Hypotension following mild bouts of resistance exercise and submaximal dynamic exercise

Our purposes were (1) to examine resting arterial blood pressure following an acute bout of resistance exercise and submaximal dynamic exercise, (2) to examine the effects of these exercises on the plasma concentrations of atrial natriuretic peptide ([ANP]), and (3) to evaluate the potential relationship between [ANP] and post-exercise blood pressure. Thirteen males [24.3 ± (2.4) years] performed 15 min of unilateral leg press exercise (65% of their one-repetition maximum) and, 1 week later, ≈15 min of cycle ergometry (at 65% of their maximum oxygen consumption). Intra-arterial pressure was monitored during exercise and for 1 h post-exercise. Arterial blood was drawn at rest, during exercise and at intervals up to 60 min post-exercise for analysis of haematocrit and [αANP]. No differences occurred in blood pressure between trials, but significant decrements occurred following exercise in both trials. Systolic pressure was ≈20 mmHg lower than before exercise after 10 min, and mean pressure was ≈7 mmHg lower from 30 min onwards. Only slight (non-significant) elevations in [αANP] were detected immediately following exercise, with the concentrations declining to pre-exercise values by 5 min post-exercise. We conclude that post-exercise hypotension occurs following acute bouts of either resistance or submaximal dynamic exercise and, in this investigation, that this decreased blood pressure was not directly related to the release of αANP. Accepted: 29 July 1998     

Influence of acute submaximal exercise on T-lymphocyte suppressor cell function in healthy young men

A defect in T-lymphocyte suppressor cell function has been reported to occur in a number of autoimmune diseases. The influence of exercise on suppressor cell function has not been determined in individuals with autoimmune diseases, nor has it been determined in healthy individuals. The purpose of this investigation was to determine the effect of an acute bout of submaximal exercise on suppressor cell function in healthy males. Each subject (n=10) completed an exercise trial (E; 1 h of cycle ergometry at 70.6% of maximal oxygen uptake, followed by 2 h of recovery) and a resting trial (R; 3 h of seated rest), separated by at least 1 week. Treatment (E or R) order was counterbalanced. Venous blood samples were obtained pre-exercise (PRE), immediately after exercise (POST), and 2 h post-exercise (2HPOST), and at the same time points in the R trial. Lymphocyte phenotype percentages were determined by flow cytometry, while concanavalin- A-induced suppressor cell function was determined on peripheral blood mononuclear cells. No change was observed in the percentage of T-cytotoxic/suppressor cells. Suppressor cell function was significantly different between treatments, with the POST E value [mean (SD) 56.8 (1.6)%] being higher than the POST R value [41.7 (1.9)%]. No significant difference was observed 2HPOST. In conclusion, acute submaximal exercise resulted in a transient increase in suppressor cell function in healthy males. Accepted: 17 January 2000     

Acute effects of hyperglycaemia with and without exercise on endothelial function in healthy young men

Post-prandial hyperglycaemia impairs endothelial function as evaluated by brachial artery flow-mediated dilation (FMD). Exercise is an intervention to protect against cardiovascular disease and to improve FMD. In this study, we examined whether the effect of acute hyperglycaemia on endothelial function in healthy young men is restored by aerobic exercise. Using a counterbalanced, randomized crossover design, we measured the brachial artery FMD at baseline and 1, 2, 3 and 4 h after 75 g glucose ingestion in 11 healthy young men, with and without a single bout of aerobic exercise. Brachial artery FMD declined from 11.4 ± 3.8% at baseline to 7.3 ± 3.4% 1 h after oral glucose ingestion, and returned to baseline after 4 h. When the oral glucose ingestion was followed immediately by 45 min of treadmill exercise at an intensity of 60% maximal oxygen uptake, FMD demonstrated no significant decrease (11.8 ± 2.5, 11.3 ± 2.8, 12.2 ± 2.7, 13.5 ± 3.5, and 12.6 ± 2.4% at baseline and 4 h after ingestion, respectively). The results indicate that the aerobic exercise restores the impaired FMD induced by oral glucose ingestion.     

The influence of blood sampling site on lactate concentration during submaximal exercise at 4 mmol · 1−1 lactate level

This study examined lactate concentration during incremental and submaximal treadmill exercise at work rates corresponding to 4 mmol· 1^–1 lactate concentration, determined by fingertip (OBLAI) and venous blood (OBLA2). Initially, eight subjects performed a 4-min incremental exercise test until exhaustion. On two other occasions, seven of the subjects undertook submaximal exercise tests (30 min) at work rates corresponding to OBLA1 and OBLA2. Blood was simultaneously obtained from both sites at rest and at the end of each exercise stage during the incremental exercise, and at 5, 10, 20 and 30 min during the submaximal exercise and 5 min into recovery. Fingertip blood lactate concentrations were significantly higher (P<0.05) than venous blood at rest, throughout the incremental exercise, consistently during exercise at OBLA1 and OBLA2, and into recovery. Data also revealed an exercise intensity-dependent lactate difference between the two sampling sites during both exercise protocols. Exercise at OBLA1 did not result in a progressive increase in lactate level nor exhaustion, and the lactate value at the end of 30 min corresponded to the predetermined value. However, exercise at OBLA2 resulted in a significantly higher (P<0.05) lactate level than OBLA1, the lactate concentration at the end of 30 min was substantially higher than the predetermined value (P<0.05) and exhaustion was evident. It is concluded that the lactate concentration value during incremental and submaximal exercise (at 4 mmol·l^–1 OBLA) is dependent on the blood sampling site. This finding should be considered in studies concerned with the determination of OBLA.     

Effect of posture on body temperature of young men in cold air

We studied eight young adult men to see whether a supine posture caused a fall in body core temperature in the cold, as it does in thermoneutral conditions. In air at 31°C (thermoneutral), a supine posture for 3 h reduced mean aural, gastric, oesophageal and rectal temperatures by 0.2–0.4°C, compared to upright and increased femoral artery blood flow from 278 (SEM 42) ml · min⁻¹ whilst upright to 437 (SEM 42) ml·min⁻¹ whilst supine. In cold air (8°C) the supine posture failed to reduce these temperature differences significantly, or to increase femoral blood flow; it reduced heart rate, and increased arterial systolic and pulse pressures adjusted to carotid sinus level, less than in thermoneutral conditions. However, the behaviour of core temperature at the four sites was significantly nonuniform between the two postures in the cold, mainly because the supine posture tended to reduce rectal temperature. It may have done so by reducing heat production in the muscles of the pelvis, since it reduced overall metabolic rate from 105 (SEM 8) to 87 (SEM 4) W · m⁻² in the cold. In other respects the results indicated that posture ceased to have an important effect on body core temperatures during cold stress.     

TSH,T3, rT3 and fT4 in maximal and submaximal physical exercise

Summary The response of various thyroid hormone parameters to maximal physical exercise (MPE) was investigated in 14 medium and long distance runners and 13 divers. The effect of submaximal long time physical exercise (SMPE) was examined in seven divers. The TSH-level decreases significantly during MPE and slightly rises again after the end of the exercise. In SMPE, however, TSH continuously rises until 15 min after the end of the exercise. The T₃ level rises significantly in MPE and falls below the initial value 15 min after the exercise finishes, during SMPE it remains practically unchanged and slightly decreases after the finish. In MPE, the rT₃ level does not change and slightly decreases after termination, while the fT₄ level continuously decreases from the beginning till 15 min after the exercise period. The latter two parameters do not show any change in SMPE. As possible reasons for the changes of TSH levels a decrease (MPE) or an increase (SMPE) of pituitary secretion might play a role. Furthermore, in MPE the rise in T₃ level might be related to hemoconcentration, and the decrease in fT₄ level to an elevated cellular utilization.     

Comparison in men of physiological responses to exercise of increasing intensity at low and moderate ambient temperatures

Summary In six male subjects the sweating thresholds, heart rate (f _c, as well as the metabolic responses to exercise of different intensities [40%, 60% and 80% maximal oxygen uptake (VO_2max)], were compared at ambient temperatures (T _a) of 5° C (LT) and 24° C (MT). Each period of exercise was preceded by a rest period at the same temperature. In LT experiments, the subjects rested until shivering occurred and in MT experiments the rest period was made to be of exactly equivalent length. Oxygen uptake (VO₂) at the end of each rest period was higher in LT than MT (P< 0.05). During 20-min exercise at 40%VO_2max performed in the cold no sweating was recorded, while at higher exercise intensities sweating occurred at similar rectal temperatures (T _re) but at lower mean skin (T _sk) and mean body temperatures (T _b) in LT than MT experiments (P<0.001). The exercise inducedVO₂ increase was greater only at the end of the light (40%VO_2max) exercise in the cold in comparison with MT (P<0.001). Bothf _c and blood lactate concentration [la]_b were lower at the end of LT than MT for moderate (60%VO_2max) and heavy (80%VO_2max) exercises. It was concluded that the sweating threshold during exercise in the cold environment had shifted towards lower (T _b) andT _sk. It was also found that subjects exposed to cold possessed a potentially greater ability to exercise at moderate and high intensities than those at 24° C since the increases inT _re,f _c and [la]_b were lower at the lowerT _a.     

Lactate concentration differences in plasma,whole blood,capillary finger blood and erythrocytes during submaximal graded exercise in humans

Summary The aim of the study was to investigate the distribution of lactate in plasma, whole blood, erythrocytes, and capillary finger blood, before and during submaximal exercise. Ten healthy male subjects performed submaximal graded cycle ergometer exercise for 20–25 min. Venous blood samples and capillary finger blood samples were taken before exercise and every 5th min during exercise for lactate determination. The plasma lactate concentration was significantly higher (P<0.001, approximately 50%) than in the erythrocytes. This difference was not altered by the venous blood lactate concentration or exercise intensity. A significant difference (P<0.01) in lactate concentration was also found between capillary whole blood and venous whole blood. It was concluded that direct comparisons between lactate in capillary finger blood, venous whole blood and plasma could not be made.The study was performed at the Department of Clinical Physiology, University Hospital, S-75185 Uppsala, Sweden     

Endurance training slows down the kinetics of heart rate increase in the transition from moderate to heavier submaximal exercise intensities

Summary To find out whether endurance training influences the kinetics of the increases in heart rate (f _c) during exercise driven by the sympathetic nervous system, the changes in the rate off _c adjustment to step increments in exercise intensities from 100 to 150 W were followed in seven healthy, previously sedentary men, subjected to 10-week training. The training programme consisted of 30-min cycle exercise at 50%–70% of maximal oxygen uptake ( O_2max) three times a week. Every week during the first 5 weeks of training, and then after the 10th week the subjects underwent the submaximal three-stage exercise test (50, 100 and 150 W) with continuousf _c recording. At the completion of the training programme, the subjects' O_2max had increased significantly(39.2 ml·min^–1·kg^–1, SD 4.7 vs 46 ml·min^–1·kg^–1, SD 5.6) and the steady-statef _c at rest and at all submaximal intensities were significantly reduced. The greatest decrease in steady-statef _c was found at 150 W (146 beats·min^–1, SD 10 vs 169 beats·min^–1, SD 9) but the difference between the steady-statef _c at 150 W and that at 100 W (f _c) did not decrease significantly (26 beats·min^–1, SD 7 vs 32 beats·min^–1, SD 6). The time constant () of thef _c increase from the steady-state at 100 W to steady-state at 150 W increased during training from 99.4 s, SD 6.6 to 123.7 s, SD 22.7 (P<0.01) and the acceleration index (A=0.63·f _c·^–1) decreased from 0.20 beats·min^–1·s^–1, SD 0.05 to 0.14 beats·min^–1·s^–1, SD 0.04 (P<0.02). The major part of the changes in and A occurred during the first 4 weeks of training. It was concluded that heart acceleration following incremental exercise intensities slowed down in the early phase of endurance training, most probably due to diminished sympathetic activation.     

Pulmonary function in normal subjects following exercise at cold ambient temperatures

Summary We measured pulmonary function in 12 healthy volunteers before and at 5-min intervals for 30 min following treadmill exercise of 30 min duration performed under control (20° C) and cold (–11 ° C) ambient temperatures. Post-run changes in forced vital capacity (FVC), residual volume (RV) and peak expiratory flow rate were similar between the two temperature conditions. FVC decreased slightly but significantly 5 min post-run (–0.25 ±0.201 and –0.21–0.201, for control and cold conditions respectively) and returned to baseline by 30 min. RV increased significantly post-exercise (+ 0.07 ± 0.091 and + 0.14 ± 0.11, control and cold respectively) and remained elevated for 30 min. Forced expired volume in 1 s was not significantly different following either run. Post-exercise, maximum mid-expiratory flow rate and flows at 50% and 25% of vital capacity were not significantly different between warm and cold conditions. These data suggest that changes in lung volumes following exercise under cold ambient conditions are similar to changes seen following warm exercise of similar duration. In non-asthmatics, moderate exertion under cold ambient conditions does not appear to cause clinically significant decreases in expiratory flow rates as compared to similar exertion under warm conditions.     

Cardiac output measured by acetylene rebreathing technique at rest and during exercise

Cardiac output ( ) was measured by a rebreathing technique, using acetylene and a mass-spectrometer for analyzing. In addition the rate of pulmonary uptake of O₂ ( ) during the rebreathing period and during a preceding steady-state period were determined. Measurements were made on 8 adult humans at rest and at different levels of exercise up to maximum at two occasions. The ratio ( ) during steady-state/ during rebreathing) was found to be significantly below 1 when the was below about 21·min^–1 and to be about 0.55 for subjects at rest. This indicates that , and hence is increased by the rebreathing procedure when this involves deeper and more frequent respirations than those of the preceding period. Accordingly, when was below about 21·min^–1, the value, calculated exclusively from acetylene concentrations recorded during rebreathing, was multiplied by the above-mentioned -ratio. It is shown that this correcting procedure gives more reasonable values than those obtained by acetylene data alone. It is pointed out in what respects this correcting procedure of calculation deviates from that originally used by Grollman, and it is shown that there are only moderate differences between the results obtained by the two procedures.List of Symbols Ac Acetylene - _Ac ^B Bunsen solubility coefficient for Ac in blood (0.700 ml·ml^–1·atm^–1, Chapman et al. 1950) - _PT ^Ac Solubility coefficient for Ac in pulmonary tissue (0.768 ml·ml^–1·atm^–1, Cander and Forster 1959) - Mixed end-capillary to mixed venous oxygen difference per ml blood - F _AC Fractional (dry) concentration of a gas (Ac) in the gas mixture during rebreathing (s) or in the initial mixture in the bag (b) - Alveolar oxygen tension (mm Hg) - pB Barometric pressure (mm Hg) - Pulmonary capillary blood flow (cardiac output), (ml·min^–1) - t Time (s) - V ^b Initial gas volume (ml STPD) in the rebreathing bag (b) - V ^L Initial gas volume in lungs and airways after a deep expiration - V ^PT Volume of pulmonary tissue and blood in the pulmonary capillaries - V _Ac ^s (t _O) Distribution compartment (system volume) of a gas (Ac) at timet _O - Oxygen uptake (ml·min^–1) during rebreathing (RB) or steady-state (SS)     

Physical work capacity in dynamic exercise with differing muscle masses in healthy young and older men

Ten young (aged 23–30 years) and nine older (aged 54–59 years) healthy men with similar estimated limb muscle volumes performed, in random order, three different types of ergometer exercise tests (one-arm cranking, two-arm cranking, and two-leg cycling) up to the maximal level. Values for work load (WL), peak oxygen consumption , peak heart rate (HR), peak ventilation , respiratory gas exchange ratio (R), recovery blood lactate concentration [La^–], and rating of perceived exertion (RPE) were compared between the age-groups in the given exercise modes. No significant age-related differences in WL, peak , peak HR, R, [La^–], or RPE were found in one-arm or two-arm cranking. During one-arm cranking the mean peak was 1.65 (SD 0.26)1 · min^–1 among the young men and 1.63 (SD 0.10)1 · min^–1 among the older men. Corresponding mean peak during two-arm cranking was 2.19 (SD 0.32)1 · min-1 and 2.09 (SD 0.18)1 · min^–1, respectively. During one-arm cranking peak was higher (P < 0.05) among the older men compared to the young men. During two-leg cycling the young men showed higher values in WL (P < 0.001), peak (P < 0.001), and peak HR (P < 0.001). The mean peak was 3.54 (SD 0.24)1 · min^–1 among the young men and 3.02 (SD 0.20)1 · min^–1 among the older men. Corresponding mean peak HR was 182 (SD 5) beats · min^–1 and 170 (SD 8) beats · min^–1, respectively. During two-leg cycling, peak , R, [La^–], and RPE did not differ between the two age-groups. In summary, the older men with similar sizes of estimated arm and leg muscle volumes as the young men had a reduced physical work capacity in two-leg cycling. In one-arm or two-arm cranking, no significant difference in work capacity was found between the age-groups. These results indicate, that in healthy men, age, at least up to the 6th decade of life, is not necessarily associated with a decline in physical work capacity in exercises using relatively small muscle groups, in which the limiting factors are more peripheral than central.     

Aerobic exercise performance correlates with post-ischemic flow-mediated dilation of the brachial artery in young healthy men

In older healthy men, aerobic exercise capacity is related to postischemic flow-mediated dilation of the brachial artery (FMD), but corresponding data in a younger population is not available. In addition, whether submaximal aerobic exercise performance also correlates with this kind of vasomotor reactivity is not known. Therefore, in 15 nonsmoking young healthy men [age 27 (5) years; body mass index: 24 (2) kg/m²; mean (SD)] with different levels of ordinary physical activity, but not performing upper-extremity training, we measured FMD at 1 min after reactive hyperemia, and pulmonary oxygen uptake (O₂) at ventilatory anaerobic threshold (O₂AT) and at peak effort (peak O₂) during an incremental exercise on a treadmill. In our participants, FMD was 9.1 (3.4)%, O₂AT was 40.72 (5.92) ml/kg per min, and peak O₂ was 52.95 (8.13) ml/kg per min. Using bivariate Pearsons correlation, and in separate multivariate regression analyses, O₂AT and peak VO₂ showed a significant and reasonably good correlation with FMD (r=0.84, P<0.001 and r=0.77, P=0.001, respectively), independent of age, body mass index and serum total cholesterol (=0.77, P<0.001, R² of the overall model=0.79 and =0.70, P<0.005, R² of the overall model=0.69, respectively). Our data provide evidence suggesting that in young healthy men a higher submaximal and maximal aerobic exercise performance is associated with a greater FMD of peripheral conduit arteries.     

Dynamics of changes in the cardiovascular response to submaximal exercise during low-intensity endurance training with particular reference to the systolic time intervals

Summary Eighteen male volunteers (aged 20–23 years), not involved in any sporting activities, were submitted to 13 weeks of training consisting of 30 min exercise [at 50%–75% maximal oxygen intake on a cycle ergometer, performed 3 times a week. Every 4 weeks cardiac function was evaluated by measuring the systolic time intervals at rest and during submaximal cycle exercise. Stroke volume (SV), heart rate (HR) and blood pressure (BP) responses to submaximal exercise, and anaerobic threshold (AT) were also determined. Significant increases in , increases in AT and SV at the submaximal exercise intensities, as well as decreases in HR and BP were found after 4 weeks of training. Resting systolic time intervals were not affected by training, but during the submaximal cycle exercise the values of the pre-ejection period (PEP) and isovolumic contraction time (ICT) corresponding to HR of 100 beats·min⁻¹ were significantly lowered after 13 weeks of training, whereas PEP, ICT and total electromechanical systole corresponding to HR of 130 beats·min⁻¹ were significantly shortened by the 4th week. The ratios of PEP:LVET (left ventricular ejection time) and ICT:LVET during submaximal exercise were significantly lowered by training starting from the 8th week. These changes might be interpreted as evidence of the training-induced enhancement of the “contractility reserve”, i.e. the ability to increase heart muscle contractility with increasing exercise intensity.     

Effect of acute sprint interval exercise on central and peripheral artery distensibility in young healthy males

Peripheral arterial distensibility is improved with sprint interval exercise training in young healthy participants (Rakobowchuk et al. in Am J Physiol Regul Integr Comp Physiol 295:R236–R242, 2008). To fully understand the mechanisms contributing to these training effects it is useful to examine the acute responses to sprint interval exercise. Following supine rest, nine healthy males completed either a single sprint interval (Wingate test) or a multiple sprint interval exercise session (4 Wingate tests each separated by 4.5 min). Following exercise, participants recovered for 60 min while central and peripheral arterial distensibility measurements were conducted at discrete time points, using applanation tonometry and ultrasound imaging and continuously, using central and peripheral pulsewave velocity (PWV). Single and multiple sprint interval exercise sessions caused similar changes in all variables. Heart rate was increased throughout recovery (p < 0.05), while central artery PWV was increased until 20 min of recovery (p < 0.05) and lower extremity PWV was decreased until ~45 min (p < 0.05). Distensibility of the superficial femoral artery showed a trend for a reduction at 2 min post-exercise (p = 0.06). These results indicate that extremely high intensity exercise transiently increases central artery stiffness, while metabolite induced vasodilation reduces peripheral stiffness in exercised limbs well into recovery.     

吸入一氧化氮对婴幼儿体外循环中肺功能的影响

目的探讨吸入一氧化氮（Nitric oxide,NO）对婴幼儿体外循环手术中肺功能的影响。方法将30例患室间隔缺损的婴幼儿随机分为对照组和NO组,NO组在体外循环期间吸入40 ppm NO直至关胸。体外循环前和术后气管插管未拔前0-1h、1-2h、2-3h测定气道压、吸入氧浓度和呼气末二氧化碳浓度（ETCO2）,并分别在同时点采动脉血进行血气分析,计算肺泡死腔率（VD/VT）肺、泡动脉血氧分压差（P（A-a）O2）、动脉血氧含量（CaO2）和肺泡氧合指数（OI）,记录术后呼吸机支持时间。体外循环前、主动脉开放后1、5、10min分别取右上肺静脉血和右心房血用于测定丙二醛（MDA）、超氧化物歧化酶（SOD）。结果与NO组相比,对照组再灌注后VD/VT、P（A-a）O2,OI明显升高（P〈0.05）,CaO2下降（P〈0.01）;MDA明显升高（P〈0.05）;SOD明显降低（P〈0.01）。结论婴幼儿体外循环术中存在明显肺损害,表现为一些亚临床性肺功能损伤。吸入40 ppm NO对体外循环期间肺功能有保护作用。     

Noninvasive ambulatory assessment of cardiac function in healthy men exposed to carbon monoxide during upper and lower body exercise

Very little is known about the cardiovascular responses of exercising individuals when exposed to carbon monoxide (CO). Sixteen healthy nonsmoking men aged 18–29 years participated in the study. Using a combination of exposures to CO by breathing from a bag or in an environmental chamber, subjects performed a randomized sequence of brief (5 min) multi-level treadmill and hand-crank exercises on different days at less than 2% carboxyhemoglobin (COHb) and after attaining target levels of 5%, 10%, 15%, and 20% COHb. To assess cardiac function changes we employed noninvasive impedance cardiography (ICG) and three-lead electrocardiograms (ECG). The ICG was used to estimate cardiac output, stroke volume, heart rate, cardiac contractility, and time-to-peak ejection time. The ECG was used to assess myocardial irritability and ischemia, and changes in cardiac rhythm. The results showed that the cardiovascular system compensated for the reduced O₂-carrying capacity of the blood by augmenting heart rate, cardiac contractility, and cardiac output for both upper-body and lower-body exercise. While this mechanism served well in submaximal exercise, the enhanced cardiovascular response to exercise was not without physiological costs because it began to fail at moderate levels of CO exposure and exercise. We concluded that young, apparently healthy men can perform submaximal upper and lower-body exercise without overt impairment of cardiovascular function after CO exposures attaining 20% COHb. Accepted: 6 June 2000     

Physiological responses of young and elderly men to prolonged exercise at critical power

Summary The critical power (CP) of a muscle group or individual may represent the highest rate of work which can be performed for an extended period. We investigated this concept in young (n = 13, 24.5 years) and elderly (n = 12, 70.7 years) active men by first determining CP and then comparing responses elicited by 24 min of cycle exercise at power outputs () corresponding to CP. Values from the final 2 min of the 24-min ride were expressed relative to maximal values established in a ramp test. CP for the elderly was only 65% that for the young, but on a relative basis, it was significantly higher both in terms of (67 vs 62% of _max) and oxygen consumption ( ) (91.5 vs 85.2% of maximum oxygen consumption). There were no group differences in relative values for ventilation ( ), heart rate or respiratory exchange ratio (R). During the 24-min ride, andR achieved a plateau in both groups, while , blood lactate and arterialPCO₂ continued to change in the young. It was concluded that CP can be determined in active elderly men, but that CP may not represent a true non-fatiguing work rate in either young or elderly men.     

Myocardial lactate extraction and release at rest and during heavy exercise in healthy men

The relationship between myocardial lactate extraction and blood lactate concentration and the possibility that simultaneous uptake and release of lactate occur in the normal human heart was investigated by measuring arterial-coronary sinus differences of lactate and of labelled lactate during infusion of ¹⁴C lactate in 13 healthy young male volunteers. Measurements were done at rest, during increased cardiac work with unaltered arterial lactate concentration achieved by atrial pacing and during increased cardiac work and increased arterial lactate concentration achieved by supine cycle ergometer exercise. There was on no occasion a significant difference in ¹⁴C lactate specific activity between arterial and coronary sinus blood, i.e. no significant admixture of non-labelled lactate occurred in the coronary sinus indicating that on no occasion was there any sign of lactate release. The myocardial extraction of lactate seemed to be a linear function of arterial lactate concentration. During exercise with an arterial lactate concentration of 6 mmol l^-1 and above, lactate could have covered approximately 75–100% of the oxidative metabolism. Thus, during short-term heavy work myocardial lactate extraction dominates over other substrates (mainly free fatty acids and glucose) taken up by the heart, and used for oxidation by the heart muscle cells.     

Effect of exercise on postprandial lipemia in men with hypertriglyceridemia

We examined the effect of exercise on postprandial lipemia (PPL) and insulin resistance in individuals with metabolic syndrome. Subjects were 10 hypertriglyceridemia (HTG) males with insulin resistance [age = 40.1 ± 2.2 years, body weight = 96.3 ± 3.3 kg, fasting triglyceride (TG) = 263 ± 25 mg/dl, VO₂max = 37 ± 1.1 ml/kg/min, and Homeostatic Model Assessment (HOMA-IR, an index of insulin resistance) = 3.05 ± 0.40]. Each subject performed a control trial (Ctr, no exercise), and three exercise trials at 40% (40%T), 60% (60%T), and 70% (70%T) of their VO₂max. The order of trials was randomized and there were 1–2 weeks wash-out period between the trials. All subjects had a fat-meal in each trial. In the exercise trials, subjects jogged on a treadmill for 1 h at a designated intensity 12 h prior to a fat-meal ingestion. Blood samples were taken at 0 h (before the meal), and 2, 4, 6, and 8 h after the meal. The plasma TG, area score under TG concentration curve for over an 8 h-period (TG AUC) after the meal, and HOMA-IR were analyzed. The TG AUC score in 40%T was 30% lower (P = 0.003), 60%T was 31% lower (P = 0.02), and 70%T was 39% lower (P = 0.02) than Ctr. There were no significant differences in the TG AUC scores among the exercise trials (P > 0.05). The insulin concentrations in both 60 and 70%T were lower than Ctr (P < 0.01) which did not differ from 40%T. HOMA-IR in both 60%T (P = 0.041) and 70%T (P = 0.002) were lower than Ctr, but not different from 40%T (HOMA-IR: Ctr = 3.05 ± 0.40, 40%T = 2.67 ± 0.35, 60%T = 2.49 ± 0.31, 70%T = 2.21 ± 0.27). The results suggest that for physically inactive individuals with metabolic syndrome, exercising at low to moderate intensity may be sufficient to attenuate PPL and increase insulin sensitivity, whereas higher intensity exercise may be needed to normalize blood glucose.