Low dose of dichloroacetate infusion reduces blood lactate after submaximal exercise in horses / Baixa dose de infusão de dicloroacetato reduz o lactato sanguíneo após exercício submáximo em cavalos

The acute administration of an indirect activator of the enzyme pyruvate dehydrogenase (PDH) in human athletes causes a reduction in blood lactate level during and after exercise. A single IV dose (2.5m.kg-1) of dichloroacetate (DCA) was administered before a submaximal incremental exercise test (IET) with five velocity steps, from 5.0 m.s-1 for 1 min to 6.0, 6.5, 7.0 and 7.5m.s-1 every 30s in four untrained mares. The blood collections were done in the period after exercise, at times 1, 3, 5, 10, 15 and 20 min. Blood lactate and glucose (mM) were determined electro-enzymatically utilizing a YSI 2300 automated analyzer. There was a 15.3% decrease in mean total blood lactate determined from the values obtained at all assessment times in both trials after the exercise. There was a decrease in blood lactate 1, 3, 5, 10, 15 and 20 min after exercise for the mares that received prior DCA treatment, with respective mean values of 6.31±0.90 vs 5.81±0.50, 6.45±1.19 vs 5.58±1.06, 6.07±1.56 vs 5.26±1.12, 4.88±1.61 vs 3.95±1.00, 3.66±1.41 vs 2.86±0.75 and 2.75±0.51 vs 2.04±0.30. There was no difference in glucose concentrations. By means of linear regression analysis, V140, V160, V180 and V200 were determined (velocity at which the rate heart is 140, 160, 180, and 200 beats/minute, respectively). The velocities related to heart rate did not differ, indicating that there was no ergogenic effect, but prior administration of a relatively low dose of DCA in mares reduced lactatemia after an IET.

A administração aguda de um ativador indireto da enzima piruvato desidrogenase (PD) em atletas da espécie humana provoca redução na concentração de lactato sanguíneo durante e após exercício. Uma dose única, intravenosa de 2.5m.kg-1 de dicloroacetato (DCA) foi administrada antes de um exercício teste incremental submáximo (ETI) com cinco etapas de velocidade sendo 5,0 ms-1 por 1 minuto e 6,0, 6,5, 7,0, e 7,5 ms-1 a cada 30 segundos em quatro éguas destreinadas. As coletas de sangue foram realizadas no período após o exercício, nos momentos de 1, 3, 5, 10, 15 e 20 min. Lactato e glicose (mM) foram determinados electro-enzimaticamente utilizando um analisador automático (YSI 2300). Houve redução de 15,3% no lactato sanguíneo total médio que foi determinado a partir dos valores obtidos em todos os momentos de avaliação em ambos os testes, após o exercício. Houve diminuição na lactatemia 1, 3, 5, 10, 15 e 20 minutos após exercício para as éguas que receberam infusão de DCA, com os respectivos valores médios de 6,31±0,90 versus 5,81±0,50, 6,45±1,19 versus 5,58±1,06, 6,07±1,56 versus 5,26±1,12, 4,88±1,61 versus 3,95±1,00, 3,66±1,41 versus 2,86±0,75 e 2,75±0,51 versus 2,04±0,30. Não houve diferença nas concentrações de glicose. Por meio de análise de regressão linear, V140, V160, V180 e V200 foram determinados (velocidades em que as taxas cardíacas alcançam 140, 160, 180 e 200 bpm, respectivamente). As velocidades relacionadas com a frequência cardíaca não diferiram, indicando que não houve efeito ergogênico, mas a administração prévia de uma dose relativamente baixa de DCA em éguas reduziu a lactatemia após um ETI.

Effect of Incremental Exercise on the of Maximum Force of Femur and Lumbar Vertebrae in SD Rats / 中国运动医学杂志

Objective The aim of the study is to investigate whether the progressive incremental exercise can induce the change in bone maximum force.Methods One hundred and seventy healthy SD rats,aged 3 months,were used as samples after adaptive exercise for one week,and then they were divided to a basic control group(C_0),8 control groups and 8 exercise groups according to the training duration(2W,4W,6W,8W,9W,11W,13W and 15W).Based on Bedford and our pre-study.the longest training duration of the rats was 15 weeks.The maximum force(F) of femoral bone and the 2nd lumbar vertebrae(L_2)were tested by three-point bending test and compressive test separately.Results It was shown that there was no pronounced difference in F of femoral bone between con trol groups and exercise groups.But significant differences in F of L_2 were found between the control groups and exercise groups(P<0.001).Conclusions Changes in different degree were found in the F of femoral bone and L_2 during the process of growth.The differential effects of incremental exercise on F were caused by the difference in training intensities and in the bone types.

The effect of different environmental conditions on blood lactate accumulation, LT and OBLA during incremental exercise / 体力科学

The purpose of this study was to compare blood lactate concentration, lactate threshold (LT) and onset of blood lactate accumulation (OBLA) during an incremental bicycle exercise under a hot dry environment with those during the same workload under a thermoneutral environment. Eight unacclimated men performed an incremental test to exhaustion on a cycle ergometer during which the work rate was increased by 30 W every three minutes under thermoneutral (25°C) and hot dry (40°C) environmental conditions. Oxygen consumption (VO<SUB>2</SUB>) -pulmonary ventilation (VE), gas exchange measures and earlobe blood samples for lactate analysis were obtained every minute during the test. LT (p<0.05) and OBLA (p<0.01) occurred at significantly lower VO<SUB>2</SUB> under the hot environment than those under the thermoneutral environment. Additionally blood lactate concentration was significantly higher (p<0.05) at each measurement period under the hot environment compared with that under the ther-moneutral environment. The correlation between LT and ventilatory threshold (VT) was not statistically significant under the thermoneutral (r=0.20) and hot dry (r=0.60) environments, These findings demonstrate that the hot dry environment may increase blood lactate concentration more and causes a leftward shift of LT and OBLA. Since blood lactate accumulation during incremental exercise is not considered to be the only factor which mediates VE, VT does not always accurately predict LT.

Power spectrum of heart rate fluctuations during incremental cycle exercise / 体力科学

Spectral analysis was applied to investigate whether the system for control of heart rate (HR) is influenced by exercise intensity. Five healthy males performed incremental exercise on an electrically braked cycle ergometer until exhaustion. The work rate was increased at 12 W/min following 2 min of exercise at a constant load of 20 W. HR was measured every second from R-R intervals. The power spectrum was calculated every 10 s using the FFT method for 64 consecutive data points. Power spectra during 20 W exercise showed a similar pattern to those in previous reports on resting HR perturbations, Although interindividual differences were observed for the spectrum patterns related to exercise intensity, there was a characteristic pattern revealing dissipation of the spectral power above a frequency of 0.2 Hz for all subjects. This pattern was not maintained for more than 1 min in any of the subjects, and was followed by a semirandom pattern whose magnitude varied among the subjects. These results support the hypothesis that the cardiac pacemaker is influenced by exercise intensity, presumably due to sympatho-vagal interaction with the respiratory control system.

Kinetics of VCO2 during increnental exercise / 体力科学

The purpose of this study was to investigate the kinetics of Vco<SUB>2</SUB>during incremental exercise. The subjects were 7 males, age 21-28 years, exercised at two steady state work loads (540 kpm/min, 810 kpm/min) and incremental work load which was increased stepwise by every 1 min from 180 kpm/min to exhaustion. The Vo<SUB>2</SUB>and Vco<SUB>2</SUB>during steady state exercise (4 to 5 min) were determined by the Douglas bag method and arterialized blood samples were taken for lactate (LA) analysis and blood gas analysis. The Vo<SUB>2</SUB>, Vco<SUB>2</SUB>, and blood lactate were also determined throughout the incremental exercise. At exhaustion, mixed venous Pco<SUB>2</SUB> (PVco<SUB>2</SUB>) was determined by the CO<SUB>2</SUB>rebreathing method.<BR>1) The Vco<SUB>2</SUB>values at rest and during steady state exercise were linearly related to the Vo<SUB>2</SUB>values. When the regression line was compared with Vco<SUB>2</SUB>during the incremental exercise on the same Vo<SUB>2</SUB>, the Vco<SUB>2</SUB>during the incremental exercise below the anaerobic threshold showed lower values.<BR>2) The total sum of the difference in Vco<SUB>2</SUB>between steady state and incremental exercise was defined as CO<SUB>2</SUB>store. The calculated CO<SUB>2</SUB>store and CO<SUB>2</SUB>store per body weight were significantly related to PVco<SUB>2</SUB>at exhaustion in incremental exercise, respectively (r=0.954, r=0.954) .<BR>3) At work load below the anaerobic threshold, Vco<SUB>2</SUB>was linearly related to Vo<SUB>2</SUB>. If the Vco<SUB>2</SUB>above the anaerobic threshold is estimated from Vo<SUB>2</SUB>using the regression line obtained at work load below the anaerobic threshold, the estimated Vco<SUB>2</SUB>will be lower than the measured Vco<SUB>2</SUB>. The total sum of the difference in the Vco<SUB>2</SUB>was defined as CO<SUB>2</SUB>excess. The CO<SUB>2</SUB>excess and the CO<SUB>2</SUB>excess per body weight were significantly related to ΔLAmax (the difference between LA at 3rd min after exhastion and LA at exercise below the anaerobic threshold), respectively (r=0.870, r=0.930) .<BR>4) HCO<SUB>3</SUB><SUP>-</SUP>calculated from blood gases (pH and Pco<SUB>2</SUB>) was significantly related to LA (r=-0.902) . The increase of 1 mM/1 in LA was corresponding to the decrease of 0.843 mEq/l in HCO<SUB>3</SUB><SUP>-</SUP>.<BR>5) From these results, it appeared that the expired Vco<SUB>2</SUB>during the incremental exercise consisted of the stored Vco<SUB>2</SUB>, the exceeded Vco<SUB>2</SUB>, and the produced Vco<SUB>2</SUB> (Vco<SUB>2</SUB>metabolically produced from Vo<SUB>2</SUB>) .