Maximal oxygen uptake,anaerobic threshold and running economy in women and men with similar performances level in marathons

Sex differences in running economy (gross oxygen cost of running, C_R), maximal oxygen uptake (VO_2max), anaerobic threshold (Th_an), percentage utilization of aerobic power (% VO_2max), and Th_an during running were investigated. There were six men and six women aged 20–30 years with a performance time of 2 h 40 min over the marathon distance. The VO_2max, Th_an, and CR were measured during controlled running on a treadmill at 1° and 3° gradient. From each subject's recorded time of running in the marathon, the average speed (v _M) was calculated and maintained during the treadmill running for 11 min. The VO_{2 max} was inversely related to body mass (m _b), there were no sex differences, and the mean values of the reduced exponent were 0.65 for women and 0.81 for men. These results indicate that for running the unit ml·kg^–0.75·min^–1 is convenient when comparing individuals with different m _b. The VO_2max was about 10% (23 ml·kg^–0.75·min^–1) higher in the men than in the women. The women had on the average 10–12 ml·kg^–0.75·min^–1 lower VO₂ than the men when running at comparable velocities. Disregarding sex, the mean value of C_R was 0.211 (SEM 0.005) ml·kg^–1·m^–1 (resting included), and was independent of treadmill speed. No sex differences in Th_an expressed as % VO_2max or percentage maximal heart rate were found, but Than expressed as VO₂ in ml·kg^–0.75·min^–1 was significantly higher in the men compared to the women. The percentage utilization of f _emax and concentration of blood lactate at v _M was higher for the female runners. The women ran 2 days more each week than the men over the first 4 months during the half year preceding the marathon race. It was concluded that the higher VO_2max and Th_an in the men was compensated for by more running, superior C_R, and a higher exercise intensity during the race in the performance-matched female marathon runners.     

Ventilatory threshold and work efficiency during exercise on cycle and paddling ergometers in young female kayakists

The aim of this study was to assess the effects of increasing specific (paddling erogmeter) and non-specific (cycle ergometer) exercise on parameters relating to the ventilatory threshold (Th_vent) and work efficiency in 11 young female flat-water kayakists. When these trained subjects were tested using non-specific workloads, their oxygen uptake (VO₂) values at Th_vent, as a percentage ofVO_2max (%VO_2max), were close to those of untrained subjects [74.2 (5.6) %VO_2max, mean (SD)]. However, when we tested the same subjects using specific exercise, we recorded values typical of highly trained athletes [84.8 (4.7) %VO_2max). For the non-specific exercise on the cycle erogmeter, we recorded work efficiency values close to those of untrained subjects [22.3 (2.5) %]; however, for the specific exercise on the paddling ergometer, we recorded much lower values [13.4 (3.0) %] both at the level of Th_vent. The work efficiency at two warm-up submaximal exercise loads on the paddling ergometer was non-significantly lower than values at Th_vent [12.3 (2.8) % and 12.9 (2.9) % respectively]. Significant correlations were found between maximal-performanceVO₂ (ml · kg^–1 · min^–1) and performance at Th_vent during paddling and race performance (0.623, 0.630 and 0.648 respectively, allP<0.05). Because the results of both specific and non-specific submaximal exercise tests are different, we suggest caution in the interpretation of physiological variables that may be sensitive to training status. The evaluation of Th_vent and work efficiency as supplementary parameters during laboratory studies enables the determination of the effectiveness of the training process and the specific adaptation of the subjects.     

Specificity effects of run versus cycle training on ventilatory threshold

Summary This study compared the effects of 9 weeks of run (RT) versus cycle (CT) training on ventilatory threshold (Th_v) determined during treadmill (TM) and cycle ergometer (CE) graded exercise testing. Sixteen college age men were assigned to a RT or CT group and performed a TM and a CE test before and after training. Both training groups performed similar training protocols which initially consisted of continuous exercise 4 days·week^–1 at 75–80% maximum heart rate (fc,_max) for 45 min. Training intensity was later increased to 80–85% fc _max and interval training (90–95% fc,_max) was incorporated 2 days·week^–1 into the continuous training. Both groups showed significantly improved maximal oxygen consumption ( O_2max) on both TM and CE tests (P<0.01) with no significant differences between the groups. Significant Th_v increases (P<0.05) were found on TM tests for RT (n=8) and CT (n=8) groups [mean (SD); 443 (438) and 373 (568) ml O₂·min^–1, respectively] with no difference between the groups. Results from the CE tests revealed a significant Th_v increase (P<0.01) for the CT group [566 (663) ml O₂·min^–1] with no change for the RT group. The Th_v improvement noted for the RT group was significantly different (P< 0.05) comparing CE with TM tests but not for the CT group. The results indicate that CT and RT improvement in Th_v for runners is dependent upon mode of training and testing, and there is an apparent dissociation of O_2maxand Th_v specific to training.     

An examination of the electromyographic fatigue threshold test

Summary The purpose of this investigation was to examine times to exhaustion at various percentages of the electromyographic fatigue threshold (EMG_FT). Eight adult males [mean (SD), 21 (1) years] volunteered for the investigation. EMG_FT was derived by determining the rate of rise in the electrical activity of the vastus lateralis [using integrated electromyography (iEMG)] over time (iEMG slope) for four fatiguing power outputs during cycle ergometry. The four power outputs were then plotted as a function of the four iEMG slope coefficients. The y-intercept of the power output versus iEMG slope coefficient graph was defined as the EMG_FT. The intraclass correlation for repeated EMG_FT tests was R=0.65 (SEE=7 W) and there was no significant (P>0.05) difference between the mean (SD) values for test [260 (11) W] versus retest [262 (32) W]. Actual times to exhaustion were determined for work bouts at power outputs equal to 85, 100, 115, 130, and 145% of EMG_FT. The mean (SD) times to exhaustion for these work bouts were 495 (231), 225 (72), 135 (35), 94 (17), and 72 (14) s, respectively. A power curve was derived using the mean power outputs and mean times to exhaustion from the five rides at various percentages of EMG_FT. The power curve provided estimates of the power outputs which could be maintained for 30 and 60 min. There were significant (P<0.05) differences between the mean EMG_FT (260 W) and the power outputs which could be maintained for 30 (151 W) and 60 (125 W) min. EMG_FT overpredicted the estimated power outputs that could be maintained for 30 and 60 min by 42% and 52%, respectively.     

Verification of the heart rate threshold

Among the methods for determining anaerobic threshold (AT), the heart rate (HR) method seems to be the simplest. On the other hand, many conflicting results from comparing this method with others have been presented over the last 10 years. Therefore, the aim of this study was to compare the heart rate threshold (HRT) with the lactate turn point (LTP) —second break point of dependence of lactate (LA) to power output, ventilatory threshold (VT) and threshold determined by electromyography (EMG_AT), all determined by the same exercise test and evaluated by the same computer algorithm. A group of 24 female students [mean age 20.5 (SD 1.6) years, maximal oxygen consumption 48.8 (SD 4.7) ml · kg^–1 · min^–1 performed an incremental exercise test on a cycle ergometer (modified Conconi test) starting with an initial power output (PO) of 40 W with intensity increments of 10 W · min^–1 until the subjects were exhausted. The HRT, LTP and EMG_AT determination was done by computer-aided break-point regression analysis from dependence of functional measures on PO. The same computer algorithm was used for VT determination from the relationship between ventilation (V) and oxygen uptake ( O₂) or carbon dioxide output ( CO₂). Nonsignificant differences were found between HRT [ O₂ 35.2 (SD 4.2) ml · kg^–1 · min^–1; HR 170.8 (SD 5.5) beats min^–1; LA 4.01 (SD 1.03) mmol · l^–1; PO 2.27 (SD 0.33) W · kg^–1 VT [ O₂ 35.1 (SD 3.7) ml · kg^–1 · min^–1 HR 168.3 (SD 4.8) beats · min^–1; LA 3.87 (SD 1:17) mmol · l^–1; PO 2.22 (SD 0.27) W · kg^–1 EMG_AT [ O₂35.6 (SD 4.1) ml · kg^–1 · min^–1 HR 171.0 (SD 5.4) beats · min^–1; LA 4.11 (SD 0.98) mmol · l^–1; PO 2.30 (SD 0.31) W · kg^–1] and LTP [ O₂) 35.3 (SD 4.1) ml · kg^–1 · min^–1; HR 170.1 (SD 6.0) beats · min^–1; LA 3.99 (SD 0.76) mmol · l^–1; PO 2.27 (SD 0.29) W · kg^–1]. Highly significant correlations (P < 0.01 in all cases) were found among all measurements made at threshold level in all the thresholds investigated. Correlation coefficients ranged in selected variables at different threshold levels from 0.842 to 0.872 in O₂ measured in ml · kg^–1 · min^–1, from 0.784 to 0.912 for LA, from 0.648 to 0.857 for HR, and from 0.895 to 0.936 for PO measured in W · kg^–1. These findings have led us to conclude that HRT could be used as an alternative method of determining anaerobic threshold in untrained subjects.     

Saliva electrolytes as a useful tool for anaerobic threshold determination

The purpose of the present study was to determine the anaerobic threshold by analysis of changes in saliva composition during an incremental exercise test on a cycle ergometer. Thirteen healthy males underwent a submaximal test with an initial load of 50 W and load increases of 50 W per 3 min, until capillary blood lactate exceeded 4 mmol · l^–1. A maximal test for maximum O₂ uptake (VO_2max) determination (initial load of 100 W and load increases of 50 W per 2 min) was also performed. Saliva and blood samples were obtained only in the submaximal test. Saliva threshold (Th_sa) was defined as the point at which the first increase in either Cl^– or Na⁺ occurred. Catecholamine threshold (Th_ca) was defined as the point at which a nonlinear increase occurred in either adrenaline or noradrenaline. The lactate (Th_la) and ventilatory (Th_ve) thresholds were determined according to published criteria. No significant differences were found between Th_sa values and the other methods of threshold determination. A high correlation was found between Th_sa and Th_la (r = 0.82, P < 0.01), and Th_sa and Th_ca (r = 0.75, P < 0.05). These results support the validity of Th_sa as a new method for noninvasive determination of the anaerobic threshold.     

Maximal lactate steady state,critical power and EMG during cycling

We hypothesised that: (1) the maximal lactate steady state (MLSS), critical power (CP) and electromyographic fatigue threshold (EMG_FT) occur at the same power output in cycling exercise, and (2) exercise above the power output at MLSS (P-MLSS) results in continued increases in oxygen uptake (V˙O₂), blood lactate concentration ([La]) and integrated electromyogram (iEMG) with time. Eight healthy subjects [mean (SD) age 25 (3) years, body mass 72.1 (8.2) kg] performed a series of laboratory tests for the determination of MLSS, CP and EMG_FT. The CP was determined from four exhaustive trials of between 2 and 15 min duration. The MLSS was determined as the highest power output at which the increase in blood [La] was less than 1.0 mM across the last 20 min of a series of 30-min trials. The EMG_FT was determined from four trials of 2 min duration at different power outputs. The surface electromyogram was recorded continuously from the vastus lateralis muscle. The CP was significantly higher than the P-MLSS [242 (25) vs. 222 (23) W; P<0.05], although the two variables were strongly correlated (r=0.95; P<0.01). The EMG_FT could not be determined in 50% of the subjects. Blood [La], V˙O₂ and minute ventilation all increased significantly with time for exercise at power outputs above the P-MLSS. In conclusion, the P-MLSS, and not the CP, represents the upper limit of the heavy exercise domain in cycling. During exercise above the P-MLSS, there is no association between changes in iEMG and increases in V˙O₂ and blood [La] with time. Electronic Publication     

Anaerobic threshold in children: determination from saliva analysis in field tests

The purpose of this study was to determine the anaerobic threshold of children by the analysis of saliva collected during field tests. A group of 25 children (mean age, 10.5 years) performed an incremental exercise test on a track, consisting of 4-min stages at increasing running velocities. Before each test (at rest) and at the end of each stage, both blood (via finger pricks) and saliva samples (for measurement of salivary concentrations of Na⁺ and Cl^–) were collected to determine lactate threshold (Th_1a-) and saliva threshold (Th_sa), respectively. There were no significant differences between values of Th_1a- and Th_sa when expressed either as running velocity [mean Th_1a-, 10.73 (SD 1.96) km · h^–1; mean Th_sa, 10.89 (SD 1.69) km · h^–1] or heart rate [Th_1a-, 182(SD 14) beats · min^–1 Th_sa 183 (SD 11) beats · min^–1]. In addition, correlations between Th_sa and Th_1a were high, when both values were expressed as running velocity in kilometres per hour (r = 0.89;P < 0.001), or heart rate in beats per minute (r = 0.90;P < 0.001). In conclusion, these findings suggested that saliva analysis would be a valid method for anaerobic threshold determination in field tests.     

Effect of previous supramaximal work on lacticaemia during supra-anaerobic threshold exercise

Summary Twelve male and female subjects (eight trained, four untrained) exercised for 30 min on a treadmill at an intensity of maximal O₂ consumption (% O_2max) 90.0%, SD 4.7 greater than the anaerobic threshold of 4 mmol ·1^–1 (Th_an =83.6% O_2max, SD 8.9). Time-dependent changes in blood lactate concentration ([la_b]) during exercise occurred in two phases: the oxygen uptake ( O₂) transient phase (from 0 to 4 min) and the O₂ steady-state phase (4–30 min). During the transient phase, [la_b] increased markedly (l.30 mmol · l ^–1 · min ^–1, SD 0.13). During the steady-state phase, [la_b] increased slightly (0.02 mmol · 1^–1 · min^–1, SD 0.06) and when individual values were considered, it was seen that there were no time-dependent increases in [la_b] in half of the subjects. Following hyperlacticaemia (8.8 mmol -l^–1, SD 2.0) induced by a previous 2 min of supramaximal exercise (120% O_2max), [la_b] decreased during the O₂ transient (–0.118 mmol · 1^–1 · min^–1, SD 0.209) and steady-state (–0.088 mmol · 1^–1 · min ^–1, SD 0.103) phases of 30 min exercise (91.4% O_2max, SD 4.8). In conclusion, it was not possible from the Th_an to determine the maximal [la_b] steady state for each subject. In addition, lactate accumulated during previous supramaximal exercise was eliminated during the O₂ transient phase of exercise performed at an intensity above the Th_an. This effect is probably largely explained by the reduction in oxygen deficit during the transient phase. Under these conditions, the time-course of changes in [la_b] during the O₂ steady state was also affected.     

Occurrence of electromyographic and ventilatory thresholds in professional road cyclists

The temporal relationship between the electromyographic (EMG) and ventilatory thresholds was investigated during incremental exercise performed by eight professional road cyclists. The exercise, performed on a cycloergometer, started at 100 W with successive increments of 26 W·min^–1 until exhaustion. Gas exchange and the root mean square value of EMG (RMS) from eight lower limb muscles were examined throughout the exercise period. Professional cyclists achieved a maximal oxygen consumption, i.e. O_2max, of 5.4 (0.5) l·min^–1 [74.6 (2.5) ml·min^–1·kg^–1, range: 67.8–82.4 ml·min^–1·kg^–1] and a maximum power (W_max) of 475 (30) W (range: 438–516 W). Our results showed at least the occurrence of a first EMG threshold (EMG_Th1) in 50% (gastrocnemius lateralis) of the subjects and a second EMG threshold (EMG_Th2) in 63% (gastrocnemius medialis). EMG_Th1 occurred significantly before the first ventilatory threshold (VT₁), i.e. at 52 (2)% and 62 (9)% of W_max, respectively. Inversely, no significant difference was observed between the occurrence of EMG_Th2 and the second ventilatory threshold (VT₂), i.e. at 86 (1)% and 89 (7)% of W_max, respectively. These results suggest that the use of EMG may be a useful non-invasive method for detecting the second ventilatory threshold in most of the muscles involved in cycling exercise.     

The ventilatory threshold gives maximal lactate steady state

Summary The purpose of this study was to examine whether the ventilatory threshold (Th _v) would give the maximal lactate steady state ([1a]_{ss, max}), which was defined as the highest work rate (W) attained by a subject without a progressive increase in blood lactate concentration [1a]_b at constant intensity exercise. Firstly, 8 healthy men repeated ramp-work tests (20 W·min^–1) on an electrically braked cycle ergometer on different days. During the tests, alveolar gas exchange was measured breath-by-breath, and theW atTh _v (W _{Th v}) was determined. The results of two-way ANOVA showed that the coefficient of variation of a singleW _{Th v} determination was 2.6%. Secondly, 13 men performed 30-min exercise atW _{Th v} (Th _v trial) and at 4.9% aboveW _{Th v} (Th _v + trial), which corresponded to the 95% confidence interval of the single determination. The [1a]_b was measured at 15 and 30 min from the onset of exercise. The [1a]_b at 15 min (3.15 mmol·1^–1, SEM 0.14) and at 30 min (2.95 mmol·1^–1, SEM 0.18) were not significantly different inTh _v trial. However, the [1a]_b ofTh _v+ trial significantly increased (P<0.05) from 15 min (3.62 mmol·1^–1, SEM 0.36) to 30 min (3.91 mmol·1^–1, SEM 0.40). These results indicate thatTh _v gives the [1a]_ss,max, at which one can perform sustained exercise without continuous [1a]_b accumulation.     

Ventilatory threshold during treadmill exercise in kindergarten children

Summary The cardiorespiratory response to graded treadmill exercise was studied in a group of kindergarten children, aged 5 to 6 years. From the non-linear change of pulmonary ventilation with increasing exercise intensity a ventilatory threshold was determined which averaged 28.1±4.9 (SD) ml O₂·min^–1·kg^–1. A significant correlation was established between this ventilatory threshold (ml O₂·min^–1) and the physical working capacity at a heart rate of 170 beats per min (PWC₁₇₀, ml O₂·min^–1):r=0.93,p<0.001. These data show that a ventilatory threshold can be obtained in young children which is an objective index of cardiorespiratory performance capacity.     

A comparison of critical force and electromyographic fatigue threshold for isometric muscle actions of the forearm flexors

The purpose of this study was twofold: (1) to determine if the mathematical model used for estimating the EMG_FT during cycle ergometry was applicable to isometric muscle actions; and (2) to compare the mean torque level from the CF test to that of the EMG_FT test. The CF was defined as the slope coefficient of the linear relationship between total “isometric work” (W _lim in N m s) and time to exhaustion (T _lim). The EMG_FT was defined as the y-intercept of the isometric torque versus EMG fatigue curve slope coefficient relationship. There was a significant (p < 0.05) mean difference between CF (6.6 ± 3.2 N m) and EMG_FT (10.9 ± 4.7 N m). The results of the present study suggested that, during isometric muscle actions of the forearm flexors, fatigue thresholds estimated from the W _lim versus T _lim relationship (CF) are different from those estimated from electromyographic fatigue curves (EMG_FT).     

Response of left ventricular diastolic filling to graded exercise relative to the lactate threshold

Summary During incremental exercise, the left ventricular ejection fraction increases up to the intensity of the anaerobic threshold and tends to level off at higher exercise intensities. Since there is a correlation between the response of peak filling rate and ejection fraction to exercise, this study was conducted to determine whether the response of left ventricular diastolic function is similar to the response of systolic function relative to lactate threshold. Twelve healthy men performed two exercise tests on a cycle ergometer. In the first test, lactate threshold and maximal power output were determined. In the second exercise test, gated radionuclide ventriculography was performed at rest, at the lactate threshold intensity, and at peak exercise to measure ejection fraction and peak filling rate. Ejection fraction increased significantly from rest [mean (SD): 62 (5)%] to lactate threshold [76 (7) %] and did not change significantly from lactate threshold to peak exercise [77 (7)%]. Likewise, peak filling rate (normalized for stroke counts) increased from resting [6.1 (0.9)V _s · s^–1] to lactate threshold [9.4 (1.8)V _s · s^–1] and did not change significantly from lactate threshold to peak exercise [9.6 (2.9)V _s · s^–1]. There was no correlation between the change in peak filling rate and the change in ejection fraction from rest to lactate threshold. Thus, during incremental exercise, left ventricular diastolic function responds qualitatively similar to systolic function.     

Peripheral and central inputs to the effort sense during cycling exercise

Summary The relationships between some physical and physiological events, and perceived effort were studied at several equivalent work outputs (V) at two pedalling rates (30 and 60 rev·min^–1). Subjects judged effort throughout a 4 min exercise bout. After 4 min at any sen it was always more effortful to pedal at 30 rev·min ^–1 even though there were no differences in V _E, VO₂ or integrated electromyography per minute (IEMG·min^–1) between pedalling rates. Effort was related to VO₂ and IEMG·min^–1 but it was more effortful to pedal at 30 rev·min^–1. Effort was also related to pedal resistance and IEMG of single contractions but was influenced by pedalling rate after 4 min of exercise. At any resistance it was more effortful to pedal at 60 rev·min ^–1, however, when effort was plotted as a function of resistance after 15 s, there was virtually no effect of pedalling rate. The rate effect grows with time from the onset of exercise and appears to be related to the central signal to the effort sense. The interaction of peripheral and central signals suggests a model of the effort sense during exercise.This research supported by NIH Training Grant No. ES00123     

Local critical power is an index of local endurance

The hypothesis that critical power (CP) is significantly lower than the maximal aerobic power of the knee extensors has been tested in nine endurance-trained subjects, seven gymnasts and seven weight lifters. CP was calculated as being equal to the slope of the linear relationship between exhaustion time and work performed at exhaustion on a knee-extension ergometer. CP was compared with the power output at the end of a progressive knee-extension exercise (P _peak) and the power outputs corresponding to exhaustion times equal to 4 (P _4 min), 6 (P _6 min), 8 (P _8 min) and 10 min (P _10 min), calculated according to the linear relationship between work and exhaustion time. The hypothesis that CP corresponds to a steady state in metabolic and physiological parameters was tested in the gymnasts and the weight lifters by comparing CP with the fatigue thresholds of the integrated electromyogram (iEMG_FT), lactate level (La_FT), oxygen uptake (V˙O_2FT) and heart rate (HR_FT). The results of the present study demonstrate that the value of CP of a local exercise cannot be considered as the equivalent of the maximal aerobic power for general exercises. The values of P _4 min, P _6 min, P _8 min, P _10 min and P _peak were significantly higher than CP, and corresponded to 138, 126, 119, 115 and 151% CP, respectively. The results of the present study indicate that CP can be considered as an index of muscular endurance. Indeed, La_FT, iEMG _FT, V˙O_2FT and HR_FT were not significantly different from CP. All of these fatigue thresholds were significantly correlated with CP (r > 0.92). Moreover, the highest coefficient of correlation (r=0.71; P < 0.01) between the percentage of maximal aerobic power in cycling that corresponds to a blood lactate concentration of 4 mmol · l⁻¹ (OBLA%) and the different local aerobic indices was observed with CP. Received: 22 February 1999 / Accepted: 16 June 1999     

Treadmill validation of an over-ground walking test to predict peak oxygen consumption

Summary The purpose of this study was to determine whether a test developed to predict maximal oxygen consumption (VO_2max) during over-ground walking, was similarly valid as a predictor of peak oxygen consumption (VO₂) when administered during a 1-mile (1.61 km) treadmill walk. Treadmill walk time, mean heart rate over the last 2 full min of the walk test, age, and body mass were entered into both generalized (GEN Eq.) and gender-specific (GSP Eq.) prediction equations. Overall results indicated a highly significant linear relationship between observed peakVO₂ and GEN Eq. predicted values (r=0.91), a total error (TE) of 5.26 ml · kg^–1 · min^–1 and no significant difference between observed and predicted peakVO₂ mean values. The peakVO₂ for women (n = 75) was predicted accurately by GSP Eq. (r = 0.85; TE = 4.5 ml · kg^–1 · min^–1), but was slightly overpredicted by GEN Eq. (overall mean difference = 1.4 ml · kg^–1 · min^–1;r=0.86; TE = 4.56 ml · kg^–1 · min^–1). No significant differences between observed peakVO₂ and either GEN Eq. (r=0.85; TE=4.3 ml · kg^–1 · min^–1) or GSP Eq. (r=0.85; TE = 4.8 ml · kg^–1 · min^–1)predicted values were noted for men (n=48) with peakVO₂ values less than or equal to 55 ml · kg^–1 · min^–1. However, both equations significantly underpredicted peakVO₂ for the remaining high peakVO₂ men (n = 22). In conclusion, the over-ground walking test, when administered on a treadmill, is a valid method of predicting peakVO₂ but underpredicts peakVO₂ of subjects with observed high peakVO₂ values. Present address: Human Performance Laboratory State University, Muncie, IN 47306, USA     

Energy cost and energy sources in karate

Energy costs and energy sources in karate (wado style) were studied in eight male practitioners (age 23.8 years, mass. 72.3 kg, maximal oxygen consumption (VO_2max) 36.8 ml · min^–1 · kg^–1) performing six katas (formal, organized movement sequences) of increasing duration (from approximately. 10 s to approximately 80 s). Oxygen consumption (VO₂) was determined during pre-exercise rest, the exercise period and the first 270 s of recovery in five consecutive expired gas collections. A blood sample for lactate (la^–) analysis was taken 5 min after the end of exercise. The overall amount of O₂ consumed during the exercise and in the following recovery increased linearly with the duration of exercise (t) from approximately 1.51 (for t equal to 10.5 s (SD 1.6)) to approximately 5.81, for t equal to 81.5 s (SD 1.0). The energy release from la^– production (VO_21a ^–) calculated assuming that an increase of 1 mmol · l^–1 la^– corresponded to a VO₂ of 3 mlO₂ · kg^–1 was negligible for t equal to or less than 20 s and increased to 17.3 ml · kg^–1 (la^– = 5.8 mmol · l^–1 above resting values) for t equal approximately to 80 s. The overall energy requirement (VO_2eq) as given by the sum of VO₂ and VO_2la ^– was described by VO_2eq = 0.87 + 0.071 · t (n = 64; r ² = 0.91), where VO_2eq is in litres and t in seconds. This equation shows that the metabolic power (VO_2eq · t ^–1) for this karate style is very high: from approximately 9.51 · min^–1 for t equal to 10 s to approximately 4.91 · min^–1 for t equal to 80 s, i.e. from 3.5 to 1.8 times the subjects' VO_2max. The fraction of VO_2eq derived from the amount of O₂ consumed during the exercise increased from 11% for t equal to 10 s to 41 % for t equal to 80 s whereas VO_21a ^– was negligible far t equal to or less than 20 s and increased to 13 % o for t equal to 80 s. The remaining fraction (from 90% for t equal to 10 s to 46% for t equal to 80 s), corresponding to the amount of O₂ consumed in the recovery after exercise, is derived from anaerobic alactic sources, i.e. from net splitting of high energy phosphates during the exercise.     

The influence of a respiratory acidosis on the exercise blood lactate response

Summary The purpose of the present study was to examine the influence of a respiratory acidosis on the blood lactate (La) threshold and specific blood La concentrations measured during a progressive incremental exercise test. Seven males performed three step-incremental exercise tests (20 W · min^–1) breathing the following gas mixtures; 21% O₂ balance-nitrogen, and 21% O₂, 4% CO₂ balance-nitrogen or balance-helium. The log-log transformation of La oxygen consumption (VO₂) relationship and a 1 mmol ·1^–1 increase above resting values were used to determine a La threshold. Also, theVO₂ corresponding to a La value of 2 (La2) and 4 (La4) mmol · 1^–1 was determined. Breathing the hypercapnic gas mixtures significantly increased the resting partial pressure of carbon dioxide (PCO₂) from 5.6 kPa (42 mm Hg) to 6.1 kPa (46 mm Hg) and decreased pH from 7.395 to 7.366. During the incremental exercise test,PCO₂ increased significantly to 7.2 kPa (54 mm Hg) and 6.8 kPa (51 mm Hg) for the hypercapnic gas mixtures with nitrogen and helium, respectively, and pH decreased to 7.194 and 7.208. In contrast, bloodPCO₂ decreased to 4.9 kPa (37 mm Hg) at the end of the normocapnic exercise test and pH decreased to 7.291. A blood La threshold determined from a log-log transformation [1.20 (0.28) 1·min^–1] or as an increase of 1 mmol·1^–1[1.84 (0.46) 1·min^–1] was unaffected by the acid-base alterations. Similarly, theVO₂ corresponding to La2 and La4 was not affected by breathing the hypercapnic gas mixtures [2.12 (0.46) 1·min^–1 and 2.81 (0.52) 1·min^–1, respectively]. Blood La values were reduced significantly at maximal exercise while breathing the hypercapnic gas mixtures (5.72±1.34 mmol ·1^–1) compared with the normocapnic test (6.96±1.14 mmol·1^–1). It is concluded that respiratory-induced acid-base manipulations due to the inspiration of 4% CO₂ have a negligible influence on the blood La response during a progressive exercise test at low and moderate power outputs. Lower blood La values are observed at maximal exercise with an induced respiratory acidosis but this negative influence is less than what has been reported for an induced metabolic acidosis.     

Dissociation between\dot V_{O_2 \max } and ventilatory threshold responses to endurance training

Summary The purpose of this investigation was to determine whether the ventilatory gas exchange threshold (T_vent) changes significantly during the first 1–3 weeks of endurance training. Six men were studied during 3 weeks of training, which consisted of pedaling on a cycle ergometer 6 d·wk 30 min per session at 70% of pretraining . At the end of each week, T_vent, and maximal and submaximal heart rates were determined during an incremental exercise test on the cycle ergometer. Constant-load submaximal exercise blood lactate concentrations were determined during training sessions on Monday, Wednesday, and Friday of each week of training. T_vent did not change significantly during the 3 weeks of training (+ 0.09 l·min^–1;P>0.05). In contrast, significant changes occurred in all other training indexes measured. increased by 0.36 l·min^–1 (P<0.05) after just 2 weeks of training and did not change further after 3 weeks. Significant reductions (40–45%;p<0.05) in blood lactate levels during training sessions occurred by the middle of the 2nd week of training. Decreases in maximal (~ 11 bt·min^–1) and submaximal (~ 14 bt·min^–1) exercise heart rates after 1 week of training were significant (P<0.05). The results demonstrate that changes in T_vent lag behind alterations in several other cardiovascular and metabolic parameters in response to endurance training. The dissociation between the significant improvement in and the lack of a significant increase in T_vent during the first 3 weeks of training indicates that the exercise-induced changes in these two parameters are regulated by different mechanisms.