Significance of time to exhaustion during exercise at the velocity associated with\dot VO_{2max}

In theory, time to exhaustion at the velocity associated with $\dot VO_{2max}$ (t _LIM atv $\dot VO_{2max}$ ) together with the anaerobic threshold (AT) should provide information about the anaerobic capacity of an individual. The primary purpose of this study was to test that hypothesis, using oxygen deficit as a criterion for anaerobic capacity. A second purpose was to identify factors that might explain the large inter-individual variability reported int _LIM atv $\dot VO_{2max}$ . Subjects were 13 female track athletes who, performed incremental treadmill tests to determinev $\dot VO_{2max}$ and AT and constant velocity tests at $\dot VO_{2max}$ to determinet _LIM and oxygen deficit. Correlations between oxygen deficit andt _LIM atv $\dot VO_{2max}$ and [(t _LIM atv $\dot VO_{2max}$ ) · ( $\dot VO_{2max}$ ? AT)], a compound variable derived based on the critical power concept, were 0.51 (p < 0.05, one-tailed) and 0.67 (p < 0.01). To identify factors related to the inter-individual variability int _LIM atv $\dot VO_{2max}$ , correlations betweent _LIM and AT, oxygen deficit, and [oxygen deficit/( $\dot VO_{2max}$ ? AT)] were calculated. Intra-individual differences in AT explained 44% of the variability int _LIM atv $\dot VO_{2max}$ , oxygen deficit explained 26% of the variance, and the compound variable explained only 36%. It was concluded that (a) alone, or in combination with AT,t _LIM atv $\dot VO_{2max}$ cannot be used to estimate anaerobic capacity and (b) factors other than anaerobic capacity and AT contribute to the relatively large intra-individual variability int _LIM atv $\dot VO_{2max}$ (CV = 21%). Determinants oft _LIM atv $\dot VO_{2max}$ must be elucidated if this measure is to be of use to sport scientists.     

The\dot VCO_2 /\dot VO_2 relationship during heavy,constant work rate exercise reflects the rate of lactic acid accumulation

Oxygen uptake ( $\dot VO_2 $ ) kinetics have been reported to be modified when lactic acid accumulates; however little attention has been given to the simultaneous carbon dioxide production ( $\dot VCO_2 $ >) kinetics. To demonstrate how $\dot VCO_2 $ changes as a function of $\dot VO_2 $ when lactic acid is buffered by bicarbonate, eight healthy subjects performed 6-min constant work rate cycle ergometer exercise tests at moderate, heavy and very heavy exercise intensities. $\dot VCO_2 $ and $\dot VO_2 $ were measured breath-by-breath, and arterial blood samples were obtained every 7.5 s during the first 3 min of exercise, and were analyzed for pH, partial pressure of carbon dioxide, standard bicarbonate, and lactate. $\dot VCO_2 $ abruptly increased relative to $\dot VO_2 $ between 40 and 50 s after the start of exercise for the high exercise intensities. These gas exchange events were observed to correlate well with the time and $\dot VO_2 $ at which lactic acid increased and plasma bicarbonate decreased (r = 0.90,r = 0.95, respectively). We conclude that bicarbonate buffering of lactic acid can be determined from the acceleration of $\dot VCO_2 $ relative to $\dot VO_2 $ kinetics in response to constant work rate exercise and the increase is quantitatively related to the magnitude of the lactic acid increase. This is easily visualized from a plot of $\dot VCO_2 $ as a function of $\dot VO_2 $ .     

Untersuchung zur Tagesperiodik verschiedener Kreislauf-und Atemgrößen bei submaximalen und maximalen Leistungen am Fahrradergometer

The maximal aerobic power of six highly trained young cyclist, mean age 16.3 years and mean \(\dot V_{O_2 \max } \) 4.9 l/min, was directly measured at intervals of 4 hrs. A Latin square design was used for the test order. At submaximal work of O₂-consumption 2.4 to 4.4 l/min no circadian variation of any single function was found. However, at maximal work load the differences between the maxima and minima values were 12.4% for maximal work output ( \(\dot W_{\max } \) ), 7.8% for expiratory minute volume ( \(\dot V_{E\max } \) ), 5.7% for maximal aerobic power ( \(\dot V_{O_2 \max } \) ) and 3.4% for maximal heart rate (HR _max). All the functions—with the exception of \(\dot V_{O_2 \max } \) —had their minima at 0300 hrs; the minima of \(\dot V_{O_2 \max } \) was reached already at 2300 hours. The maxima-values of \(\dot V_{E\max } \) and \(\dot V_{O_2 \max } \) were measured at 1500 hrs, of \(\dot W_{\max } \) andHR _max at 0700 and ofHR _rest at 1900 hrs correspondingly. A one-tailed test showed significant differences between the maxima and minima values of all variables (P<0.05). The results suggest a decreased cardiopulmonary working capacity at night. However, this impairment is only of practical importance if the work will be done near the limit of endurance capacity. Besides it will suggest, that the indirect methods for assessing the cardiopulmonary capacity based on \(\dot V_{O_2 \max } \) and \(\dot W_{170} \) are not useful at nighttime, because the presuppositions for these methods are limited of the time of day.     

Increases in \dot{V} O2max with “live high–train low” altitude training: role of ventilatory acclimatization

The purpose of this study was to estimate the percentage of the increase in whole body maximal oxygen consumption ( $ \dot{V} $ O_2max) that is accounted for by increased respiratory muscle oxygen uptake after altitude training. Six elite male distance runners ( $ \dot{V} $ O_2max = 70.6 ± 4.5 ml kg^?1 min^?1) and one elite female distance runner ( $ \dot{V} $ O_2max = 64.7 ml kg^?1 min^?1) completed a 28-day “live high–train low” training intervention (living elevation, 2,150 m). Before and after altitude training, subjects ran at three submaximal speeds, and during a separate session, performed a graded exercise test to exhaustion. A regression equation derived from published data was used to estimate respiratory muscle $ \dot{V} $ O₂ ( $ \dot{V} $ O_2RM) using our ventilation ( $ \dot{V} $ _E) values. $ \dot{V} $ O_2RM was also estimated retrospectively from a larger group of distance runners (n = 22). $ \dot{V} $ O_2max significantly (p < 0.05) increased from pre- to post-altitude (196 ± 59 ml min^?1), while $ \dot{V} $ _E at $ \dot{V} $ O_2max also significantly (p < 0.05) increased (13.3 ± 5.3 l min^?1). The estimated $ \dot{V} $ O_2RM contributed 37 % of Δ $ \dot{V} $ O_2max. The retrospective group also saw a significant increase in $ \dot{V} $ O_2max from pre- to post-altitude (201 ± 36 ml min^?1), along with a 10.8 ± 2.1 l min^?1 increase in $ \dot{V} $ _E, thus requiring an estimated 27 % of Δ $ \dot{V} $ O_2max. Our data suggest that a substantial portion of the improvement in $ \dot{V} $ O_2max with chronic altitude training goes to fuel the respiratory muscles as opposed to the musculature which directly contributes to locomotion. Consequently, the time-course of decay in ventilatory acclimatization following return to sea-level may have an impact on competitive performance.     

Effects of hypoxic training on normoxic maximal aerobic power output

The responses to 1-leg submaximal and maximal exercise have been studied in four male subjects before and after a 5 week training programme. One leg was trained under normoxic conditions and the other under hypoxic ( \(F_{IO_2 } \) =0.12) conditions for 30 min/day, 3 times/week at a fixed absolute work load which approximated to 75% of the limb's normoxic \(\dot V_{O_2 \max } \) . Before and after training both limbs were measured in normoxia, one limb was additionally measured in hypoxia. The aim of the experiments being to use each subject as his own control and to try and elucidate the effects of hypoxia per se as a training stimulus to the improvement of maximal aerobic power output ( \(\dot V_{O_2 \max } \) ) measured in normoxia. The results showed that before training the responses to exercise at submaximal and maximal levels were identical in each limb; the effects of hypoxia being to raise V _E1.5 and f _H1.5, to reduce \(\dot V_{O_2 \max } \) and to leave \(\dot V_{O_2 450} \) unchanged. The effects of the two types of training were to reduce \(\dot V_{O_2 450} \) , decrease f _H1.5 and increase \(\dot V_{O_2 \max } \) , the effects being independent of the \(F_{IO_2 } \) . The changes in \(\dot V_{O_2 \max } \) of the hypoxic and normoxic trained legs were related to the initial \(\dot V_{O_2 \max } \) of each subjects' limb. It was concluded that our investigation lends no support to the view that hypoxia has either an additive or potentiating effect with exercise during a training programme on the improvement of aerobic power output measured under normoxic conditions.     

Indirect determination of maximal aerobic power output during work with one or two limbs

The cardiac frequency (f _H ) and oxygen intake ( \(\dot V_{O_2 } \) ) responses to submaximal and maximal work with 1- and 2-arms and 1- and 2-legs on suitably modified bicycle ergometers in relation to the prediction of maximal aerobic power output ( \(\dot V_{{\text{O}}_{{\text{2max}}} }\) ) have been examined in 12 healthy male subjects. The results showed that the physiological responses to the different forms of submaximal and maximal exercise were distinct and dependent upon the effective muscle mass used to perform the work. The observed \(\dot V_{{\text{O}}_{{\text{2max}}} }\) of 1-limb could be converted to respective 2-limb value with a coefficient of variation ranging from 4 to 7%, but maximal work with the arms gave no guide to that of the legs. Extrapolation of the \(\dot V_{O_2 } \) /f _H curve to the f _{H max} in 1-leg (175 beats/min) and 2-arm (165 beats/min) resulted in an overestimation of \(\dot V_{{\text{O}}_{{\text{2max}}} }\) of +70 ± 200 ml · min^?1 and +70 ± 240 ml · min^?1; but in 1-arm work (153 beats/min), \(\dot V_{{\text{O}}_{{\text{2max}}} }\) was underestimated by ?70 ± 270 ml · min^?1. The bias in predictions for the 3 forms of exercise could be removed by applying the appropriate regression equations relating predicted to observed \(\dot V_{{\text{O}}_{{\text{2max}}} }\) , but the overall accuracy of the extrapolation method was limited to ± 8%, ± 15% and ± 23% in 1-leg, 2-arm and 1-arm work respectively. It was concluded that maximal work with the upper and lower limbs should be treated separately and if an accuracy of greater than ± 8 to ± 23% is required in situations where through injury, two limb exercise cannot be performed, attempts should be made to ascertain the \(\dot V_{{\text{O}}_{{\text{2max}}} }\) of a single limb directly.     

Skeletal muscle \dot{V} {\text{O}_2} kinetics from cardio-pulmonary measurements: assessing distortions through O2 transport by means of stochastic work-rate signals and circulatory modelling

During non-steady-state exercise, dynamic changes in pulmonary oxygen uptake ( $\dot{V} {\text{O}_{\text{2pulm}}}$ ) are dissociated from skeletal muscle $ \dot{V} {\text{O}_2}$ ( $\dot{V} {\text{O}_{\text{2musc}}}$ ) by changes in lung and venous O₂ concentrations (CvO₂), and the dynamics and distribution of cardiac output (CO) between active muscle and remaining tissues ( $ \dot{Q}_{\text{rem}}$ ). Algorithms can compensate for fluctuations in lung O₂ stores, but the influences of CO and CvO₂ kinetics complicate estimation of $\dot{V} {\text{O}_{\text{2musc}}}$ from cardio-pulmonary measurements. We developed an algorithm to estimate $\dot{V} {\text{O}_{\text{2musc}}}$ kinetics from $\dot{V} {\text{O}_{\text{2pulm}}}$ and heart rate (HR) during exercise. 17 healthy volunteers (28 ± 7 years; 71 ± 12 kg; 7 females) performed incremental exercise using recumbent cycle ergometry ( $\dot{V} {\text{O}_{\text{2peak}}}$ 52 ± 8 ml min^?1 kg^?1). Participants completed a pseudo-random binary sequence (PRBS) test between 30 and 80 W. $\dot{V} {\text{O}_{\text{2pulm}}}$ and HR were measured, and CO was estimated from HR changes and steady-state stroke volume. $\dot{V} {\text{O}_{\text{2musc}}}$ was derived from a circulatory model and time series analyses, by solving for the unique combination of venous volume and the perfusion of non-exercising tissues that provided close to mono-exponential $\dot{V} {\text{O}_{\text{2musc}}}$ kinetics. Independent simulations showed that this approach recovered the $\dot{V} {\text{O}_{\text{2musc}}}$ time constant (τ) to within 7 % (R ² = 0.976). Estimates during PRBS were venous volume 2.96 ± 0.54 L; $ \dot{Q}_{\text{rem}}$ 3.63 ± 1.61 L min^?1; τHR 27 ± 11 s; τ $\dot{V} {\text{O}_{\text{2musc}}}$ 33 ± 8 s; τ $\dot{V} {\text{O}_{\text{2pulm}}}$ 43 ± 14 s; $\dot{V} {\text{O}_{\text{2pulm}}}$ time delay 19 ± 8 s. The combination of stochastic test signals, time series analyses, and a circulatory model permitted non-invasive estimates of $\dot{V} {\text{O}_{\text{2musc}}}$ kinetics. Large kinetic dissociations exist between muscular and pulmonary $\dot{V} {\text{O}_{\text{2}}}$ during rapid exercise transients.     

The effects of breathing a helium–oxygen gas mixture on maximal pulmonary ventilation and maximal oxygen consumption during exercise in acute moderate hypobaric hypoxia

To test the hypothesis that maximal exercise pulmonary ventilation ( $ \dot{V}{\text{E}}_{ \max } $ ) is a limiting factor affecting maximal oxygen uptake ( $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ ) in moderate hypobaric hypoxia (H), we examined the effect of breathing a helium–oxygen gas mixture (He–O₂; 20.9% O₂), which would reduce air density and would be expected to increase $ \dot{V}{\text{E}}_{ \max } $ . Fourteen healthy young male subjects performed incremental treadmill running tests to exhaustion in normobaric normoxia (N; sea level) and in H (atmospheric pressure equivalent to 2,500 m above sea level). These exercise tests were carried out under three conditions [H with He–O₂, H with normal air and N] in random order. $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ and arterial oxy-hemoglobin saturation (SaO₂) were, respectively, 15.2, 7.5 and 4.0% higher (all p < 0.05) with He–O₂ than with normal air ( $ \dot{V}{\text{E}}_{ \max } $ _, 171.9 ± 16.1 vs. 150.1 ± 16.9 L/min; $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ , 52.50 ± 9.13 vs. 48.72 ± 5.35 mL/kg/min; arterial oxyhemoglobin saturation (SaO₂), 79 ± 3 vs. 76 ± 3%). There was a linear relationship between the increment in $ \dot{V}{\text{E}}_{ \max } $ and the increment in $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ in H (r = 0.77; p < 0.05). When subjects were divided into two groups based on their $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ , both groups showed increased $ \dot{V}{\text{E}}_{ \max } $ and SaO₂ in H with He–O₂, but $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ was increased only in the high $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ group. These findings suggest that in acute moderate hypobaric hypoxia, air-flow resistance can be a limiting factor affecting $ \dot{V}{\text{E}}_{ \max } $ ; consequently, $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ is limited in part by $ \dot{V}{\text{E}}_{ \max } $ , especially in subjects with high $ \dot{V}{\text{O}}_{{ 2 {\text{max}}}} $ .     

The validity of the Moxus Modular metabolic system during incremental exercise tests: impacts on detection of small changes in oxygen consumption

Purpose

We investigated the accuracy of the Moxus Modular Metabolic System (MOXUS) against the Douglas Bag Method (DBM) during high-intensity exercise, and whether the two methods agreed when detecting small changes in $\dot{V}{\text{O}}_{2}$ between two consecutive workloads ( $\Delta {\dot{{V}}\text{O}}_{ 2}$ ).

Methods

Twelve trained male runners performed two maximal incremental running tests while gas exchange was analyzed simultaneously by the two systems using a serial setup for four consecutive intervals of 30 s on each test. Comparisons between methods were performed for $\dot{V}{\text{O}}_{2}$ , ${\dot{{V}}}_{\text{E}}$ , fractions of expired O₂ (FeO₂) and CO₂ (FeCO₂) and $\Delta {\dot{{V}}\text{O}}_{ 2}$ .

Results

The MOXUS produced significant higher (mean ± SD, n = 54) readings for $\dot{V}{\text{O}}_{2}$ (80 ± 200 mL min^?1, p = 0.005) and ${\dot{{V}}}_{\text{E}}$ (2.9 ± 4.2 L min^?1, p < 0.0001), but not FeO₂ (?0.01 ± 0.09). Log-transformed 95 % limits of agreement for readings between methods were 94–110 % for $\dot{V}{\text{O}}_{2}$ , 97–108 % for $\dot{V}_{\text{E}}$ and 99–101 % for FeO₂. $\Delta \dot{V}{\text{O}}_{2}$ for two consecutive measurements was not different between systems (120 ± 110 vs. 90 ± 190 mL min^?1 for MOXUS and DBM, respectively, p = 0.26), but agreement between methods was very low (r = 0.25, p = 0.12).

Discussion

Although it was tested during high-intensity exercise and short sampling intervals, the MOXUS performed within the acceptable range of accuracy reported for automated analyzers. Most of the differences between equipments were due to differences in $\dot{V}_{\text{E}}$ . Detecting small changes in $\dot{V}{\text{O}}_{2}$ during an incremental test with small changes in workload, however, might be beyond the equipment’s accuracy.     

Relationship of pulmonary diffusing capacity (D L ) and cardiac output (\dot Q_c ) in exercise

The present study was designed to investigate the interrelationships of pulmonary diffusing capacity for CO ( \(D_{L_{{\text{CO}}} } \) ), pulmonary capillary blood flow ( \(\dot Q_c \) ), oxygen uptake ( \(\dot V_{{\text{O}}_{\text{2}} } \) ), and related functions in exercise. Six young adult men were tested on a bicycle ergometer on 9–20 occasions at various intensities of exercise up to the maximal level that could be sustained for 5 min. Measurements at each exercise level included work load (kgm/min), heart rate (HR), minute ventilation (V _I ), \(\dot Q_c \) , \(D_{L_{{\text{CO}}} } \) , and \(\dot V_{{\text{O}}_{\text{2}} } \) . Using regression analysis, it was established that \(\dot Q_c \) and D _{L CO} increased linearly with \(\dot V_{{\text{O}}_{\text{2}} } \) throughout the work range in each subject and no tendency toward a plateau was observed. While the maximal value varied from subject to subject, there was no difference between individuals in the coefffcient describing the relationship of D _L and \(\dot Q_c \) to \(\dot V_{{\text{O}}_{\text{2}} } \) . Combining all subjects, D _L was found to increase linearly with \(\dot Q_c \) the regression equation being: $$D_L = 26.4 + 1.03{\text{ }}\dot Q_c ,{\text{ }}r = .79$$ These results suggest that high-intensity short-duration exercise (5 min) is probably not limited by either of these functions in normals.     

The perceptually regulated exercise test is sensitive to increases in maximal oxygen uptake

The aim of this study was to assess the sensitivity of a perceptually regulated exercise test (PRET) to predict maximal oxygen uptake ( $ \dot{V} $ O₂max) following an aerobic exercise-training programme. Sedentary volunteers were assigned to either a training (TG n = 16) or control (CG n = 10) group. The TG performed 30 min of treadmill exercise, regulated at 13 on the Borg Rating of Perceived Exertion (RPE) Scale, 3× per week for 8 weeks. All participants completed a 12-min PRET to predict $ \dot{V} $ O₂max followed by a graded exercise test (GXT) to measure $ \dot{V} $ O₂max before and after training. The PRET required participants to control the speed and incline on the treadmill to correspond to RPE intensities of 9, 11, 13 and 15. Predictive accuracy of extrapolation end-points RPE19 and RPE20 from a submaximal RPE range of 9–15 was compared. Measured $ \dot{V} $ O₂max increased by 17 % (p < 0.05) from baseline to post-intervention in TG. This was reflected by a similar change in $ \dot{V} $ O₂max predicted from PRET when extrapolated to RPE 19 (baseline $ \dot{V} $ O₂max: 31.3 ± 5.5, 30.3 ± 9.5 mL kg^?1 min^?1; post-intervention $ \dot{V} $ O₂max: 36.7 ± 6.4, 37.4 ± 7.9 mL kg^?1 min^?1, for measured and predicted values, respectively). There was no change in CG (measured vs. predicted $ \dot{V} $ O₂max: 39.3 ± 6.5; 40.3 ± 8.2 and 39.2 ± 7.0; 37.7 ± 6.0 mL kg^?1 min^?1) at baseline and post-intervention, respectively. The results confirm that PRET is sensitive to increases in $ \dot{V} $ O₂max following aerobic training.     

The effect of increased body temperature due to exercise on the heart rate and on the maximal aerobic power

The effect of an increased body temperature (T _r) elicited by prolonged heavy exercise at normal ambient temperature in absence of any heat stress, on the maximal aerobic power ( \(\dot V_{O_2 \max } \) ) and on heart rate (HR) has been studied. The prolonged exercise consisted in running for 1 hr on a motor driven treadmill, this leading to an average increase of T _r of 1.2° C. Oxygen consumption ( \(\dot V_{O_2 } \) ), ventilation (V _I ), HR and T _r were measured at rest and every 10 min during the prolonged exercise. Before and after this exercise indirect measurement of \(\dot V_{O_2 \max } \) were made. After the exercise, HR in submaximal exercise was increased, the increase being less pronounced the heavier the exercise. The HR increment was 17.5 beats/min per 1° C rise in T _r in the exercise involving an oxygen comsumption of 22 ml/kg·min and it dropped to 7.5 b/min · °C when the O₂ consumption increased to 32.4 ml/kg · · min. \(\dot V_{O_2 \max } \) as calculated indirectly from HR values in submaximal exercise remained essentially the same before and after the treadmill run.     

Central and peripheral adjustments during high-intensity exercise following cold water immersion

Purpose

We investigated the acute effects of cold water immersion (CWI) or passive recovery (PAS) on physiological responses during high-intensity interval training (HIIT).

Methods

In a crossover design, 14 cyclists completed 2 HIIT sessions (HIIT1 and HIIT2) separated by 30 min. Between HIIT sessions, they stood in cold water (10 °C) up to their umbilicus, or at room temperature (27 °C) for 5 min. The natural logarithm of square-root of mean squared differences of successive R–R intervals (ln rMSSD) was assessed pre- and post-HIIT1 and HIIT2. Stroke volume (SV), cardiac output ( $ \dot{Q} $ ), O₂ uptake ( $ \dot{V} $ O₂), total muscle hemoglobin (t _Hb) and oxygenation of the vastus lateralis were recorded (using near infrared spectroscopy); heart rate, $ \dot{Q} $ , and $ \dot{V} $ O₂ on-kinetics (i.e., mean response time, MRT), muscle de-oxygenation rate, and anaerobic contribution to exercise were calculated for HIIT1 and HIIT2.

Results

ln rMSSD was likely higher [between-trial difference (90 % confidence interval) [+13.2 % (3.3; 24.0)] after CWI compared with PAS. CWI also likely increased SV [+5.9 % (?0.1; 12.1)], possibly increased $ \dot{Q} $ [+4.4 % (?1.0; 10.3)], possibly slowed $ \dot{Q} $ MRT [+18.3 % (?4.1; 46.0)], very likely slowed $ \dot{V} $ O₂ MRT [+16.5 % (5.8; 28.4)], and likely increased the anaerobic contribution to exercise [+9.7 % (?1.7; 22.5)].

Conclusion

CWI between HIIT slowed $ \dot{V} $ O₂ on-kinetics, leading to increased anaerobic contribution during HIIT2. This detrimental effect of CWI was likely related to peripheral adjustments, because the slowing of $ \dot{V} $ O₂ on-kinetics was twofold greater than that of central delivery of O₂ (i.e., $ \dot{Q} $ ). CWI has detrimental effects on high-intensity aerobic exercise performance that persist for ≥45 min.     

Experimental study of the performance of competition swimmers

The purpose of this study was to consider which characteristics are related to a high velocity in water during swimming. The study was performed on 13 of the best competition swimmers of the region of Lyon (France). The collected data were: \(\dot V_{O_2 } \) max, measured during leg-work ( \(\dot V_{O_2 } \) max LW), during arm-work ( \(\dot V_{O_2 } \) max AW), and the hydrodynamic resistances measured when the swimmers were towed at the speed of 1.80 m/sec. The cardiac output was measured for four of the subjects. The swimmers were characterized by a mean \(\dot V_{O_2 } \) max LW of 56 ml/kg/min and by a high value of the ratio \(\frac{{\dot V_{O_2 } \max {\text{ }}AW}}{{\dot V_{O_2 } \max {\text{ }}LW}}\) which reached 99% for three of them. There was a very high correlation (r = 0.90 and 0.91) between the mean speed calculated from the best performances in competition swims of 400 m and 1500 m and a value which is thought to express the aerobic energy available to the swimmer: $$\dot V_{O_2 } \max water:\dot V_{O_2 } \max {\text{ }}AW + \frac{{\dot V_{O_2 } \max {\text{ }}LW - \dot V_{O_2 } \max {\text{ }}AW}}{6}$$      

Metabolic and performance adaptations to interval training in endurance-trained cyclists

This study examined the effects of sustained high-intensity interval training (HIT) on the athletic performances and fuel utilisation of eight male endurance-trained cyclists. Before HIT, each subject undertook three baseline peak power output ${\dot W}_{\rm peak}$ tests and two simulated 40-km time-trial cycling performance (TT₄₀) tests, of which the variabilities were 1.5 (1.3)% and 1.0 (0.5)%, respectively [mean (SD)]. Over 6 weeks, the cyclists then replaced 15 (2)% of their 300 (66) km?·?week^?1 endurance training with 12 HIT sessions, each consisting of six to nine 5-min rides at 80% of ${\dot W}_{\rm peak}$ , separated by a 1-min recovery. HIT increased ${\dot {W}}_{\rm peak}$ from 404 (40) to 424 (53) W (P?40 speeds from 42.0 (3.6) to 43.0 (4.2) km?·?h^?1 (P?40 performances were due to increases in both the absolute work rates from 291 (43) to 327 (51) W (P? ${\dot {W}}_{\rm peak}$ to 78.1 (2.8)% of post-HIT ${\dot {W}}_{\rm peak}$ (P? ${\dot {W}}_{\rm peak}$ (P? ${\dot { W}}_{\rm peak}$ ) work rates. Thus, the ability of the cyclists to sustain higher percentages of ${\dot {W}}_{\rm peak}$ in TT₄₀ performances after HIT was not due to lower rates of CHO oxidation. Higher relative work rates in the TT₄₀ rides following HIT increased the estimated rates of CHO oxidation from ≈?4.3 to ≈?5.1 g?·?min^?1.     

Plasma catecholamine concentration during dynamic exercise involving different muscle groups

The change in plasma catecholamine concentration (ΔC) has been studied in four healthy male subjects during work, involving different muscle groups, whilst breathing air and 45% oxygen. The results show that during arm and (1- and 2-) leg(s) work ΔC was more closely associated with relative (expressed as a % of \(\dot V_{{\text{O}}_{{\text{2max}}} }\) ) than absolute work load; a rise in C occurred at ～ 60% \(\dot V_{{\text{O}}_{{\text{2max}}} }\) in all 3 forms of exercise. However, in arm and 1-leg work the curves relating ΔC to % \(\dot V_{{\text{O}}_{{\text{2max}}} }\) were displaced to the right indicating the independence of the two variables. Further, breathing 45% oxygen reduced ΔC but was without effect on either \(\dot V_{O_2 } \) at a given work load or \(\dot V_{{\text{O}}_{{\text{2max}}} }\) . For a given \(\dot V_{O_2 } \) , ΔC was inversely related to the effective muscle (plus bone) volume used to perform the work and associated with change of blood lactic acid (LA) concentration, but again the use of exercise involving different muscle groups indicated that the changes in C and LA were essentially independent. This was also true of the changes of C with cardiac output but not cardiac frequency (f _H ). Plasma C changed as a curvilinear function of f _H , the association between the two variables being independent of type of exercise and inspired O₂ concentration within the range used in this study. This suggests that the rise in C and f _H in exercise may be closely related to circulatory stress and may reflect the degree of vasoconstriction present in ‘non-active’ tissues and efficacy of the body's ability to maintain the integrity of systemic blood pressure in the face of increased demands of the exercising muscles for blood and the transport of oxygen.     

Assessment of aerobic and anaerobic capacity of athletes in treadmill running tests

The criteria of max \(\dot V_{O_2 } \) and max O₂ D which are traditionally used in studying aerobic and anaerobic work capacity, have the different dimensions. While max \(\dot V_{O_2 } \) is an index of the power of aerobic energy output, max O₂ D assesses the capacity of anaerobic sources. For a comprehensive assessment of physical working capacity of athletes, both aerobic and anaerobic capabilities should be represented in three dimensions,i.e. in indexes of power, capacity and efficiency. Experimental procedures have been developed for assessing these three parameters in treadmill running tests. It is proposed to assess anaerobic power by measuring excess CO₂, concurrently with determination of max \(\dot V_{O_2 } \) . Maximal aerobic capacity is established as the product of max \(\dot V_{O_2 } \) by the time of max \(\dot V_{O_2 } \) maintenance determined in a special test with running at critical speed. The ergometric criteria derived on the basis of the tests proposed, may be used for systematization of various physical work loads.     

Perceived exertion as a tool to self-regulate exercise in individuals with tetraplegia

The purpose of this investigation was to examine the use of subjective rating of perceived exertion (RPE) as a tool to self-regulate the intensity of wheelchair propulsive exercise in individuals with tetraplegia. Eight motor complete tetraplegic (C5/6 and below; ASIA Impairment Scale = A) participants completed a submaximal incremental exercise test followed by a graded exercise test to exhaustion to determine peak oxygen uptake ( $ \dot{V}O_{{ 2 {\text{peak}}}} $ ) on a wheelchair ergometer. On a separate day, a 20-min exercise bout was completed at an individualised imposed power output (PO) equating to 70 % of $ \dot{V}O_{{ 2 {\text{peak}}}} $ . On a third occasion, participants were instructed to maintain a workload equivalent to the average RPE for the 20-min imposed condition. $ \dot{V}O_{2} $ , heart rate (HR) and PO were measured at 1-min intervals and blood lactate concentration [BLa^?] was measured at 0, 10 and 20 min. No differences (P > 0.17) were found between mean $ \dot{V}O_{2} $ , %  $ \dot{V}O_{{ 2 {\text{peak}}}} $ , HR, % HR_peak, [BLa^?], velocity or PO between the imposed and RPE-regulated trials. No significant (P > 0.05) time-by-trial interaction was present for $ \dot{V}O_{2} $ data. A significant interaction (P < 0.001) for the PO data represented a trend for an increase in PO from 10 min to the end of exercise during the RPE-regulated condition. However, post hoc analysis revealed none of the differences in PO across time were significant (P > 0.05). In conclusion, these findings suggest that RPE can be an effective tool for self-regulating 20 min of wheelchair propulsion in a group of trained participants with tetraplegia who are experienced in wheelchair propulsion.