Effects of glycogen depletion and pedaling speed on "anaerobic threshold"

Understanding optimal cadence dynamics: a systematic analysis of the power-velocity relationship in track cyclists with increasing exercise intensity

Background: This study aimed to investigate the changes in force-velocity (F/v) and power-velocity (P/v) relationships with increasing work rate up to maximal oxygen uptake and to assess the resulting alterations in optimal cadence, particularly at characteristic metabolic states. Methods: Fourteen professional track cyclists (9 sprinters, 5 endurance athletes) performed submaximal incremental tests, high-intensity cycling trials, and maximal sprints at varied cadences (60, 90, 120 rpm) on an SRM bicycle ergometer. Linear and non-linear regression analyses were used to assess the relationship between heart rate, oxygen uptake (V.O2), blood lactate concentration and power output at each pedaling rate. Work rates linked to various cardiopulmonary and metabolic states, including lactate threshold (LT1), maximal fat combustion (FATmax), maximal lactate steady-state (MLSS) and maximal oxygen uptake (V.O2max), were determined using cadence-specific inverse functions. These data were used to calculate state-specific force-velocity (F/v) and power-velocity (P/v) profiles, from which state-specific optimal cadences were derived. Additionally, fatigue-free profiles were generated from sprint data to illustrate the entire F/v and P/v continuum. Results: HR, V.O2 demonstrated linear relationships, while BLC exhibited an exponential relationship with work rate, influenced by cadence (p < 0.05, η2 ≥ 0.655). Optimal cadence increased sigmoidally across all parameters, ranging from 66.18 ± 3.00 rpm at LT1, 76.01 ± 3.36 rpm at FATmax, 82.24 ± 2.59 rpm at MLSS, culminating at 84.49 ± 2.66 rpm at V.O2max (p < 0.01, η2 = 0.936). A fatigue-free optimal cadence of 135 ± 11 rpm was identified. Sprinters and endurance athletes showed no differences in optimal cadences, except for the fatigue-free optimum (p < 0.001, d = 2.215). Conclusion: Optimal cadence increases sigmoidally with exercise intensity up to maximal aerobic power, irrespective of the athlete's physical condition or discipline. Threshold-specific changes in optimal cadence suggest a shift in muscle fiber type recruitment toward faster types beyond these thresholds. Moreover, the results indicate the need to integrate movement velocity into Henneman's hierarchical size principle and the critical power curve. Consequently, intensity zones should be presented as a function of movement velocity rather than in absolute terms.

Validation of a non-linear index of heart rate variability to determine aerobic and anaerobic thresholds during incremental cycling exercise in women

Studies highlight the usage of non-linear time series analysis of heart rate variability (HRV) using the short-term scaling exponent alpha1 of Detrended Fluctuation Analysis (DFA-alpha1) during exercise to determine aerobic and anaerobic thresholds. The present study aims to further verify this approach in women. Gas exchange and HRV data were collected from 26 female participants with different activity levels. Oxygen uptake (VO₂) and heart rate (HR) at first (VT1) and second ventilatory thresholds (VT2) were compared with DFA-alpha1-based thresholds 0.75 (HRVT1) and 0.50 (HRVT2). Results: VO₂ at VT1 and VT2 were 25.2 ml/kg/min (± 2.8) and 31.5 ml/kg/min (± 3.6) compared with 26.5 ml/kg/min (± 4.0) and 31.9 ml/kg/min (± 4.5) for HRVT1 and HRVT2, respectively (ICC_3,1 = 0.77, 0.84; r = 0.81, 0.86, p < 0.001). The mean HR at VT1 was 147 bpm (± 15.6) and 167 bpm (± 12.7) for VT2, compared with 152 bpm (± 15.5) and 166 bpm (± 13.2) for HRVT1 and HRVT2, respectively (ICC_3,1 = 0.87, 0.90; r = 0.87, 0.90, p < 0.001). Bland-Altman analysis for VT1 vs. HRVT1 showed a mean difference of - 1.3 ml/kg/min (± 2.4; LoA: 3.3, - 6.0 ml/kg/min) for VO₂ and of - 4.7 bpm (± 7.8; LoA: 10.6, - 20.0 bpm) for HR. VT2 vs. HRVT2 showed a mean difference of - 0.4 ml/kg/min (± 2.3; LoA: 4.1, - 4.9 ml/kg/min) for VO₂ and 0.5 bpm (± 5.7; LoA: 11.8, - 10.8 bpm) for HR. DFA-alpha1-based thresholds showed good agreement with traditionally used thresholds and could be used as an alternative approach for marking organismic transition zones for intensity distribution in women.

Cardiopulmonary Exercise Test Parameters in Athletic Population: A Review

Although still underutilized, cardiopulmonary exercise testing (CPET) allows the most accurate and reproducible measurement of cardiorespiratory fitness and performance in athletes. It provides functional physiologic indices which are key variables in the assessment of athletes in different disciplines. CPET is valuable in clinical and physiological investigation of individuals with loss of performance or minor symptoms that might indicate subclinical cardiovascular, pulmonary or musculoskeletal disorders. Highly trained athletes have improved CPET values, so having just normal values may hide a medical disorder. In the present review, applications of CPET in athletes with special attention on physiological parameters such as VO₂max, ventilatory thresholds, oxygen pulse, and ventilatory equivalent for oxygen and exercise economy in the assessment of athletic performance are discussed. The role of CPET in the evaluation of possible latent diseases and overtraining syndrome, as well as CPET-based exercise prescription, are outlined.

Effect of Carbohydrate Content in a Pre-event Meal on Endurance Performance-Determining Factors: A Randomized Controlled Crossover-Trial

The current study aimed to investigate the effect of the relative CHO content in a pre-event meal on time to exhaustion (TTE), peak oxygen uptake (V∙O2peak), the 2nd lactate threshold (LT2), onset of blood lactate accumulation (OBLA), and work economy (WE) and to compare responses between well-trained and recreationally trained individuals. Eleven well-trained and 10 recreationally trained men performed three trials in a randomized cross-over design, in which they performed exercise tests (1) after a high-CHO pre-event meal (3 g · kg⁻¹), (2) a low-CHO pre-event meal (0.5 g · kg⁻¹), or (3) in a fasted-state. The test protocol consisted of five submaximal 5-min constant-velocity bouts of increasing intensity and a graded exercise test (GXT) to measure TTE. A repeated measure ANOVA with a between-subjects factor (well-trained vs. recreational) was performed. A main effect of pre-event meal was found (p = 0.001), with TTE being 8.0% longer following the high-CHO meal compared to the fasted state (p = 0.009) and 7.2% longer compared to the low-CHO meal (p = 0.010). No significant effect of pre-event meal on V∙O2peak, LT2, OBLA, or WE (p ≥ 0.087) was found and no significant interaction effect between training status and pre-event CHO intake was found for TTE or any of the performance-determining variables (p ≥ 0.257). In conclusion, high-CHO content in the pre-event meal led to a longer TTE compared to a meal with a low-CHO content or exercising in a fasted state, both in well-trained and recreationally trained participants. However, the underlying physiological reason for the increased TTE is unclear, as no effect of pre-event meal on the main physiological performance-determining variables was found. Thus, pre-event CHO intake should be standardized when the goal is to assess endurance performance but seems to be of less importance when assessing the main performance-determining variables.

Degradation of energy cost with fatigue induced by trail running: effect of distance

PURPOSE

The effect of trail running competitions on cost of running (Cr) remains unclear and no study has directly examined the effect of distances in similar conditions on Cr. Accordingly, the aims of this study were to (i) assess the effect of trail running races of 40-170 km on Cr and (ii) to assess whether the incline at which Cr is measured influences changes in Cr.

METHODS

Twenty trail runners completed races of < 100 km (SHORT) and 26 trail runners completed races of > 100 km (LONG) on similar courses and environmental conditions. Oxygen uptake, respiratory exchange ratio, ventilation, and blood lactate were measured before and after the events on a treadmill with 0% (FLAT) and 15% incline (UH) and Cr was calculated.

RESULTS

Cr increased significantly after SHORT but not LONG races. There was no clear relationship between changes in Cr and changes in ventilation or blood lactate. There was a significant correlation (r = 0.75, p < 0.01) between changes in FLAT and UH Cr, and the change in Cr was not affected by the incline at which Cr was measured.

CONCLUSION

The distance of the trail running race, but not the slope at which it is measured, influence the changes in Cr with fatigue. The mechanism by which Cr increases only in SHORT is not related to increased cost of breathing.

Cardiovascular Functional Changes in Chronic Kidney Disease: Integrative Physiology, Pathophysiology and Applications of Cardiopulmonary Exercise Testing

The development of cardiovascular disease during renal impairment involves striking multi-tiered, multi-dimensional complex alterations encompassing the entire oxygen transport system. Complex interactions between target organ systems involving alterations of the heart, vascular, musculoskeletal and respiratory systems occur in Chronic Kidney Disease (CKD) and collectively contribute to impairment of cardiovascular function. These systemic changes have challenged our diagnostic and therapeutic efforts, particularly given that imaging cardiac structure at rest, rather than ascertainment under the stress of exercise, may not accurately reflect the risk of premature death in CKD. The multi-systemic nature of cardiovascular disease in CKD patients provides strong rationale for an integrated approach to the assessment of cardiovascular alterations in this population. State-of-the-art cardiopulmonary exercise testing (CPET) is a powerful, dynamic technology that enables the global assessment of cardiovascular functional alterations and reflects the integrative exercise response and complex machinery that form the oxygen transport system. CPET provides a wealth of data from a single assessment with mechanistic, physiological and prognostic utility. It is an underutilized technology in the care of patients with kidney disease with the potential to help advance the field of cardio-nephrology. This article reviews the integrative physiology and pathophysiology of cardio-renal impairment, critical new insights derived from CPET technology, and contemporary evidence for potential applications of CPET technology in patients with kidney disease.

Effects of a 2-km Swim on Markers of Cycling Performance in Elite Age-Group Triathletes

The purpose of this study was to examine the effects of a 2-km swim on markers of subsequent cycling performance in well-trained, age-group triathletes. Fifteen participants (10 males, five females, 38.3 ± 8.4 years) performed two progressive cycling tests between two and ten days apart, one of which was immediately following a 2-km swim (33.7 ± 4.1 min). Cycling power at 4-mM blood lactate concentration decreased after swimming by an average of 3.8% (p = 0.03, 95% CI −7.7, 0.2%), while heart rate during submaximal cycling (220 W for males, 150 W for females) increased by an average of 4.0% (p = 0.02, 95% CI 1.7, 9.7%), compared to cycling without prior swimming. Maximal oxygen consumption decreased by an average of 4.0% (p = 0.01, 95% CI −6.5, −1.4%), and peak power decreased by an average of 4.5% (p < 0.01, 95% CI −7.3, −2.3%) after swimming, compared to cycling without prior swimming. Results from this study suggest that markers of submaximal and maximal cycling are impaired following a 2-km swim.

The choice of freely preferred cadence by trained nonprofessional cyclists may not be characterized by mechanical efficiency

BACKGROUND

Most cycling studies involve professional cyclists. Because training may affect riding style, it is of interest to determine the physiological basis for the personal choice of cycling cadence in nonprofessional cyclists.

METHODS

Eleven nonprofessional (5.2±1.7-year-riding experience) male road cyclists, aged 35.0±11.0 years, underwent four separate laboratory test sessions. The first two sessions included habituation, anthropometry, V˙O2max,$\dot V{{\text{O}}_{\text{2}}}{\text{max}},$ and lactate threshold (LaTH) measurements. Freely preferred cadence at LaTH was determined during the second session (mean±SD=94.7±2.9 rev·min-1). During the third and fourth sessions participants performed LaTH tests at 60 and 95 rev·min-1 in a randomized order, with power output (PO) increments of 25 W every 4 min, up to ~90% of V˙O2max.$\dot V{{\text{O}}_{\text{2}}}{\text{max}}{\text{.}}$ Results: V˙O2,$\dot V{{\text{O}}_{\text{2}}},$ expired ventilation (V˙E),$({\dot V_E}),$ blood lactate (La), and calculated net mechanical efficiency (MEnet) rose with increased PO. At 95 rev·min-1, V˙O2, V˙E,$\dot V{{\text{O}}_2},{\text{ }}{\dot V_{\text{E}}},$ and La were significantly higher than at 60 rev·min-1 at all POs. MEnet at 95 rev·min-1 was lower than at 60 rev·min-1. Mean PO attained at LaTh did not differ significantly between 60 and 95 rev·min-1 (220.9±29.0 and 214.5±9.2 W, respectively). La values at LaTH were higher at 95 rev·min-1 than at 60 rev·min-1 (3.01±0.17 vs. 2.10±0.13 mM, p<0.05, respectively).

CONCLUSIONS

Our findings indicate that mechanical and physiological efficiencies may not determine the choice of cycling cadence by nonprofessional cyclists. This choice may reflect the need to maintain endurance at the expense of riding at a lower than optimal riding efficiency.

Using lactate threshold to predict 5-km treadmill running performance in veteran athletes

Measuring lactate threshold to predict endurance performance is difficult among veteran athletes, due to age-related decreases in net lactate concentration. The objective of this study was to determine whether lactate threshold, as assessed using the maximal deviation method (D_max), which is not dependent on net values of lactate, could be used as a more valid measure of 5-km treadmill running performance than other methods of determining lactate threshold. Veteran runners (18 male and 18 female, aged 47.3±6.7 years) performed an incremental exercise test to establish mean treadmill velocity at lactate threshold using D_max, a log-log method, a visual method, and a 4-mmol·L^-1 method, and, on a separate occasion, completed a 5-km time trial. Mean treadmill velocity at D_max was 12.2±1.8 km·h^-1, not being significantly different to mean treadmill velocity (12.1±1.8 km·h^-1) attained during the 5-km time trial (p>0.05); velocities were also significantly correlated (r=0.92, p<0.001), and limits of agreement narrow (-1.61 to 1.35 km·h^-1). Correlations were weaker and limits of agreement wider for the other methods of lactate threshold determination. Using a two-way, mixed-methods ANOVA, there was no significant effect of sex when using the different methods of determining T_lac (F_4,136=3.70, p=0.15). Mean treadmill velocity, when using D_max for determining lactate threshold, can be used to predict 5-km running performance among male and female veteran athletes.

High cycling cadence reduces carbohydrate oxidation at given low intensity metabolic rate

Cycling cadence (RPM)-related differences in blood lactate concentration (BLC) increase with increasing exercise intensity, whilst corresponding divergences in oxygen uptake (V.O₂) and carbon dioxide production (V.CO₂) decrease. Aim of the present study was to test whether a higher RPM reduces the fraction (%) of the V.O₂ used for carbohydrate oxidation (relCHO) at a given BLC. Eight males (23.9 ± 1.6 yrs; 177 ± 3 cm; 70.3 ± 3.4 kg) performed incremental load tests at 50 and 100 RPM. BLC, V.O₂ and V.CO₂ were measured. At respiratory exchange ratios (RER) < 1, relCHO were calculated and the constant determining 50 % relCHO (k_CHO) was approximated as a function of the BLC. At submaximal workload V.O₂, V.CO₂, and relCHO were lower (all p < 0.002; η² > 0.209) at 50 than at 100 RPM. No differences were observed in V.O₂peak (3.96 ± 0.22 vs. 4.00 ± 0.25 l · min⁻¹) and RER_peak (1.18 ± 0.02 vs. 1.15 ± 0.02). BLC was lower (p < 0.001; η² = 0.680) at 50 than at 100 RPM irrespective of cycling intensity. At 50 RPM, kCHO (4.2 ± 1.4 (mmol · l⁻¹)³) was lower (p = 0.043; η² = 0.466) than at 100 RPM (5.9 ± 1.9 (mmol · l⁻¹)³). This difference in k_CHO reflects a reduced CHO oxidation at a given BLC at 100 than at 50 RPM. At a low exercise intensity, a higher cycling cadence can substantially reduce the reliance on CHO at a given metabolic rate and/or BLC.

Effects of 2 weeks of low-intensity cycle training with different pedaling rates on the work rate at lactate threshold

PURPOSE

This study examined (1) the effects of a single bout of exercise at different pedaling rates on physiological responses, pedal force, and muscle oxygenation, and (2) the effects of 2 weeks of training with different pedaling rates on work rate at lactate threshold (WorkLT).

METHODS

Sixteen healthy men participated in the study. An incremental exercise test involving pedaling a cycling ergometer at 50 rpm was conducted to assess maximal oxygen consumption and WorkLT. The participants performed constant workload, submaximal exercise tests at WorkLT intensity with three different pedaling rates (35, 50, and 75 rpm). Oxygen consumption ([Formula: see text]O2), blood pressure, heart rate (HR), blood lactate, and pedal force were measured and oxy-hemoglobin/myoglobin concentration (OxyHb/Mb) at vastus lateralis was monitored by near-infrared spectroscopy during exercise. The participants were then randomly assigned to cycling exercise training at WorkLT in either the low or high frequency pedaling rate (LFTr, 35 rpm or HFTr, 75 rpm) group. Each 60-min training session was performed five times/week.

RESULTS

Despite maintaining the same work rate, [Formula: see text]O2 and HR were significantly lower at 35 than 75 rpm. Conversely, integrated pedal force was significantly higher at 35 than 75 rpm. Peripheral OxyHb/Mb was significantly lower at 35 than 75 rpm. After 2 weeks of training, WorkLT normalized to body mass significantly increased in the LFTr, but not the HFTr group.

CONCLUSIONS

Pedaling rate and the corresponding pedal force and peripheral oxygenation during cycling exercise influence the effect of training at LT on WorkLT.

Ventilation and respiratory mechanics

During dynamic exercise, the healthy pulmonary system faces several major challenges, including decreases in mixed venous oxygen content and increases in mixed venous carbon dioxide. As such, the ventilatory demand is increased, while the rising cardiac output means that blood will have considerably less time in the pulmonary capillaries to accomplish gas exchange. Blood gas homeostasis must be accomplished by precise regulation of alveolar ventilation via medullary neural networks and sensory reflex mechanisms. It is equally important that cardiovascular and pulmonary system responses to exercise be precisely matched to the increase in metabolic requirements, and that the substantial gas transport needs of both respiratory and locomotor muscles be considered. Our article addresses each of these topics with emphasis on the healthy, young adult exercising in normoxia. We review recent evidence concerning how exercise hyperpnea influences sympathetic vasoconstrictor outflow and the effect this might have on the ability to perform muscular work. We also review sex-based differences in lung mechanics.

Differences in lactate exchange and removal abilities between high-level African and Caucasian 400-m track runners

The present study aimed to investigate (1) whether high-level 400-m track runners of different ethnic origin displayed divergent post-run blood lactate concentrations (p400m[La]) and (2) if this discrepancy was based on differences in lactate exchange and removal abilities. Twenty male African (n = 12) and Caucasian (n = 8) runners, paired in terms of personal record, performed (1) an all-out 400-m run to measure p400m[La] at 3, 5 and 7 min into recovery and (2) a 1-min 25.2 km h(-1) running (not maximal but standardized) exercise followed by 90-min passive recovery to determine individual blood lactate recovery curves (IBLRC). IBLRCs were fitted to a bi-exponential time function: [Formula: see text] where γ 1 and γ 2 denote lactate exchange ability between the previously worked muscles and blood, and overall ability for lactate removal, respectively. The quantity of lactate accumulated at the end of the 1-min exercise (Q LaA) was also estimated. Our study showed that after the all-out 400-m run, p400m[La] was lower in African than in Caucasian runners at 3 and 5 min but not at 7 min into recovery. After the standardized exercise, γ 1 and γ 2 were lower (p < 0.01) and Q LaA was higher (p < 0.05) in African than in Caucasian runners. These data suggest that for similar performance levels, ethnicity involves differences in lactate accumulation, exchange and removal.

Effects of 2 different prior endurance exercises on whole-body fat oxidation kinetics: light vs. heavy exercise

This study aimed to compare the effects of 2 different prior endurance exercises on subsequent whole-body fat oxidation kinetics. Fifteen men performed 2 identical submaximal incremental tests (Incr2) on a cycle ergometer after (i) a ∼40-min submaximal incremental test (Incr1) followed by a 90-min continuous exercise performed at 50% of maximal aerobic power-output and a 1-h rest period (Heavy); and (ii) Incr1 followed by a 2.5-h rest period (Light). Fat oxidation was measured using indirect calorimetry and plotted as a function of exercise intensity during Incr1 and Incr2. A sinusoidal equation, including 3 independent variables (dilatation, symmetry and translation), was used to characterize the fat oxidation kinetics and to determine the intensity (Fatmax) that elicited the maximal fat oxidation (MFO) during Incr. After the Heavy and Light trials, Fatmax, MFO, and fat oxidation rates were significantly greater during Incr2 than Incr1 (p < 0.001). However, Δ (i.e., Incr2–Incr1) Fatmax, MFO, and fat oxidation rates were greater in the Heavy compared with the Light trial (p < 0.05). The fat oxidation kinetics during Incr2Heavy showed a greater dilatation and rightward asymmetry than Incr1Heavy, whereas only a greater dilatation was observed in Incr2Light (p < 0.05). This study showed that although to a lesser extent in the Light trial, both prior exercise sessions led to an increase in Fatmax, MFO, and absolute fat oxidation rates during Incr2, inducing significant changes in the shape of the fat oxidation kinetics.

Reverse lactate threshold: a novel single-session approach to reliable high-resolution estimation of the anaerobic threshold

The multisession maximal lactate steady-state (MLSS) test is the gold standard for anaerobic threshold (AnT) estimation. However, it is highly impractical, requires high fitness level, and suffers additional shortcomings. Existing single-session AnT-estimating tests are of compromised validity, reliability, and resolution. The presented reverse lactate threshold test (RLT) is a single-session, AnT-estimating test, aimed at avoiding the pitfalls of existing tests. It is based on the novel concept of identifying blood lactate's maximal appearance-disappearance equilibrium by approaching the AnT from higher, rather than from lower exercise intensities. Rowing, cycling, and running case data (4 recreational and competitive athletes, male and female, aged 17-39 y) are presented. Subjects performed the RLT test and, on a separate session, a single 30-min MLSS-type verification test at the RLT-determined intensity. The RLT and its MLSS verification exhibited exceptional agreement at 0.5% discrepancy or better. The RLT's training sensitivity was demonstrated by a case of 2.5-mo training regimen following which the RLT's 15-W improvement was fully MLSS-verified. The RLT's test-retest reliability was examined in 10 trained and untrained subjects. Test 2 differed from test 1 by only 0.3% with an intraclass correlation of 0.997. The data suggest RLT to accurately and reliably estimate AnT (as represented by MLSS verification) with high resolution and in distinctly different sports and to be sensitive to training adaptations. Compared with MLSS, the single-session RLT is highly practical and its lower fitness requirements make it applicable to athletes and untrained individuals alike. Further research is needed to establish RLT's validity and accuracy in larger samples.

Toe and earlobe capillary blood sampling for lactate threshold determination in rowing

PURPOSE

In rowing ergometry, blood for determining lactate concentration can be removed from the toe tip without the rower having to stop. The purpose of the study was to examine whether sampling blood from the toe versus the earlobe would affect lactate threshold (Tlac) determination.

METHODS

Ten physically active males (mean ± age 21.2 ± 2.3 y; stature 179.2 ± 7.5 cm; body mass 81.7 ± 12.7 kg) completed a multistage, 3 min incremental protocol on the Concept II rowing ergometer. Blood was sampled simultaneously from the toe tip and earlobe between stages. Three different methods were used to determine Tlac.

RESULTS

There were wider variations due to the method of Tlac determination than due to the sample site; for example, ANOVA results for power output were F(1.25, 11.25) = 11.385, P = .004 for method and F(1, 9) = 0.633, P = .45 for site. The greatest differences in Tlac due to sample site in rowing occurred when Tlac was determined using an increase in blood lactate concentration by >1 mmol/L from baseline (TlacΔ1).

CONCLUSIONS

The toe tip can be used as a suitable sample site for blood collection during rowing ergometry, but caution is needed when using the earlobe and toe tip interchangeably to prescribe training intensities based on Tlac, especially when using TlacΔ1 or at lower concentrations of lactate.

Eccentric exercise-induced muscle damage dissociates the lactate and gas exchange thresholds

We tested the hypothesis that exercise-induced muscle damage would increase the ventilatory (V(E)) response to incremental/ramp cycle exercise (lower the gas exchange threshold) without altering the blood lactate profile, thereby dissociating the gas exchange and lactate thresholds. Ten physically active men completed maximal incremental cycle tests before (pre) and 48 h after (post) performing eccentric exercise comprising 100 squats. Pulmonary gas exchange was measured breath-by-breath and fingertip blood sampled at 1-min intervals for determination of blood lactate concentration. The gas exchange threshold occurred at a lower work rate (pre: 136 ± 27 W; post: 105 ± 19 W; P < 0.05) and oxygen uptake (VO(2)) (pre: 1.58 ± 0.26 litres · min(-1); post: 1.41 ± 0.14 litres · min(-1); P < 0.05) after eccentric exercise. However, the lactate threshold occurred at a similar work rate (pre: 161 ± 19 W; post: 158 ± 22 W; P > 0.05) and VO(2) (pre: 1.90 ± 0.20 litres · min(-1); post: 1.88 ± 0.15 litres · min(-1); P > 0.05) after eccentric exercise. These findings demonstrate that exercise-induced muscle damage dissociates the V(E) response to incremental/ramp exercise from the blood lactate response, indicating that V(E) may be controlled by additional or altered neurogenic stimuli following eccentric exercise. Thus, due consideration of prior eccentric exercise should be made when using the gas exchange threshold to provide a non-invasive estimation of the lactate threshold.

The effect of pre-test carbohydrate ingestion on the anaerobic threshold, as determined by the lactate-minimum test

The purpose of this study was to investigate the effect of pre-test carbohydrate (CHO) ingestion on anaerobic-threshold assessment using the lactate-minimum test (LMT). Fifteen competitive male distance runners capable of running 10 km in 33.5-43 min were used as subjects. LMT was performed following CHO (2x300 mL, 7% solution) or comparable placebo (Pl) ingestion, in a double-blind, randomized order. The LMT consisted of two high-intensity 1 min treadmill runs (17-21 km.h(-1)), followed by an 8 min recovery period. Subsequently, subjects performed 5 min running stages, incremented by 0.6 km.h(-1) and separated by 1 min blood-sampling intervals. Tests were terminated after 3 consecutive increases in blood-lactate concentration ([La]) had been observed. Finger-tip capillary blood was sampled for [La] and blood-glucose determination 30 min before the test's onset, during the recovery phase following the 2 high-intensity runs, and following each of the subsequent 5 min stages. Heart rate (HR) and rating of perceived exertion (RPE) were recorded after each stage. The lactate-minimum speed (LMS) was determined from the individual [La]-velocity plots and was considered reflective of the anaerobic threshold. Pre-test CHO ingestion had no effect on LMS (13.19+/-1.12 km.h(-1) vs. 13.17+/-1.08 km.h(-1) in CHO and Pl, respectively), nor on [La] and glucose concentration at that speed, or on HR and RPE responses. Pre-test CHO ingestion therefore does not affect LMS or the LMT-estimated anaerobic threshold.

Why does chronic heart failure cause breathlessness and fatigue?

Traditional explanations for the symptoms of fatigue and breathlessness experienced by patients with chronic heart failure (CHF) focus on how reduced cardiac output on exercise leads to impaired skeletal muscle blood supply, thus causing fatigue, and on how the requirement for a raised left ventricular filling pressure to maintain cardiac output results in reduced pulmonary diffusion owing to interstitial edema, thus causing breathlessness. However, indices of left ventricular function relate poorly to exercise capacity and symptoms, suggesting that the origin of symptoms may lie elsewhere. There is a specific heart failure myopathy that is present early in the condition which may contribute largely to the sensation of fatigue. Receptors present in skeletal muscle sensitive to work (ergoreceptors) are overactive in patients with CHF, presumably as a consequence of the myopathy, and their activity is related both to the ventilatory response to exercise and breathlessness, and to the sympathetic overactivity of CHF. In the present paper, we review the systemic consequences of left ventricular dysfunction to understand how they relate to the symptoms of heart failure.

Incremental Exercise Test Design and Analysis

Physiological variables, such as maximum work rate or maximal oxygen uptake (VO2max), together with other submaximal metabolic inflection points (e.g. the lactate threshold [LT], the onset of blood lactate accumulation and the pulmonary ventilation threshold [VT]), are regularly quantified by sports scientists during an incremental exercise test to exhaustion. These variables have been shown to correlate with endurance performance, have been used to prescribe exercise training loads and are useful to monitor adaptation to training. However, an incremental exercise test can be modified in terms of starting and subsequent work rates, increments and duration of each stage. At the same time, the analysis of the blood lactate/ventilatory response to incremental exercise may vary due to the medium of blood analysed and the treatment (or mathematical modelling) of data following the test to model the metabolic inflection points. Modification of the stage duration during an incremental exercise test may influence the submaximal and maximal physiological variables. In particular, the peak power output is reduced in incremental exercise tests that have stages of longer duration. Furthermore, the VT or LT may also occur at higher absolute exercise work rate in incremental tests comprising shorter stages. These effects may influence the relationship of the variables to endurance performance or potentially influence the sensitivity of these results to endurance training. A difference in maximum work rate with modification of incremental exercise test design may change the validity of using these results for predicting performance, and prescribing or monitoring training. Sports scientists and coaches should consider these factors when conducting incremental exercise testing for the purposes of performance diagnostics.

Using functional data analysis to summarise and interpret lactate curves

John Tukey used the term exploratory data analysis (EDA) to describe a philosophy for analyzing data where graphical and numerical summaries are used to uncover interesting structures. The applied statistician today has a much more sophisticated set of methods to use when applying the EDA philosophy. One such collection of methods is functional data analysis (FDA), which was used to explore the structure of lactate curves. A principal components analysis and plots of the second derivatives provide new intuitive endurance markers which correlates highly with other numerical summaries of lactate curves that have been suggested in the literature.

Ventilatory and gas-exchange responses to incremental exercise performed with reduced muscle glycogen content

This study examined the relationship between minute ventilation (VE), CO2 production (VCO2), and blood lactate concentration ([La-]) during incremental exercise performed with reduced muscle glycogen stores. Nine untrained female subjects (25.3+/-4.2 year) performed incremental cycling in a normal glycogen (NG) state and under conditions of reduced muscle glycogen (RG) content. To reduce muscle glycogen stores, subjects cycled to exhaustion (124+/-33 min) at a power output corresponding to their gas-exchange anaerobic threshold. Peak oxygen uptake (VO2peak) was unchanged with glycogen reduction, even though subjects achieved a significantly lower maximal power output in the RG state (p<0.05). Peak blood [La-] decreased significantly by 37% in the RG state (p<0.001). At any percentage of VO2peak, O2 uptake and VE were similar for both treatment conditions, whereas VCO2 and respiratory exchange ratio values were lower during the RG trial than under NG conditions. Therefore, VE/VCO2 tended to be higher and end-tidal CO2 partial pressure tended to be lower during exercise performed in the RG state. VE was significantly correlated with VCO2 under both treatment conditions (NG: r=0.99, p<0.01; RG: r=0.99, p<0.01). However, the slope of the VE-VCO2 relationship was significantly elevated during the RG trial (p<0.01). VE during exercise was similar under both treatment conditions, even though VCO2 and blood [La-] were lower during the RG trial compared to the NG trial. This suggests that factors other than CO2 delivery to the lung and metabolic acidosis play an important role in regulating VE during exercise.

Performance at High Pedaling Cadences in Well-Trained Cyclists

PURPOSE

This study was conducted to determine the effect of high pedaling cadences on maximal cycling power output (W(max)).

METHODS

Nine well-trained cyclists performed a continuous, incremental cycle-ergometer test to exhaustion (25 W increases every 3 min) either at 80, 100, or 120 rpm on three different occasions.

RESULTS

W(max) was approximately 9% lower during 120 rpm in comparison with 80 and 100 rpm (335 +/- 9, 363 +/- 7, and 370 +/- 12 W, respectively; P < 0.05). During 120 rpm, ventilation rate (V(E)) increased above the increases in expired CO(2), which reduced the power output (PO) at the ventilatory anaerobic threshold (VT(2)) by 11% (P < 0.05). Gross efficiency (GE) did not differ among trials. At 120 rpm, capillary blood lactate concentration ([Lac]) increased above the 80-rpm trial (5.3 +/- 1.2 vs 3.0 +/- 0.7 mM at 300 W; P < 0.05), although pH was not reduced. At 120 rpm, expired CO(2) increased and reduced blood bicarbonate concentration ([HCO(3)(-)]) was reduced, maintaining blood pH similar to the other trials.

CONCLUSION

A high pedaling cadence (i.e., 120 rpm) reduces performance (i.e., W(max)) and anaerobic threshold during an incremental test in well-trained cyclists. The data suggest that ventilatory anaerobic threshold (VT(2)) is a sensitive predictor of optimal pedaling cadence for performance, whereas blood pH or efficiency is not.

Comparação entre limiar anaeróbio determinado por variáveis ventilatórias e pela resposta do lactato sanguíneo em ciclistas

Muitas investigações têm demonstrado que a coincidência entre os limiares ventilatórios e os limiares que se utilizam da resposta do lactato nem sempre ocorre, sugerindo que não existe relação entre causa e efeito entre os fenômenos. Dessa forma, o presente estudo teve como objetivos comparar e correlacionar os valores de consumo de oxigênio (VO2), potência (W) e freqüência cardíaca (FC) obtidos por protocolos de determinação do limiar ventilatório (LV) e limiar anaeróbio individual (IAT). A amostra foi constituída por oito ciclistas de níveis paulista e nacional (idade: 27,88 ± 8,77 anos; massa corporal: 65,19 ± 4,40kg; estatura: 169,31 ± 5,77cm). O IAT foi determinado iniciando-se com aquecimento de três minutos a 50W com aumentos progressivos de 50W.3min-1 até a exaustão voluntária, com as coletas de sangue aos 20 segundos finais de cada estágio e durante a recuperação. Para a determinação do LV, utilizou-se o mesmo protocolo adotado para a determinação do IAT, porém, sem efetuar as coletas de sangue. O LV foi identificado pelas mudanças da ventilação pulmonar e dos equivalentes ventilatórios de O2 e CO2. O teste t de Student não revelou diferenças estatisticamente significantes em nenhuma das variáveis obtidas. As associações encontradas foram altas e significativas. O VO2 (ml.kg-1.min-1), P (W) e FC (bpm) correspondente ao LV e IAT, e as associações entre as variáveis foram, respectivamente, de: 48,00 ± 3,82 vs 48,08 ± 3,71 (r = 0,90); 256,25 ± 32,04 vs 246,88 ± 33,91 (r = 0,84); 173,75 ± 9,18 vs 171,25 ± 12,02 (r = 0,97). De acordo com os resultados obtidos, pode-se concluir que o IAT e o LV produzem valores semelhantes de VO2, W e FC, o que favorece a adoção do LV por ser um método não-invasivo para determinação do limiar anaeróbio em ciclistas.

Assessment of ventilatory thresholds during graded and maximal exercise test using time varying analysis of respiratory sinus arrhythmia

OBJECTIVE

To test whether ventilatory thresholds, measured during an exercise test, could be assessed using time varying analysis of respiratory sinus arrhythmia frequency (f(RSA)).

METHODS

Fourteen sedentary subjects and 12 endurance athletes performed a graded and maximal exercise test on a cycle ergometer: initial load 75 W (sedentary subjects) and 150 W (athletes), increments 37.5 W/2 min. f(RSA) was extracted from heart period series using an evolutive model. First (T(V1)) and second (T(V2)) ventilatory thresholds were determined from the time course curves of ventilation and ventilatory equivalents for O(2) and CO(2).

RESULTS

f(RSA) was accurately extracted from all recordings and positively correlated to respiratory frequency (r = 0.96 (0.03), p<0.01). In 21 of the 26 subjects, two successive non-linear increases were determined in f(RSA), defining the first (T(RSA1)) and second (T(RSA2)) f(RSA) thresholds. When expressed as a function of power, T(RSA1) and T(RSA2) were not significantly different from and closely linked to T(V1) (r = 0.99, p<0.001) and T(V2) (r = 0.99, p<0.001), respectively. In the five remaining subjects, only one non-linear increase was observed close to T(V2). Significant differences (p<0.04) were found between athlete and sedentary groups when T(RSA1) and T(RSA2) were expressed in terms of absolute and relative power and percentage of maximal aerobic power. In the sedentary group, T(RSA1) and T(RSA2) were 150.3 (18.7) W and 198.3 (28.8) W, respectively, whereas in the athlete group T(RSA1) and T(RSA2) were 247.3 (32.8) W and 316.0 (28.8) W, respectively.

CONCLUSIONS

Dynamic analysis of f(RSA) provides a useful tool for identifying ventilatory thresholds during graded and maximal exercise test in sedentary subjects and athletes.

Circadian rhythms in blood lactate concentration during incremental ergometer rowing

This study examined whether circadian rhythms affect lactate threshold (Th(lac)) during rowing exercise. Eleven male, endurance-trained athletes [mean (SD) age 29.5 (6.1) years] rowed at 0200, 0600, 1000, 1400, 1800 and 2200 hours under the same experimental conditions. Capillary blood (25 microl) was obtained from the tip of the toe during the last 30 s of a continuous, multi-stage, 3-min, incremental protocol on the Concept II ergometer. To determine Th(lac), a curve-fitting procedure (the D(max) method), a visual method (Th(lac-vis)) and the fixed blood lactate concentration of 4.0 mmol l(-1) (Th(lac-4 mM)) were used. Circadian rhythms were apparent for oxygen consumption and heart rate at Th(lac) using the D(max) method (P=0.02 and P=0.04 respectively), with the acrophases at 2139 hours and 2032 hours respectively coinciding in phase with that of core body temperature. The conclusion is that tests should be completed at the same time of day at which the athlete usually trains, to ensure precision of Th(lac) determination, especially when the D(max )method is used to determine Th(lac).

Ventilatory thresholds in arm and leg exercises with spontaneously chosen crank and pedal rates

The present study assessed whether the first and the second ventilatory thresholds (VT1 and VT2) were dependent on the muscle groups solicited when spontaneously chosen crank and pedal rates are used. 20 physical education male students (22 +/- 2.2 yr.) performed two maximal incremental tests randomly assigned using an increment of 15 and 30 W every minute for arm and leg exercises, respectively. These tests were used to measure the maximal oxygen uptake (VO2 max) and to identify VT1 and VT2. The absolute oxygen uptake (VO2) values measured at VT1, VT2, and at maximal workload were significantly (p < .05) lower during arm and leg exercises. However, VT1 and VT2 expressed in percent of VO2 max were not significantly different between arm and leg exercises (54.1 +/- 8.2 vs 57.2 +/- 11.4%; and 82.5 +/- 6.4 vs 84.6 +/- 5.1% at VT1 and VT2, respectively). In addition, at the two thresholds, none of the variables measured during arm and leg exercises were significantly correlated with the exception of spontaneously chosen crank and pedal rates (p < .01; r = .75 and r = .69 for VT1 and VT2, respectively). Probably due to the different training status and skill level, no extrapolation can be made to specify the arm thresholds from the leg. These results underline the need to specify the ventilatory thresholds from specific arm ergometer measures obtained from tests performed with spontaneously chosen crank and pedal rates and, thus, close to sport and recreational activities, when they are used for training and rehabilitation programs.

Methods to determine aerobic endurance

Physiological testing of elite athletes requires the correct identification and assessment of sports-specific underlying factors. It is now recognised that performance in long-distance events is determined by maximal oxygen uptake (V(2 max)), energy cost of exercise and the maximal fractional utilisation of V(2 max) in any realised performance or as a corollary a set percentage of V(2 max) that could be endured as long as possible. This later ability is defined as endurance, and more precisely aerobic endurance, since V(2 max) sets the upper limit of aerobic pathway. It should be distinguished from endurance ability or endurance performance, which are synonymous with performance in long-distance events. The present review examines methods available in the literature to assess aerobic endurance. They are numerous and can be classified into two categories, namely direct and indirect methods. Direct methods bring together all indices that allow either a complete or a partial representation of the power-duration relationship, while indirect methods revolve around the determination of the so-called anaerobic threshold (AT). With regard to direct methods, performance in a series of tests provides a more complete and presumably more valid description of the power-duration relationship than performance in a single test, even if both approaches are well correlated with each other. However, the question remains open to determine which systems model should be employed among the several available in the literature, and how to use them in the prescription of training intensities. As for indirect methods, there is quantitative accumulation of data supporting the utilisation of the AT to assess aerobic endurance and to prescribe training intensities. However, it appears that: there is no unique intensity corresponding to the AT, since criteria available in the literature provide inconsistent results; and the non-invasive determination of the AT using ventilatory and heart rate data instead of blood lactate concentration ([La(-)](b)) is not valid. Added to the fact that the AT may not represent the optimal training intensity for elite athletes, it raises doubt on the usefulness of this theory without questioning, however, the usefulness of the whole [La(-)](b)-power curve to assess aerobic endurance and predict performance in long-distance events.

Effect of mild dehydration on the lactate threshold in women

PURPOSE

The purpose of this investigation was to examine the effects of dehydration on the lactate threshold and performance time to exhaustion in women.

METHODS

Seven moderately trained women (age = 23.6 +/- 1.6 yr) performed two graded exercise tests on separate occasions, once in a normally hydrated state (HY) and once in a dehydrated state (DE). Dehydration was achieved by a 45-min submaximal exercise the evening before testing, followed by a 12-h period of fluid restriction. VO2, VCO2, V(E), R-values, blood lactate, and catecholamine concentrations were measured at baseline and during each workload. Plasma volume and plasma osmolality were also determined. Body weight dropped significantly for the dehydrated trial (2.6 +/- 0.7%).

RESULTS

There was a corresponding decrease in plasma volume measured (3.5 +/- 2.6%). The VO2max (3.1 +/- 0.3 L x min(-1) HY; 3.0 +/- 0.1 L x min(-1) DE) obtained was not significantly different between the hydration and dehydration trial. Plasma norepinephrine, epinephrine, and lactate concentrations were not significantly different at baseline or maximum intensity although epinephrine concentrations were higher for the dehydrated trial during submaximal workloads. Lactate concentrations were highly correlated with epinephrine (r = 0.95 HY; r = 0.97 DE). The lactate threshold occurred at a significantly lower relative percent of VO2max for the dehydrated trial (72.2 +/- 1.1% HY; 65.5 +/- 1.8% DE) as well as a lower absolute power output when compared with that in the hydrated trial. There was a significant decrease in time to exhaustion for the dehydrated trial (17.3 +/- 0.7 min HY; 16.3 + 0.7 min DE). Time to exhaustion for the dehydrated trial was correlated with the % VOmax at which the lactate threshold occurred (r = 0.74).

CONCLUSIONS

These data indicate that low levels of dehydration induced a shift in the lactate threshold, in part because of elevated epinephrine concentrations. This shift may have been one cause for the decrease in time to exhaustion for the dehydrated trial.

Carbonic anhydrase inhibition delays plasma lactate appearance with no effect on ventilatory threshold

The effect of carbonic anhydrase (CA) inhibition with acetazolamide (Acz, 10 mg/kg body wt iv) on exercise performance and the ventilatory (VET) and lactate (LaT) thresholds was studied in seven men during ramp exercise (25 W/min) to exhaustion. Breath-by-breath measurements of gas exchange were obtained. Arterialized venous blood was sampled from a dorsal hand vein and analyzed for plasma pH, PCO(2), and lactate concentration ([La(-)](pl)). VET [expressed as O(2) uptake (VO(2)), ml/min] was determined using the V-slope method. LaT (expressed as VO(2), ml/min) was determined from the work rate (WR) at which [La(-)](pl) increased 1.0 mM above rest levels. Peak WR was higher in control (Con) than in Acz sutdies [339 +/- 14 vs. 315 +/- 14 (SE) W]. Submaximal exercise VO(2) was similar in Acz and Con; the lower VO(2) at exhaustion in Acz than in Con (3.824 +/- 0. 150 vs. 4.283 +/- 0.148 l/min) was appropriate for the lower WR. CO(2) output (VCO(2)) was lower in Acz than in Con at exercise intensities >/=125 W and at exhaustion (4.375 +/- 0.158 vs. 5.235 +/- 0.148 l/min). [La(-)](pl) was lower in Acz than in Con during submaximal exercise >/=150 W and at exhaustion (7.5 +/- 1.1 vs. 11.5 +/- 1.1 mmol/l). VET was similar in Acz and Con (2.483 +/- 0.086 and 2.362 +/- 0.110 l/min, respectively), whereas the LaT occurred at a higher VO(2) in Acz than in Con (2.738 +/- 0.223 vs. 2.190 +/- 0.235 l/min). CA inhibition with Acz is associated with impaired elimination of CO(2) during the non-steady-state condition of ramp exercise. The similarity in VET in Con and Acz suggests that La(-) production is similar between conditions but La(-) appearance in plasma is reduced and/or La(-) uptake by other tissues is enhanced after the Acz treatment.

The effect of glycogen depletion on the curvature constant parameter of the power-duration curve for cycle ergometry

For high-intensity cycle ergometer exercise, the relation between power (P) and its tolerable duration (t) has been well characterized by the hyperbolic relationship: (P-thetaF) t = W', or P = W' (1/t)+thetaF, where thetaF may be termed the 'fatigue threshold'. The curvature constant (W') reflects a constant amount of work which is postulated to be equivalent to a finite energy store that relates to the oxygen-deficit: phosphagen pool, anaerobic glycolysis and oxygen stores. Compared to thetaF, the physiological nature of W' has received little consideration. The purpose of this study was therefore to establish the parameters of the power-duration curve (thetaF and W') for subjects in normal glycogen (NG) and glycogen depleted (GD) states. Seven healthy male subjects (aged 22 to 41 years) each performed four high-intensity square-wave exercise bouts on an electrically braked cycle ergometer under two different muscular glycogen content conditions, i.e. NG and GD states. Subjects performed the following exercise on the evening before the trial day to induce the GD state. Initially, they performed a 75-min cycling exercise at 60% of VO2max. After a 5-min rest period, they subsequently repeated a 1-min cycling bout at 115% of VO2max (separated by 1-min rest periods) until the subject could no longer maintain the prescribed pedal rate for the full minute. Subjects then reported to the laboratory after an overnight fast and performed a single high-intensity exercise bout. The GD procedure was repeated four times at 1-week intervals. In the GD state, the respiratory exchange ratio (RER) (VO2/VCO2) value during a recumbent control period prior to the trial was significantly lower than that in the NG state [GD: 0.84+/-0.02, NG: 0.94+/-0.04, mean +/- SD]. There was no significant difference for thetaF between GD and NG state [NG: 197.1+/-31.9 W, GD: 190.6+/-28.2 W]. W' in contrast was significantly reduced by the GD procedure [NG: 12.83+/-2.21 kJ, GD: 10.33+/-2.41 kJ]. The present results indicate that the muscular glycogen store seems to be an important determinant of the curvature constant (W') of the power-duration curve for cycle ergometry.

Repeated bouts of exercise alter the blood lactate-RPE relation

PURPOSE

To examine the effects of repeated bouts of exercise on the blood lactate [HLa]-ratings of perceived exertion (RPE) relation.

METHODS

Six moderately trained males were studied on two occasions: a sequential exercise bouts day (SEB: 1000 h, 1130 h, and 1300 h) and a delayed exercise bouts day (DEB: 1000 h, 1400 h, and 1800 h). Each of the three exercise bouts within a given condition were 30 min in duration at the power output (PO) associated with 70% of VO2peak on a cycle ergometer. A standardized meal was provided at 0600 h. VO2, PO, HR, and RER were recorded every min during exercise and blood [HLa] and RPE were measured every 5 min during exercise.

RESULTS

A 2 x 3 analysis of variance with repeated measures revealed that blood [HLa] decreased significantly with each repeated exercise bout (X +/- SEM: bout 1: SEB = 3.5 (0.3), DEB = 3.8 (0.4); bout 2: SEB = 2.6 (0.3), DEB = 2.8 (0.3); bout 3: SEB = 2.0 (0.2), DEB = 2.1 (0.4); mM). No differences were observed in the blood [HLa] response to repeated bouts of exercise between SEB and DEB. RPE-peripheral (legs, RPE-L) was higher during bout 3 compared with bout 1 (P <0.05) (bout 1: SEB = 11.8 (0.8), DEB = 12.3 (0.2); bout 2: SEB = 12.3 (0.5), DEB = 13.3 (0.4); bout 3: SEB = 13.5 (0.8), DEB = 14.0 (0.7); RPE-central (chest and breathing, RPE-C) was not affected by repeated bouts of exercise, whereas RPE-Overall (RPE-O) was higher during bout 3 compared with bouts 1 and 2 (P < 0.05) (bout 1: SEB = 12.5 (0.2), DEB = 12.3 (0.4); bout 2: SEB = 12.8 (0.4), DEB = 12.7 (0.4); bout 3: SEB = 13.7 (0.7), DEB = 13.2 (0.3)). No interaction for RPE x condition was observed. HR increased with repeated bouts of exercise with HR during exercise bout 3 being higher than HR during exercise bout 1 (164 vs. 156 bpm, P < 0.05). There was also a strong trend for HR during exercise bout 3 to be higher than HR during exercise bout 2 (P < 0.06). A trend for a reduction in VO2 with repeated exercise was observed (P < 0.07), with the reduction apparently related to the SEB condition (P < 0.12 for VO2 x condition). PO and kcal.min-1 were not affected by repeated bouts of exercise. RER decreased significantly with each repeated bout of exercise (from RER = 0.96 to RER = 0.89, P < 0.05) with no difference observed between SEB and DEB.

CONCLUSIONS

We conclude that the blood [HLa]-RPE relation is altered by repeated bouts of exercise and that this alteration does not appear to be affected by recovery time between exercise bouts (up to 3.5 h of recovery). These data suggest that, after the first exercise bout, RPE should not be used to produce a specific blood [HLa] on subsequent exercise bouts.

Effect of exercise on acid-base status of horses

Exercise in horses is associated with a wide variety of physiological changes in fluid, electrolyte and acid base balance. The integration of physiologic and physiochemical mechanisms acts to minimize alterations in pH and enhance removal of carbon dioxide produced by exercising muscles. This article provides a description of the changes that take place during exercise and how these changes affect acid-base balance in the horse.

Importance of the lactate anion in control of breathing

The purpose of this study was to examine the effects of raising the arterial La- and K+ levels on minute ventilation (VE) in rats. Either La- or KCl solutions were infused in anesthetized spontaneously breathing Wistar rats to raise the respective ion arterial concentration ([La-] and [K+]) gradually to levels similar to those observed during strenuous exercise. VE, blood pressure, and heart rate were recorded continuously, and arterial [La-], [K+], pH, and blood gases were repeatedly measured from blood samples. To prevent changes in pH during the La- infusions, a solution of sodium lactate and lactic acid was used. Raising [La-] to 13.2 +/- 0.6 (SE) mM induced a 47.0 +/- 4.0% increase in VE without any concomitant changes in either pH or PCO2. Raising [K+] to 7.8 +/- 0.11 mM resulted in a 20.3 +/- 5.28% increase in VE without changes in pH. Thus our results show that La- itself, apart from lactic acidosis, may be important in increasing VE during strenuous exercise, and we confirm earlier results regarding the role of arterial [K+] in the control of VE during exercise.

Skeletal muscle chemoreflex and pHi in exercise ventilatory control

To determine whether skeletal muscle hydrogen ion mediates ventilatory drive in humans during exercise, 12 healthy subjects performed three bouts of isotonic submaximal quadriceps exercise on each of 2 days in a 1.5-T magnet for 31P-magnetic resonance spectroscopy (31P-MRS). Bilateral lower extremity positive pressure cuffs were inflated to 45 Torr during exercise (BLPPex) or recovery (BLPPrec) in a randomized order to accentuate a muscle chemoreflex. Simultaneous measurements were made of breath-by-breath expired gases and minute ventilation, arterialized venous blood, and by 31P-MRS of the vastus medialis, acquired from the average of 12 radio-frequency pulses at a repetition time of 2.5 s. With BLPPex, end-exercise minute ventilation was higher (53.3 +/- 3.8 vs. 37.3 +/- 2.2 l/min; P < 0.0001), arterialized PCO2 lower (33 +/- 1 vs. 36 +/- 1 Torr; P = 0.0009), and quadriceps intracellular pH (pHi) more acid (6.44 +/- 0.07 vs. 6.62 +/- 0.07; P = 0.004), compared with BLPPrec. Blood lactate was modestly increased with BLPPex but without a change in arterialized pH. For each subject, pHi was linearly related to minute ventilation during exercise but not to arterialized pH. These data suggest that skeletal muscle hydrogen ion contributes to the exercise ventilatory response.

Blood lactate and perceived exertion relative to ventilatory threshold: boys versus men

The purpose of this study was to examine blood lactate (BLa) levels and ratings of perceived exertion (RPE) in nine boys (10.5 +/- 0.7 yr) and nine men (25.3 +/- 2.0 yr) during exercise relative to ventilatory threshold (VT). VT and VO2max were determined during a graded exercise test on a cycle ergometer. On three additional days each subject exercised for 10 min at either 80, 100, or 120% of the VO2 at VT. Capillary BLa levels and RPE were assessed at minutes 5 and 10 of each trial. VO2max averaged 47.7 +/- 5.4 and 50.2 +/- 6.2 mL x g(-1) x min(-1) in the boys and men, respectively (P > 0.05). VT expressed as %VO2max was 67.2 +/- 3.5% in the boys and 67.3 +/- 4.9% in the men (P > 0.05). BLa levels ranged from 2.0 +/- 0.7 to 4.7 +/- 0.9 mmol x L(-1) in the boys and from 2.6 +/- 0.5 to 8.2 +/- 2.1 mmol x L(-1) in the men across the three intensities. Corresponding RPE values ranged from 11.2 +/- 1.8 to 16.2 +/- 2.2 in the boys and from 10.2 +/- 1.2 to 15.8 +/- 1.7 in the men. A group x time x intensity interaction (P < 0.05) indicated that BLa in the men increased more so across time and intensity. There were no significant group difference or interactions involving RPE during exercise. Setting exercise intensity relative to VT did not abolish child-adult differences with respect to submaximal BLa levels. Despite maintaining lower BLa levels, RPE values were similar between boys and men.

Training adaptation and biological changes among well-trained male triathletes

The distinction between training and overtraining responses is an important prerequisite for any potential marker for monitoring overtraining in athletes. In this study, eight well-trained male triathletes undertook physical performance assessments, at 6 weekly intervals, throughout a 9-month intensive training season. At each assessment, a resting blood sample was obtained for determination of a number of biological parameters previously associated with overtraining. All athletes produced significant (P < 0.05) improvements in running speed at anaerobic threshold (ATRS) from 15.6 +/- 0.2 k.h-1 at the start of the season to 16.6 +/- 0.6 k.h-1 at the time of major competitions. This improvement in performance was taken as evidence of well balanced training programs. Significant changes (P < 0.05) in plasma glutamine and plasma uric acid concentrations were observed during the training season, and both correlated moderately with ATRS (r = 0.365 and r = -0.328, respectively). None of the other parameters measured showed any significant changes during the training season. The elevations in plasma glutamine concentration observed in response to long-term balanced training may be distinguishable from previous reports of decreased glutamine concentrations in overtrained athletes, making it a potentially valuable tool in the monitoring of overtraining in athletes.

1996 J.B. Wolffe Memorial Lecture. Challenging beliefs: ex Africa semper aliquid novi

The basis of the scientific method is the development of intellectual models, the predictions of which are then subjected to scientific evaluation. The more robust test of any such model is one that aims to refute or falsify its predictions. Successful refutation forces revision of the model: the revised model persists as the "truth" until its predictions are, in turn, refuted. Thus, any scientific model should persist only as long as it resists refutation. An unusual feature of the exercise sciences is that certain core beliefs are based on an historical physiological model that, it will be argued, has somehow escaped modern, disinterested intellectual scrutiny. This particular model holds that the cardiovascular system has a limited capacity to supply oxygen to the active muscles, especially during maximal exercise. As a result, skeletal muscle oxygen demand outstrips supply causing the development of skeletal muscle hypoxia or even anaerobiosis during vigorous exercise. This hypoxia stimulates the onset of lactate production at the "anaerobic," "lactate," or ventilation thresholds and initiates biochemical processes that terminate maximal exercise. The model further predicts that the important effect of training is to increase oxygen delivery to and oxygen utilization by the active muscles during exercise. Thus, adaptations that reduce skeletal muscle anaerobiosis during exercise explain all the physiological, biochemical, and functional changes that develop with training. The historical basis for this model is the original research of Nobel Laureate A. V. Hill which was interpreted as evidence that oxygen consumption "plateaus" during progressive exercise to exhaustion, indicating the development of skeletal muscle anaerobiosis. This review confirms that Hill's research failed to establish the existence of the "plateau phenomenon" during exercise and argues that this core component of the historical model remains unproven. Furthermore, definitive evidence that skeletal muscle anaerobiosis develops during submaximal exercise at the anaerobic threshold initiating lactate production by muscle and its accumulation in blood is not currently available. The finding that exercise performance can improve and metabolism alter before there are measurable skeletal muscle mitochondrial adaptations could indicate that variables unrelated to oxygen use by muscle might explain some, if not all, training-induced changes. To accommodate these uncertainties, an alternate physiological model is proposed in which skeletal muscle contractile activity is regulated by a series of central, predominantly neural, and peripheral, predominantly chemical, regulators that act to prevent the development of organ damage or even death during exercise in both health and disease and under demanding environmental conditions. During maximal exercise, the peripheral regulation of skeletal muscle function and hence of oxygen use by skeletal muscle, perhaps by variables related to blood flow, would prevent the development of muscle rigor, especially in persons with an impaired capacity to produce ATP by mitochondrial or glycolytic pathways. Regulation of skeletal muscle contractile function by central mechanisms would prevent the development of hypotension and myocardial ischemia during exercise in persons with heart failure, of hyperthermia during exercise in the heat, and of cerebral hypoxia during exercise at extreme altitude. The challenge for future generations of exercise physiologists is to identify how the body anticipates the possibility of organ damage and evokes the appropriate control mechanism(s) at the appropriate instant.

Role of decreased carbohydrate oxidation on slower rises in ventilation with increasing exercise intensity after training

In these studies, we examined whether the rightward shift in steady-state minute ventilation (VE) versus O2 uptake curves after training is more closely linked to the reduced CO2 production from carbohydrate oxidation (CHOOX) after training than to the attenuated increase in blood lactate concentration. Steady state VE values and gas exchange were measured in eight previously sedentary men who underwent exercise tests of 60 W + 40 W every 6 min before and after a 9 week training programme of cycling approximately 40 min a day. Following training, the slower rises in VE with increasing exercise intensities were associated with a reduced reliance on CHOOX, (P < 0.01). Both before and after training, VE values in litres per minute rose as a linear VE = 18.CHOOX + 14, function of rates of CHOOX in grams per minute (r = 0.99), irrespective of a marked shift to the right in arterialized venous blood lactate concentration versus CHOOX curves following training (P < 0.01). Thus, slower increases in steady-state VE values with increasing exercise intensities following endurance training appeared to be more closely linked to the decreased reliance on CHOOX than to the attenuated increase in blood lactate concentration.