The response to submaximal ramp cycle exercise: Influence of ramp slope and training status

Assessing Acute Responses to Exercises Performed Within and at the Upper Boundary of Severe Exercise Domain

Purpose: The highest work-rate that provides maximal oxygen uptake (V ˙ O 2 m a x ) may be one of the best exercise stimuli to yield both V ˙ O 2 m a x and lactate accumulation. The aim of this study was to analyze physiological and metabolic acute responses of an exercise modality performed at the upper boundary of the severe exercise domain, and compare those responses with exercise modalities applied within the severe exercise domain. Method: Ten trained male cyclists participated in this study. The V ˙ O 2 m a x , corresponding power output (POVO2max), and the highest work-rate that provides the V ˙ O 2 m a x (IHIGH) were determined by constant work-rate exercises. Cyclists performed three high-intensity interval training (HIIT) strategies as follows; HIIT-1: 4-6 × 3-min at 95% of POVO2max with 1:1 (workout/rest ratio); HIIT-2: 16-18 × 1-min at 105% of POVO2max with 1:1; HIIT-3: 4-7 × 1-2-min at the IHIGH with 1:2. Capillary blood samples were analyzed before, immediately after HIIT sessions, and at the first, third, and fifth minutes of recovery periods. Lactate difference between the highest lactate response and resting status was considered as the peak lactate response for each HIIT modality. Results: Time spent at V ˙ O 2 m a x was greater at HIIT-1 and HIIT-3 (272 ± 127 and 208 ± 111 seconds, respectively; p = 0.155; effect size = 0.43) when compared to the HIIT-2 (~26 seconds; p < 0.001), while there was a greater lactate accumulation at HIIT-3 (~16 mmol·L-1) when compared to HIIT-1 and HIIT-2 (12 and 14 mmol·L-1, respectively; p < 0.001). Conclusions: In conclusion, HIIT-3 performed at IHIGH was successful to provide time spent at V ˙ O 2 m a x with a greater lactate accumulation in a single session.

Alterations in aerobic fitness and muscle deoxygenation during ramp incremental exercise in trained youth cyclists: a ~3-year longitudinal study

Alterations of aerobic fitness and muscle deoxygenation during a ramp incremental exercise test (GXT) were assessed on two occasions within a time-frame of 2.9 ± 0.1y in competitive youth cyclists. Nine cyclists (age, 14.5 ± 1.1y; peak oxygen uptake (V˙O_2peak), 62.6 ± 4.2 mL.min^-1.kg^-1) participated in this investigation. V˙O_2peak, the gas exchange threshold (GET) and the respiratory compensation point (RCP), as well as the muscle deoxygenation response pattern were determined during a GXT using open circuit spirometry and near-infrared spectroscopy, respectively. T-tests and Pearson's correlations were used to assess effects of time on the dependent variables and relationships between changes of parameter estimates of aerobic fitness and the muscle deoxygenation response, respectively. Workrate and metabolic rate at GET (33 ± 20 and 42 ± 23%) and RCP (36 ± 20 and 40 ± 22%), and V˙O_2peak (30 ± 18%) significantly increased throughout the study (P < 0.05). The muscle deoxygenation response showed a significant rightward shift from occasion one to two (P < 0.05). Alterations in the workrate/metabolic rate at RCP, and V˙O_2peak, were correlated with alterations of the muscle deoxygenation response (R = 0.71-0.89, P < 0.05). Together, this is thought to indicate a superior muscle perfusion within the tissue of interrogation at the same metabolic rate on occasion two vs. one, which partially contributed to the improved aerobic fitness in the cyclists herein.

Prolonged mean response time in older adults with cardiovascular risk compared to healthy older adults

Background

During incremental exercise (Inc-Ex), the mean response time (MRT) of oxygen uptake (V̇O₂) represents the time delay before changes in muscle V̇O₂ reflect at the mouth level. MRT calculation by linear regression or monoexponential (τ’) fitting of V̇O₂ data are known to be highly variable, and a combination of incremental and constant load exercise (CL-Ex) is more reproducible.

Methods

We evaluated MRT in older adults using linear regression and combination methods. We recruited 20 healthy adults (male: 9, 69.4 ± 6.8 years) and 10 cardiovascular risk subjects (male: 8, 73.0 ± 8.8 years). On day 1, they performed Inc-Ex using a 10W/min ramp protocol, for determination of the ventilatory anaerobic threshold (VAT) using the V-slope method. On day 2, they performed Inc-Ex to VAT exercise intensity and CL-Ex for 25min total. The MRT was calculated from the CL-Ex V̇O₂ average and the time at equivalent V̇O₂ in the Inc-Ex. We also assessed the amount of physical activity using the International Physical Activity Questionnaire short form (IPAQ-SF).

Results

The MRT of healthy participants and those at cardiovascular risk were 49.2 ± 36.3 vs. 83.6 ± 45.4s (p = 0.033). Total physical activity in the IPAQ-SF was inversely correlated with MRT.

Conclusion

The MRT was significantly prolonged in cardiovascular risk participants compared to healthy participants, possibly related to the amount of daily physical activity. Individual MRT may be useful for adjustment of exercise intensity, but this should also be based on daily physical activity and individual condition during exercise.

Elite versus non-elite cyclist - Stepping up to the international/elite ranks from U23 cycling

This study investigated the physiological, performance and training characteristics of U23 cyclists and assessed the requirements of stepping up to the elite/international ranks. Twenty highly trained U23 cyclists (age, 22.1 ± 0.8 years; body mass, 69.1 ± 6.8 kg; VO_2max, 76.1 ± 3.9 ml·kg^-1·min^-1) participated in this study. The cyclists were a posteriori divided into two groups based on whether or not they stepped up to elite/international level cycling (U23_ELITE vs. U23_NON-ELITE). Physiological, performance and training and racing characteristics were determined and compared between groups. U23_ELITE demonstrated higher absolute peak power output (p = .016), 2 min (p = .026) 5 min (p = .042) and 12 min (p ≤ .001) power output as well as higher absolute critical power (p = .002). Further, U23_ELITE recorded more accumulated hours (p ≤ .001), covered distance (p ≤ .001), climbing metres (p ≤ .001), total sessions (p ≤ .001), total work (p ≤ .001) and scored more UCI points (p ≤ .001). These findings indicate that U23_ELITE substantially differed from U23_NON-ELITE regarding physiological, performance and training and racing characteristics derived from laboratory and field. These variables should be considered by practitioners supporting young cyclists throughout their development towards the elite/international ranks.

Modeling VO2 on-kinetics based on intensity-dependent Delayed Adjustment and Loss of Efficiency (DALE)

This study presents and evaluates a new mathematical model of V̇O₂ on-kinetics, with the following properties: (i) a progressively slower primary phase following the size-principle of motor unit recruitment, explaining the delayed V̇O₂ steady state seen in the heavy exercise intensity domain, and (ii) a severe-domain slow component modelled as a time-dependent decrease in efficiency. Breath-by-breath V̇O₂ measurements from eight subjects performing step cycling transitions, in the moderate, heavy and severe exercise domains, were fitted to the conventional 3-phase model and the new model. Model performance was evaluated with a residual analysis and by comparing Bayesian (BIC) and corrected Akaike (AICc) information criteria. The residual analysis showed no systematic deviations, except perhaps for the initial part of the primary phase. BIC favored the new model, being 9.3 (SD 7.1) lower than the conventional model while AICc was similar between models. Compared to the conventional 3-phase model, the proposed model distinguishes between the kinetic adaptations in the heavy and severe domains by predicting a delayed steady state V̇O₂ in the heavy and no steady state V̇O₂ in the severe domain. This allows to determine when stable oxygen costs of exercise are attainable and it also represents a first step in defining time-dependent oxygen costs when stable energy conversion efficiency is not attainable.

Grey Zone: A Gap Between Heavy and Severe Exercise Domain

ABSTRACT

Ozkaya, O, Balci, GA, As, H, Cabuk, R, and Norouzi, M. Grey zone: A gap between heavy and severe exercise domain. J Strength Cond Res 36(1): 113-120, 2022-The aim of this study was to determine a critical threshold (CT) interpreted as "the highest exercise intensity where V̇o2 can be stabilized before reaching 95% of V̇o2max (V̇o2peak)" and compare it with commonly used anaerobic threshold indices. Ten well-trained male cyclists volunteered for this study. Ventilatory threshold (VT) was determined from incremental tests. Multisession constant-load trials were performed to reveal V̇o2max. Mathematically modeled critical power (CP) was estimated through the best individual fit parameter method. Maximal lactate steady state (MLSS) was detected by 30-minute constant-load exercises. The individual CT load of each cyclist was tested by constant-load exercises to exhaustion with +15 W intervals until minimal power output to elicit V̇o2peak. The results showed that work rate corresponding to CT (329.5 ± 41.5 W) was significantly greater than that of the MLSS (269.5 ± 38.5 W; p = 0.000), VT (279.6 ± 33 W; p = 0.000), and CP (306.3 ± 39.4 W; p = 0.000), and CP overestimated both VT and MLSS (p = 0.000). There was no significant V̇o2 difference between the 10th and 30th minute of MLSS and MLSS + 15 W exercise (0.36-0.13 ml·min-1·kg-1; p = 0.621). Exercising V̇o2 response of MLSS + 15 W could not exceed the level of 95% V̇o2max (57.02 ± 3.87 ml·min-1·kg-1 and 87.2 ± 3.1% of V̇o2max; p = 0.000), whereas V̇o2 responses greater than 95% of V̇o2max were always attained during exercises performed at CT + 15 W (64.52 ± 4.37 ml·min-1·kg-1 and 98.6 ± 1% of V̇o2max; p > 0.05). In conclusion, this study indicates that there is a "grey zone" between heavy and severe exercise domain. This information may play a key role in enhancing athletic performance by improving the quality of training programs.

W' Recovery Kinetics after Exhaustion: A Two-Phase Exponential Process Influenced by Aerobic Fitness

PURPOSE

The aims of this study were 1) to model the temporal profile of W' recovery after exhaustion, 2) to estimate the contribution of changing V˙O2 kinetics to this recovery, and 3) to examine associations with aerobic fitness and muscle fiber type (MFT) distribution.

METHODS

Twenty-one men (age = 25 ± 2 yr, V˙O2peak = 54.4 ± 5.3 mL·min-1·kg-1) performed several constant load tests to determine critical power and W' followed by eight trials to quantify W' recovery. Each test consisted of two identical exhaustive work bouts (WB1 and WB2), separated by a variable recovery interval of 30, 60, 120, 180, 240, 300, 600, or 900 s. Gas exchange was measured and muscle biopsies were collected to determine MFT distribution. W' recovery was quantified as observed W' recovery (W'OBS), model-predicted W' recovery (W'BAL), and W' recovery corrected for changing V˙O2 kinetics (W'ADJ). W'OBS and W'ADJ were modeled using mono- and biexponential fitting. Root-mean-square error (RMSE) and Akaike information criterion (∆AICC) were used to evaluate the models' accuracy.

RESULTS

The W'BAL model (τ = 524 ± 41 s) was associated with an RMSE of 18.6% in fitting W'OBS and underestimated W' recovery for all durations below 5 min (P < 0.002). Monoexponential modeling of W'OBS resulted in τ = 104 s with RMSE = 6.4%. Biexponential modeling of W'OBS resulted in τ1 = 11 s and τ2 = 256 s with RMSE = 1.7%. W'ADJ was 11% ± 1.5% lower than W'OBS (P < 0.001). ∆AICC scores favored the biexponential model for W'OBS, but not for W'ADJ. V˙O2peak (P = 0.009) but not MFT distribution (P = 0.303) was associated with W'OBS.

CONCLUSION

We showed that W' recovery from exhaustion follows a two-phase exponential time course that is dependent on aerobic fitness. The appearance of a fast initial recovery phase was attributed to an enhanced aerobic energy provision resulting from changes in V˙O2 kinetics.

A new technique to analyse threshold-intensities based on time dependent change-points in the ratio of minute ventilation and end-tidal partial pressure of carbon-dioxide production

The aim of this study was to test the utility and effectiveness of an alternative computational approach to threshold-intensities based on time dependent change-points in minute ventilation divided by end-tidal partial pressure of CO₂ (V_E/P_ETCO₂) to reveal whether respiratory compensation point (RCP) is a third ventilatory threshold, or not. Ten recreationally active young adults and ten well-trained athletes volunteered to take part in this study. Following incremental ramp tests, gas exchange threshold (GET) and respiratory compensation point (RCP) were respectively evaluated by the slopes of VCO₂-VO₂ and V_E-VCO₂ using the Innocor system automatically. Respiratory threshold (RT) was analysed based on time dependent change-points in the V_E/P_ETCO₂ using binary segmentation algorithm. Additionally, those intersections were analysed independently by two experienced investigators using a visual identification technique in a double-blind design. According to the results, in the recreationally active group, there were the first (GET₁) and the second (GET₂) gas exchange thresholds which were identical with the RT₁ (139 W; 1.9 L⋅min^-1 of VO₂; 1.73 L⋅min^-1 of VCO₂; 49.9 L⋅min^-1 of V_E versus 139 W; 1.88 L⋅min^-1; 1.7 L⋅min^-1; 49 L⋅min^-1, respectively) and RT₂ (186 W; 2.39 L⋅min^-1 of VO₂; 2.44 L⋅min^-1 of VCO₂; 66 L⋅min^-1 of V_E versus 187 W; 2.41 L⋅min^-1; 2.49 L⋅min^-1; 65.7 L⋅min^-1, respectively). However, there were three threshold intensities which were determined by GET₁, GET₂, and RCP in well-trained athletes. Additionally, RT₁, RT₂, and RT₃ were determined as valid surrogates of the GET₁ (194 W; 2.56 L⋅min^-1 of VO₂; 1.99 L⋅min^-1 of VCO₂; 57.5 L⋅min^-1 of V_E versus 192 W; 2.61 L⋅min^-1; 1.99 Lmin^-1; 57.7 L⋅min^-1, respectively), GET₂ (267 W; 3.6 L⋅min^-1 of VO₂; 3.29 L⋅min^-1 of VCO₂; 94.5 L⋅min^-1 of V_E versus 266 W; 3.58 L⋅min^-1; 3.26 L⋅min^-1; 93.4 L⋅min^-1, respectively), and RCP (324 W; 4.05 L⋅min^-1 of VO₂; 4.13 L⋅min^-1 of VCO₂; 124 L⋅min^-1 of V_E versus 322 W; 4.02 L⋅min^-1; 4.07 L⋅min^-1; 122 L⋅min^-1, respectively) in well-trained athletes. There were high levels of agreements between the power outputs determined by traditional techniques and newly proposed change-points in RT. All markers were strongly correlated (p < 0.001). It was shown that RT technique can provide an accurate threshold determination. Furthermore, the RCP was observed as a third threshold-intensity for well-trained athletes but not for recreationally active young adults.

Histamine H1 and H2 receptors are essential transducers of the integrative exercise training response in humans

Exercise training is a powerful strategy to prevent and combat cardiovascular and metabolic diseases, although the integrative nature of the training-induced adaptations is not completely understood. We show that chronic blockade of histamine H₁/H₂ receptors led to marked impairments of microvascular and mitochondrial adaptations to interval training in humans. Consequently, functional adaptations in exercise capacity, whole-body glycemic control, and vascular function were blunted. Furthermore, the sustained elevation of muscle perfusion after acute interval exercise was severely reduced when H₁/H₂ receptors were pharmaceutically blocked. Our work suggests that histamine H₁/H₂ receptors are important transducers of the integrative exercise training response in humans, potentially related to regulation of optimal post-exercise muscle perfusion. These findings add to our understanding of how skeletal muscle and the cardiovascular system adapt to exercise training, knowledge that will help us further unravel and develop the exercise-is-medicine concept.

Association between [Formula: see text]O2 kinetics and [Formula: see text]O2max in groups differing in fitness status

PURPOSE

This study evaluated (i) the relationship between oxygen uptake ([Formula: see text]O₂) kinetics and maximal [Formula: see text]O₂ ([Formula: see text]O_2max) within groups differing in fitness status, and (ii) the adjustment of [Formula: see text]O₂ kinetics compared to that of central [cardiac output (Q̇), heart rate (HR)] and peripheral (deoxyhemoglobin over [Formula: see text]O₂ ratio ([HHb]/[Formula: see text]O₂)] O₂ delivery, during step-transitions to moderate-intensity exercise.

METHODS

Thirty-six young healthy male participants (18 untrained; 18 trained) performed a ramp-incremental test to exhaustion and 3 step-transitions to moderate-intensity exercise. Q̇ and HR kinetics were measured in 18 participants (9 untrained; 9 trained).

RESULTS

No significant correlation between τ̇[Formula: see text]O₂ and [Formula: see text]O_2max was found in trained participants (r = 0.29; p > 0.05) whereas a significant negative correlation was found in untrained (r = - 0.58; p < 0.05) and all participants (r = - 0.82; p < 0.05). τQ̇ (18.8 ± 5.5 s) and τHR (20.1 ± 6.2 s) were significantly greater than τ[Formula: see text]O₂ (13.9 ± 2.7 s) for trained (p < 0.05). No differences were found between τQ̇ (22.8 ± 8.45 s), τHR (21.2 ± 8.3 s) and τ[Formula: see text]O₂ (28.9 ± 5.7 s) for untrained (p > 0.05). τQ̇ demonstrated a significant strong positive correlation with τHR in trained (r = 0.76; p < 0.05) but not untrained (r = 0.61; p > 0.05). A significant overshoot in the [HHb]/[Formula: see text]O₂ ratio was found in the untrained groups (p < 0.05) but not in the trained groups (p > 0.05) CONCLUSION: The results indicated that when comparing participants of different fitness status (i) there is a point at which greater V̇O_2max values are not accompanied by faster [Formula: see text]O₂ kinetics; (ii) central delivery of O₂ does not seem to limit the kinetics of [Formula: see text]O₂; and (iii) O₂ delivery within the active tissues might contribute to the slower [Formula: see text]O₂ kinetics response in untrained participants.

Impact of supine versus upright exercise on muscle deoxygenation heterogeneity during ramp incremental cycling is site specific

PURPOSE

We tested the hypothesis that incremental ramp cycling exercise performed in the supine position (S) would be associated with an increased reliance on muscle deoxygenation (deoxy[heme]) in the deep and superficial vastus lateralis (VLd and VLs, respectively) and the superficial rectus femoris (RFs) when compared to the upright position (U).

METHODS

11 healthy men completed ramp incremental exercise tests in S and U. Pulmonary [Formula: see text]O₂ was measured breath-by-breath; deoxy[heme] was determined via time-resolved near-infrared spectroscopy in the VLd, VLs and RFs.

RESULTS

Supine exercise increased the overall change in deoxy[heme] from baseline to maximal exercise in the VLs (S: 38 ± 23 vs. U: 26 ± 15 μM, P < 0.001) and RFs (S: 36 ± 21 vs. U: 25 ± 15 μM, P < 0.001), but not in the VLd (S: 32 ± 23 vs. U: 29 ± 26 μM, P > 0.05).

CONCLUSIONS

The present study supports that the impaired balance between O₂ delivery and O₂ utilization observed during supine exercise is a regional phenomenon within superficial muscles. Thus, deep muscle defended its O₂ delivery/utilization balance against the supine-induced reductions in perfusion pressure. The differential responses of these muscle regions may be explained by a regional heterogeneity of vascular and metabolic control properties, perhaps related to fiber type composition.

Effect of Hyperoxia on Critical Power and V˙O2 Kinetics during Upright Cycling

INTRODUCTION/PURPOSE

Critical power (CP) is a fundamental parameter defining high-intensity exercise tolerance; however, its physiological determinants are incompletely understood. The present study determined the impact of hyperoxia on CP, the time constant of phase II pulmonary oxygen uptake kinetics (τV˙O2), and muscle oxygenation (assessed by near-infrared spectroscopy) in nine healthy men performing upright cycle ergometry.

METHODS

Critical power was determined in normoxia and hyperoxia (fraction of inspired O2 = 0.5) via four severe-intensity constant load exercise tests to exhaustion on a cycle ergometer, repeated once in each condition. During each test, τV˙O2 and the time constant of muscle deoxyhemoglobin kinetics (τ[HHb]), alongside absolute concentrations of muscle oxyhemoglobin ([HbO2]), were determined.

RESULTS

Critical power was greater (hyperoxia, 216 ± 30 W vs normoxia, 197 ± 29 W; P < 0.001), whereas W' was reduced (hyperoxia, 15.4 ± 5.2 kJ; normoxia, 17.5 ± 4.3 W; P = 0.037) in hyperoxia compared with normoxia. τV˙O2 (hyperoxia, 35 ± 12 s vs normoxia, 33 ± 10 s; P = 0.33) and τ[HHb] (hyperoxia, 11 ± 5 s vs normoxia, 14 ± 5 s; P = 0.65) were unchanged between conditions, whereas [HbO2] during exercise was greater in hyperoxia compared with normoxia (hyperoxia, 73 ± 20 vs normoxia, 66 ± 15 μM; P < 0.001).

CONCLUSIONS

This study provides novel insights into the physiological determinants of CP and by extension, exercise tolerance. Microvascular oxygenation and CP were improved during exercise in hyperoxia compared with normoxia. Importantly, the improved microvascular oxygenation afforded by hyperoxia did not alter τV˙O2, suggesting that microvascular O2 availability is an independent determinant of the upper limit for steady-state exercise, that is, CP.

A Pilot Study on the Association of Mitochondrial Oxygen Metabolism and Gas Exchange During Cardiopulmonary Exercise Testing: Is There a Mitochondrial Threshold?

Background: Mitochondria are the key players in aerobic energy generation via oxidative phosphorylation. Consequently, mitochondrial function has implications on physical performance in health and disease ranging from high performance sports to critical illness. The protoporphyrin IX-triplet state lifetime technique (PpIX-TSLT) allows in vivo measurements of mitochondrial oxygen tension (mitoPO₂). Hitherto, few data exist on the relation of mitochondrial oxygen metabolism and ergospirometry-derived variables during physical performance. This study investigates the association of mitochondrial oxygen metabolism with gas exchange and blood gas analysis variables assessed during cardiopulmonary exercise testing (CPET) in aerobic and anaerobic metabolic phases. Methods: Seventeen volunteers underwent an exhaustive CPET (graded multistage protocol, 50 W/5 min increase), of which 14 were included in the analysis. At baseline and for every load level PpIX-TSLT-derived mitoPO₂ measurements were performed every 10 s with 1 intermediate dynamic measurement to obtain mitochondrial oxygen consumption and delivery (mito V . O₂, mito D . O₂). In addition, variables of gas exchange and capillary blood gas analyses were obtained to determine ventilatory and lactate thresholds (VT, LT). Metabolic phases were defined in relation to VT1 and VT2 (aerobic: <VT1, aerobic-anaerobic transition: ≥VT1 and <VT2 and anaerobic: ≥VT2). We used linear mixed models to compare variables of PpIX-TSLT between metabolic phases and to analyze their associations with variables of gas exchange and capillary blood gas analyses. Results: MitoPO₂ increased from the aerobic to the aerobic-anaerobic phase followed by a subsequent decline. A mitoPO₂ peak, termed mitochondrial threshold (MT), was observed in most subjects close to LT2. Mito D . O₂ increased during CPET, while no changes in mito V . O₂ were observed. MitoPO₂ was negatively associated with partial pressure of end-tidal oxygen and capillary partial pressure of oxygen and positively associated with partial pressure of end-tidal carbon dioxide and capillary partial pressure of carbon dioxide. Mito D . O₂ was associated with cardiovascular variables. We found no consistent association for mito V . O₂. Conclusion: Our results indicate an association between pulmonary respiration and cutaneous mitoPO₂ during physical exercise. The observed mitochondrial threshold, coinciding with the metabolic transition from an aerobic to an anaerobic state, might be of importance in critical care as well as in sports medicine.

Impact of supine exercise on muscle deoxygenation kinetics heterogeneity: mechanistic insights into slow pulmonary oxygen uptake dynamics

Oxygen uptake (V̇o₂) kinetics are slowed in the supine (S) position purportedly due to impaired muscle O₂ delivery ([Formula: see text]); however, these conclusions are predicated on single-site measurements in superficial muscle using continuous-wave near-infrared spectroscopy (NIRS). This study aimed to determine the impact of body position [i.e., upright (U) versus S] on deep and superficial muscle deoxygenation (deoxy[heme]) using time-resolved (TR-) NIRS, and how these relate to slowed pulmonary V̇o₂ kinetics. Seventeen healthy men completed constant power tests during 1) S heavy-intensity exercise and 2) U exercise at the same absolute work rate, with a subset of 10 completing additional tests at the same relative work rate as S. Pulmonary V̇o₂ was measured breath-by-breath and, deoxy- and total[heme] were resolved via TR-NIRS in the superficial and deep vastus lateralis and superficial rectus femoris. The fundamental phase V̇o₂ time constant was increased during S compared with U (S: 36 ± 10 vs. U: 27 ± 8 s; P < 0.001). The deoxy[heme] amplitude (S: 25-28 vs. U: 13-18 µM; P < 0.05) and total[heme] amplitude (S: 17-20 vs. U: 9-16 µM; P < 0.05) were greater in S compared with U and were consistent for the same absolute (above data) and relative work rates (n = 10, all P < 0.05). The greater deoxy- and total[heme] amplitudes in S vs. U supports that reduced perfusive [Formula: see text] in S, even within deep muscle, necessitated a greater reliance on fractional O₂ extraction and diffusive [Formula: see text]. The slower V̇o₂ kinetics in S versus U demonstrates that, ultimately, these adjustments were insufficient to prevent impairments in whole body oxidative metabolism.NEW & NOTEWORTHY We show that supine exercise causes a greater degree of muscle deoxygenation in both deep and superficial muscle and increases the spatial heterogeneity of muscle deoxygenation. Therefore, this study suggests that any O₂ delivery gradient toward deep versus superficial muscle is insufficient to mitigate impairments in oxidative function in response to reduced whole muscle O₂ delivery. More heterogeneous muscle deoxygenation is associated with slower V̇o₂ kinetics.

Physiological and anthropometric determinants of critical power, W' and the reconstitution of W' in trained and untrained male cyclists

Purpose

This study examined the relationship of physiological and anthropometric characteristics with parameters of the critical power (CP) model, and in particular the reconstitution of W′ following successive bouts of maximal exercise, amongst trained and untrained cyclists.

Methods

Twenty male adults (trained nine; untrained 11; age 39 ± 15 year; mass 74.7 ± 8.7 kg; V̇O_2max 58.0 ± 8.7 mL kg⁻¹ min⁻¹) completed three incremental ramps (20 W min⁻¹) to exhaustion interspersed with 2-min recoveries. Pearson’s correlation coefficients were used to assess relationships for W′ reconstitution after the first recovery (W′_rec1), the delta in W′ reconstituted between recoveries (∆W′_rec)_, CP and W′.

Results

CP was strongly related to V̇O_2max for both trained (r = 0.82) and untrained participants (r = 0.71), whereas W′ was related to V̇O_2max when both groups were considered together (r = 0.54). W′_rec1 was strongly related to V̇O_2max for the trained (r = 0.81) but not untrained (r = 0.18); similarly, ∆W′_rec was strongly related to V̇O_2max (r = − 0.85) and CP (r = − 0.71) in the trained group only.

Conclusions

Notable physiological relationships between parameters of aerobic fitness and the measurements of W′ reconstitution were observed, which differed among groups. The amount of W′ reconstitution and the maintenance of W′ reconstitution that occurred with repeated bouts of maximal exercise were found to be related to key measures of aerobic fitness such as CP and V̇O_2max. This data demonstrates that trained cyclists wishing to improve their rate of W′ reconstitution following repeated efforts should focus training on improving key aspects of aerobic fitness such as V̇O_2max and CP.

Effect of priming exercise and body position on pulmonary oxygen uptake and muscle deoxygenation kinetics during cycle exercise

We hypothesized that the performance of prior heavy exercise would speed pulmonary oxygen uptake (V̇o₂) kinetics (i.e., as described by the time constant, [Formula: see text]) and reduce the amplitude of muscle deoxygenation (deoxy[heme]) kinetics in the supine (S) but not upright (U) body position. Seventeen healthy men completed heavy-intensity constant-work rate exercise tests in S and U consisting of two bouts of 6-min cycling separated by 6-min cycling at 20 W. Pulmonary V̇o₂ was measured breath by breath; total and deoxy[heme] were determined via time-resolved near-infrared spectroscopy (NIRS) at three muscle sites. Priming exercise reduced [Formula: see text] in S (bout 1: 36 ± 10 vs. bout 2: 28 ± 10 s, P < 0.05) but not U (bout 1: 27 ± 8 s vs. bout 2: 25 ± 7 s, P > 0.05). Deoxy[heme] amplitude was increased after priming in S (bout 1: 25-28 μM vs. bout 2: 30-35 μM, P < 0.05) and U (bout 1: 13-18 μM vs. bout 2: 17-25 μM, P > 0.05), whereas baseline total[heme] was enhanced in S (bout 1: 110-179 μM vs. bout 2: 121-193 μM, P < 0.05) and U (bout 1: 123-186 μM vs. bout 2: 137-197 μM, P < 0.05). Priming exercise increased total[heme] in both S and U, likely indicating enhanced diffusive O₂ delivery. However, the observation that after priming the amplitude of the deoxy[heme] response was increased in S suggests that the reduction in [Formula: see text] subsequent to priming was related to a combination of both enhanced intracellular O₂ utilization and increased O₂ delivery.NEW & NOTEWORTHY Here we show that oxygen uptake (V̇o₂) kinetics are slower in the supine compared with upright body position, an effect that is associated with an increased amplitude of skeletal muscle deoxygenation in the supine position. After priming in the supine position, the amplitude of muscle deoxygenation remained markedly elevated above that observed during upright exercise. Hence, the priming effect cannot be solely attributed to enhanced O₂ delivery, and enhancements to intracellular O₂ utilization must also be contributory.

Sigmoidal VO2 on-kinetics: A new pattern in VO2 responses at the lower district of extreme exercise domain

The aim of the study was to analyse the VO₂ on-kinetics belonging to the work rates within the lower district of extreme exercise domain. Maximal O₂ utilisation and peak power outputs of eight well-trained cyclists were revealed by multisession trails. Critical threshold (CT) as the lower boundary of severe domain and aerobic limit power (ALP) as the upper boundary of severe domain were determined by multisession constant-load exercises. VO₂ on-kinetics over time were best fitted by multicomponent exponential models described by an initial concave-up response known as cardio-dynamic phase (τ = 18.2 ± 2.88 s; a = 1.56 ± 0.39 L·min^-1) before a primary concave-up phase (τ = 35.4 ± 12.4 s; a = 1.53 ± 0.36 L·min^-1), and then a slow component in two of the participants (τ = 80.8 ± 37 s; a = 0.47 ± 0.05 L·min^-1) or without a slow component in six of the participants during exercises performed at 50 W above the CT (R²≥0.96; SEE ≤ 0.24; p < 0.001). However, VO₂ on-kinetics over time belonging to exercises performed at 50 W above the ALP were best fitted by sigmoidal model (R²≥0.98; SEE ≤ 0.14; p < 0.001) in comparison with linear (R² = 0.37-0.66; SEE = 0.46-0.64; p < 0.01), or exponential functions (p> 0.05). Indeed, during those exercises, a short period of convex-up response (τ = 16.8 ± 3.1 s; a = 1.72 ± 0.39 L·min^-1) was determined just before a concave-up primary phase in VO₂ over time (τ = 24.6 ± 5.86 s; a = 1.31 ± 0.20 L·min^-1). It was shown that multicomponent exponential trend in VO₂ transformed into a sigmoidal shape, once the work rate exceeded the upper boundary of severe exercise domain.

Limitations to exercise tolerance in type 1 diabetes: the role of pulmonary oxygen uptake kinetics and priming exercise

We compared the time constant (τV̇O2) of the fundamental phase of pulmonary oxygen uptake (V̇o₂) kinetics between young adult men with type 1 diabetes and healthy control subjects. We also assessed the impact of priming exercise on τV̇O2, critical power, and muscle deoxygenation in a subset of participants with type 1 diabetes. Seventeen men with type 1 diabetes and 17 healthy male control subjects performed moderate-intensity exercise to determine τV̇O2. A subset of seven participants with type 1 diabetes performed an additional eight visits, in which critical power, τV̇O2, and muscle deoxyhemoglobin + myoglobin ([HHb+Mb], via near-infrared spectroscopy) kinetics (described by a time constant, τ_[HHb+Mb]) were determined with (PRI) and without (CON) a prior 6-min bout of heavy exercise. τV̇O2 was greater in participants with type 1 diabetes compared with control subjects (type 1 diabetes 50 ± 13 vs. control 32 ± 12 s; P < 0.001). Critical power was greater in PRI compared with CON (PRI 161 ± 25 vs. CON 149 ± 22 W; P < 0.001), whereas τV̇O2 (PRI 36 ± 15 vs. CON 50 ± 21 s; P = 0.006) and τ_[HHb+Mb] (PRI 10 ± 5 vs. CON 17 ± 11 s; P = 0.037) were reduced in PRI compared with CON. Type 1 diabetes patients showed slower pulmonary V̇o₂ kinetics compared with control subjects; priming exercise speeded V̇o₂ and [HHb + Mb] kinetics and increased critical power in a subgroup with type 1 diabetes. These data therefore represent the first characterization of the power-duration relationship in type 1 diabetes and the first experimental evidence that τV̇O2 is an independent determinant of critical power in this population.NEW & NOTEWORTHY Patients with type 1 diabetes demonstrated slower oxygen uptake (V̇o₂) kinetics compared with healthy control subjects. Furthermore, a prior bout of high-intensity exercise speeded V̇o₂ kinetics and increased critical power in people with type 1 diabetes. Prior exercise speeded muscle deoxygenation kinetics, indicating that V̇o₂ kinetics in type 1 diabetes are limited primarily by oxygen extraction and/or intracellular factors. These findings highlight the potential for interventions that decrease metabolic inertia for enhancing exercise tolerance in this condition.

Training-Induced Changes in the Respiratory Compensation Point, Deoxyhemoglobin Break Point, and Maximal Lactate Steady State: Evidence of Equivalence

PURPOSE

To evaluate whether the coherence in the oxygen uptake (V˙O2) associated with the respiratory compensation point (RCP), near-infrared spectroscopy-derived muscle deoxyhemoglobin ([HHb]) break point ([HHb]BP), and maximal lactate steady state (MLSS) would persist at the midpoint and endpoint of a 7-month training and racing season.

METHODS

Eight amateur male cyclists were tested in 3 separate phases over the course of a cycling season (PRE, MID, and POST). Testing at each phase included a ramp-incremental test to exhaustion to determine RCP and [HHb]BP. The PRE and POST phases also included constant power output rides to determine MLSS.

RESULTS

Compared with PRE, V˙O2 at both RCP and [HHb]BP was greater at MID (delta: RCP 0.23 [0.14] L·min-1, [HHb]BP 0.33 [0.17] L·min-1) and POST (delta: RCP 0.21 [0.12], [HHb]BP 0.30 [0.14] L·min-1) (P < .05). V˙O2 at MLSS also increased from PRE to POST (delta: 0.17 [12] L·min-1) (P < .05). V˙O2 was not different at RCP, [HHb]BP, and MLSS at PRE (3.74 [0.34], 3.64 [0.40], 3.78 [0.23] L·min-1) or POST (3.96 [0.25], 3.95 [0.32], 3.94 [0.18] L·min-1) respectively, and RCP (3.98 [0.33] L·min-1) and [HHb]BP (3.97 [0.34] L·min-1) were not different at MID (P > .05). PRE-MID and PRE-POST changes in V˙O2 associated with RCP, [HHb]BP, and MLSS were strongly correlated (range: r = .85-.90) and demonstrated low mean bias (range = -.09 to .12 L·min-1).

CONCLUSIONS

At all measured time points, V˙O2 at RCP, [HHb]BP, and MLSS were not different. Irrespective of phase comparison, direction, or magnitude of V˙O2 changes, intraindividual changes between each index were strongly related, indicating that interindividual differences were reflected in the group mean response and that their interrelationships are beyond coincidental.

Asthma, body mass and aerobic fitness, the relationship in adolescents: The exercise for asthma with commando Joe's® (X4ACJ) trial

Although an association has been suggested between asthma, obesity, fitness and physical activity, the relationship between these parameters remains to be elucidated in adolescents. Six-hundred and sixteen adolescents were recruited (334 boys; 13.0 ± 1.1years; 1.57 ± 0.10m; 52.6 ± 12.9kg), of which 155 suffered from mild-to-moderate asthma (78 boys). Participants completed a 20-metre shuttle run test, lung function and 7-day objective physical activity measurements and completed asthma control and quality of life questionnaires. Furthermore, 69 adolescents (36 asthma; 21 boys) completed an incremental ramp cycle ergometer test. Although participants with asthma completed significantly fewer shuttle runs than their peers, peak V̇O₂ did not differ between the groups. However, adolescents with asthma engaged in less physical activity (53.9 ± 23.5 vs 60.5 ± 23.6minutes) and had higher BMI (22.2 ± 4.8 vs 20.4 ± 3.7kg·m-2), than their peers. Whilst a significant relationship was found between quality of life and cardiorespiratory fitness according to peak V̇O₂, only BMI was revealed as a significant predictor of asthma status. The current findings highlight the need to use accurate measures of cardiorespiratory fitness rather than indirect estimates to assess the influence of asthma during adolescence. Furthermore, the present study suggests that BMI and fitness may be key targets for future interventions seeking to improve asthma quality of life.

Establishing the V̇o2 versus constant-work-rate relationship from ramp-incremental exercise: simple strategies for an unsolved problem

The dissociation between constant work rate of O₂ uptake (V̇o₂) and ramp V̇o₂ at a given work rate might be mitigated during slowly increasing ramp protocols. This study characterized the V̇o₂ dynamics in response to five different ramp protocols and constant-work-rate trials at the maximal metabolic steady state (MMSS) to characterize 1) the V̇o₂ gain (G) in the moderate, heavy, and severe domains, 2) the mean response time of V̇o₂ (MRT), and 3) the work rates at lactate threshold (LT) and respiratory compensation point (RCP). Eleven young individuals performed five ramp tests (5, 10, 15, 25, and 30 W/min), four to five time-to-exhaustions for critical power estimation, and two to three constant-work-rate trials for confirmation of the work rate at MMSS. G was greatest during the slowest ramp and progressively decreased with increasing ramp slopes (from ~12 to ~8 ml·min^-1·W^-1, P < 0.05). The MRT was smallest during the slowest ramp slopes and progressively increased with faster ramp slopes (1 ± 1, 2 ± 1, 5 ± 3, and 10 ± 4, 15 ± 6 W, P < 0.05). After "left shifting" the ramp V̇o₂ by the MRT, the work rate at LT was constant regardless of the ramp slope (~150 W, P > 0.05). The work rate at MMSS was 215 ± 55 W and was similar and highly correlated with the work rate at RCP during the 5 W/min ramp (P > 0.05, r = 0.99; Lin's concordance coefficient = 0.99; bias = -3 W; root mean square error = 6 W). Findings showed that the dynamics of V̇o₂ (i.e., G) during ramp exercise explain the apparent dichotomy existing with constant-work-rate exercise. When these dynamics are appropriately "resolved", LT is constant regardless of the ramp slope of choice, and RCP and MMSS display minimal variations between each other.NEW & NOTEWORTHY This study demonstrates that the dynamics of V̇o₂ during ramp-incremental exercise are dependent on the characteristics of the increments in work rate, such that during slow-incrementing ramp protocols the magnitude of the dissociation between ramp V̇o₂ and constant V̇o₂ at a given work rate is reduced. Accurately accounting for these dynamics ensures correct characterizations of the V̇o₂ kinetics at ramp onset and allows appropriate comparisons between ramp and constant-work-rate exercise-derived indexes of exercise intensity.

"Work-to-Work" exercise slows pulmonary oxygen uptake kinetics, decreases critical power, and increases W' during supine cycling

We have previously demonstrated that the phase II time constant of pulmonary oxygen uptake kinetics ( τ v ˙ o 2 ) is an independent determinant of critical power (CP) when O2 availability is not limiting, that is, during upright cycle exercise in young, healthy individuals. Whether this causative relationship remains when O2 availability is impaired remains unknown. During supine exercise, which causes an O2 availability limitation during the exercise transition, we therefore determined the impact of a raised baseline work rate on τ v ˙ o 2 and CP. CP, τ v ˙ o 2 , and muscle oxygenation status (the latter via near-infrared spectroscopy) were determined via four severe-intensity constant-power exercise tests completed in two conditions: (1) with exercise initiated from an unloaded cycling baseline (U→S), and (2) with exercise initiated from a moderate-intensity baseline work rate of 90% of the gas exchange threshold (M→S). In M→S, critical power was lower (U→S = 146 ± 39 W vs. M→S = 132 ± 33 W, P = 0.023) and τ v ˙ o 2 was greater (U→S = 45 ± 16 sec, vs. M→S = 69 ± 129 sec, P = 0.001) when compared to U→S. There was no difference in tissue oxyhemoglobin concentration ([HbO2  + MbO2 ]) at baseline or during exercise. The concomitant increase in τ v ˙ o 2 and reduction in CP during M→S compared to U→S shows for the first time that τ v ˙ o 2 is an independent determinant of CP in conditions where O2 availability is limiting.

Metabolic and performance-related consequences of exercising at and slightly above MLSS

Exercising at the maximal lactate steady state (MLSS) results in increased but stable metabolic responses. We tested the hypothesis that even a slight increase above MLSS (10 W), by altering the metabolic steady state, would reduce exercise performance capacity. Eleven trained men in our study performed: one ramp-incremental tests; two to four 30-minute constant-load cycling exercise trials to determine the PO at MLSS (MLSS_p ), and ten watts above MLSS (MLSS_p+10 ), which were immediately followed by a time-to-exhaustion test; and a time-to-exhaustion test with no-prior exercise. Pulmonary O₂ uptake V.O₂ ) and blood lactate concentration ([La^- ]_b ) as well as local muscle O₂ extraction ([HHb]) and muscle activity (EMG) of the vastus lateralis (VL) and rectus femoris (RF) muscles were measured during the testing sessions. When exercising at MLSS_p+10 , although V.O₂ was stable, there was an increase in ventilatory responses and EMG activity, along with a non-stable [La^- ]_b response (P < 0.05). The [HHb] of VL muscle achieved its apex at MLSS_p with no additional increase above this intensity, whereas the [HHb] of RF progressively increased during MLSS_p+10 and achieved its apex during the time-to-exhaustion trials. Time-to-exhaustion performance was decreased after exercising at MLSS_p (37.3 ± 16.4%) compared to the no-prior exercise condition, and further decreased after exercising at MLSS_p+10 (64.6 ± 6.3%) (P < 0.05). In summary, exercising for 30 min slightly above MLSS led to significant alterations of metabolic responses which disproportionately compromised subsequent exercise performance. Furthermore, the [HHb] signal of VL seemed to achieve a "ceiling" at the intensity of exercise associated with MLSS.

Elevated baseline work rate slows pulmonary oxygen uptake kinetics and decreases critical power during upright cycle exercise

Critical power is a fundamental parameter defining high-intensity exercise tolerance, and is related to the phase II time constant of pulmonary oxygen uptake kinetics (τV˙O2). Whether this relationship is causative is presently unclear. This study determined the impact of raised baseline work rate, which increases τV˙O2, on critical power during upright cycle exercise. Critical power was determined via four constant-power exercise tests to exhaustion in two conditions: (1) with exercise initiated from an unloaded cycling baseline (U→S), and (2) with exercise initiated from a baseline work rate of 90% of the gas exchange threshold (M→S). During these exercise transitions, τV˙O2 and the time constant of muscle deoxyhemoglobin kinetics (τ[HHb + Mb] ) (the latter via near-infrared spectroscopy) were determined. In M→S, critical power was lower (M→S = 203 ± 44 W vs. U→S = 213 ± 45 W, P = 0.011) and τV˙O2 was greater (M→S = 51 ± 14 sec vs. U→S = 34 ± 16 sec, P = 0.002) when compared with U→S. Additionally, τ[HHb + Mb] was greater in M→S compared with U→S (M→S = 28 ± 7 sec vs. U→S = 14 ± 7 sec, P = 0.007). The increase in τV˙O2 and concomitant reduction in critical power in M→S compared with U→S suggests a causal relationship between these two parameters. However, that τ[HHb + Mb] was greater in M→S exculpates reduced oxygen availability as being a confounding factor. These data therefore provide the first experimental evidence that τV˙O2 is an independent determinant of critical power. Keywords critical power, exercise tolerance, oxygen uptake kinetics, power-duration relationship, muscle deoxyhemoglobin kinetics, work-to-work exercise.

Prior exercise speeds pulmonary oxygen uptake kinetics and increases critical power during supine but not upright cycling

NEW FINDINGS

What is the central question of this study? Critical power (CP) represents the highest work rate for which a metabolic steady state is attainable. The physiological determinants of CP are unclear, but research suggests that CP might be related to the time constant of phase II oxygen uptake kinetics (τV̇O2). What is the main finding and its importance? We provide the first evidence that τV̇O2 is mechanistically related to CP. A reduction of τV̇O2 in the supine position was observed alongside a concomitant increase in CP. This effect may be contingent on measures of oxygen availability derived from near-infrared spectroscopy. Critical power (CP) is a fundamental parameter defining high-intensity exercise tolerance and is related to the time constant of phase II pulmonary oxygen uptake kinetics (τV̇O2). To test the hypothesis that this relationship is causal, we determined the impact of prior exercise ('priming') on CP and τV̇O2 in the upright and supine positions. Seventeen healthy men were assigned to either upright or supine exercise groups, whereby CP, τV̇O2 and muscle deoxyhaemoglobin kinetics (τ_[HHb] ) were determined via constant-power tests to exhaustion at four work rates with (primed) and without (control) priming exercise at ∼31%Δ. During supine exercise, priming reduced τV̇O2 (control 54 ± 18 s versus primed 39 ± 11 s; P < 0.001), increased τ_[HHb] (control 8 ± 4 s versus primed 12 ± 4 s; P = 0.003) and increased CP (control 177 ± 31 W versus primed 185 ± 30 W, P = 0.006) compared with control conditions. However, priming exercise had no effect on τV̇O2 (control 37 ± 12 s versus primed 35 ± 8 s; P = 0.82), τ_[HHb] (control 10 ± 5 s versus primed 14 ± 10 s; P = 0.10) or CP (control 235 ± 42 W versus primed 232 ± 35 W; P = 0.57) during upright exercise. The concomitant reduction of τV̇O2 and increased CP following priming in the supine group, effects that were absent in the upright group, provide the first experimental evidence that τV̇O2 is mechanistically related to critical power. The increased τ_[HHb+Mb] suggests that this effect was mediated, at least in part, by improved oxygen availability.

Peak oxygen uptake in a sprint interval testing protocol vs. maximal oxygen uptake in an incremental testing protocol and their relationship with cross-country mountain biking performance

In the literature, the exercise capacity of cyclists is typically assessed using incremental and endurance exercise tests. The aim of the present study was to confirm whether peak oxygen uptake (V̇O_2peak) attained in a sprint interval testing protocol correlates with cycling performance, and whether it corresponds to maximal oxygen uptake (V̇O_2max) determined by an incremental testing protocol. A sample of 28 trained mountain bike cyclists executed 3 performance tests: (i) incremental testing protocol (ITP) in which the participant cycled to volitional exhaustion, (ii) sprint interval testing protocol (SITP) composed of four 30 s maximal intensity cycling bouts interspersed with 90 s recovery periods, (iii) competition in a simulated mountain biking race. Oxygen uptake, pulmonary ventilation, work, and power output were measured during the ITP and SITP with postexercise blood lactate and hydrogen ion concentrations collected. Race times were recorded. No significant inter-individual differences were observed in regards to any of the ITP-associated variables. However, 9 individuals presented significantly increased oxygen uptake, pulmonary ventilation, and work output in the SITP compared with the remaining cyclists. In addition, in this group of 9 cyclists, oxygen uptake in SITP was significantly higher than in ITP. After the simulated race, this group of 9 cyclists achieved significantly better competition times (99.5 ± 5.2 min) than the other cyclists (110.5 ± 6.7 min). We conclude that mountain bike cyclists who demonstrate higher peak oxygen uptake in a sprint interval testing protocol than maximal oxygen uptake attained in an incremental testing protocol demonstrate superior competitive performance.

Gender differences in V˙O2 and HR kinetics at the onset of moderate and heavy exercise intensity in adolescents

The majority of the studies on V˙O2 kinetics in pediatric populations investigated gender differences in prepubertal children during submaximal intensity exercise, but studies are lacking in adolescents. The purpose of this study was to test the hypothesis that gender differences exist in the V˙O2 and heart rate (HR) kinetic responses to moderate (M) and heavy (H) intensity exercise in adolescents. Twenty-one healthy African-American adolescents (9 males, 15.8 ± 1.1 year; 12 females, 15.7 ± 1 year) performed constant work load exercise on a cycle ergometer at M and H. The V˙O2 kinetics of the male group was previously analyzed (Lai et al., Appl. Physiol. Nutr. Metab. 33:107-117, 2008b). For both genders, V˙O2 and HR kinetics were described with a single exponential at M and a double exponential at H. The fundamental time constant (τ₁) of V˙O2 was significantly higher in female than male at M (45 ± 7 vs. 36 ± 11 sec, P < 0.01) and H (41 ± 8 vs. 29 ± 9 sec, P < 0.01), respectively. The functional gain (G₁) was not statistically different between gender at M and statistically higher in females than males at H: 9.7 ± 1.2 versus 10.9 ± 1.3 mL min^-1 W^-1, respectively. The amplitude of the slow component was not significantly different between genders. The HR kinetics were significantly (τ₁, P < 0.01) slower in females than males at M (61 ± 16 sec vs. 45 ± 20 sec, P < 0.01) and H (42 ± 10 sec vs. 30 ± 8 sec, P = 0.03). The G₁ of HR was higher in females than males at M: 0.53 ± 0.11 versus 0.98 ± 0.2 bpm W^-1 and H: 0.40 ± 0.11 versus 0.73 ± 0.23 bpm W^-1, respectively. Gender differences in the V˙O2 and HR kinetics suggest that oxygen delivery and utilization kinetics of female adolescents differ from those in male adolescents.

Aerobic training enhances muscle deoxygenation in early post-myocardial infarction

Purpose

Exercise-induced skeletal muscle deoxygenation is startling by its absence in early post-myocardial infarction (MI) patients. Exercise training early post-MI is associated with reduced cardiovascular risk and increased aerobic capacity. We therefore investigated whether aerobic training could enhance the muscle deoxygenation in early post-MI patients.

Methods

21 ± 8 days after the first MI patients (n = 16) were divided into 12-week aerobic training (TR, n = 10) or non-training (CON, n = 6) groups. Before and after intervention, patients performed ramp bicycle exercise until exhaustion. Muscle deoxygenation was measured at vastus lateralis by near-infrared spectroscopy during exercise.

Results

Aerobic training significantly increased peak oxygen uptake (VO₂) (18.1 ± 3.0 vs. 22.9 ± 2.8 mL/kg/min), decreased the change in muscle oxygen saturation from rest to submaximal and peak exercise (∆SmO₂; 2.4 ± 5.7 vs. −7.0 ± 3.4 %), and increased the relative change in deoxygenated hemoglobin/myoglobin concentration from rest to submaximal (−1.5 ± 2.3 vs. 3.0 ± 3.6 μmol/L) and peak exercise (1.1 ± 4.5 vs. 8.2 ± 3.5 μmol/L). Change in total hemoglobin/myoglobin concentration in muscle was not significantly affected by training. In CON, no significant alterations were found after 12 weeks in either muscle deoxygenation or peak VO₂ (18.6 ± 3.8 vs. 18.9 ± 4.6 mL/kg/min). An increase in peak VO₂ was significantly negatively correlated with change in ∆SmO₂ (r = −0.65) and positively associated with change in ∆deoxy-Hb/Mb at peak exercise (r = 0.64) in TR.

Conclusions

In early post-MI patients, aerobic training enhanced skeletal muscle deoxygenation, and the enhancement was related to increased aerobic capacity.

Influence of muscle metabolic heterogeneity in determining the V̇o2p kinetic response to ramp-incremental exercise

The pulmonary O2 uptake (V̇o2p) response to ramp-incremental (RI) exercise increases linearly with work rate (WR) after an early exponential phase, implying that a single time constant (τ) and gain (G) describe the response. However, variability in τ and G of V̇o2p kinetics to different step increments in WR is documented. We hypothesized that the "linear" V̇o2p-WR relationship during RI exercise results from the conflation between WR-dependent changes in τ and G. Nine men performed three or four repeats of RI exercise (30 W/min) and two step-incremental protocols consisting of four 60-W increments beginning from 20 W or 50 W. During testing, breath-by-breath V̇o2p was measured by mass spectrometry and volume turbine. For each individual, the V̇o2p RI response was characterized with exponential functions containing either constant or variable τ and G values. A relationship between τ and G vs. WR was determined from the step-incremental protocols to derive the variable model parameters. τ and G increased from 21 ± 5 to 98 ± 20 s and from 8.7 ± 0.6 to 12.0 ± 1.9 ml·min(-1)·W(-1) for WRs of 20-230 W, respectively, and were best described by a second-order (τ) and a first-order (G) polynomial function of WR (lowest Akaike information criterion score). The sum of squared residuals was not different (P > 0.05) when the V̇o2p RI response was characterized with either the constant or variable models, indicating that they described the response equally well. Results suggest that τ and G increase progressively with WR during RI exercise. Importantly, these relationships may conflate to produce a linear V̇o2p-WR response, emphasizing the influence of metabolic heterogeneity in determining the apparent V̇o2p-WR relationship during RI exercise.

Constructing quasi-linear V̇O2 responses from nonlinear parameters

Oxygen uptake (V̇O2) kinetics have been shown to be governed by a nonlinear control system across a range of work rates. However, the linearity of the V̇O2 response to ramp incremental exercise would appear to be the result of a linear control system. This apparent contradiction could represent a balancing of changing V̇O2 kinetics parameter values across a range of work rates. To test this, six healthy men completed bouts of ramp incremental exercise at 15, 30, and 60 W/min (15R, 30R, 60R, respectively) and four bouts of an extended-step incremental exercise. V̇O2 parameter values were derived from the step exercise using two monoexponential models: one starting at time zero and encompassing the entire stage (MONO), and the other truncated to the first 5 min and allowing a time delay (5TD). The resulting parameter values were applied to an integrative model to estimate the ramp responses. As work rate increased, gain values increased (P < 0.001 for MONO and 5TD), as did mean response time (or time constant) values (MONO: P < 0.001; 5TD: P = 0.003). Up to maximal V̇O2 (V̇O(2 max)), the gains of the estimated ramp responses from both models were not different from the gains of the actual observed V̇O2 responses for 15R and 30R (15R: 11.3 ± 1.2, 11.7 ± 0.7, 10.9 ± 0.3; 30R: 10.5 ± 0.8, 11.0 ± 0.5, 10.7 ± 0.3 ml O2·min(-1)·W(-1), for actual, MONO, 5TD, respectively) but were significantly greater for 60R (8.7 ± 1.0, 9.9 ± 0.4, 10.3 ± 0.3 ml O2·min(-1)·W(-1) for actual, MONO, 5TD, respectively). Up to 80%V̇O(2 max) gain values were not significantly different for any ramp rate (P > 0.05 for all). We conclude that the apparent linearity of the V̇O2 response to ramp incremental exercise is consequent to a balancing of increasing time constant and gain parameter values.

Effect of pedaling cadence on muscle oxygenation during high-intensity cycling until exhaustion: a comparison between untrained subjects and triathletes

PURPOSE

The aim of this study was to compare the muscle oxygenation between trained and untrained subjects during heavy exercise until exhaustion at two extreme pedaling cadences using a NIRS system.

METHODS

Nine untrained male subjects and nine male competitive triathletes cycled until exhaustion at an intensity corresponding to 90 % of the power output achieved at peak oxygen uptake at 40 and 100 rpm. Gas exchanges were measured breath-by-breath during each exercise. Muscle (de)oxygenation was monitored continuously by near-infrared spectroscopy on the Vastus Lateralis.

RESULTS

Muscle deoxygenation (∆deoxy[Hb + Mb], i.e., O2 extraction) and ∆total[Hb + Mb] were significantly higher at 40 rpm compared to 100 rpm during the exercise in untrained subjects but not in triathletes (p < 0.05). The time performed until exhaustion was significantly higher at 40 than at 100 rpm in untrained subjects (373 ± 55 vs. 234 ± 37 s, respectively) but not in triathletes (339 ± 69 vs. 325 ± 66 s).

CONCLUSIONS

These results indicate that high aerobic fitness (1) allows for better regulation between [Formula: see text]O2M and VO2M following the change in pedaling cadence, and (2) is the most important factor in the relationship between pedaling cadence and performance.

Oxygen uptake kinetics and exercise capacity in children with cystic fibrosis

Exercise capacity, an objective measure of exercise intolerance, is known to predict quality of life and mortality in cystic fibrosis (CF). The mechanisms for exercise intolerance in patients with cystic fibrosis (CF), however, have yet to be fully elucidated. Accordingly, this study sought to investigate oxygen uptake kinetics and the impact of fat-free mass (FFM) on exercise capacity in young patients with CF. 16 young patients with CF (age 13 ± 4 years; 10 female) and 15 matched controls (age 14 ± 3 years; nine female) participated. Pulmonary function and a maximal exercise test on a cycle ergometer using the Godfrey protocol were performed. Exercise capacity (VO2 peak), VO2 response time (VO2 RT), and functional VO2 gain (ΔVO2 /ΔWR) were all determined. Lung function was the only demographic parameter significantly lower (P < 0.05) in CF compared to controls. Exercise capacity was lower in CF (P < 0.014) only when VO2 peak was normalized for FFM (43.5 ± 7.7 vs. 50.6 ± 7.4 ml/kg-FFM/min) or expressed as % predicted (70.1 ± 14.3 vs. 85.4 ± 16.0%). The VO2 RT was slower (36.1 ± 15.1 vs. 25.0 ± 12.4 sec; P = 0.03) and the ΔVO2 /ΔWR slope was lower (8.4 ± 3 ml/min/watt vs. 10.1 ± 1.4 ml/min/watt; P = 0.02) in patients compared to controls, respectively. In conclusion, a delayed VO2 response time coupled with the lower functional VO2 gain (ΔVO2 /ΔWR) suggest that young patients with CF have impairment in oxygen transport and oxygen utilization by the muscles. These data in addition to differences in VO2 peak normalized for FFM provide some insight that muscle mass and muscle metabolism contribute to exercise intolerance in CF.

VE/VCO2 slope and its prognostic value in patients with chronic heart failure

The minute ventilation/carbon dioxide production (VE/VCO₂) slope has been widely demonstrated to have strong prognostic value in patients with chronic heart failure (CHF), and the risk of mortality is believed to increase when the VE/VCO₂ slope is >32.8; however, there is little evidence concerning the prognostic value of the VE/VCO₂ slope in Chinese patients. In the present study, the prognostic value of the VE/VCO₂ slope was investigated in patients with CHF. A total of 258 subjects underwent symptom-limited cardiopulmonary exercise testing (CPET) and were divided into CHF (113 males and 16 females; LVEF <0.49) and control (106 males and 23 females) groups. The cardiac-related events over a median 33.7-month follow-up period subsequent to the CPET were evaluated using receiver operating characteristic curve analysis. The VE/VCO₂ slope was significantly different between the CHF and control groups (P<0.001). The area under the curve (AUC) for the VE/VCO₂ slope in predicting cardiac-related mortalities in the patients with CHF was 0.670 (P<0.05), and the sensitivity and specificity of the VE/VCO₂ slope were 0.667 and 0.620, respectively. The optimal threshold of the VE/VCO₂ slope for predicting cardiac-related mortalities in patients with CHF was ≥39.3. The AUC for the VE/VCO₂ slope in predicting cardiac-related hospitalizations in patients with CHF was 0.682 (P<0.05), and the sensitivity and specificity of the VE/VCO₂ slope were 0.631 and 0.778, respectively. The optimal threshold of the VE/VCO₂ slope for predicting cardiac-related hospitalizations in patients with CHF was ≥32.9. In conclusion, ventilatory efficiency decreases in patients with CHF. The VE/VCO₂ slope is a strong predictor of cardiac-related mortalities in the patients with CHF analyzed.

The impact of pedal rate on muscle oxygenation, muscle activation and whole-body VO₂ during ramp exercise in healthy subjects

PURPOSE

The aim of this project was to study the impact of pedal rate on breakpoints in muscle oxygenation (deoxy[Hb + Mb] and total[Hb + Mb]) and activation (iEMG and MPF) at high intensities during ramp exercise.

METHODS

Twelve physically active students performed incremental ramp exercises at 60 rpm, starting either at 50 or 80 W (i.e., 60rpm50 and 60rpm80), and at 100 rpm, starting at 50 W (100rpm50). Pulmonary VO2, muscle activation (iEMG and MPF) and oxygenation were recorded with EMG and NIRS, respectively. IEMG, MPF, deoxy[Hb + Mb] and total[Hb + Mb] were expressed as functions of work rate (WR) and pulmonary VO2 (%VO2peak) and analyzed with double-linear models.

RESULTS

The breakpoints (BP) of iEMG, MPF, total[Hb + Mb] and deoxy[Hb + Mb] in %VO2peak did not differ among the pedal rate conditions (P > 0.05), whereas the BPs in WR were significantly lower in 100rpm50 compared to 60rpm50 and 60rpm80 (P < 0.01). Across the pedal rate conditions the BP (in %VO2peak) of total[Hb + Mb] (82.7 ± 1.5 %VO2peak) was significantly lower (P < 0.01) compared to the BP in iEMG (84.3 ± 1.7 %VO2peak) and MPF (84.2 ± 1.6 %VO2peak), whereas the BP in deoxy[Hb + Mb] (87.4 ± 1.4 %VO2peak) and respiratory compensation point (89.9 ± 1.8 %VO2peak) were significantly higher (P < 0.01) compared to the BP in total[Hb + Mb], iEMG and MPF. Additionally, the BPs in iEMG, MPF, total[Hb + Mb] and deoxy[Hb + Mb], and the RCP were highly correlated (r > 0.90; P < 0.001).

CONCLUSIONS

The present study showed that muscle activation and oxygenation at high intensities during incremental exercise are related to pulmonary VO2 rather than external WR, with a close interrelationship between that muscle activation, oxygenation and pulmonary VO2.

Exercise: Kinetic considerations for gas exchange

The activities of daily living typically occur at metabolic rates below the maximum rate of aerobic energy production. Such activity is characteristic of the nonsteady state, where energy demands, and consequential physiological responses, are in constant flux. The dynamics of the integrated physiological processes during these activities determine the degree to which exercise can be supported through rates of O₂ utilization and CO₂ clearance appropriate for their demands and, as such, provide a physiological framework for the notion of exercise intensity. The rate at which O₂ exchange responds to meet the changing energy demands of exercise--its kinetics--is dependent on the ability of the pulmonary, circulatory, and muscle bioenergetic systems to respond appropriately. Slow response kinetics in pulmonary O₂ uptake predispose toward a greater necessity for substrate-level energy supply, processes that are limited in their capacity, challenge system homeostasis and hence contribute to exercise intolerance. This review provides a physiological systems perspective of pulmonary gas exchange kinetics: from an integrative view on the control of muscle oxygen consumption kinetics to the dissociation of cellular respiration from its pulmonary expression by the circulatory dynamics and the gas capacitance of the lungs, blood, and tissues. The intensity dependence of gas exchange kinetics is discussed in relation to constant, intermittent, and ramped work rate changes. The influence of heterogeneity in the kinetic matching of O₂ delivery to utilization is presented in reference to exercise tolerance in endurance-trained athletes, the elderly, and patients with chronic heart or lung disease.

Towards an individualized protocol for workload increments in cardiopulmonary exercise testing in children and adolescents with cystic fibrosis

BACKGROUND

There is no single optimal exercise testing protocol for children and adolescents with cystic fibrosis (CF) that differs widely in age and disease status. The aim of this study was to develop a CF-specific, individualized approach to determine workload increments for a cycle ergometry testing protocol.

METHODS

A total of 409 assessments consisting of maximal exercise data, anthropometric parameters, and lung function measures from 160 children and adolescents with CF were examined. 90% of the database was analyzed with backward linear regression with peak workload (W(peak)) as the dependent variable. Afterwards, we [1] used the remaining 10% of the database (model validation group) to validate the model's capacity to predict W(peak) and [2] validated the protocol's ability to provide a maximal effort within a 10±2 minute time frame in 14 adolescents with CF who were tested using this new protocol (protocol validation group).

RESULTS

No significant differences were seen in W(peak) and predicted W(peak) in the model validation group or in the protocol validation group. Eight of 14 adolescents with CF in the protocol validation group performed a maximal effort, and seven of them terminated the test within the 10±2 minute time frame. Backward linear regression analysis resulted in the following equation: W(peak) (W)=-142.865+2.998×Age (years)-19.206×Sex (0=male; 1=female)+1.328×Height (cm)+23.362×FEV(1) (L) (R=.89; R(2)=.79; SEE=21). Bland-Altman analysis showed no systematic bias between the actual and predicted W(peak).

CONCLUSION

We developed a CF-specific linear regression model to predict peak workload based on standard measures of anthropometry and FEV(1), which could be used to calculate individualized workload increments for a cycle ergometry testing protocol.

Effects of training at mild exercise intensities on quadriceps muscle energy metabolism in patients with chronic obstructive pulmonary disease

AIM

To study the effects of physical training at mild intensities on skeletal muscle energy metabolism in eight patients with chronic obstructive pulmonary disease (COPD) and eight paired healthy sedentary subjects.

METHODS

Energy metabolism of patients and controls vastus lateralis muscle was studied before and after 3 months of cycling training at mild exercises intensities.

RESULTS

The total amount of work accomplished was about 4059 ± 336 kJ in patients with COPD and 7531 ± 1693 kJ in control subjects. This work corresponds to a mechanical power set at 65.2 ± 7.5% of the maximum power for patients with COPD and 52 ± 3.3% of the maximum power in control group. Despite this low level of exercise intensities, we observed an improvement in mitochondrial oxidative phosphorylation through the creatine kinase system revealed by the increased apparent K(m) for ADP (from 105.5 ± 16.1 to 176.9 ± 26.5 μm, P < 0.05 in the COPD group and from 126.9 ± 16.8 to 177.7 ± 17.0, P > 0.05 in the control group). Meanwhile, maximal mechanical and metabolic power increased significantly from 83.1 ± 7.1 to 91.3 ± 7.4 Watts (P < 0.05) and from 16 ± 0.8 to 18.7 ± 0.98 mL O(2) kg(-1) min(-1) (P < 0.05) only in the COPD group.

CONCLUSION

This study shows that physical training at mild intensity is able to induce comparable changes in skeletal muscles oxidative energy metabolism in patients with COPD and sedentary healthy subjects, but different changes of maximal mechanical and metabolic power.

Resposta da cinética de consumo de oxigênio e da eficiência mecânica delta de homens e mulheres em diferentes intensidades de esforço

INTRODUÇÃO:A eficiência mecânica delta (EMΔ ) e a cinética do consumo de oxigênio (K<img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2) são influenciadas por parâmetros metabólicos musculares e pelo transporte de <img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2. O objetivo do presente estudo foi determinar a diferença na K<img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2 e na EMΔ em três intensidades de esforço nos dois gêneros. MÉTODOS: 56 sujeitos (26 mulheres) foram submetidos ao protocolo de esforço escalonado, contínuo e máximo (GxT) no cicloergômetro mecânico para determinação da potência aeróbia máxima (<img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2máx), carga máxima (Wmax), limiar anaeróbio (AT) e ponto de compensação respiratória (PCR). O AT foi determinado através dos métodos V-slope e E <img src="/img/revistas/rbme/v17n4/a13cr02.jpg" align="absmiddle" /><img src="/img/revistas/rbme/v17n4/a13cr02.jpg" align="absmiddle" />E / <img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2; o PCR através da relação <img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2 versus <img src="/img/revistas/rbme/v17n4/a13cr02.jpg" align="absmiddle" />E ; ambos por dois avaliadores. A EMΔ e a K <img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2 foram consideradas como a inclinação entre <img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2 versus Watts e <img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2 versus tempo (s), respectivamente, do começo do teste até o AT (S1), do AT ao PCR (S2) e do PCR ao <img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2máx (S3), determinada por análise de regressão linear. RESULTADOS: Para a EMΔ, diferenças significativas foram observadas entre S1 versus S2 (p = 0,001), S1 versus S3 (p = 0,001) e S2 versus S3 (p = 0,006). Não foi observada diferença (p = 0,060) ou interação significativa (p = 0,062) entre homens versus mulheres. Para a K <img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2 diferenças significativas foram observadas entre S1 versus S3 (p = 0,001) e S2 versus S3 (p = 0,001) em ambos gêneros. Diferenças (p = 0,001) e interação significativa (p = 0,006) foram observadas entre homens versus mulheres, no último parâmetro. CONCLUSÕES: A EMΔ decresce com o incremento da intensidade de trabalho, porém, não há diferenças quando se compara homens e mulheres. Por outro lado, as mulheres apresentam K <img src="/img/revistas/rbme/v17n4/a13cr01.jpg" align="absmiddle" />2 mais rápida do que os homens.