Combining heat stress and moderate hypoxia reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics.

PURPOSE: This study investigated the isolated and combined effects of heat [temperate (22 °C/30 % rH) vs. hot (35 °C/40 % rH)] and hypoxia [sea level (FiO2 0.21) vs. moderate altitude (FiO2 0.15)] on exercise capacity and neuromuscular fatigue characteristics. METHODS: Eleven physically active subjects cycled to exhaustion at constant workload (66 % of the power output associated with their maximal oxygen uptake in temperate conditions) in four different environmental conditions [temperate/sea level (control), hot/sea level (hot), temperate/moderate altitude (hypoxia) and hot/moderate altitude (hot + hypoxia)]. Torque and electromyography (EMG) responses following electrical stimulation of the tibial nerve (plantar-flexion; soleus) were recorded before and 5 min after exercise. RESULTS: Time to exhaustion was reduced (P < 0.05) in hot (-35 ± 15 %) or hypoxia (-36 ± 14 %) compared to control (61 ± 28 min), while hot + hypoxia (-51 ± 20 %) further compromised exercise capacity (P < 0.05). However, the effect of temperature or altitude on end-exercise core temperature (P = 0.089 and P = 0.070, respectively) and rating of perceived exertion (P > 0.05) did not reach significance. Maximal voluntary contraction torque, voluntary activation (twitch interpolation) and peak twitch torque decreased from pre- to post-exercise (-9 ± 1, -4 ± 1 and -6 ± 1 % all trials compounded, respectively; P < 0.05), with no effect of the temperature or altitude. M-wave amplitude and root mean square activity were reduced (P < 0.05) in hot compared to temperate conditions, while normalized maximal EMG activity did not change. Altitude had no effect on any measured parameters. CONCLUSION: Moderate hypoxia in combination with heat stress reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics. Impaired oxygen delivery or increased cardiovascular strain, increasing relative exercise intensity, may have also contributed to earlier exercise cessation.

Cardiorespiratory adaptations induced by aerobic training in middle-aged men: the importance of a decrease in sympathetic stimulation for the contribution of dynamic exercise tachycardia

We investigated the effects of aerobic training on the efferent autonomic control of heart rate (HR) during dynamic exercise in middle-aged men, eight of whom underwent exercise training (T) while the other seven continued their sedentary (S) life style. The training was conducted over 10 months (three 1-h sessions/week on a field track at 70-85% of the peak HR). The contribution of sympathetic and parasympathetic exercise tachycardia was determined in terms of differences in the time constant effects on the HR response obtained using a discontinuous protocol (4-min tests at 25, 50, 100 and 125 watts on a cycle ergometer), and a continuous protocol (25 watts/min until exhaustion) allowed the quantification of the parameters (anaerobic threshold, VO2 AT; peak O2 uptake, VO2 peak; power peak) that reflect oxygen transport. The results obtained for the S and the T groups were: 1) a smaller resting HR in T (66 beats/min) when compared to S (84 beats/min); 2) during exercise, a small increase in the fast tachycardia (D0-10 s) related to vagal withdrawal (P<0.05, only at 25 watts) was observed in T at all powers; at middle and higher powers a significant decrease (P<0.05 at 50, 100 and 125 watts) in the slow tachycardia (D1-4 min) related to a sympathetic-dependent mechanism was observed in T; 3) the VO2 AT (S = 1.06 and T = 1.33 l/min) and VO2 peak (S = 1.97 and T = 2.47 l/min) were higher in T (P<0.05). These results demonstrate that aerobic training can induce significant physiological adaptations in middle-aged men, mainly expressed as a decrease in the sympathetic effects on heart rate associated with an increase in oxygen transport during dynamic exercise.

Intensity and physiological responses to the 6-minute walk test in middle-aged and older adults: a comparison with cardiopulmonary exercise testing

The 6-minute walk test (6MWT) is a simple field test that is widely used in clinical settings to assess functional exercise capacity. However, studies with healthy subjects are scarce. We hypothesized that the 6MWT might be useful to assess exercise capacity in healthy subjects. The purpose of this study was to evaluate 6MWT intensity in middle-aged and older adults, as well as to develop a simple equation to predict oxygen uptake ( V ˙ O 2 ) from the 6-min walk distance (6MWD). Eighty-six participants, 40 men and 46 women, 40-74 years of age and with a mean body mass index of 28±6 kg/m2, performed the 6MWT according to American Thoracic Society guidelines. Physiological responses were evaluated during the 6MWT using a K4b2 Cosmed telemetry gas analyzer. On a different occasion, the subjects performed ramp protocol cardiopulmonary exercise testing (CPET) on a treadmill. Peak V ˙ O 2 in the 6MWT corresponded to 78±13% of the peak V ˙ O 2 during CPET, and the maximum heart rate corresponded to 80±23% of that obtained in CPET. Peak V ˙ O 2 in CPET was adequately predicted by the 6MWD by a linear regression equation: V ˙ O 2 mL·min-1·kg-1 = -2.863 + (0.0563×6MWDm) (R2=0.76). The 6MWT represents a moderate-to-high intensity activity in middle-aged and older adults and proved to be useful for predicting cardiorespiratory fitness in the present study. Our results suggest that the 6MWT may also be useful in asymptomatic individuals, and its use in walk-based conditioning programs should be encouraged.

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.

Neuromuscular adaptations in endurance-trained boys and men

Competitive sports participation in youth is becoming increasingly more common in the Western world. It is widely accepted that sports participation, specifically endurance training, is beneficial for physical, psychomotor, and social development of children. The research on the effect of endurance training in children has focused mainly on healthrelated benefits and physiological adaptations, particularly on maximal oxygen uptake. However, corresponding research on neuromuscular adaptations to endurance training and the latter's possible effects on muscle strength in youth is lacking. In children and adults, resistance training can enhance strength and mcrease muscle activation. However, data on the effect of endurance training on strength and neuromuscular adaptations are limited. While some evidence exists demonstrating increased muscle activation and possibly increased strength in endurance athletes compared with untrained adults, the neuromuscular adaptations to endurance training in children have not been examined. Thus, the purpose of this study was to examine maximal isometric torque and rate of torque development (RID), along with the pattern of muscle activation during elbow and knee flexion and extension in muscle-endurancetrained and untrained men and boys. Subjects included 65 males: untrained boys (n=18), endurance-trained boys (n=12), untrained men (n=20) and endurance-trained men (n=15). Maximal isometric torque and rate of torque development were measured using an isokinetic dynamometer (Biodex III), and neuromuscular activation was assessed using surface electromyography (SEMG). Muscle strength and activation were assessed in the dominant arm and leg, in a cross-balanced fashion during elbow and knee flexion and extension. The main variables included peak torque (T), RTD, rate of muscle activation (Q30), Electro-mechanical delay (EMD), time to peak RTD and co-activation index. Age differences in T, RTD, electro-mechanical delay (EMD) and rate of muscle activation (Q30) were consistently observed in the four contractions tested. Additionally, Q30, nonnalized for peak EMG amplitude, was consistently higher in the endurancetrained men compared with untrained men. Co-activation index was generally low in all contractions. For example, during maximal voluntary isometric knee extension, men were stronger, had higher RTD and Q30, whether absolute or nonnalized values were used. Moreover, boys exhibited longer EMD (64.8 ± 18.5 ms vs. 56.6 ± 15.3 ms, for boys and men respectively) and time to peak RTD (112.4 ± 33.4 ms vs. 100.8 ± 39.1 ms for boys and men, respectively). In addition, endurance-trained men had lower T compared with untrained men, yet they also exhibited significantly higher nonnalized Q30 (1.9 ± 1.2 vs. 1.1 ± 0.7 for endurance-trained men and untrained men, respectively). No training effect was apparent in the boys. In conclusion, the findings demonstrate muscle strength and activation to be lower in children compared with adults, regardless of training status. The higher Q30 of the endurance-trained men suggests neural adaptations, similar to those expected in response to resistance training. The lower peak torque may su9gest a higher relative involvement oftype I muscle fibres in the endurance-trained athletes. Future research is required to better understand the effect of growth and development on muscle strength and activation patterns during dynamic and sub-maximal isometric contractions. Furthennore, training intervention studies could reveal the effects of endurance training during different developmental stages, as well as in different muscle groups.

A comparison of two time-domain analysis procedures in the determination of VO2 kinetics by pseudorandom binary sequence exercise testing

The purpose of this study was to apply and compare two time-domain analysis procedures in the determination of oxygen uptake (VO2) kinetics in response to a pseudorandom binary sequence (PRBS) exercise test. PRBS exercise tests have typically been analysed in the frequency domain. However, the complex interpretation of frequency responses may have limited the application of this procedure in both sporting and clinical contexts, where a single time measurement would facilitate subject comparison. The relative potential of both a mean response time (MRT) and a peak cross-correlation time (PCCT) was investigated. This study was divided into two parts: a test-retest reliability study (part A), in which 10 healthy male subjects completed two identical PRBS exercise tests, and a comparison of the VO2 kinetics of 12 elite endurance runners (ER) and 12 elite sprinters (SR; part B). In part A, 95% limits of agreement were calculated for comparison between MRT and PCCT. The results of part A showed no significant difference between test and retest as assessed by MRT [mean (SD) 42.2 (4.2) s and 43.8 (6.9) s] or by PCCT [21.8 (3.7) s and 22.7 (4.5) s]. Measurement error (%) was lower for MRT in comparison with PCCT (16% and 25%, respectively). In part B of the study, the VO2 kinetics of ER were significantly faster than those of SR, as assessed by MRT [33.4 (3.4) s and 39.9 (7.1) s, respectively; P<0.01] and PCCT [20.9 (3.8) s and 24.8 (4.5) s; P < 0.05]. It is possible that either analysis procedure could provide a single test measurement Of VO2 kinetics; however, the greater reliability of the MRT data suggests that this method has more potential for development in the assessment Of VO2 kinetics by PRBS exercise testing.

Can physical exercise during gestation attenuate the effects of a maternal perinatal low-protein diet on oxygen consumption in rats?

A protocol of physical exercise, based on maximal oxygen uptake ((V) over dot(O2max)), for female rats before and during pregnancy was developed to evaluate the impact of a low-protein diet on oxygen consumption during gestation and growth rate of the offspring. Virgin female Wistar rats were divided into four groups as follows: untrained (NT, n = 5); trained (T, n = 5); untrained with low-protein diet (NT+LP, n = 5); and trained with low-protein diet (T+LP, n = 5). Trained rats were submitted to a protocol of moderate physical training on a treadmill over a period of 4 weeks (5 days week(-1) and 60 min day(-1), at 65% of (V) over dot(O2max)). At confirmation of pregnancy, the intensity and duration of the exercise was reduced. Low-protein groups received an 8% casein diet, and their peers received a 17% casein diet. The birthweight and growth rate of the pups up to the 90th day were recorded. Oxygen consumption ((V) over dot(O2)), CO(2) production and respiratory exchange ratio (RER) were determined using an indirect open-circuit calorimeter. Exercise training increased. (V) over dot(O2max) by about 20% when compared with the initial values (45.6 +/- 1.0 ml kg(-1) min(-1)). During gestation, all groups showed a progressive reduction in the resting (V) over dot(O2) values. Dams in the NT+LP group showed lower values of resting (V) over dot(O2) than those in the NT group. The growth rate of pups from low-protein-fed mothers was around 50% lower than that of their respective controls. The T group showed an increase in body weight from the 60th day onwards, while the NT+LP group presented a reduced body weight from weaning onwards. In conclusion, physical training attenuated the impact of the low- protein

Comparação das respostas fisiológicas entre diferentes testes funcionais em obesos

obesity affects rightly functional capacity diminishing the cardiovascular system efficiency and oxygen uptake (VO2). Field tests, such as, Incremental Shuttle Walking Test (ISWT) and Six Minute Walk Test (6MWT) has been employed as alternative of Cardiopulmonary Exercise Test (CPX), to functional assessing for conditions which transport of oxygen to peripheral is diminished. Nevertheless, the knowing about metabolic variables response in real time and it comparing among different maximal and submaximal tests in obese is absent. Aim: to compare cardiopulmonary, metabolic response during CPX, ISWT and 6MWT and to analyse it influence of adiposity markers in obese. Material e Method: crosssectional, prospective study. Obese included if: (BMI>30Kg/m2; FVC>80%), were assessed as clinical, anthropometric (BMI, body adiposity index-BAI, waist-WC, hip- HC and neck-NC circumferences) and spirometry (forced vital capacity-FVC, Forced expiratory volume-1°second-FEV1, maximal voluntary ventilation-MVV) variables. Obese performed the sequence of tests: CPX, ISWT and 6MWT. Throughout tests was assessed breath-by-breath by telemetry system (Cortex-Biophysik-Metamax3B) variables; oxygen uptake on peak of activity (VO2peak); carbon dioxide production (VCO2); Volume Expiratory (VE); ventilatory equivalents for VO2 (VE/VO2) and CO2 (VE/VCO2); respiratory exchange rate (RER) and perceived effort-Borg6-20). Results: 15 obese (10women) 39.4+10.1years, normal spirometry (%CVF=93.7+9.7) finished all test. They have BMI (43.5+6.6kg/m2) and different as %adiposity (BAI=50.0+10.5% and 48.8+16.9% respectively women and men). Difference of VO2ml/kg/min and %VO2 were finding between CPX (18.6+4.0) and 6MWT (13.2+2.5) but not between ISWT (15.4+2.9). Agreement was found for ISWT and CPX on VO2Peak (3.2ml/kg/min; 95%; IC-3.0 9.4) and %VO2 (16.4%). VCO2(l/min) confirms similarity in production for CPX (2.3+1.0) and ISWT (1.7+0.7) and difference for 6MWT (1.4+0.6). WC explains more the response of CPX and ISWT than other adiposity markers. Adiposity diminishes 3.2% duration of CPX. Conclusion: ISWT promotes similar metabolic and cardiovascular response than CPX in obese. It suggesting that ISWT could be useful and reliable to assess oxygen uptake and functional capacity in obese

Meal size and specific dynamic action in the rattlesnake Crotalus durissus (Serpentes : Viperidae)

We studied the effect of meal size on specific dynamic action (SDA) in the South American rattlesnake Crotalus durissus, by measuring oxygen consumption rates (VO2) prior to and after the ingestion of meals ranging from 10-50% of snake's body mass. Regardless of meal size, variation in VO2 with time during digestion demonstrated the same general pattern. Oxygen consumption rates peaked between 15 and 33 h post-feeding, at values 3.7-7.3 times those prior to feeding. Snakes, while digesting meals of 30% and 50% of their body mass, experienced VO2 that exceeded rates measured during forced activity. Following peaks in VO2, rates returned to prefeeding values within 62-170 h post-feeding. Post-prandial peak in VO2 and the duration of the metabolic response to feeding increased with meal size. Digestion is an energetically demanding activity for C. durissus, with an estimated cost equaling 12-18% of the ingested assimilated energy.

Velocidade de corrida associada ao consumo máximo de oxigênio em meninos de 10 a 15 anos

O objetivo deste estudo foi determinar a influência da idade cronológica e da maturação biológica sobre o consumo máximo de oxigênio (VO2max) e a velocidade de corrida correspondente ao VO2max em crianças e adolescentes brasileiros, do sexo masculino, com idade entre 10 e 15 anos, não praticantes de atividade física sistemática. Participaram do estudo 40 voluntários, divididos em dois grupos, segundo a idade cronológica (GC1 - n = 20; 11,4 ± 0,6 anos; 38,8 ± 8,6kg; 143,6 ± 8,2cm e GC2 - n = 20; 14,1 ± 0,6 anos; 55,9 ± 14,2kg; 163,3 ± 10,2cm) e maturação biológica (GB1 - n = 20; estágios 1, 2 e 3; e GB2 - n = 20; estágios 4 e 5). O VO2max foi mensurado em um teste progressivo e intermitente de corrida em esteira rolante, com estágios de três minutos e pausa de 20 segundos, incrementos de 1km/h a começar com 9km/h, até a exaustão voluntária. A velocidade correspondente ao VO2max (vVO2max) foi considerada como a menor velocidade em que se observou o maior valor de VO2. A máxima velocidade aeróbia (Va max) foi calculada pela fórmula proposta por di Prampero (1986). Houve diferença significante para os valores de VO2max(l/min), Va max(km/h)e vVO2max(km/h) entre os grupos GC1 e GC2 (1,84 ± 0,41 / 2,81 ± 0,61; 11,8 ± 1,2 / 12,6 ± 1,2; 12,1 ± 1,2 / 12,9 ± 1,1, respectivamente), GB1 e GB2 (1,80 ± 0,37 / 2,87 ± 0,56; 12,1 ± 1,2 / 12,9 ± 1,1; 11,8 ± 1,2 / 12,5 ± 1,1, respectivamente), mas não para os valores de VO2max em ml.kg-1.min-1 para todos os grupos (GC1 e GC2: 47,9 ± 6,8 / 50,4 ± 5,5; GB1 e GB2: 47,9 ± 6,8 / 50,3 ± 5,5, respectivamente). Com base nos resultados obtidos, pode-se concluir que o VO2max (l/min), aVa max e a vVO2max têm seus valores aumentados como um provável efeito do crescimento e desenvolvimento, podendo, ainda, expressar melhora da economia de movimento, mesmo em indivíduos não praticantes de atividade física sistemática.

RESPIRATORY RESPONSES IN A BRAZILIAN MILLIPEDE, PSEUDONANNOLENE-TRICOLOR, TO DECLINING OXYGEN PRESSURES

Oxygen uptake and the influence of declining oxygen pressures (Po2's) were examined in a Brazilian spirostreptid millipede, Pseudonannolene tricolor. The data were obtained in a Warburg respirometer at 25-degrees-C from both male and female animals, sexually inactive, in the intermolt stage, and fasting for 24 h. In a sudden exposure to a decreased Po2 the millipedes regulated respiration down to at least 71 mmHg O2. From a Po2 of 35 mmHg O2 downward the animals started to show oxyconformity. When the millipedes were exposed to a stepwise declining Po2 the results indicated only conformation. After exposure to hypoxia, P. tricolor showed a pattern of underrepayment on return to normoxia, but larger millipedes accumulated more O2 debt than smaller ones.

Influência da seleção dos estágios incrementais sobre a intensidade de lactato mínimo: Estudo piloto

The purposes of this study were to assess the influence of stage selection from the incremental phase and the use of peak lactate after hyperlactatemia induction on the determination of the lactate minimum intensity (iLACmin). Twelve moderately active university students (23±5 years, 78.3±14.1 kg, 175.3±5.1 cm) performed a maximal incremental test to determine the respiratory compensation point (RCP) (initial intensity at 70 W and increments of 17.5 W every 2 minutes) and a lactate minimum test (induction with the Wingate test, the incremental test started at 30 W below RCP with increments of 10 W every 3 minutes) on a cycle ergometer. The iLACmin was determined using second order polynomial adjustment applying five exercise stage selection: 1) using all stages (iLACmin P); 2) using all stages below and two stages above iLACminP(iLACminA); 3) using two stages below and all stages above iLACminP(iLACminB); 4) using the largest and same possible number of stages below and above the iLACminP(iLACminI); 5) using all stages and peak lactate after hyperlactatemia induction (iLACminD). No differences were found between the iLACminP(138.2±30.2 W), iLACminA(139.1±29.1 W), iLACminB(135.3±14.2 W), iLACminI(138.6±20.5 W) and iLACmiD(136.7±28.5 W) protocols, and a high level of agreement between these intensities and iLACminPwas observed. Oxygen uptake, heart rate, rating of perceived exertion and lactate corresponding to these intensities was not different and was strongly correlated. However, the iLACminBpresented the lowest success rate (66.7%). In conclusion, stage selection did not influence the determination of iLACmin but modified the success rate. © Creative Commom.

Efeitos do treinamento de caminhada com restrição do fluxo sanguíneo sobre economia de corrida em indivíduos ativos

Pós-graduação em Desenvolvimento Humano e Tecnologias - IBRC

Efeito do exercício excêntrico sobre as propriedades mecânicas do músculo e índices de aptidão aeróbia

Pós-graduação em Ciências da Motricidade - IBRC

Correlações entre parâmetros aeróbios e desempenho em esforços intermitentes de alta intensidade

The purpose of the study was to examine the relationships between intermittent high-intensity efforts (RAST) parameters and variables related to aerobic metabolism (anaerobic threshold; LAN, maximal oxygen uptake; VO2MAX and velocity correspondent to VO2MAX; iVO(2MAX)). Eight under-17 (U17) soccer players (16 +/- 1 years) participated in the study. The participants were submitted to a graded exercise test and six maximal sprints of 35m with 10 seconds of passive recovery between each effort (RAST). The RAST parameters were not significant correlated with VO2MAX and LAN. However absolute and relative mean power were significantly correlated with iVO(2MAX) (r=0.79 e r=0.85, respectively). Furthermore, the fatigue index and the relative peak power were significantly correlated with the iVO(2MAX) (r=-0,57 e r=0,73, respectively). In conclusion, the only aerobic variable correlated with performance in consecutive efforts with brief recovery periods, such as RAST, is iVO(2MAX).