6); C=28.5 (5.8) and 32.7 (5.7); T=32.5 (5.6) and 40.7 (7.5); U=52.7 (8.5) and 62.2 (15.3); for the treadmill and cycle ergometer, respectively]; no effects of exercise mode were found in any of the groups. It is concluded that tauVO(2) during the exercise performed at I(V)over dot O-2max is dependent on the training status, but not dependent on the exercise mode and specificity of training. Moreover, the transfer of the training effects on tau(V)over dotO(2) between both exercise modes may be higher compared with (V)over dot O-2max.

Electromyographic fatigue threshold of erector spinae muscle induced by a muscular endurance test in health men

Purpose: To identify the electromyographic fatigue threshold in the erector spinae muscle. Methods: Eight 19 to 24-year-old male volunteers participated in this study, in which surface electrodes were used, as well as a biological signals acquisition module (Lynx) with a sampling frequency of 1000Hz, a 1000 times gain, a 20Hz high pass filter and a 500Hz low pass filter. The test consisted of repeated isometric contractions of the erector spinae muscle in a 45° hip flexion posture, with 30%, 40%, 50% and 60% of the maximum voluntary isometric contraction. Results: A positive correlation of the RMS (root mean square) value as a function of time was found for most of the subjects with 40% (N = 6), 50% (N = 7) and 60% (N = 8) loads of the maximum voluntary isometric contraction. Conclusions: It was concluded, from this study, that the proposed protocol provides evidence, through the electromyographic signal, of the development of fatigue in the erector spinae muscle with loads of 40%, 50% and 60% of the maximum voluntary isometric contraction. The protocol also allows the electromyographic fatigue threshold and its probable applicability in the diagnosis of this phenomenon during repetitive activities to be determined.

Relação da potência aeróbica máxima e da força muscular com a economia de corrida em atletas de endurance

The objective of this study was to analyze the relationship of maximal aerobic power and the muscular strength (maximal isotonic strength and vertical jump explosive power) with the running economy (RE) in endurance athletes. Twenty-six male runners (27.9 ± 6.4 years; 62.7 ± 4.3 kg; 168.6 ± 6.1 cm; 6.6 ± 3.1% of body fat) performed in different days the following tests: a) incremental test to determine the maximal oxygen uptake (V̇O2max) and the intensity corresponding to the V̇O2max (IV̇O2max); b) constant-velocity treadmill run to determine RE; c) 1-RM test in the leg press and; d) maximal vertical jump test (VJ). V̇O2max (63.8 ± 8.3 ml/kg/min) was significantly correlated (r = 0.63; p < 0.05) with RE (48.0 ± 6.6 ml/kg/min). However, the IV̇O2max (18.7 ± 1.1 km/h), the maximal isotonic strength (230.3 ± 41.2 kg) and the VJ (30.8 ± 3.8 cm) were not significantly correlated with RE. One concludes that the maximal aerobic power can explain in part the inter-individual RE variability in endurance athletes. However, maximal isotonic strength and explosive strength seem not to be associated with RE values observed in this group of athletes.

Critical speed and endurance capacity in young swimmers: Effects of gender and age

This study analyzed the relationship between critical speed (CS) and maximal speed for 30 min (S30) in swimmers of ages 10-15 years. Fifty-one swimmers were divided by chronological age (10-12 years = G10-12, 13-15 years = G13-15), sexual maturation (pubic hair stages; P1-P3 and P4-P5), and gender (M = boys, F = girls). The CS was determined through the slope of the linear regression between the distances (100, 200, and 400 m) and participants' respective times. CS and S30 were similar in the younger (G10-12M = 0.97 vs. 0.97 m/s, and G10-12F = 1.01 vs. 0.97 m/s, respectively), and older swimmers (G13-15M = 1.10 vs. 1.07 m/s and G13-15F = 0.93 vs. 0.91 m/s, respectively). In conclusion, the CS can be used in young swimmers for the evaluation of aerobic capacity, independent of gender and age. © 2005 Human Kinetics, Inc.

Electromyographic fatigue threshold of the biceps brachii: The effect of endurance time

Muscle fatigue can be a limiting factor to determine index as the electromyographic fatigue threshold (EMGFT) due the alterations in motivation and disconfots. This way, the purpose of this study was to identify the right biceps brachii and left biceps brachii obtained from repetitive elbow flexions at each 10% of total time. Nine healthy subjects performed the exercise named biceps curl until exhaustion with 25%, 35%, and 45% of one repetition maximum, in three different days. EMG amplitude (root mean square - RMS) was obtained for concentric contractions during these load levels and correlated with time to determine the slope values for each load and them detemine the EMGFT. The EMGFT was obtained within of each 10% of total time and they were compared by analysis of variance. The results showed a progressive increase in RMS with time, for both muscles in all loads, characterizing the muscle fatigue process, and for the EMGFT values ware not found predominantly significant differences between the execution time, as well as between muscles (right biceps × left biceps). This protocol allowed to identify the EMGFT to both muscles during the biceps curl, which was similar at different percentage of total time, indicating the possibility to reduce the length of the contraction test without the need to maintain the contraction until exhaustion. Further studies are needed to evaluate the applicability of this method to determining the effects on performance.

Endurance swimming periodized training in rats

The aim of this study was to develop an experimental protocol for endurance swimming periodization training in rats similar to high performance training in humans, and compare it to continuous training. Three groups of male Wistar rats (90 days old) were allocated to Sedentary Control (SC); Continuous Training (CT); and Periodized Experimental Training (PET) groups. PET and CT trained 5 days/week, over five weeks, CT: continuous training supporting a 5% body mass (bm) load for 40 min/day; PET: training subdivided into basic, specific, and taper periods, with overload changed daily (volume-intensity, continuous, and interval training). Total training overload was quantified (% bm X exercise time in training session) and equalized for the two trained groups. Glucose ([ 3H]2-deoxyglucose) uptake, incorporation to glycogen (synthesis), glucose oxidation (CO 2 production), and lactate production from [U- 14C]glucose by soleus muscle strips incubated in presence of insulin (100μU/mL) were evaluated 48h after the last training session. The load equivalent at 5.5mM blood lactate concentration ([La-5.5]) was determined in the incremental test. Lactate production was similar in all groups. PET presented higher glucose uptake (59%) than SC, and higher glycogen synthesis (51 and 22%) and glucose oxidation (147 and 178%) than SC and CT, respectively. CT presented higher glycogen synthesis rates (23%) than SC. Load [La-5.5] was similar between trained groups and higher than SC. PET presented higher values for glucose metabolism than CT and SC. These results open up new perspectives for studying training methods used in high performance sport through swimming exercise in rats.

Endurance training does not change the relative intensity at lactate threshold in elderly

Aim. The aim of the study was to verify whether endurance training may induce changes on the percentage of peak heart rate (% peak HR) at the lactate threshold (LT) intensity in untrained elderly. Methods. Sixteen healthy men (64.3 ± 4.1 yrs) underwent an incremental test on cycloergometer to determine the LT and the corresponding % peak HR at LT intensity. Afterwards, they were randomly distributed into two groups (n = 8 each): endurance training (ET) and control (C). The ET exercised 3 days a week for 12 weeks. The training session was divided into warm-up (5 min at 50% of LT;), a main part, and a cool-down (5 min 50% below of LT). The main part had a gradual increased volume through the weeks of 2 min. The initial volume on the 1st week was 25 min reaching 47 min at the 12th week. The relative intensity was kept constant (90 to 100% of LT). Results. After 12 weeks, the % peak HR at LT did not change significantly for both groups P > 0.05 (ET 82.9 ± 4.1 vs. 82.5 ± 3.4 and Ç 80.2 ± 7.1 vs. 81.8 ± 7.1). Conclusion. We conclude that endurance training proposed does not change the relative intensity at LT in elderly.

Effects of elbow flexor muscle resistance training on strength, endurance and perceived exertion

Purpose. To verify the effects of resistance training at the electromyographic fatigue threshold (EMGFT) based on one-repetition maximum strength (1RM), heart rate (HR), rate of perceived exertion (PE) and endurance time (EndT). Methods. Nineteen subjects (training group [TG]: n = 10; control group [CG]: n = 9), performed 1-min bicep curl exercises sets at 25%, 30%, 35% and 40% 1RM. Electromyography (biceps brachii and brachiorradialis), HR and PE were registered. Biceps brachii EMGFT was used to create a load index for an eight-week resistance training programme (three sets until exhaustion/session, two sessions/week) for the TG. The CG only attended one session in the first week and another session in the last week of the eight-week training period for EndT measurement. EndT was determined from the number of repetitions of each of the three sets performed in the first and last training sessions. After training, 1RM, EMGFT, EndT, HR and PE at the different bicep curl load intensities were again measured for both groups. Results. Increases in 1RM (5.9%, p < 0.05) and EndT (> 60%, p < 0.001) after training were found. In addition, PE was reduced at all load intensities (p < 0.05), while no changes were found for HR and EMGFT after training. Conclusions. Strength-endurance training based on the EMGFT improved muscular endurance and also, to a lesser extent, muscular strength. Moreover, the reduced levels of physical exertion after training at the same intensity suggest that endurance training exercises may improve comfort while performing strength exercises.

Physiological adaptations during endurance training below anaerobic threshold in rats

To assess the effects of continuous exercise training at intensities corresponding to 80 and 90 % of the lactate minimum test (LM), we evaluated antioxidant activity, hormone concentration, biochemical analyses and aerobic and anaerobic performance, as well as glycogen stores, during 12 weeks of swimming training in rats. One-hundred rats were separated into three groups: control (CG, n = 40), exercise at 80 (EG80, n = 30) and 90 % (EG90, n = 30) of LM. The training lasted 12 weeks, with sessions of 60 min/day, 6 days/week. The intensity was based at 80 and 90 % of the LM. The volume did not differ between training groups (Ẋ of EG80 = 52 ± 4 min; Ẋ of EG90 = 56 ± 2 min). The glycogen concentration (mg/100 mg) in the gastrocnemius increased after the training in EG80 (0.788 ± 0.118) and EG90 (0.795 ± 0.157) in comparison to the control (0.390 ± 0.132). The glycogen stores in the soleus enhanced after the training in EG90 (0.677 ± 0.230) in comparison to the control (0.343 ± 0.142). The aerobic performance increased by 43 and 34 % for EG80 and EG90, respectively, in relation to baseline. The antioxidant enzymes remain unchanged during the training. Creatine kinase (U/L) increased after 8 weeks in both groups (EG80 = 427.2 ± 97.4; EG90 = 641.1 ± 90.2) in relation to the control (246.9 ± 66.8), and corticosterone (ng/mL) increased after 12 weeks in EG90 (539 ± 54) in comparison to the control (362 ± 44). The continuous exercise at 80 and 90 % of the LM has a marked aerobic impact on endurance performance without significantly biomarkers changes compared to control. © 2013 Springer-Verlag Berlin Heidelberg.

The psychobiological model: a new explanation to intensity regulation and (in)tolerance in endurance exercise

The mechanisms underpinning fatigue and exhaustion, and the specific sources of exercise-endurance intensity regulation and (in)tolerance have been investigated for over a century. Although several scientific theories are currently available, over the past five years a new framework called Psychobiological model has been proposed. This model gives greater attention to perceptual and motivational factors than its antecedents, and their respective influence on the conscious process of decision-making and behavioral regulation. In this review we present experimental evidences and summarize the key points of the Psychobiological model to explain intensity regulation and (in)tolerance in endurance exercise. Still, we discuss how the Psychobiological model explains training-induced adaptations related to improvements in performance, experimental manipulations, its predictions, and propose future directions for this investigative area. The Psychobiological model may give a new perspective to the results already published in the literature, helping scientists to better guide their research problems, as well as to analyze and interpret new findings more accurately.

Predição da performance de corredores de endurance por meio de testes de laboratório e pista

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Endurance exercise training increases APPL1 expression and improves insulin signaling in the hepatic tissue of diet-induced obese mice, independently of weight loss

Hepatic insulin resistance is the major contributor to fasting hyperglycemia in type 2 diabetes. The protein kinase Akt plays a central role in the suppression of gluconeogenesis involving forkhead box O1 (Foxo1) and peroxisome proliferator-activated receptor gamma co-activator 1 alpha (PGC-1a), and in the control of glycogen synthesis involving the glycogen synthase kinase beta (GSK3 beta) in the liver. It has been demonstrated that endosomal adaptor protein APPL1 interacts with Akt and blocks the association of Akt with its endogenous inhibitor, tribbles-related protein 3 (TRB3), improving the action of insulin in the liver. Here, we demonstrated that chronic exercise increased the basal levels and insulin-induced Akt serine phosphorylation in the liver of diet-induced obese mice. Endurance training was able to increase APPL1 expression and the interaction between APPL1 and Akt. Conversely, training reduced both TRB3 expression and TRB3 and Akt association. The positive effects of exercise on insulin action are reinforced by our findings that showed that trained mice presented an increase in Foxo1 phosphorylation and Foxo1/PGC-1a association, which was accompanied by a reduction in gluconeogenic gene expressions (PEPCK and G6Pase). Finally, exercised animals demonstrated increased at basal and insulin-induced GSK3 beta phosphorylation levels and glycogen content at 24?h after the last session of exercise. Our findings demonstrate that exercise increases insulin action, at least in part, through the enhancement of APPL1 and the reduction of TRB3 expression in the liver of obese mice, independently of weight loss. J. Cell. Physiol. 227: 29172926, 2012. (C) 2011 Wiley Periodicals, Inc.