Short-term low-intensity blood flow restricted interval training improves both aerobic fitness and muscle strength.

The present study aimed to analyze and compare the effects of four different interval-training protocols on aerobic fitness and muscle strength. Thirty-seven subjects (23.8 ± 4 years; 171.7 ± 9.5 cm; 70 ± 11 kg) were assigned to one of four groups: low-intensity interval training with (BFR, n = 10) or without (LOW, n = 7) blood flow restriction, high-intensity interval training (HIT, n = 10), and combined HIT and BFR (BFR + HIT, n = 10, every session performed 50% as BFR and 50% as HIT). Before and after 4 weeks training (3 days a week), the maximal oxygen uptake (VO2max ), maximal power output (Pmax ), onset blood lactate accumulation (OBLA), and muscle strength were measured for all subjects. All training groups were able to improve OBLA (BFR, 16%; HIT, 25%; HIT + BFR, 22%; LOW, 6%), with no difference between groups. However, VO2max and Pmax improved only for BFR (6%, 12%), HIT (9%, 15%) and HIT + BFR (6%, 11%), with no difference between groups. Muscle strength gains were only observed after BFR training (11%). This study demonstrates the advantage of short-term low-intensity interval BFR training as the single mode of training able to simultaneously improve aerobic fitness and muscular strength.

Stroking parameters during continuous and intermittent exercise in regional-level competitive swimmers.

This study aimed to determine whether maximal lactate steady state (MLSS) represents a boundary above which not only physiological but also technical changes occur. On different days, 13 male swimmers (23 ± 9 years) performed the following tests: 1) a 400-m all-out swim, to determine maximal aerobic speed (S-400); 2) a series of 30-min sub-maximal swims, to determine continuous MLSS (MLSSc), and; 3) a series of 12×150 s sub-maximal swims, to determine intermittent MLSS (MLSSi). Stroke rate (SR), distance per stroke cycle (DS) and stroke index (SI) were analyzed at and above (102.5%) MLSSc and MLSSi. MLSSi (1.17 ± 0.09 m.s (- 1)) was significantly higher than MLSSc (1.13 ± 0.08 m.s (- 1)) while blood lactate concentration (mmol.L (- 1)) was similar between the 2 conditions (4.3 ± 1.1 and 4.4 ± 1.5, respectively). The increase in SR and decreases in DS and SI were significant during MLSSi, 102.5% MLSSc and 102.5% MLSSi. During MLSSc, DS also decreased significantly (- 3.6%) but with no change in SR or SI. Thus, stroking technique of regional-level competitive swimmers changes over time when they swim at or above MLSS. This is the case during both continuous and intermittent swimming, despite steady state blood lactate concentrations.

VO2 kinetics during heavy and severe exercise in swimming.

The purpose of this study was to describe the VO2 kinetics above and below respiratory compensation point (RCP) during swimming. After determination of the gas-exchange threshold (GET), RCP and VO(2max), 9 well-trained swimmers (21.0 ± 7.1 year, VO(2max)=57.9 ± 5.1 ml.kg (- 1).min (- 1)), completed a series of "square-wave" swimming transitions to a speed corresponding to 2.5% below (S - 2.5%) and 2.5% above (S+2.5%) the speed observed at RCP for the determination of pulmonary VO2 kinetics. The trial below (~2.7%) and above RCP (~2%) was performed at 1.28 ± 0.05 m.s (- 1) (76.5 ± 6.3% VO(2max)) and 1.34 0.05 m.s (- 1) (91.3 ± 4.0% VO(2max)), respectively. The time constant of the primary component was not different between the trials below (17.8 ± 5.9 s) and above RCP (16.5 ± 5.1 s). The amplitude of the VO(2)slow component was similar between the exercise intensities performed around RCP (S - 2.5%=329.2 ± 152.6 ml.min (- 1) vs. S+2.5%=313.7 ± 285.2 ml.min (- 1)), but VO(2max) was attained only during trial performed above RCP (S-2.5%=91.4 ± 5.9% VO(2max) vs. S+2.5%=103.0 ± 8.2% VO(2max)). Thus, similar to the critical power during cycling exercise, the RCP appears to represent a physiological boundary that dictates whether VO(2) kinetics is characteristic of heavy- or severe-intensity exercise during swimming.

Effects of strength training on running economy.

The objective of this study was to compare the effect of different strength training protocols added to endurance training on running economy (RE). Sixteen well-trained runners (27.4 +/- 4.4 years; 62.7 +/- 4.3 kg; 166.1 +/- 5.0 cm), were randomized into two groups: explosive strength training (EST) (n = 9) and heavy weight strength training (HWT) (n = 7) group. They performed the following tests before and after 4 weeks of training: 1) incremental treadmill test to exhaustion to determine of peak oxygen uptake and the velocity corresponding to 3.5 mM of blood lactate concentration; 2) submaximal constant-intensity test to determine RE; 3) maximal countermovement jump test and; 4) one repetition maximal strength test in leg press. After the training period, there was an improvement in RE only in the HWT group (HWT = 47.3 +/- 6.8 vs. 44.3 +/- 4.9 ml . kg (-1) . min (-1); EST = 46.4 +/- 4.1 vs. 45.5 +/- 4.1 ml . kg (-1) . min (-1)). In conclusion, a short period of traditional strength training can improve RE in well-trained runners, but this improvement can be dependent on the strength training characteristics. When comparing to explosive training performed in the same equipment, heavy weight training seems to be more efficient for the improvement of RE.

Effects of prolonged running performed at the intensity corresponding to the onset of blood lactate accumulation, on maximum isokinetic strength in active non-athletic individuals

OBJECTIVE: The objective of this study was to analyze the effects of prolonged continuous running performed at the intensity corresponding to the onset of blood lactate accumulation (OBLA), on the peak torque of the knee extensors, analyzed in relation to different types of contraction and movement velocities in active individuals. METHOD: Eight men (23.4 ± 2.1 years; 75.8 ± 8.7 kg; 171.1 ± 4.5 cm) participated in this study. First, the subjects performed an incremental test until volitional exhaustion to determine the velocity corresponding to OBLA. Then, the subjects returned to the laboratory on two occasions, separated by at least seven days, to perform five maximal isokinetic contractions of the knee extensors at two angular velocities (60 and 180º.s-1) under eccentric and concentric conditions. Eccentric peak torque (EPT) and Concentric peak torque (CPT) were measured at each velocity. One session was performed after a standardized warm-up period (5 min at 50 percent VO2max). The other session was performed after continuous running at OBLA until volitional exhaustion. These sessions were conducted in random order. RESULTS: There was a significant reduction in CPT only at 60º.s-1 (259.0 ± 46.4 and 244.0 ± 41.4 N.m). However, the reduction in EPT was significant at 60º.s-1 (337.3 ± 43.2 and 321.7 ± 60.0 N.m) and 180º.s-1 (346.1 ± 38.0 and 319.7 ± 43.6 N.m). The relative strength losses after the running exercise were significant different between contraction types only at 180º.s-1. CONCLUSION: We can conclude that, in active individuals, the reduction in peak torque after prolonged continuous running at OBLA may be dependent on the type of contraction and angular velocity.

OBJETIVO: O objetivo deste estudo foi analisar os efeitos da corrida contínua prolongada realizada na intensidade correspondente ao início do acúmulo do lactato no sangue (OBLA) sobre o torque máximo dos extensores do joelho analisado em diferentes tipos de contração e velocidade de movimento em indivíduos ativos. MÉTODO: Oito indivíduos do gênero masculino (23,4 ± 2,1 anos; 75,8 ± 8,7 kg; 171,1 ± 4,5 cm) participaram deste estudo. Primeiramente, os sujeitos realizaram um teste incremental até a exaustão voluntária para determinar a velocidade correspondente ao OBLA. Posteriormente, os sujeitos retornaram ao laboratório em duas ocasiões, separadas por pelo menos sete dias, para realizar 5 contrações isocinéticas máximas para os extensores do joelho em duas velocidades angulares (60 e 180º.s-1) sob as condições excêntrica (PTE) e concêntrica (PTC). Uma sessão foi realizada após um período de aquecimento padronizado (5 min a 50 por centoVO2max). A outra sessão foi realizada após uma corrida contínua no OBLA até a exaustão voluntária. Essas sessões foram executadas em ordem randômica. RESULTADOS: Houve redução significante do PTC somente a 60º.s-1 (259,0 ± 46,4 e 244,0 ± 41,4 N.m). Entretanto, a redução do PTE foi significante a 60º.s-1 (337,3 ± 43,2 e 321,7 ± 60,0 N.m) e 180º.s-1 (346,1 ± 38,0 e 319,7 ± 43,6 N.m). As reduções relativas da força após o exercício de corrida foram significantemente diferentes entre os tipos de contração somente a 180º.s-1. CONCLUSÃO: Podemos concluir que, em indivíduos ativos, a redução no torque máximo após uma corrida contínua prolongada no OBLA pode ser dependente do tipo de contração e da velocidade angular.

Exercise mode affects the time to achieve VO2max without influencing maximal exercise time at the intensity associated with VO2max in triathletes.

The objective of this study was to analyze, in triathletes, the possible influence of the exercise mode (running x cycling) on time to exhaustion (TTE) and oxygen uptake (VO2) response during exercise performed at the intensity associated with the achievement of maximal oxygen uptake (IVO2max). Eleven male triathletes (21.8 +/- 3.8 yr) performed the following tests on different days on a motorized treadmill and on a cycle ergometer: 1) incremental tests in order to determine VO2max and IVO2max and, 2) constant work rate tests to exhaustion at IVO2max to determine TTE and to describe VO2 response (time to achieve VO2max - TAVO2max, and time maintained at VO2max-TMVO2max). No differences were found in VO2max, TTE and TMVO2max obtained on the treadmill tests (63.7 +/- 4.7 ml . kg (-1) . min (-1); 324.6 +/- 109.1 s; 178.9 +/- 93.6 s) and cycle ergometer tests (61.4 +/- 4.5 ml . kg (- 1) . min (-1); 390.4 +/- 114.4 s; 213.5 +/- 102.4 s). However, TAVO2max was influenced by exercise mode (145.7 +/- 25.3 vs. 176.8 +/- 20.1 s; in treadmill and cycle ergometer, respectively; p = 0.006). It is concluded that exercise modality affects the TAVO2max, without influencing TTE and TMVO2max during exercise at IVO2max in triathletes.

Relationships and significance of lactate minimum, critical velocity, heart rate deflection and 3 000 m track-tests for running.

AIM: The running velocities associated to lactate minimum (V(lm)), heart rate deflection (V(HRd)), critical velocity (CV), 3.000 m (V(3000)) and 10 000 m performance (V10km) were compared. Additionally the ability of V(lm) and V(HRd) on identifying sustainable velocities was investigated. METHODS: Twenty runners (28.5+/-5.9 y) performed 1) 3,000 m running test for V3000; 2) an all-out 500 m sprint followed by 6x800 m incremental bouts with blood lactate ([lac]) measurements for V(lm); 3) a continuous velocity-incremented test with heart rate measurements at each 200 m for V(HRd); 4) participants attempted to 30 min of endurance test both at V(lm)(ETV(lm)) and V(HRd)(ETV(HRd)). Additionally, the distance-time and velocity-1/time relationships produced CV by 2 (500 m and 3 000 m) or 3 predictive trials (500 m, 3,000 m and distance reached before exhaustion during ETV(HRd)), and a 10 km race was recorded for V10km. RESULTS: The CV identified by different methods did not differ to each other. The results (m.min(-1)) revealed that V(lm) (281+/-14.8)

Effect of the aerobic capacity on the validity of the anaerobic threshold for determination of the maximal lactate steady state in cycling

The maximal lactate steady state (MLSS) is the highest blood lactate concentration that can be identified as maintaining a steady state during a prolonged submaximal constant workload. The objective of the present study was to analyze the influence of the aerobic capacity on the validity of anaerobic threshold (AT) to estimate the exercise intensity at MLSS (MLSS intensity) during cycling. Ten untrained males (UC) and 9 male endurance cyclists (EC) matched for age, weight and height performed one incremental maximal load test to determine AT and two to four 30-min constant submaximal load tests on a mechanically braked cycle ergometer to determine MLSS and MLSS intensity. AT was determined as the intensity corresponding to 3.5 mM blood lactate. MLSS intensity was defined as the highest workload at which blood lactate concentration did not increase by more than 1 mM between minutes 10 and 30 of the constant workload. MLSS intensity (EC = 282.1 ± 23.8 W; UC = 180.2 ± 24.5 W) and AT (EC = 274.8 ± 24.9 W; UC = 187.2 ± 28.0 W) were significantly higher in trained group. However, there was no significant difference in MLSS between EC (5.0 ± 1.2 mM) and UC (4.9 ± 1.7 mM). The MLSS intensity and AT were not different and significantly correlated in both groups (EC: r = 0.77; UC: r = 0.81). We conclude that MLSS and the validity of AT to estimate MLSS intensity during cycling, analyzed in a cross-sectional design (trained x sedentary), do not depend on the aerobic capacity.

Effect of the aerobic capacity on the validity of the anaerobic threshold for determination of the maximal lactate steady state in cycling.

The maximal lactate steady state (MLSS) is the highest blood lactate concentration that can be identified as maintaining a steady state during a prolonged submaximal constant workload. The objective of the present study was to analyze the influence of the aerobic capacity on the validity of anaerobic threshold (AT) to estimate the exercise intensity at MLSS (MLSS intensity) during cycling. Ten untrained males (UC) and 9 male endurance cyclists (EC) matched for age, weight and height performed one incremental maximal load test to determine AT and two to four 30-min constant submaximal load tests on a mechanically braked cycle ergometer to determine MLSS and MLSS intensity. AT was determined as the intensity corresponding to 3.5 mM blood lactate. MLSS intensity was defined as the highest workload at which blood lactate concentration did not increase by more than 1 mM between minutes 10 and 30 of the constant workload. MLSS intensity (EC = 282.1 +/- 23.8 W; UC = 180.2 +/- 24.5 W) and AT (EC = 274.8 +/- 24.9 W; UC = 187.2 +/- 28.0 W) were significantly higher in trained group. However, there was no significant difference in MLSS between EC (5.0 +/- 1.2 mM) and UC (4.9 +/- 1.7 mM). The MLSS intensity and AT were not different and significantly correlated in both groups (EC: r = 0.77; UC: r = 0.81). We conclude that MLSS and the validity of AT to estimate MLSS intensity during cycling, analyzed in a cross-sectional design (trained x sedentary), do not depend on the aerobic capacity.

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 LMS 1 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.

The lactate minimum test protocol provides valid measures of cycle ergometer VO(2)peak.

AIM: The aim of the present study was to investigate the validity of the Lactate Minimum Test (LMT) for the determination of peak VO(2) on a cycle ergometer and to determine the submaximal oxygen uptake (VO(2)) and pulmonary ventilation (VE) responses in an incremental exercise test when it is preceded by high intensity exercise (i.e., during a LMT). METHODS: Ten trained male athletes (triathletes and cyclists) performed 2 exercise tests in random order on an electromagnetic cycle ergometer: 1). Control Test (CT): an incremental test with an initial work rate of 100 W, and with 25 W increments at 3-min intervals, until voluntary exhaustion; 2). LMT: an incremental test identical to the CT, except that it was preceded by 2 supramaximal bouts of 30-sec (approximately 120% VO(2)peak) with a 30-sec rest to induce lactic acidosis. This test started 8 min after the induction of acidosis. RESULTS: There was no significant difference in peak VO(2) (65.6+/-7.4 ml x kg(-1) x min(-1); 63.8 +/- 7.5 ml x kg(-1) x min(-1) to CT and LMT, respectively). However, the maximal power output (POmax) reached was significantly higher in CT (300.6+/-15.7 W) than in the LMT (283.2+/-16.0 W). VO(2) and VE were significantly increased at initial power outputs in LMT. CONCLUSION: Although the LMT alters the submaximal physiological responses during the incremental phase (greater initial metabolic cost), this protocol is valid to evaluate peak VO(2), although the POmax reached is also reduced.

Oxygen uptake kinetics and time to exhaustion in cycling and running: a comparison between trained and untrained subjects.

The objective of the present study was to compare pulmonary gas exchange kinetics (VO2 kinetics) and time to exhaustion (Tlim) between trained and untrained individuals during severe exercise performed on a cycle ergometer and treadmill. Eleven untrained males in running (UR) and cycling (UC), nine endurance cyclists (EC), and seven endurance runners (ER) were submitted to the following tests on separate days: (i) incremental test for determination of maximal oxygen uptake (VO2max) and the intensity associated with the achievement of VO2max (IVO2max) on a mechanical braked cycle ergometer (EC and UC) and on a treadmill (ER and UR); (ii) all-out exercise bout performed at IVO2max to determine the time to exhaustion at IVO2max (Tlim) and the time constant of oxygen uptake kinetics (tau). The tau was significantly faster in trained group, both in cycling (EC = 28.2 +/- 4.7s; UC = 63.8 +/- 25.0s) and in running (ER = 28.5 +/- 8.5s; UR = 59.3 +/- 12.0s). Tlim of untrained was significantly lower in cycling (EC = 384.4 +/- 66.6s vs. UC; 311.1 +/- 105.7 s) and higher in running (ER = 309.2 +/- 176.6 s vs. UR = 439.8 +/- 104.2 s). We conclude that the VO2 kinetic response at the onset of severe exercise, carried out at the same relative intensity is sensitive to endurance training, irrespective of the exercise type. The endurance training seems to differently influence Tlim during exercise at IVO2max in running and cycling.

Effect of an acute beta-adrenergic blockade on the blood glucose response during lactate minimum test.

The aim of this study was to determine the relationship between blood lactate and glucose during an incremental test after exercise induced lactic acidosis, under normal and acute beta-adrenergic blockade. Eight fit males (cyclists or triathletes) performed a protocol to determine the intensity corresponding to the individual equilibrium point between lactate entry and removal from the blood (incremental test after exercise induced lactic acidosis), determined from the blood lactate (Lacmin) and glucose (Glucmin) response. This protocol was performed twice in a double-blind randomized order by ingesting either propranolol (80 mg) or a placebo (dextrose), 120 min prior to the test. The blood lactate and glucose concentration obtained 7 minutes after anaerobic exercise (Wingate test) was significantly lower (p < 0.01) with the acute beta-adrenergic blockade (9.1 +/- 1.5 mM; 3.9 +/- 0.1 mM), respectively than in the placebo condition (12.4 +/- 1.8 mM; 5.0 +/- 0.1 mM). There was no difference (p > 0.05) between the exercise intensity determined by Lacmin (212.1 +/- 17.4 W) and Glucmin (218.2 +/- 22.1 W) during exercise performed without acute beta-adrenergic blockade. The exercise intensity at Lacmin was lowered (p < 0.05) from 212.1 +/- 17.4 to 181.0 +/- 15.6 W and heart rate at Lacmin was reduced (p < 0 .01) from 161.2 +/- 8.4 to 129.3 +/- 6.2 beats min(-1) as a result of the blockade. It was not possible to determine the exercise intensity corresponding to Glucmin with beta-adrenergic blockade, since the blood glucose concentration presented a continuous decrease during the incremental test. We concluded that the similar pattern response of blood lactate and glucose during an incremental test after exercise induced lactic acidosis, is not present during beta-adrenergic blockade suggesting that, at least in part, this behavior depends upon adrenergic stimulation.

Blood lactate response and critical speed in swimmers aged 10-12 years of different standards.

It has previously been shown that measurement of the critical speed is a non-invasive method of estimating the blood lactate response during exercise. However, its validity in children has yet to be demonstrated. The aims of this study were: (1) to verify if the critical speed determined in accordance with the protocol of Wakayoshi et al. is a non-invasive means of estimating the swimming speed equivalent to a blood lactate concentration of 4 mmol x l(-1) in children aged 10-12 years; and (2) to establish whether standard of performance has an effect on its determination. Sixteen swimmers were divided into two groups: beginners and trained. They initially completed a protocol for determination of speed equivalent to a blood lactate concentration of 4 mmol x l(-1). Later, during training sessions, maximum efforts were swum over distances of 50, 100 and 200 m for the calculation of the critical speed. The speeds equivalent to a blood lactate concentration of 4 mmol x l(-1) (beginners = 0.82 +/- 0.09 m x s(-1), trained = 1.19 +/- 0.11 m x s(-1); mean +/- s) were significantly faster than the critical speeds (beginners = 0.78 +/- 0.25 m x s(-1), trained = 1.08 +/- 0.04 m x s(-1)) in both groups. There was a high correlation between speed at a blood lactate concentration of 4 mmol x l(-1) and the critical speed for the beginners (r= 0.96, P < 0.001), but not for the trained group (r= 0.60, P> 0.05). The blood lactate concentration corresponding to the critical speed was 2.7 +/- 1.1 and 3.1 +/- 0.4 mmol x l(-1) for the beginners and trained group respectively. The percent difference between speed at a blood lactate concentration of 4 mmol x l(-1) and the critical speed was not significantly different between the two groups. At all distances studied, swimming performance was significantly faster in the trained group. Our results suggest that the critical speed underestimates swimming intensity corresponding to a blood lactate concentration of 4 mmol x l(-1) in children aged 10-12 years and that standard of performance does not affect the determination of the critical speed.

The effects of wet suits on physiological and biomechanical indices during swimming.

The objectives of this study were to verify the effects of wet suits (WS) on the performance during 1500m swimming (V1500), on the velocity corresponding to the anaerobic threshold (VAT) and on the drag force (AD) as well as its coefficient (Cx). 19 swimmers randomly completed the following protocols on different days (with and without WS): 1) maximal performance of 1500m swimming; 2) VAT in field test, with fixed concentration of blood lactate (4 mM) and 3) determination of hydrodynamic indices (AD and Cx). The results demonstrated significant differences (p < 0.05) in the VAT (1.27 +/- 0.09; 1.21 +/- 0.06 m.s-1), and in the V1500 (1.21 +/- 0.08; 1.17 +/- 0.08 m.s-1), with and without WS, respectively. However the AD, and its Cx did not present significant differences (p>0.05) for the respective maximal speeds of swimming. In summary, we can conclude that WS allows swimmers to reach greater speeds in both, long- and short-course swims. This improvement can be related to the decrease of the AD, since with higher speeds (with WS) the subjects presented the same resistance, as they did when compared to speeds without a WS. Moreover, these data suggest that the methodology used in this study to determine the Cx is unable to detect the improvement caused by WS.

Blood glucose responses in humans mirror lactate responses for individual anaerobic threshold and for lactate minimum in track tests.

The equilibrium point between blood lactate production and removal (La-(min)) and the individual anaerobic threshold (IAT) protocols have been used to evaluate exercise. During progressive exercise, blood lactate [La-]b, catecholamine and cortisol concentrations, show exponential increases at upper anaerobic threshold intensities. Since these hormones enhance blood glucose concentrations [Glc]b, this study investigated the [Glc] and [La-]b responses during incremental tests and the possibility of considering the individual glucose threshold (IGT) and glucose minimum (Glc(min)) in addition to IAT and La-(min) in evaluating exercise. A group of 15 male endurance runners ran in four tests on the track 3000 m run (v3km); IAT and IGT - 8 x 800 m runs at velocities between 84% and 102% of v3km; La-(min) and Glc(min) - after lactic acidosis induced by a 500-m sprint, the subjects ran 6 x 800 m at intensities between 87% and 97% of v3km; endurance test (ET) - 30 min at the velocity of IAT. Capillary blood (25 microl) was collected for [La-]b and [Glc]b measurements. The IAT and IGT were determined by [La-]b and [Glc]b kinetics during the second test. The La-(min) and Glc(min) were determined considering the lowest [La-] and [Glc]b during the third test. No differences were observed (P < 0.05) and high correlations were obtained between the velocities at IAT [283 (SD 19) and IGT 281 (SD 21) m. x min(-1); r = 0.096; P < 0.001] and between La-(min) [285 (SD 21)] and Glc(min) [287 (SD 20) m. x min(-1) r = 0.77; P < 0.05]. During ET, the [La-]b reached 5.0 (SD 1.1) and 5.3 (SD 1.0) mmol x l(-1) at 20 and 30 min, respectively (P > 0.05). We concluded that for these subjects it was possible to evaluate the aerobic capacity by IGT and Glc(min) as well as by IAT and La-(min).

Effects of caffeine on time to exhaustion in exercise performed below and above the anaerobic threshold.

Controversy still exists concerning the potential ergogenic benefit of caffeine (CAF) for exercise performance. The purpose of this study was to compare the effects of CAF ingestion on endurance performance during exercise on a bicycle ergometer at two different intensities, i.e., approximately 10% below and 10% above the anaerobic threshold (AT). Eight untrained males, non-regular consumers of CAF, participated in this study. AT, defined as the intensity (watts) corresponding to a lactate concentration of 4 mM, was determined during an incremental exercise test from rest to exhaustion on an electrically braked cycle ergometer. On the basis of these measurements, the subjects were asked to cycle until exhaustion at two different intensities, i.e., approximately 10% below and 10% above AT. Each intensity was performed twice in a double-blind randomized order by ingesting either CAF (5 mg/kg) or a placebo (PLA) 60 min prior to the test. Venous blood was analyzed for free fatty acid, glucose, and lactate, before, during, and immediately after exercise. Rating of perceived exertion and time to exhaustion were also measured during each trial. There were no differences in free fatty acids or lactate levels between CAF and PLA during and immediately after exercise for either intensity. Immediately after exercise glucose increased in the CAF trial at both intensities. Rating of perceived exertion was significantly lower (CAF = 14.1 +/- 2.5 vs PLA = 16.6 +/- 2.4) and time to exhaustion was significantly higher (CAF = 46.54 +/- 8.05) min vs PLA = 32.42 +/- 14.81 min) during exercise below AT with CAF. However, there was no effect of CAF treatment on rating of perceived exertion (CAF = 18.0 +/- 2.7 vs PLA = 17.6 +/- 2.3) and time to exhaustion (CAF = 18.45 +/- 7.28 min vs PLA = 19.17 +/- 4.37 min) during exercise above AT. We conclude that in untrained subjects caffeine can improve endurance performance during prolonged exercise performed below AT and that the decrease of perceived exertion can be involved in this process.

Effects of caffeine on time to exhaustion in exercise performed below and above the anaerobic threshold

Controversy still exists concerning the potential ergogenic benefit of caffeine (CAF) for exercise performance. The purpose of this study was to compare the effects of CAF ingestion on endurance performance during exercise on a bicycle ergometer at two different intensities, i.e., approximately 10 percent below and 10 percent above the anaerobic threshold (AT). Eight untrained males, non-regular consumers of CAF, participated in this study. AT, defined as the intensity (watts) corresponding to a lactate concentration of 4mM, was determined during an incremental exercise test from rest to exhaustion on an electrically braked cycle ergometer. On the basis of these measurements, the subjects were asked to cycle until exhaustion at two different intensities, i.e., approximately 10 percent below and 10 percent above AT. Each intensity was performed twice in a double-blind randomized order by ingesting either CAF (5 mg/kg) or a placebo (PLA) 60 min prior to the test. Venous blood was analyzed for free fatty acid, glucose, and lactate, before, during, and immediately after exercise. Rating of perceived exertion and time to exhaustion were also measured during each trial. There were no differences in free fatty acids or lactate levels between CAF and PLA during and immediately after exercise for either intensity. Immediately after exercise glucose increased in the CAF trial at both intensities. Rating of perceived exertion was singificantly lower (CAF = 14.1 + 2.5 vs PLA = 16.6 + 2.4) and time to exhaustion was significantly higher (CAF = 46.54 + 8.05 min vs PLA = 32.42 + 14.81 min) during exercise below AT with CAF. However, there was no effect of CAF treatment on rating of perceived exertion (CAF = 18.0 + 2.7 vs PLA = 17.6 + 2.3) and time to exhaustion (CAF = 18.45 + 7.28 min vs PLA = 19.17 + 4.37 min) during exercise above AT. We conclude that in untrained subjects caffeine can improve endurance performance during prolonged exercise performed below AT and that decrease of perceived exertion can be involved in this process.

High intensity exercise during pregnancy of rats. Effects on mother and offspring.

We see in this study the effect of high intensity exercise (90% VO2 max) in pregnant rats and their offspring depending on the length of pregnancy. The findings were compared with those obtained for sedentary pregnant rats and non-pregnant rats for similar exercise. This allowed for analysing the isolated effects of exercise (against the sedentary non-pregnant rat control group), of pregnancy and of the interaction between the two factors. For checking the effect of the length of pregnancy, each group of rats was subdivided into those with pregnancy terminated or sacrificed on the seventh, fourteenth or twentieth day of the experiment. VO2 max, post-exertion blood lactic acid level, body weight gain, food intake, feed efficiency, glucose, triglyceride, total cholesterol, total protein and albumin plasmatic concentrations in adult rats, and weight and number of offspring of pregnant rats were determined. Pregnancy increased weight gain and feed efficiency from the first week of the study, accompanied by a greater food intake (from the twelfth day). In the group of pregnant rats subjected to exercise, there was a reduction in weight gain percentage and feed efficiency in the first and third weeks, staying the same in the second week. A greater food intake during the period accompanied this recovery in the second week. In the group of non-pregnant rats subjected to exercise, food intake did not vary. As the weight gain percentage was less in relation to the non-pregnant control group, feed efficiency decreased. Pregnancy induced a drop in blood sugar level starting in the second week, and the exercise performed during pregnancy did not change this behavior. Pregnancy produced, however, an increase in plasmatic concentration of triglycerides and total cholesterol during the third week of pregnancy. Exercise performed by pregnant rats also did not change this behavior, but the increase observed in the third week was less. Exercise performed by non-pregnant rats did not change the blood sugar level and plasmatic concentration of triglycerides and total cholesterol during the entire experiment. Plasmatic concentration of total proteins and albumin showed a drop in the third week of pregnancy, probably due to high fetal use of proteins in this stage. Exercise performed by the pregnant group caused a lower protein drop in the third week, and in the non-pregnant group, determined an increase in plasmatic protein concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of caffeine on the metabolism of rats exercising by swimming.

Several studies have demonstrated that caffeine improves endurance exercise performance but the mechanisms are not fully understood. Possibilities include increased free fatty acid (FFA) oxidation with consequent sparing of muscle glycogen as well as enhancement of neuromuscular function during exercise. The present study was designed to investigate the effects of caffeine on liver and muscle glycogen of 3-month old, male Wistar rats (250-300 g) exercising by swimming. Caffeine (5 mg/kg) dissolved in saline (CAF) or 0.9% sodium chloride (SAL) was administered by oral intubation (1 microliter/g) to fed rats 60 min before exercise. The rats (N = 8-10 per group) swam bearing a load corresponding to 5% body weight for 30 or 60 min. FFA levels were significantly elevated to 0.475 +/- 0.10 mEq/l in CAF compared to 0.369 +/- 0.06 mEq/l in SAL rats at the beginning of exercise. During exercise, a significant difference in FFA levels between CAF and SAL rats was observed at 30 min (0.325 +/- 0.06 vs 0.274 +/- 0.05 mEq/l) but not at 60 min (0.424 +/- 0.13 vs 0.385 +/- 0.10 mEq/l). Blood glucose showed an increase due to caffeine only at the end of exercise (CAF = 142.1 +/- 27.4 and SAL = 120.2 +/- 12.9 mg/100 ml). No significant difference in liver or muscle glycogen was observed in CAF as compared to SAL rats, at rest or during exercise. Caffeine increased blood lactate only at the beginning of exercise (CAF = 2.13 +/- 0.2 and SAL = 1.78 +/- 0.2 mmol/l). These data indicate that caffeine (5 mg/kg) has no glycogen-sparing effect on rats exercising by swimming even though the FFA levels of CAF rats were significantly higher at the beginning of exercise.