Psychomotor performance during prolonged exercise above and below the blood lactate threshold

Previous investigations from this laboratory have demonstrated that during graded exercise with exercise intensities increasing every 3 min until exhaustion the multiple choice reaction time (RT) decreased until the intensity exceeded the lactate threshold (LT) by approximately 25%, and then rapidly increased. The aim of this study was to follow up changes in RT during prolonged exercise at constant intensities above and below LT and to relate these changes to changes in venous blood lactate [La⁻]_b, and plasma catecholamine [CA]_pl concentration responses to the exercise. For this purpose eight young soccer players exercised for 20-min on a cycle ergometer at 10% above LT, and nine exercised for 60 min at an intensity 30% below LT. During both tests RT, heart rate (HR), as well as [La⁻]_b, and [CA]_pl were measured. Above LT, RT decreased from the 5th min until the end of exercise, whilst HR, [La⁻]_b, and [CA]_pl increased progressively. Significant inverse correlations were ascertained between RT and plasma adrenaline (r = − 0.651) and noradrenaline concentrations (r = − 0.678). During exercise below LT, RT decreased up to approximately 40 min, then it reached a nadir, and stabilized at this level. This was accompanied by only small changes in [La⁻]_b and [CA]_pl. The present findings would indicate that young athletes are able to maintain for a relatively long time, or even increase, their psychomotor performance during endurance exercise both below and above the LT. Accepted: 23 June 1997     

Maximal voluntary hyperpnoea increases blood lactate concentration during exercise

Ventilatory work during heavy endurance exercise has not been thought to influence systemic lactate concentration. We evaluated the effect of maximal isocapnic volitional hyperpnoea upon arterialised venous blood lactate concentration ([lac⁻]_B) during leg cycling exercise at maximum lactate steady state (MLSS). Seven healthy males performed a lactate minimum test to estimate MLSS, which was then resolved using separate 30 min constant power tests (MLSS=207±8 W, mean ± SEM). Thereafter, a 30 min control trial at MLSS was performed. In a further experimental trial, the control trial was mimicked except that from 20 to 28 min maximal isocapnic volitional hyperpnoea was superimposed on exercise. Over 20–28 min minute ventilation, oxygen uptake, and heart rate during the control and experimental trials were 87.3±2.4 and 168.3±7.0 l min⁻¹ (P<0.01), the latter being comparable to that achieved in the maximal phase of the lactate minimum test (171.9±6.8 l min⁻¹), 3.46±0.20 and 3.83 ± 0.20 l min⁻¹ (P<0.01), and 158.5±2.7 and 166.8±2.7 beats min⁻¹ (P<0.05), respectively. From 20 to 30 min of the experimental trial [lac⁻]_B increased from 3.7±0.2 to 4.7±0.3 mmol l⁻¹ (P<0.05). The partial pressure of carbon dioxide in arterialised venous blood increased approximately 3 mmHg during volitional hyperpnoea, which may have attenuated the [lac⁻]_B increase. These results show that, during heavy exercise, respiratory muscle work may affect [lac⁻]_B. We speculate that the changes observed were related to the altered lactate turnover in respiratory muscles, locomotor muscles, or both.     

Change in post-exercise vagal reactivation with exercise training and detraining in young men

We studied the effects of aerobic exercise training and detraining in humans on post-exercise vagal reactivation. Ten healthy untrained men trained for 8 weeks using a cycle ergometer [70% of initial maximal oxygen uptake ( ) for 1 h, 3–4 days·week^–1] and then did not exercise for the next 4 weeks. Post-exercise vagal reactivation was evaluated as the time constant of the beat-by-beat decrease in heart rate during the 30 s (t₃₀) immediately following 4 min exercise at 80% of ventilatory threshold (VT). The and the oxygen uptake at VT had significantly increased after the 8 weeks training programme (P<0.0001, P<0.001, respectively). The t₃₀ had shortened after training, and values after 4 weeks and 8 weeks of training were significantly shorter than the initial t₃₀ (P<0.05, P<0.01, respectively). The change in the t₃₀ after 8 weeks of training closely and inversely correlated with the initial t₃₀ (r=–0.965, P<0.0001). The reduced t₃₀ was prolonged significantly after 2 weeks of detraining, and had returned almost to the baseline level after a further 2 weeks of detraining. These results suggest that aerobic exercise training of moderate intensity accelerates post-exercise vagal reactivation, but that the accelerated function regresses within a few weeks of detraining. Electronic Publication     

Physiological effects of micropauses in isometric handgrip exercise

Summary The physiological response to continuous and intermittent handgrip exercise was evaluated. Three experiments were performed until exhaustion at 25% of maximal voluntary contraction (MVC): experiment 1, continuous handgrip (CH) (n = 8); experiment 2, intermittent handgrip with 10-s rest pause every 3 min (IH) (n=8); and experiment 3, as IH but with electrical stimulation (ES) of the forearm extensors in the pauses (IHES) (n=4). Before, during, and after exercise, recordings were made of heart rate (HR), arterial blood pressure (BP), exercising forearm blood flow, and concentrations of potassium [K⁺] and lactate [La^–] in venous blood from both arms. The electromyogram (EMG) of the exercising forearm extensors and perceived exertion were monitored during exercise. Before and up to 24 h after exercise, observations were made of MVC, of force response to electrical stimulation and of the EMG response to a 10-s test contraction (handgrip) at 25% of the initial MVC. Maximal endurance time (t _tim) was significantly longer in IH (23.1 min) than in CH (16.2 min). The ES had no significant effect ont _lim. During exercise, no significant differences were seen between CH and IH in blood flow, venous [K⁺] and [La^–], or EMG response. The HR and BP increased at the same rate in CH and IH but, because of the longer duration of IH, the levels at exhaustion were higher in this protocol. The subjects reported less subjective fatigue in IH. During recovery, return to normal MVC was slower after CH (24 h) than after IH (4 h). However, the frequency content of the EMG during the 10-s test contractions was still reduced 24 h after IH, but only 4 h after CH. This may be explained by the larger amount of potassium lost up to the first hour of recovery in IH. None of the measured physiological parameters could provide a satisfactory explanation, either of the 43% difference int _lim between CH and IH, or of the sense of relief reported by all subjects during the short rest pauses in IH. Therefore, a plausible explanation was that the prolongation oft _lim in IH may have been related to differences at a sensory level. It was concluded that short rest periods, if introduced in exercise with long cycle-times, could give an immediate sense of relief, postponing the subjective threshold of fatigue. Thus the results of this study provided experimental support for the hypothesis that the introduction of micropauses may create an increased risk of musculoskeletal disorders.     

Blood lactate response to overtraining in male endurance athletes

Many physiological markers vary similarly during training and overtraining. This is the case for the blood lactate concentration ([La⁻]_b), since a right shift of the lactate curve is to be expected in both conditions. We examined the possibility of separating the changes in training from those of overtraining by dividing [La⁻]_b by the rating of perceived exertion ([La⁻]_b/RPE) or by converting [La⁻]_b into a percentage of the peak blood lactate concentration ([La⁻]_b,peak). Ten experienced endurance athletes increased their usual amount of training by 100% within 4 weeks. An incremental test and a time trial were performed before (baseline) and after this period of overtraining, and after 2 weeks of recovery (REC). The [La⁻]_b and RPE were measured during the recovery of each stage of the incremental test. We diagnosed overtraining in seven athletes, using both physiological and psychological criteria. We found a decrease in mean [La⁻]_b,peak from baseline to REC [9.64 (SD 1.17), 8.16 (SD 1.31) and 7.69 (SD 1.84) mmol · l⁻¹, for the three tests, respectively; P < 0.05] and a right shift of the lactate curve. Above 90% of maximal aerobic speed (MAS) there was a decrease of mean [La⁻]_b/RPE from baseline to REC [at 100% of MAS of 105.41 (SD 17.48), 84.61 (SD 12.56) and 81.03 (SD 22.64) arbitrary units, in the three tests, respectively; P < 0.05), but no difference in RPE, its variability accounting for less than 25% of the variability of [La⁻]_b/RPE (r=0.49). Consequently, [La⁻]_b/RPE provides little additional information compared to [La⁻]_b alone. Expressing [La⁻]_b as a %[La⁻]_b,peak resulted in a suppression of the right shift of the lactate curve, suggesting it was primarily the consequence of a decreased production of lactate by the muscle. Since the right shift of the curve induced by optimal training is a result of improved lactate utilization, the main difference between the two conditions is the decrease of [La⁻]_b,peak during overtraining. We propose retaining it as a marker of overtraining for long duration events, and repeating its measurement after a sufficient period of rest to make the distinction with overreaching. Accepted: 26 September 2000     

Effect of cold exposure (−15°C) and Salbutamol treatment on physical performance in elite nonasthmatic cross-country skiers

The effects of whole-body exposure to ambient temperatures of −15°C and 23°C on selected performance-related physiological variables were investigated in elite nonasthmatic cross-country skiers. At an ambient temperature of −15°C we also studied the effects of the selective β₂-adrenergic agonist Salbutamol (0.4 mg × 3) which was administered 10 min before the exercise test. Eight male cross-country skiers with known maximal oxygen uptakes (V˙O_{2 max} ) of more than 70 ml · kg⁻¹ · min⁻¹ participated in the study. Oxygen uptake (V˙O₂), heart rate (f _c), blood lactate concentration ([La⁻]_b) and time to exhaustion were measured during controlled submaximal and maximal running on a treadmill in a climatic chamber. Lung function measured as forced expiratory volume in 1 s (FEV₁) was recorded immediately before the warm-up period and at the conclusion of the exercise protocol. Submaximal V˙O₂ and [La⁻]_b at the two highest submaximal exercise intensities were significantly higher at −15°C than at 23°C. Time to exhaustion was significantly shorter in the cold environment. However, no differences in V˙O_{2 max} or f _c were observed. Our results would suggest that exercise stress is higher at submaximal exercise intensities in a cold environment and support the contention that aerobic capacity is not altered by cold exposure. Furthermore, we found that after Salbutamol inhalation FEV₁ was significantly higher than after placebo administration. However, the inhaled β₂-agonist Salbutamol did not influence submaximal and maximal V˙O₂, f _c, [La⁻]_b or time to exhaustion in the elite, nonasthmatic cross-country skiers we studied. Thus, these results did not demonstrate any ergogenic effect of the β₂-agonist used. Accepted: 18 August 1997     

Blood lactate responses in incremental exercise as predictors of constant load performance

Summary Seven trained male cyclists ( =4.42±0.23 l·min⁻¹; weight 71.7±2.7 kg, mean ± SE) completed two incremental cycling tests on the cycle ergometer for the estimation of the “individual anaerobic threshold” (IAT). The cyclists completed three more exercises in which the work rate incremented by the same protocol, but upon reaching selected work rates of approximately 40, 60 and 80% , the subjects cycled for 60 min or until exhaustion. In these constant load studies, blood lactate concentration was determined on arterialized venous ([La⁻]a_v) and deep venous blood ([La⁻]_v) of the resting forearm. The a_v-v lactate gradient across the inactive forearm muscle was −0.08 mmol·l⁻¹ at rest. After 3 min at each of the constant load work rates, the gradients were +0.05, +0.65* and +1.60* mmol·l⁻¹ (*P<0.05). The gradients after 10 min at these same work rates were −0.09, +0.24 and +1.03* mmol·l⁻¹. For the two highest work rates taken together, the lactate gradient was less at 10 min than 3 min constant load exercise (P<0.05). The [La⁻]a_v was consistently higher during prolonged exercise at both 60 and 80% than that observed at the same work rate during progressive exercise. At the highest work rate (at or above the IAT), time to exhaustion ranged from 3 to 36 min in the different subjects. These data showed that [La⁻] uptake across resting muscle continued to increase to work rates above the IAT. Further, the greater a_v-v lactate gradient at 3 min than 10 min constant load exercise supports the concept that inactive muscle might act as a passive sink for lactate in addition to a metabolic site.     

Exercise-induced changes in blood levels of alpha-tocopherol

Levels of α-tocopherol (αT) in plasma and red blood cells (RBC) are assumed to be modulated by exercise. The mechanisms involved remain to be established. We examined the influence of different running bouts on the content of αT in RBC (αT_RBC), the concentration in plasma (αT_plasma), and their relationship with lipolysis, as indicated by changes (Δ) in plasma glycerol concentration ([glycerol]). Eleven healthy runners [mean (SD) age 35 (9) years, height 177.3 (7.6) cm, body mass 69.6 (9.4) kg, and peak oxygen consumption, , 57.8 (4.8) ml^.kg^–1.min^–1] performed an incremental treadmill test [duration 17 (2) min, peak velocity, v _peak 4.8 (0.4) m^.s^–1], a training run [173 (12) min, 57 (4)% v _peak] and a marathon [197 (24) min, 75 (5)% v _peak]. Before (pre) and after (post) each run, haematological and lipid parameters, αT_RBC and αT_Plasma were determined. Haemoconcentration was observed after each run. Δ[glycerol] was +0.10 (0.10) mmol^.l^–1, +0.40 (0.14) mmol^.l^–1 and +0.51 (0.15) mmol^.l^–1 in the treadmill test, training run and marathon, respectively. When corrected for haemoconcentration, values of αT_plasma decreased [–5.4 (7.5)%, P<0.05] in the treadmill test, were unchanged [+0.7 (8.7)%] in the training run and increased [+7.8 (8.3)%, P<0.05] in the marathon. αT_RBC decreased [pre vs post: 22.7 (3.2) nmol^.g haemoglobin^–1 (nmol^.g Hb^–1) vs 18.9 (3.8) nmol^.g Hb^–1, P<0.05] in the treadmill test and was not significantly changed in either the training run [20.8 (1.9) nmol^.g Hb^–1 vs 19.1 (3.0) nmol^.g Hb^–1] or the marathon [21.6 (2.9) nmol^.g Hb^–1 vs 23.4 (2.7) nmol^.g Hb^–1]. ΔαT_RBC and ΔαT_plasma were positively related to Δ[glycerol]. The reduction in αT_RBC and αT_plasma after short-lasting heavy exercise indicates the consumption of αT, whereas the association between ΔαT and Δ[glycerol] suggests mobilisation of αT, especially in long-lasting exercises. However, although αT appears to be influenced by exercise, the results suggest a well-balanced regulation of αT during exercise resulting in small, and only in part, significant ΔαT in blood. Electronic Publication     

Relationship of exercise test variables to cycling performance in an Ironman triathlon

The purpose of this study was, firstly, to investigate the intensity of exercise performanceof highly trained ultra-endurance triathletes during the cycling portion of an Ironman triathlon, and, secondly, to examine the anaerobic threshold and its relationship to this performance. Following a peak oxygen consumption (VO_2peak) test on a cycle ergometer to determine the heart rate (HR_Th,vent) and power output (PO_Th,vent) at the ventilatory threshold (Th_vent), 11 highly trained male triathletes [mean (SEM) age 35.8 (1.6) years, body fat 11.7 (1.2)%. VO_2peak 67.5 (1.0) ml·kg^–1·min^–1] who were participating in an Ironman triathlon, in random order: (1) cycled at their PO_Th,vent (Bi_Th,vent) until they were exhausted, and (2) cycled for 5 h at a self-selected intensity (Bi_SSI). Cycling power output (PO), oxygen uptake (VO₂), heart rate (HR) and blood lactate concentration ([La^–]_b) were recorded at regular intervals during these trials, while performance HR was recorded during the cycling phase of the Ironman triathlon. Significantly greater (P<0.05) values were attained during Bi_Th,vent than during Bi_SSI for PO [274 (9) compared to 188 (9) W], VO₂ [3.61 (0.15) compared to 2.64 (0.09) l·min^–1], and [La^–]_b [6.7 (0.8) compared to 2.8 (0.4) mmol·l^–1]. Moreover, mean HR during the Ironman triathlon cycle phase [146.3 (2.4) beats·min^–1; n=7] was significantly greater than mean HR during Bi_SSI [130 (4) beats·min^–1], and significantly less than mean HR during Bi_Th,vent [159 (3) beats·min^–1; all P<0.05]. However, HR during the cycle portion of the Ironman triathlon was highly related to (r=0.873; P<0.05) and not significantly different to HR_Th,vent [150 (4) beats·min^–1]. These data suggest that ultra-endurance triathletes cycle during the Ironman triathlon at a HR intensity that approximates to HR_Th,vent, but at a PO that is significantly below PO_Th,vent. Electronic Publication     

Threshold increases in plasma growth hormone in relation to plasma catecholamine and blood lactate concentrations during progressive exercise in endurance-trained athletes

Plasma human growth hormone ([HGH]), adrenaline ([A]), noradrenaline ([NA]) and blood lactate ([La^–]_b) concentrations were measured during progressive, multistage exercise on a cycle ergometer in 12 endurance-trained athletes [aged 32.0 (SEM 2.0) years]. Exercise intensities (3 min each) were increased by 50 W until the subjects felt exhausted. Venous blood samples were taken after each intensity. The [HGH] and catecholamine concentrations increased negligibly during exercise of low to moderate intensities revealing an abrupt rise at the load corresponding to the lactate threshold ([La^–]-T). Close correlations (P < 0.001) were found between [La^–]_b and plasma [HGH] (r = 0.64), [A] (r = 0.71) and [NA] (r = 0.81). The mean threshold exercise intensities for [HGH], [A] and [NA], detected by log-log transformation, [154 (SEM 19) W, 162 (SEM 15) W and 160 (SEM 17) W, respectively] were not significantly different from the [La^–]-T [161 (SEM 12) W]. The results indicated that the threshold rise in plasma [HGH] followed the patterns of plasma catecholamine and blood lactate accumulation during progressive exercise in the endurancetrained athletes.     

The effect of cycling followed by running on respiratory muscle performance in elite and competition triathletes

This study investigated the possibility of there being differences in respiratory muscle strength and endurance in elite and competition triathletes who have similar maximal oxygen uptakes (VO_2max) and ventilatory thresholds (Th_vent). Five internationally-ranked elite, [mean (SD) age 23.8 (1.4) years] and six nationally- and regionally-ranked competition [age 21.1 (1.1) years] male triathletes performed two successive trials: first an incremental cycle test to assess VO_2max and Th_vent and second 20 min of cycling followed by 20 min of running (C-R) at intensities higher than 85% VO_2max. Cardioventilatory data were collected every minute during the two trials, using an automated breath-by-breath system. Maximal expiratory and inspiratory (P _Imax) strength were assessed before and 10 min after C-R from the functional residual capacity. Respiratory muscle endurance was assessed 1 day before and 30 min after C-R by measuring the time limit (t _lim). The results showed firstly that during C-R, the competition triathletes had significantly (P<0.05) higher minute ventilation [mean (SEM) 107.4 (3.1) compared to 99.8 (3.7) l·min^–1], breathing frequency [44.4 (2.0) compared to 40.2 (3.4) ·min^–1] and heart rate [166 (3) compared to 159 (4) beats·min^–1] and secondly that after C-R, they had significantly lower P _Imax [127.1 (4.2) compared to 130.7 (3.0) cmH₂O] and t_lim [2:35 (0:29) compared to 4:12 (0:20) min] than the elite triathletes. We conclude that, despite similar VO_2max and Th_vent, the competition triathletes showed less extensive adaptive mechanisms, including those in the respiratory muscles, than did the elite triathletes. This led to higher ventilation, which appeared to be the cause of the faster development of fatigue in the inspiratory muscles in this group. Electronic Publication     

Maintenance of testosterone status in fitness joggers after increased training mileage

The primary objective was to evaluate the early effect of increased training mileage on testosterone (T) status in recreational joggers. Serum total (T_tot) and free (T_free) concentrations at rest, overnight urinary T_tot excretion, and the T_tot and T_free responses to maximal exercise were used as indicators of T status. A group of 13 male [mean (SD) age 24.5 (2.5) years] fitness joggers [maximal oxygen consumption, , 52.9 (4.9) ml·kg^–1·min^–1] qualified as subjects. The training intervention consisted of a 100% increase in the habitual distance run [12 (3) miles·week^–1] for 2 consecutive weeks, while maintaining the customary training intensity. Blood samples were obtained at rest and after maximal exercise tests, at the beginning and end of a control week of habitual jogging (baseline) and also following the 1st and 2nd weeks of the intervention. The and treadmill exercise endurance time were unchanged across sampling times. Serum T_tot and T_free concentrations averaged 565 (62) and 24 (2.6) ng·dl^–1, respectively, at baseline and did not change significantly. Urinary T_tot excretion averaged 1.5 (0.21) ng·min^–1 at baseline, and also remained unchanged during the intervention. Relative increases in T_tot (23%) and T_free (22%) were observed following maximal exercise compared to rest (P<0.05). However, the exercise-related increases in serum T_tot and T_free were not evident after adjustment for the change in plasma volume. It was concluded, that the training intervention did not alter T status in these fitness joggers. Electronic Publication     

Near infrared spectroscopy-derived interstitial hydrogen ion concentration and tissue oxygen saturation during ambulation

The objective of this study was to determine whether walking and running at different treadmill speeds resulted in different metabolic and cardiovascular responses in the vastus lateralis (VL) and lateral gastrocnemius (LG) by examining metabolite accumulation and tissue oxygen saturation. Ten healthy subjects (6 males, 4 females) completed a submaximal treadmill exercise test, beginning at 3.2 km h⁻¹ and increasing by 1.6 km h⁻¹ increments every 3 min until reaching 85% of age-predicted maximal heart rate. Muscle tissue oxygenation (SO₂), total hemoglobin (HbT) and interstitial hydrogen ion concentration ([H⁺]) were calculated from near infrared spectra collected from VL and LG. The [H⁺] threshold for each muscle was determined using a simultaneous bilinear regression. Muscle and treadmill speed effects were analyzed using a linear mixed model analysis. Paired t-tests were used to test for differences between muscles in the [H⁺] threshold. SO₂ decreased (P = 0.001) during running in the VL and LG, but the SO₂ response across treadmill speeds was different between muscles (P = 0.047). In both muscles, HbT and [H⁺] increased as treadmill speed increased (P < 0.001), but the response to exercise was not different between muscles. The [H⁺] threshold occurred at a lower whole-body VO₂ in the LG (1.22 ± 0.63 L min⁻¹) than in the VL (1.46 ± 0.58 L min⁻¹, P = 0.01). In conclusion, interstitial [H⁺] and SO₂ are aggregate measures of local metabolite production and the cardiovascular response. Inferred from simultaneous SO₂ and [H⁺] measures in the VL and LG muscles, muscle perfusion is well matched to VL and LG work during walking, but not running.     

The relationship between critical velocity, maximal lactate steady-state velocity and lactate turnpoint velocity in runners

In cycle exercise, it has been suggested that critical power, maximal lactate steady state, and lactate turnpoint all demarcate the transition between the heavy exercise domain (in which blood lactate is elevated above resting values but remains stable over time) and the very heavy exercise domain (in which blood lactate increases continuously throughout constant-intensity exercise). The purpose of the present study was to assess the level of agreement between critical velocity (CV), maximal lactate steady-state velocity (MLSSV), and lactate turnpoint velocity (LTPV) during treadmill running. Eight male subjects [mean (SD) age 28 (5) years, body mass 71.2 (8.0) kg, maximum oxygen uptake 54.9 (3.2) ml·kg^–1·min^–1) performed an incremental treadmill test for the determination of LTPV (defined as a sudden and sustained increase in blood lactate concentration ([La]) at ≅2.0–5.0 mM). The subjects returned to the laboratory on eight or nine occasions for the determination of CV and MLSSV. The CV was determined from four treadmill runs at velocities that were chosen to result in exhaustion within 2–12 min. The MLSSV was determined from four or five treadmill runs of up to 30 min duration and defined as the highest velocity at which blood [La] increased by no more than 1.0 mM after between 10 and 30 min of exercise. Analysis of variance revealed no significant differences between [mean (SD)] CV [14.4 (1.1) km·h^–1], MLSSV [13.8 (1.1) km·h^–1] and LTPV [13.7 (0.6) km·h^–1]. However, the bias ±95% limits of agreement for comparisons between CV and MLSSV [0.6 (2.2) km·h^–1], CV and LTPV [0.7 (2.7) km·h^–1], and MLSSV and LTPV [0.1 (1.8) km·h^–1] suggest that the extent of disagreement is too great to allow one variable to be estimated accurately from another in individual subjects. Direct determination of MLSSV is necessary if precision is required in experimental studies. Electronic Publication     

A comparison of blood gases and acid-base measurements in arterial,arterialized venous,and venous blood during short-term maximal exercise

Summary The purpose of this study was to determine the relationship between blood gases and acid-base measurements in arterial, arterialized venous, and venous blood measured simultaneously during short-term maximal exercise. Ten well-trained male cyclists performed a graded maximal exercise test on a cycle ergometer to determine the power output corresponding to their peak oxygen consumption (test I), and a short-term maximal test on a cycle ergometer at peak power output (test 11). During test 11 arterial, arterialized venous and venous blood were sampled simultaneously for determination of partial pressures of oxygen and carbon dioxide, pH, bicarbonate (HCO₃ ^–), base excess (BE), and lactate (La). Samples were taken at rest, the end of 1 min of exercise (1 ME), at the end of exercise (EE), and at 2 min of recovery (REC). During test II, subjects maintained a peak power output of 370.6 (62.1) W [mean (SD)] for 4.5, SD 1.6 min. Except at rest venous and arterialized venous measurements tended to be the same at all sampling intervals, but differed significantly from measurements in arterial blood (P<0.05). BE was the only variable that rendered consistently significant correlations between arterial and arterialized venous blood at each sampling interval. The pooled correlation coefficient between arterial and arterialized venous BE was r=0.83 [regression equation: BE_a=(0.84 BE_av)–0.51]. Arterial La was significantly higher than venous La at 1 ME (2.8, 0.7 vs 0.8, 0.3mmol · 1^–1) and higher than both venous and arterialized venous La at EE. At EE La concentration was 9.2, SD 2.0, 4.6, SD 0.4, and 5.1, SD 0.1 mmol · 1^–1 in arterial, venous, and arterialized venous blood respectively. It is concluded that except for base excess, blood gases and acid base measurements in venous and arterialized venous blood do not accurately reflect values found in arterial blood during short-term maximal exercise. We suggest that these differences may be due in part to clearance by inactive muscle near the sampling site or vasoconstriction at the inactive sampling site.     

Effect of a 1 year combined aerobic- and weight-training exercise programme on aerobic capacity and ventilatory threshold in patients suffering from coronary artery disease

Weight-training is recommended as a complement to conventional aerobic-training for most low to moderate risk patients suffering from coronary artery disease (CAD). The purpose of this study was to evaluate the effect of a 1 year exercise programme combining weight- and aerobic-training on peak oxygen uptake (VO_2,peak) and ventilatory threshold (VT). We studied 40 men suffering CAD who were divided into three groups: 14 subjects to weight-training plus aerobic-training [mean (SD] [combined exercise group, age 55 (10) years], 14 to aerobic-training only [aerobic-training group, age 57 (11) years], and 12 to a control group [standard care, age 57 (11) years]. A symptom-limited graded exercise test using the standard Bruce protocol was performed using a 12-lead electrocardiogram, and gas analysis techniques. Muscle strength was determined only in the combined exercise group using the one-repetition maximum method on each of eight weight exercises. Arm and leg strength increased by 21.9% and 27.8% respectively (P<0.0001) from pre to post-tests. The VO_2,peak did not differ between the combined and aerobic-training groups but their adjusted means were greater than those of the control group [39 (1.8) and 35.3 (1.8) compared to 26.2 (2.7) ml·kg^–1·min^–1 (P<0.001)]. The oxygen uptake at VT was higher in the combined group [24.7 (1.4) ml·kg^–1·min^–1] compared to aerobic [18.7 (1.4) ml·kg^–1·min^–1] and control [13.6 (1.7) ml·kg^–1min^–1] groups (P<0.001). Similar results were found for exercise tolerance (treadmill time to peak and at VT). Combined exercise training increased the VT more than aerobic-training alone. Combined exercise training did not improve the VO_2,peak or the functional capacity more than aerobic-training alone. Electronic Publication     

The relationship between plasma potassium,muscle membrane excitability and force following quadriceps fatigue

To examine the simultaneous changes in plasma [K⁺], muscle excitability and force during fatigue, ten male adults (mean age = 22 ± 0.5 years) held an isometric contraction of their right quadriceps muscle at an intensity of 30% maximum voluntary contraction (MVC) for 3 min. Femoral venous and brachial arterial [K⁺] were determined from serial samples drawn before, during, and for 15 min following the 3-min contraction. Each blood sample was synchronized with a maximal stimulation of the right femoral nerve to evoke a twitch and compound muscle action potential (M-wave). Immediately post-exercise, twitch torque was only 42% of baseline and femoral venous plasma [K⁺] had increased significantly from 4.02 ± 0.08 mmol/l to 5.9 ± 0.22 mmol/l. Femoral venous plasma lactate rose to a peak level of 10.0 ± 0.8 mmol/l at 1 min post exercise. The recovery of the twitch torque was exponentially related to the recovery of femoral venous plasma [K⁺] (r ² = 0.93, P < 0.01). There was no evidence for any loss of muscle membrane excitability during the period of increased extracellular [K⁺], in fact, the M-waves tended to be potentiated in the early phases of the recovery period. These results suggest that muscle membrane excitability is maintained in spite of increased extracellular [K⁺] following fatigue induced by a sustained submaximal quadriceps contraction. However, the strong relationship between twitch torque and femoral venous plasma [K⁺] suggests that K⁺ may be exerting its effect distal to surface membrane action potential propagation, most likely in the T-tubular region. Received: 20 April 1995/Received after revision and accepted: 8 January 1996     

Effects of compression stockings during exercise and recovery on blood lactate kinetics

This study aimed to investigate if wearing compression stockings (CS) during exercise and recovery could affect lactate profile in sportsmen. Eight young healthy trained male subjects performed two maximal exercise tests on a cycle ergometer on two different occasions performed randomly: CS during both exercise and recovery, and no CS. Blood lactate concentration was taken during exercise and at 0, 3, 5, 10, 15, 30 and 60 min post-exercise. The individual blood lactate recovery curves were fitted to a biexponential time function: \textLa_(t) = \textLa₍₀₎ + A ₁ ( 1- \texte ^{- g₁ t} ) + A ₂ ( 1- \texte ^{- g₂ t} ) {\text{La}}_{(t)} = {\text{La}}_{(0)} + A_{ 1} ( 1- {\text{e}}^{{ - \gamma_{1} t}} ) + A_{ 2} ( 1- {\text{e}}^{{ - \gamma_{2} t}} ) , where γ ₁ and γ ₂ denote the abilities to exchange lactate between the previously active muscles and the blood and to remove lactate from the organism, respectively. A significantly higher blood lactate value at the end of the maximal exercise was found (12.1 ± 0.5 vs. 10.8 ± 0.5 mmol l⁻¹) wearing CS as compared to no CS (P < 0.05). Lower γ ₁ and higher γ ₂ values were observed with CS during recovery, as compared to no CS. It was concluded that CS during graded exercise leads to a significant higher blood lactate value at exhaustion. Since lactate exchanges were expected to be decreased during exercise due to CS, this result was likely attributable to a higher lactate accumulation related to a greater overall contribution of anaerobic glycolysis. Although the lactate removal ability was significantly improved when wearing CS during recovery, its efficacy in promoting blood lactate clearance after high-intensity exercise is limited.     

Changes in performance,maximal oxygen uptake and maximal accumulated oxygen deficit after 5, 10 and 15 days of live high:train low altitude exposure

Nineteen well-trained cyclists (14 males and 5 females, mean initial V˙O_2max 62.3 ml kg^–1 min^–1) completed a multistage cycle ergometer test to determine maximal mean power output in 4 min (MMPO_4min), maximal oxygen uptake (V˙O_2max) and maximal accumulated oxygen deficit (MAOD). The athletes were divided into three groups, each of which completed 5, 10 or 15 days of both a control condition (C) and live high:train low altitude exposure (LHTL). The C groups lived and trained at the ambient altitude of 610 m. The LHTL groups spent 8–10 h night^–1 in normobaric hypoxia at a simulated altitude of 2,650 m, and trained at the ambient altitude of 610 m. The changes to MMPO_4min, V˙O_2max and MAOD in response to LHTL altitude exposure were not significantly different for the 5-, 10- and 15-day treatment periods. For the pooled data from all three treatment periods, there were significant increases in MMPO_4min [mean (SD) 5.15 (0.83) W kg^–1 vs 5.34 (0.78) W kg^–1] and MAOD [50.1 (14.2) ml kg^–1 vs 54.9 (13.1) ml kg^–1] in the LHTL athletes between pre- and post-altitude exposure. There were no significant changes in MMPO_4min [5.09 (0.76) W kg^–1 vs 5.16 (0.86) W kg^–1] or MAOD [50.5 (14.1) ml kg^–1 vs 49.1 (13.0) ml kg^–1] in the C athletes over the corresponding period. There were significant increases in V˙O_2max in the athletes during both the LHTL [63.2 (9.0) ml kg^–1 min^–1 vs 64.1 (9.0) ml kg^–1 min^–1] and C [62.0 (8.6) ml kg^–1 min^–1 vs 63.4 (9.2) ml kg^–1 min^–1] conditions. In these athletes, there was no difference in the impact of 5, 10 or 15 days of LHTL on the increases observed in MMPO_4min, V˙O_2max or MAOD; and LHTL increased MMPO_4min and MAOD more than training at low altitude alone. Electronic Publication     

Maximal heart rates and plasma lactate concentrations observed in middle-aged men and women during a maximal cycle ergometer test

Summary The purpose of this study was to investigate criteria for maximal effort in middle-aged men and women undertaking a maximal exercise test until they were exhausted if no measurements of oxygen uptake are made. A large group of 2164 men and 975 women, all active in sports and aged between 40 and 65 years, volunteered for a medical examination including a progressive exercise test to exhaustion on a cycle ergometer. In the 3rd min of recovery a venous blood sample was taken to determine the plasma lactate concentration ([la^–]_{p, 3min}). Lactate concentration and maximal heart rate (f _{c, max}) were lower in the women than in the men (P<0.001). Multiple regression analyses were performed to assess the contribution of sex to [la^–]_{p, 3 min}, independent of age and f _c max, It was found that [la^–]_{p,3 min} was about 2.5 mmol·l^–1 lower in women than in men of the same age and f _{c, max}. In our population 88% of the men and 85% of the women met a combination of the following f _{c, max} and [la^–]_{p, 3min} criteria: f _{c, max} equal to or greater than 220 minus age beats·min^–1 and/or [la^–]_{p, 3min} equal to or greater than 8 mmol·l^–1 in the men and f _{c, max} equal to or greater than 220 minus age beats·min^–1 and/or [la^–]_{p, 3min} equal to or greater than 5.5 mmol·1^–1 in the women.