Oxygen uptake kinetics during severe intensity running and cycling

Prescription of High-intensity Aerobic Interval Training Based on Oxygen Uptake Kinetics

Endurance training results in diverse adaptations that lead to increased performance and health benefits. A commonly measured training response is the analysis of oxygen uptake kinetics, representing the demand of a determined load (speed/work) on the cardiovascular, respiratory, and metabolic systems, providing useful information for the prescription of constant load or interval-type aerobic exercise. There is evidence that during high-intensity aerobic exercise some interventions prescribe brief interval times (<1-min), which may lead to a dissociation between the load prescribed and the oxygen uptake demanded, potentially affecting training outcomes. Therefore, this review explored the time to achieve a close association between the speed/work prescribed and the oxygen uptake demanded after the onset of high-intensity aerobic exercise. The evidence assessed revealed that at least 80% of the oxygen uptake amplitude is reached when phase II of oxygen uptake kinetics is completed (1 to 2 minutes after the onset of exercise, depending on the training status). We propose that the minimum work-time during high-intensity aerobic interval training sessions should be at least 1 minute for athletes and 2 minutes for non-athletes. This suggestion could be used by coaches, physical trainers, clinicians and sports or health scientists for the prescription of high-intensity aerobic interval training.

High-intensity interval training: optimizing oxygen consumption and time to exhaustion taking advantage of the exponential reconstitution behaviour of D'

PURPOSE

Accumulating the time near maximum aerobic power [Formula: see text] is considered to be the most effective way to improve aerobic capacity. The aims of this study were: (1) to verify whether postponing the first recovery interval improves time to exhaustion during a high-intensity interval training (HIIT) test, and (2) to verify whether a HIIT protocol with decreasing interval duration (HIDIT) is more effective in accumulating time near [Formula: see text] compared with two classical protocols with short intervals (SI_HIIT) and long intervals (LI_HIIT).

METHODS

Nine active males (35 ± 11 years, [Formula: see text] 52 ± 5 mL·min^-1·kg^-1) performed a graded exercise test on an athletic track. Critical velocity and D' were estimated from three to five high-intensity trials to exhaustion. Then, the subjects performed three trials with a single recovery interval after 30 s (Rec_30s), after 3 min (Rec_3min) and after exhaustion (Rec_Tlim) to verify whether postponing the first recovery interval enhances the time to exhaustion. Finally, the subjects performed the three HIIT protocols mentioned above.

RESULTS

The time to exhaustion was significantly greater in Rec_Tlim (464 ± 67 s) than in Rec_3min (388 ± 48 s) (p < 0.0078) and Rec_30s (308 ± 44 s) (p > 0.0001). Additionally, it was significantly greater in Rec_3min than in Rec_30s (p = 0.0247). Furthermore, the time accumulated near [Formula: see text] was significantly longer in HIDIT (998 ± 129 s) than in SI_HIIT (678 ± 116 s) (p = 0.003) and LI_HIIT (673 ± 115 s) (p < 0.031).

CONCLUSIONS

During the trials, postponing the first recovery interval was effective in improving the time to exhaustion. Moreover, HIDIT was effective in prolonging the time near [Formula: see text].

The physiological, perceptual and neuromuscular responses of team sport athletes to a running and cycling high intensity interval training session

PURPOSE

The acute physiological, perceptual and neuromuscular responses to volume-matched running and cycling high intensity interval training (HIIT) were studied in team sport athletes.

METHODS

In a randomized cross-over design, 11 male team sport players completed 3 × 6 min (with 5 min between sets) repeated efforts of 15 s exercising at 120% speed (s[Formula: see text]O_2max) or power (p[Formula: see text]O_2max) at [Formula: see text]O_2max followed by 15 s passive recovery on a treadmill or cycle ergometer, respectively.

RESULTS

Absolute mean [Formula: see text]O₂ (ES [95% CI] = 1.46 [0.47-2.34], p < 0.001) and heart rate (ES [95% CI] = 1.53 [0.53-2.41], p = 0.001) were higher in running than cycling HIIT. Total time at > 90% [Formula: see text]O_2max during the HIIT was higher for running compared to cycling (ES [95% CI] = 1.21 [0.26-2.07], p = 0.015). Overall differential RPE (dRPE) (ES [95% CI] = 0.55 [- 0.32-1.38], p = 0.094) and legs dRPE (ES [95% CI] = - 0.65 [- 1.48-0.23], p = 0.111) were similar, whereas breathing dRPE (ES [95% CI] = 1.01 [0.08-1.85], p = 0.012) was higher for running. Maximal isometric knee extension force was unchanged after running (ES [95% CI] = - 0.04 [- 0.80-0.8], p = 0.726) compared to a moderate reduction after cycling (ES [95% CI] = - 1.17 [- 2.02-0.22], p = 0.001).

CONCLUSION

Cycling HIIT in team sport athletes is unlikely to meet the requirements for improving run-specific metabolic adaptation but might offer a greater lower limb neuromuscular load.

Novel CPET Reference Values in Healthy Adults: Associations with Physical Activity

PURPOSE

Cardiopulmonary exercise testing (CPET) is an important measurement in clinical practice, and its primary outcome, maximal oxygen uptake (V˙O2peak), is inversely associated with morbidity and mortality. The purposes of this study are to provide CPET reference values for maximal and submaximal parameters across the adult age spectrum of a healthy European cohort, to compare V˙O2peak values with other reference data sets, and to analyze the associations between physical activity (PA) levels and CPET parameters.

METHODS

In this cross-sectional study, we prospectively recruited 502 participants (47% female) from 20 to 90 yr old. The subjects performed a CPET on a cycle ergometer using a ramp protocol. PA was objectively and continuously measured over 14 d using a triaxial accelerometer. Quantile curves were calculated for CPET parameters. To investigate the associations between CPET parameters and PA levels, linear regression analysis was performed.

RESULTS

V˙O2peak values observed in the group of 20-29 yr were 46.6 ± 7.9 and 39.3 ± 6.5 mL·kg⋅min for males and females, respectively. On average, each age category (10-yr increments) showed a 10% lower V˙O2peak relative to the next younger age category. V˙O2peak values of previous studies were on average 7.5 mL·kg⋅min (20%) lower for males and 6.5 mL·kg⋅min (21%) lower for females. There was strong evidence supporting a positive association between the V˙O2peak (mL·kg⋅min) and the level of habitual PA performed at vigorous PA (estimate, 0.26; P < 0.001].

CONCLUSION

Maximal and submaximal CPET reference values over a large age range are novel, and differences to other studies are clinically highly relevant. Objectively measured vigorous-intensity PA showed a strong positive association with higher V˙O2peak and other performance-related CPET parameters, supporting the implementation of higher-intensity aerobic exercise in health promotion.

Oxidative ATP synthesis in human quadriceps declines during 4 minutes of maximal contractions

KEY POINTS

During maximal exercise, skeletal muscle metabolism and oxygen consumption remain elevated despite precipitous declines in power. Presently, it is unclear whether these responses are caused by an increased ATP cost of force generation (ATP_COST ) or mitochondrial uncoupling; a process that reduces the efficiency of oxidative ATP synthesis (ATP_OX ). To address this gap, we used 31-phosphorus magnetic resonance spectroscopy to measure changes in ATP_COST and ATP_OX in human quadriceps during repeated trials of maximal intensity knee extensions lasting up to 4 min. ATP_COST remained unchanged. In contrast, ATP_OX plateaued by ∼2 min and then declined (∼15%) over the final 2 min. The maximal capacity for ATP_OX (V_max ), as well as ADP-specific rates of ATP_OX , were also significantly diminished. Collectively, these results suggest that mitochondrial uncoupling, and not increased ATP_COST , is responsible for altering the regulation of skeletal muscle metabolism and oxygen consumption during maximal exercise.

ABSTRACT

The relationship between skeletal muscle oxygen consumption and power output is augmented during exercise at workloads above the lactate threshold. Potential mechanisms for this response have been hypothesized, including increased ATP cost of force generation (ATP_COST ) and mitochondrial uncoupling, a process that reduces the efficiency of oxidative ATP synthesis (ATP_OX ). To test these hypotheses, we used phosphorus magnetic resonance spectroscopy to non-invasively measure changes in phosphate concentrations and pH in the vastus lateralis muscle of nine young adults during repeated trials of maximal, all-out dynamic knee extensions (120°s^-1 , 1 every 2 s) lasting 24, 60, 120, and 240 s. ATP_OX was measured at each time point from the initial velocity of PCr resynthesis, and ATP_COST was calculated as the sum of ATP synthesized by the creatine and adenylate kinase reactions, non-oxidative glycolysis, ATP_OX and net changes in [ATP]. Power output declined in a reproducible manner for all four trials. ATP_COST did not change over time (main effect P = 0.45). ATP_OX plateaued from 60 to 120 s and then decreased over the final 120 s (main effect P = 0.001). The maximal capacity for oxidative ATP synthesis (V_max ), as well as ADP-specific rates of ATP_OX , also decreased over time (main effect P = 0.001, both). Collectively, these results demonstrate that prolonged maximal contraction protocols impair oxidative energetics and implicate mitochondrial uncoupling as the mechanism for this response. The causes of mitochondrial uncoupling are presently unknown but may offer a potential explanation for the dissociation between skeletal muscle power output and oxygen consumption during maximal, all-out exercise protocols.

Mechanistic and methodological perspectives on the impact of intense interval training on post-exercise metabolism

The post-exercise recovery period is associated with an elevated metabolism known as excess post-exercise oxygen consumption (EPOC). The relationship between exercise duration and EPOC magnitude is thought to be linear whereas the relationship between EPOC magnitude and exercise intensity is thought to be exponential. Accordingly, near-maximal and supramaximal protocols such as high-intensity interval training (HIIT) and sprint interval training (SIT) protocols have been hypothesized to produce greater EPOC magnitudes than submaximal moderate-intensity continuous training (MICT). This review updates previous reviews by focusing on the impact of HIIT and SIT on EPOC. Research to date suggests small differences in EPOC post-HIIT compared to MICT in the immediate (<1 hour) recovery period, but greater EPOC values post-HIIT when examined over 24 hours. Conversely, differences in EPOC post-SIT are more pronounced, as SIT tends to produce a larger EPOC vs MICT at all time points. We discuss potential mechanisms that may drive the EPOC response to interval training (eg, glycogen resynthesis, mitochondrial uncoupling, and protein turnover among others) and also consider the role of EPOC as one of the potential contributors to fat loss following HIIT/SIT interventions. Lastly, we highlight a number of methodological shortcomings related to the measurement of EPOC following HIIT and SIT.

Exercise tolerance during flat over-ground intermittent running: modelling the expenditure and reconstitution kinetics of work done above critical power

Purpose

We compared a new locomotor-specific model to track the expenditure and reconstitution of work done above critical power (W´) and balance of W´ (W´_BAL) by modelling flat over-ground power during exhaustive intermittent running.

Method

Nine male participants completed a ramp test, 3-min all-out test and the 30–15 intermittent fitness test (30–15 IFT), and performed a severe-intensity constant work-rate trial (S_CWR) at the maximum oxygen uptake velocity (vV̇O_2max). Four intermittent trials followed: 60-s at vV̇O_2max + 50% Δ₁ (Δ₁ = vV̇O_2max − critical velocity [V_Crit]) interspersed by 30-s in light (S_L; 40% vV̇O_2max), moderate (S_M; 90% gas-exchange threshold velocity [V_GET]), heavy (S_H; V_GET + 50% Δ₂ [Δ₂ = V_Crit − V_GET]), or severe (S_S; vV̇O_2max − 50% Δ₁) domains. Data from Global Positioning Systems were derived to model over-ground power. The difference between critical and recovery power (D_CP), time constant for reconstitution of W´ (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau_{{W^{\prime}}}$$\end{document}τW′), time to limit of tolerance (T_LIM), and W´_BAL from the integral (W´_BALint), differential (W´_BALdiff), and locomotor-specific (OG-W´_BAL) methods were compared.

Results

The relationship between \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau_{{W^{\prime}}}$$\end{document}τW′ and D_CP was exponential (r² = 0.52). The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau_{{W^{{\prime}}}}$$\end{document}τW′ for S_L, S_M, and S_H trials were 119 ± 32-s, 190 ± 45-s, and 336 ± 77-s, respectively. Actual T_LIM in the 30–15 IFT (968 ± 117-s) compared closely to T_LIM predicted by OG-W´_BAL (929 ± 94-s, P > 0.100) and W´_BALdiff (938 ± 84-s, P > 0.100) but not to W´_BALint (848 ± 91-s, P = 0.001).

Conclusion

The OG-W´_BAL accurately tracked W´ kinetics during intermittent running to exhaustion on flat surfaces.

The Severe Exercise Domain Amplitude: A Comparison Between Endurance Runners and Cyclists

PURPOSE

Metabolic perturbation and V˙O2 on-kinetics are potential modifiers of fatigue and vary in importance depending on the exercise task. Thus, performance fatigability during high-intensity exercise seems to be exercise mode dependent, affecting tolerance in the severe domain. However, the effects of exercise mode on severe domain amplitude are still unknown. The aims of this study were to compare the severe domain amplitude in endurance runners and cyclists and to verify its possible determinants.

METHODS

Ten runners and eleven cyclists were tested to determine V˙O2 max, maximal velocity/power output of incremental test (v V˙O2 max/p V˙O2 max), critical velocity/power (CV/CP), distance/work above CV/CP (D'/W'), and the highest velocity/power output which V˙O2 max is attained during constant exercise (V_HIGH/P_HIGH). The severe domain amplitude was considered as V_HIGH/P_HIGH relative to CV/CP.

RESULTS

When normalized by v V˙O2 max/p V˙O2 max, although V_HIGH and P_HIGH were similar, CV (89.0 ± 2.2% v V˙O2 max) was higher than CP (84.0 ± 4.1% p V˙O2 max; p < .05; ES = 1.51). Consequently, the severe domain amplitude was higher in cyclists (153.6 ± 14.4% CP vs. 137.2 ± 14.6% CV; p < .05; ES = 1.13). Runners presented faster V˙O2 on-kinetics than cyclists at V_HIGH/P_HIGH. The severe domain amplitude was correlated with D' (r = .65) and W' (r = .71), but not with V˙O2 on-kinetics.

CONCLUSIONS

Cyclists have a lower CP (%p V˙O2 max) and a greater severe domain amplitude than runners, providing a greater range of intensities for attainment of V˙O2 max. Furthermore, the severe domain amplitude appears to be linked to finite energy reserves, but unrelated to V˙O2 on-kinetics.

Oxygen uptake kinetics and speed-time correlates of modified 3-minute all-out shuttle running in soccer players

How parameters derived from oxygen uptake V˙O2 kinetics relate to critical speed is not fully understood, and how such parameters relate to more sport-specific performances, such as shuttle running, has not been investigated. Therefore, the primary aims of the present student were to examine the V˙O2 kinetics during all-out linear and shuttle running and compare physiological variables of all-out running to variables measured during a graded exercise test (GXT). Fifteen male soccer players performed a graded exercise test (GXT) and the V˙O2 kinetics from a series of three different 3-min all-out tests (3MT’s) were evaluated. V˙O2max achieved during the GXT did not differ from maximal V˙O2 achieved during the all-out tests (F = 1.85, p = 0.13) (overall ICC = 0.65; typical error = 2.48 ml∙kg^-1∙min^-1; coefficient of variation = 4.8%). A moderate, inverse correlation (r = -0.62, p = 0.02) was observed between τ (14.7 ± 1.92 s) and CS (3.96 ± 0.52 m∙s^-1) despite the narrow SD for τ. No differences (p > 0.05) were observed for any of the V˙O2 kinetics between continuous and shuttle running bouts. The linear running 3MT (r3MT) represents a viable surrogate to the GXT and data beyond CS and D’ may be gleaned by using the bi-exponential speed-time model.

The effect of running versus cycling high-intensity intermittent exercise on local tissue oxygenation and perceived enjoyment in 18-30-year-old sedentary men

BACKGROUND

High-intensity interval training (HIIT) has been proposed as a time-efficient exercise format to improve exercise adherence, thereby targeting the chronic disease burden associated with sedentary behaviour. Exercise mode (cycling, running), if self-selected, will likely affect the physiological and enjoyment responses to HIIT in sedentary individuals. Differences in physiological and enjoyment responses, associated with the mode of exercise, could potentially influence the uptake and continued adherence to HIIT. It was hypothesised that in young sedentary men, local and systemic oxygen utilisation and enjoyment would be higher during a session of running HIIT, compared to a session of cycling HIIT.

METHODS

A total of 12 sedentary men (mean ± SD; age 24 ± 3 years) completed three exercise sessions: a maximal incremental exercise test on a treadmill (MAX) followed by two experiment conditions, (1) free-paced cycling HIIT on a bicycle ergometer (HIITCYC) and (2) constant-paced running HIIT on a treadmill ergometer (HIITRUN). Deoxygenated haemoglobin (HHb) in the gastrocnemius (GN), the left vastus lateralis (LVL) and the right vastus lateralis (RVL) muscles, oxygen consumption (VO2), heart rate (HR), ratings of perceived exertion (RPE) and physical activity enjoyment (PACES) were measured during HIITCYC and HIITRUN.

RESULTS

There was a higher HHb in the LVL (p = 0.001) and RVL (p = 0.002) sites and a higher VO2 (p = 0.017) and HR (p < 0.001) during HIITCYC, compared to HIITRUN. RPE was higher (p < 0.001) and PACES lower (p = 0.032) during HIITCYC compared to HIITRUN.

DISCUSSION

In sedentary individuals, free-paced cycling HIIT produces higher levels of physiological stress when compared to constant-paced running HIIT. Participants perceived running HIIT to be more enjoyable than cycling HIIT. These findings have implications for selection of mode of HIIT for physical stress, exercise enjoyment and compliance.

Oxygen Uptake Kinetics Is Slower in Swimming Than Arm Cranking and Cycling during Heavy Intensity

Oxygen uptake (V·O2) kinetics has been reported to be influenced by the activity mode. However, only few studies have compared V·O₂ kinetics between activities in the same subjects in which they were equally trained. Therefore, this study compared the V·O₂ kinetics response to swimming, arm cranking, and cycling within the same group of subjects within the heavy exercise intensity domain. Ten trained male triathletes (age 23.2 ± 4.5 years; height 180.8 ± 8.3 cm; weight 72.3 ± 6.6 kg) completed an incremental test to exhaustion and a 6-min heavy constant-load test in the three exercise modes in random order. Gas exchange was measured by a breath-by-breath analyzer and the on-transient V·O₂ kinetics was modeled using bi-exponential functions. V·O_2peak was higher in cycling (65.6 ± 4.0 ml·kg⁻¹·min⁻¹) than in arm cranking or swimming (48.7 ± 8.0 and 53.0 ± 6.7 ml·kg⁻¹·min⁻¹; P < 0.01), but the V·O₂ kinetics were slower in swimming (τ₁ = 31.7 ± 6.2 s) than in arm cranking (19.3 ± 4.2 s; P = 0.001) and cycling (12.4 ± 3.7 s; P = 0.001). The amplitude of the primary component was lower in both arm cranking and swimming (21.9 ± 4.7 and 28.4 ± 5.1 ml·kg⁻¹·min⁻¹) compared with cycling (39.4 ± 4.1 ml·kg⁻¹·min⁻¹; P = 0.001). Although the gain of the primary component was higher in arm cranking compared with cycling (15.3 ± 4.2 and 10.7 ± 1.3 ml·min⁻¹·W⁻¹; P = 0.02), the slow component amplitude, in both absolute and relative terms, did not differ between exercise modes. The slower V·O₂ kinetics during heavy-intensity swimming is exercise-mode dependent. Besides differences in muscle mass and greater type II muscle fibers recruitment, the horizontal position adopted and the involvement of trunk and lower-body stabilizing muscles could be additional mechanisms that explain the differences between exercise modalities.

A comparison of methods to estimate anaerobic capacity: Accumulated oxygen deficit and W' during constant and all-out work-rate profiles

This study investigated (i) whether the accumulated oxygen deficit (AOD) and curvature constant of the power-duration relationship (W') are different during constant work-rate to exhaustion (CWR) and 3-min all-out (3MT) tests and (ii) the relationship between AOD and W' during CWR and 3MT. Twenty-one male cyclists (age: 40 ± 6 years; maximal oxygen uptake [V̇O_2max]: 58 ± 7 ml · kg^-1 · min^-1) completed preliminary tests to determine the V̇O₂-power output relationship and V̇O_2max. Subsequently, AOD and W' were determined as the difference between oxygen demand and oxygen uptake and work completed above critical power, respectively, in CWR and 3MT. There were no differences between tests for duration, work, or average power output (P ≥ 0.05). AOD was greater in the CWR test (4.18 ± 0.95 vs. 3.68 ± 0.98 L; P = 0.004), whereas W' was greater in 3MT (9.55 ± 4.00 vs. 11.37 ± 3.84 kJ; P = 0.010). AOD and W' were significantly correlated in both CWR (P < 0.001, r = 0.654) and 3MT (P < 0.001, r = 0.654). In conclusion, despite positive correlations between AOD and W' in CWR and 3MT, between-test differences in the magnitude of AOD and W', suggest that both measures have different underpinning mechanisms.

Physiological Responses During the Time Limit at 100% of the Peak Velocity in the Carminatti's Test in Futsal Players

The aim of this study was to investigate the physiological responses during the time limit at the intensity of the peak velocity of the Carminatti's test (T-CAR). Ten professional futsal players (age, 27.4 ± 5.8 years, body mass, 78.8 ± 8.5 kg, body height, 175.8 ± 6.8 cm, body fat mass, 14.1 ± 2.6%) took part in the study. The players performed three tests, with an interval of at least 48 hours, as follows: the T-CAR to determine the peak velocity and the maximal heart rate; an incremental treadmill protocol to determine the maximal physiological responses; and a time limit running test at the peak velocity reached in the T-CAR. During the last two tests, a portable gas analyzer was used for direct measurement of cardiorespiratory variables. It was shown that the peak velocity was not significantly different from the maximal aerobic speed achieved in the laboratory (p = 0.213). All athletes reached their maximum oxygen uptake during the time limit test. The maximum oxygen uptake achieved during the time limit test was not different from that observed in the laboratory condition (51.1 ± 4.7 vs. 49.6 ± 4.7 ml·kg^-1·min^-1, respectively, p = 0.100). In addition, Bland and Altman plots evidenced acceptable agreement between them. On average, athletes took ~140 s to achieve maximum oxygen uptake and maintained it for ~180 s. Therefore, the peak velocity intensity can be used as an indicator of maximal aerobic power of futsal athletes and the time limit can be used as a reference for training prescription.

β-alanine supplementation to improve exercise capacity and performance: a systematic review and meta-analysis

OBJECTIVE

To conduct a systematic review and meta-analysis of the evidence on the effects of β-alanine supplementation on exercise capacity and performance.

DESIGN

This study was designed in accordance with PRISMA guidelines. A 3-level mixed effects model was employed to model effect sizes and account for dependencies within data.

DATA SOURCES

3 databases (PubMed, Google Scholar, Web of Science) were searched using a number of terms ('β-alanine' and 'Beta-alanine' combined with 'supplementation', 'exercise', 'training', 'athlete', 'performance' and 'carnosine').

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Inclusion/exclusion criteria limited articles to double-blinded, placebo-controlled studies investigating the effects of β-alanine supplementation on an exercise measure. All healthy participant populations were considered, while supplementation protocols were restricted to chronic ingestion. Cross-over designs were excluded due to the long washout period for skeletal muscle carnosine following supplementation. A single outcome measure was extracted for each exercise protocol and converted to effect sizes for meta-analyses.

RESULTS

40 individual studies employing 65 different exercise protocols and totalling 70 exercise measures in 1461 participants were included in the analyses. A significant overall effect size of 0.18 (95% CI 0.08 to 0.28) was shown. Meta-regression demonstrated that exercise duration significantly (p=0.004) moderated effect sizes. Subgroup analyses also identified the type of exercise as a significant (p=0.013) moderator of effect sizes within an exercise time frame of 0.5-10 min with greater effect sizes for exercise capacity (0.4998 (95% CI 0.246 to 0.753)) versus performance (0.1078 (95% CI -0.201 to 0.416)). There was no moderating effect of training status (p=0.559), intermittent or continuous exercise (p=0.436) or total amount of β-alanine ingested (p=0.438). Co-supplementation with sodium bicarbonate resulted in the largest effect size when compared with placebo (0.43 (95% CI 0.22 to 0.64)).

SUMMARY/CONCLUSIONS

β-alanine had a significant overall effect while subgroup analyses revealed a number of modifying factors. These data allow individuals to make informed decisions as to the likelihood of an ergogenic effect with β-alanine supplementation based on their chosen exercise modality.

Ventilatory and Physiological Responses in Swimmers Below and Above Their Maximal Lactate Steady State

The purpose of this study was to understand the ventilatory and physiological responses immediately below and above the maximal lactate steady-state (MLSS) velocity and to determine the relationship of oxygen uptake (VO2) kinetics parameters with performance, in swimmers. Competitive athletes (N = 12) completed in random order and on different days a 400-m all-out test, an incremental step test comprising 5 × 250- and 1 × 200-m stages and 30 minutes at a constant swimming velocity (SV) at 87.5, 90, and 92.5% of the maximal aerobic velocity for MLSS velocity (MLSSv) determination. Two square-wave transitions of 500 m, 2.5% above and below the MLSSv were completed to determine VO2 on-kinetics. End-exercise VO2 at 97.5 and 102.5% of MLSSv represented, respectively, 81 and 97% of VO2max; the latter was not significantly different from maximal VO2 (VO2max). The VO2 at MLSSv (49.3 ± 9.2 ml·kg(-1)·min(-1)) was not significantly different from the second ventilatory threshold (VT2) (51.3 ± 7.6 ml·kg(-1)·min(-1)). The velocity associated with MLSS seems to be accurately estimated by the SV at VT2 (vVT2), and vVO2max also seems to be estimated with accuracy from the central 300-m mean velocity of a 400-m trial, indicators that represent a helpful tool for coaches. The 400-m swimming performance (T400) was correlated with the time constant of the primary phase VO2 kinetics (τp) at 97.5% MLSSv, and T800 was correlated with τp in both 97.5 and 102.5% of MLSSv. The assessment of the VO2 kinetics in swimming can help coaches to build training sets according to a swimmer's individual physiological response.

Parasympathetic reactivation after maximal CPET depends on exercise modality and resting vagal activity in healthy men

Purpose

The main purpose of this study was to investigate parasympathetic reactivation of the heart [evaluated through heart rate recovery (HRR) and HR variability (HRV)] after maximal cardiopulmonary exercise testing (CPET) using three different exercise modalities.

Methods

Twenty healthy men, aged 17 to 28 yr, performed three maximal CPETs (cycling, walking, and running) separated by 72 h and in a randomized, counter-balanced order. HRR was determined from the absolute differences between HR_peak and HR at 1–3 min after exercise. The root mean square of successive R-R differences calculated for consecutive 30-s windows (rMSSD_30s) was calculated to assess the parasympathetic reactivation after maximal CPET.

Results

Lower HR_peak, VO_2peak and energy expenditure were observed after the cycling CPET than the walking and running CPETs (P < 0.001). Both HRR and rMSSD_30s were significantly greater during recovery from the cycling CPET compared to the walking and running CPETs (P < 0.001). Furthermore, Δ rMSSD (i.e. resting minus postexercise rMSSD every 30 s into the recovery period) was positively related to the resting high-frequency component (HF), rMSSD, and standard deviation of all normal R-R intervals (SDNN) (r_s = 0.89 to 0.98; P < 0.001), and negatively related to the resting low-frequency component (LF) and sympathovagal balance (LF:HF ratio) after all exercise conditions (r_s = −0.73 to −0.79 and −0.86 to −0.90, respectively; P < 0.001).

Conclusions

These findings support that parasympathetic reactivation after maximal CPET (as assessed by HRR and rMSSD_30s) depends on exercise modality and cardiac autonomic control at rest.

Mode of exercise and sex are not important for oxygen consumption during and in recovery from sprint interval training

Most sprint interval training (SIT) research involves cycling as the mode of exercise and whether running SIT elicits a similar excess postexercise oxygen consumption (EPOC) response to cycling SIT is unknown. As running is a more whole-body–natured exercise, the potential EPOC response could be greater when using a running session compared with a cycling session. The purpose of the current study was to determine the acute effects of a running versus cycling SIT session on EPOC and whether potential sex differences exist. Sixteen healthy recreationally active individuals (8 males and 8 females) had their gas exchange measured over ∼2.5 h under 3 experimental sessions: (i) a cycle SIT session, (ii) a run SIT session, and (iii) a control (CTRL; no exercise) session. Diet was controlled. During exercise, both SIT modes increased oxygen consumption (cycle: male, 1.967 ± 0.343; female, 1.739 ± 0.296 L·min−1; run: male, 2.169 ± 0.369; female, 1.791 ± 0.481 L·min−1) versus CTRL (male, 0.425 ± 0.065 L·min−1; female, 0.357 ± 0.067; P < 0.001), but not compared with each other (P = 0.234). In the first hour postexercise, oxygen consumption was still increased following both run (male, 0.590 ± 0.065; female, 0.449 ± 0.084) and cycle SIT (male, 0.556 ± 0.069; female, 0.481 ± 0.110 L·min−1) versus CTRL and oxygen consumption was maintained through the second hour postexercise (CTRL: male, 0.410 ± 0.048; female, 0.332 ± 0.062; cycle: male, 0.430 ± 0.047; female, 0.395 ± 0.087; run: male, 0.463 ± 0.051; female, 0.374 ± 0.087 L·min−1). The total EPOC was not significantly different between modes of exercise or males and females (P > 0.05). Our data demonstrate that the mode of exercise during SIT (cycling or running) is not important to O2 consumption and that males and females respond similarly.

High-intensity interval training, solutions to the programming puzzle: Part I: cardiopulmonary emphasis

High-intensity interval training (HIT), in a variety of forms, is today one of the most effective means of improving cardiorespiratory and metabolic function and, in turn, the physical performance of athletes. HIT involves repeated short-to-long bouts of rather high-intensity exercise interspersed with recovery periods. For team and racquet sport players, the inclusion of sprints and all-out efforts into HIT programmes has also been shown to be an effective practice. It is believed that an optimal stimulus to elicit both maximal cardiovascular and peripheral adaptations is one where athletes spend at least several minutes per session in their 'red zone,' which generally means reaching at least 90% of their maximal oxygen uptake (VO2max). While use of HIT is not the only approach to improve physiological parameters and performance, there has been a growth in interest by the sport science community for characterizing training protocols that allow athletes to maintain long periods of time above 90% of VO2max (T@VO2max). In addition to T@VO2max, other physiological variables should also be considered to fully characterize the training stimulus when programming HIT, including cardiovascular work, anaerobic glycolytic energy contribution and acute neuromuscular load and musculoskeletal strain. Prescription for HIT consists of the manipulation of up to nine variables, which include the work interval intensity and duration, relief interval intensity and duration, exercise modality, number of repetitions, number of series, as well as the between-series recovery duration and intensity. The manipulation of any of these variables can affect the acute physiological responses to HIT. This article is Part I of a subsequent II-part review and will discuss the different aspects of HIT programming, from work/relief interval manipulation to the selection of exercise mode, using different examples of training cycles from different sports, with continued reference to T@VO2max and cardiovascular responses. Additional programming and periodization considerations will also be discussed with respect to other variables such as anaerobic glycolytic system contribution (as inferred from blood lactate accumulation), neuromuscular load and musculoskeletal strain (Part II).

Oxygen uptake kinetics

Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population.

Oxygen uptake kinetics and middle distance swimming performance

OBJECTIVE

The aim of this study was to determine whether V˙O(2) kinetics and specifically, the time constant of transitions from rest to heavy (τ(p)H) and severe (τ(p)S) exercise intensities, are related to middle distance swimming performance.

DESIGN

Fourteen highly trained male swimmers (mean ± SD: 20.5 ± 3.0 yr; 75.4 ± 12.4 kg; 1.80 ± 0.07 m) performed an discontinuous incremental test, as well as square wave transitions for heavy and severe swimming intensities, to determine V˙O(2) kinetics parameters using two exponential functions.

METHODS

All the tests involved front-crawl swimming with breath-by-breath analysis using the Aquatrainer swimming snorkel. Endurance performance was recorded as the time taken to complete a 400 m freestyle swim within an official competition (T400), one month from the date of the other tests.

RESULTS

T400 (Mean ± SD) (251.4 ± 12.4 s) was significantly correlated with τ(p)H (15.8 ± 4.8s; r=0.62; p=0.02) and τ(p)S (15.8 ± 4.7s; r=0.61; p=0.02). The best single predictor of 400 m freestyle time, out of the variables that were assessed, was the velocity at V˙O(2max)vV˙O(2max), which accounted for 80% of the variation in performance between swimmers. However, τ(p)H and V˙O(2max) were also found to influence the prediction of T400 when they were included in a regression model that involved respiratory parameters only.

CONCLUSIONS

Faster kinetics during the primary phase of the V˙O(2) response is associated with better performance during middle-distance swimming. However, vV˙O(2max) appears to be a better predictor of T400.

Time to exhaustion and time spent at a high percentage of VO2max in severe intensity domain in children and adults

The aim of the study was to compare time spent at a high percentage of VO2max (>90% of VO2max) (ts90%), time to achieve 90% of VO2max (ta90%), and time to exhaustion (TTE) for exercise in the severe intensity domain in children and adults. Fifteen prepubertal boys (10.3 ± 0.9 years) and 15 men (23.5 ± 3.6 years) performed a maximal graded exercise to determine VO2max, maximal aerobic power (MAP) and power at ventilatory threshold (PVTh). Then, they performed 4 constant load exercises in a random order at PVTh plus 50 and 75% of the difference between MAP and PVTh (PΔ50 and PΔ75) and 100 and 110% of MAP (P100 and P110). VO2max was continuously monitored. The P110 test was used to determine maximal accumulated oxygen deficit (MAOD). No significant difference was found in ta90% between children and adults. ts90% and TTE were not significantly different between children and adults for the exercises at PΔ50 and PΔ75. However, ts90% and TTE during P100 (p < 0.05 and p < 0.01, respectively) and P110 (p < 0.001) exercises were significantly shorter in children. Children had a significantly lower MAOD than adults (34.3 ± 9.4 ml · kg vs. 53.6 ± 11.1 ml · kg). A positive relationship (p < 0.05) was obtained between MAOD and TTE values during the P100 test in children. This study showed that only for intensities at, or higher than MAP, lower ts90% in children was linked to a reduced TTE, compared to adults. Shorter TTE in children can partly be explained by a lower anaerobic capacity (MAOD). These results give precious information about exercise intensity ranges that could be used in children's training sessions. Moreover, they highlight the implication of both aerobic and anaerobic processes in endurance performances in both populations.

Are oxygen uptake kinetics modified when using a respiratory snorkel?

PURPOSE

The aim of this study was to compare VO2 kinetics during constant power cycle exercise measured using a conventional facemask (CM) or a respiratory snorkel (RS) designed for breath-by-breath analysis in swimming.

METHODS

VO2 kinetics parameters-obtained using CM or RS, in randomized counterbalanced order-were compared in 10 trained triathletes performing two submaximal heavy-intensity cycling square-wave transitions. These VO2 kinetics parameters (ie, time delay: td1, td2; time constant: τ1, τ2; amplitude: A1, A2, for the primary phase and slow component, respectively) were modeled using a double exponential function. In the case of the RS data, this model incorporated an individually determined snorkel delay (ISD).

RESULTS

Only td1 (8.9 ± 3.0 vs 13.8 ± 1.8 s, P < .01) differed between CM and RS, whereas all other parameters were not different (τ1 = 24.7 ± 7.6 vs 21.1 ± 6.3 s; A1 = 39.4 ± 5.3 vs 36.8 ± 5.1 mL x min(-1) x kg(-1); td2 = 107.5 ± 87.4 vs 183.5 ± 75.9 s; A2' (relevant slow component amplitude) = 2.6 ± 2.4 vs 3.1 ± 2.6 mL x min(-1) x kg(-1) for CM and RS, respectively).

CONCLUSIONS

Although there can be a small mixture of breaths allowed by the volume of the snorkel in the transition to exercise, this does not appear to significantly influence the results. Therefore, given the use of an ISD, the RS is a valid instrument for the determination of VO2 kinetics within submaximal exercise.

Time to exhaustion at maximal lactate steady state is similar for cycling and running in moderately trained subjects

We compared time to exhaustion (t(lim)) at maximal lactate steady state (MLSS) between cycling and running, investigated if oxygen consumption, ventilation, blood lactate concentration, and perceived exertion differ between the exercise modes, and established whether MLSS can be determined for cycling and running using the same criteria. MLSS was determined in 15 moderately trained men (30 +/- 6 years, 77 +/- 6 kg) by several constant-load tests to exhaustion in cycling and running. Heart rate, oxygen consumption, and ventilation were recorded continuously. Blood lactate concentration and perceived exertion were measured every 5 min. t (lim) (37.7 +/- 8.9 vs. 34.4 +/- 5.4 min) and perceived exertion (7.2 +/- 1.7 vs. 7.2 +/- 1.5) were similar for cycling and running. Heart rate (165 +/- 8 vs. 175 +/- 10 min(-1); P < 0.01), oxygen consumption (3.1 +/- 0.3 vs. 3.4 +/- 0.3 l min(-1); P < 0.001) and ventilation (93 +/- 12 vs. 103 +/- 16 l min(-1); P < 0.01) were lower for cycling compared to running, respectively, whereas blood lactate concentration (5.6 +/- 1.7 vs. 4.3 +/- 1.3 mmol l(-1); P < 0.05) was higher for cycling. t(lim) at MLSS is similar for cycling and running, despite absolute differences in heart rate, ventilation, blood lactate concentration, and oxygen consumption. This may be explained by the relatively equal cardiorespiratory demand at MLSS. Additionally, the similar t(lim) for cycling and running allows the same criteria to be used for determining MLSS in both exercise modes.

Physiological differences between cycling and running: lessons from triathletes

The purpose of this review was to provide a synopsis of the literature concerning the physiological differences between cycling and running. By comparing physiological variables such as maximal oxygen consumption (V O(2max)), anaerobic threshold (AT), heart rate, economy or delta efficiency measured in cycling and running in triathletes, runners or cyclists, this review aims to identify the effects of exercise modality on the underlying mechanisms (ventilatory responses, blood flow, muscle oxidative capacity, peripheral innervation and neuromuscular fatigue) of adaptation. The majority of studies indicate that runners achieve a higher V O(2max) on treadmill whereas cyclists can achieve a V O(2max) value in cycle ergometry similar to that in treadmill running. Hence, V O(2max) is specific to the exercise modality. In addition, the muscles adapt specifically to a given exercise task over a period of time, resulting in an improvement in submaximal physiological variables such as the ventilatory threshold, in some cases without a change in V O(2max). However, this effect is probably larger in cycling than in running. At the same time, skill influencing motor unit recruitment patterns is an important influence on the anaerobic threshold in cycling. Furthermore, it is likely that there is more physiological training transfer from running to cycling than vice versa. In triathletes, there is generally no difference in V O(2max) measured in cycle ergometry and treadmill running. The data concerning the anaerobic threshold in cycling and running in triathletes are conflicting. This is likely to be due to a combination of actual training load and prior training history in each discipline. The mechanisms surrounding the differences in the AT together with V O(2max) in cycling and running are not largely understood but are probably due to the relative adaptation of cardiac output influencing V O(2max) and also the recruitment of muscle mass in combination with the oxidative capacity of this mass influencing the AT. Several other physiological differences between cycling and running are addressed: heart rate is different between the two activities both for maximal and submaximal intensities. The delta efficiency is higher in running. Ventilation is more impaired in cycling than in running. It has also been shown that pedalling cadence affects the metabolic responses during cycling but also during a subsequent running bout. However, the optimal cadence is still debated. Central fatigue and decrease in maximal strength are more important after prolonged exercise in running than in cycling.

'Priming' exercise and O2 uptake kinetics during treadmill running

We tested the hypothesis that priming exercise would speed V(O2) kinetics during treadmill running. Eight subjects completed a square-wave protocol, involving two bouts of treadmill running at 70% of the difference between the running speeds at lactate threshold (LT) and V(O2) max, separated by 6-min of walking at 4 km h(-1), on two occasions. Oxygen uptake was measured breath-by-breath and subsequently modelled using non-linear regression techniques. Heart rate and blood lactate concentration were significantly elevated prior to the second exercise bout compared to the first. However, V(O2) kinetics was not significantly different between the first and second exercise bouts (mean+/-S.D., phase II time constant, Bout 1: 16+/-3s vs. Bout 2: 16+/-4s; V(O2) slow component amplitude, Bout 1: 0.24+/-0.10 L min(-1)vs. Bout 2: 0.20+/-0.12 L min(-1); mean response time, Bout 1: 34+/-4s vs. Bout 2: 34+/-6s; P>0.05 for all comparisons). These results indicate that, contrary to previous findings with other exercise modalities, priming exercise does not alter V(O2) kinetics during high-intensity treadmill running, at least in physically active young subjects. We speculate that the relatively fast V(O2) kinetics and the relatively small V(O2) slow component in the control ('un-primed') condition negated any enhancement of V(O2) kinetics by priming exercise in this exercise modality.

VO2 attained during treadmill running: the influence of a specialist (400-m or 800-m) event

PURPOSE

Previously it has been observed that, in well-trained 800-m athletes, VO2max is not attained during middle-distance running events on a treadmill, even when a race-type pacing strategy is adopted. Therefore, the authors investigated whether specialization in a particular running distance (400-m or 800-m) influences the VO2 attained during running on a treadmill.

METHODS

Six 400-m and six 800-m running specialists participated in the study.A 400-m trial and a progressive test to determine VO2max were completed in a counterbalanced order. Oxygen uptakes attained during the 400-m trial were compared to examine the influence of specialist event.

RESULTS

A VO2 plateau was observed in all participants for the progressive test, demonstrating the attainment of VO2max. The VO2max values were 56.2 +/- 4.7 and 69.3 +/- 4.5 mL x kg-1 x min-1 for the 400-m- and 800-m-event specialists, respectively (P = .0003). Durations for the 400-m trial were 55.1 +/- 4.2 s and 55.8 +/- 2.3 s for the 400-m- and 800-m-event specialists, respectively. The VO2 responses achieved were 93.1% +/- 2.0% and 85.7% +/- 3.0% VO2max for the 400-m- and 800-m-event specialists, respectively (P = .001).

CONCLUSIONS

These results demonstrate that specialist running events do appear to influence the percentage of VO2max achieved in the 400-m trial, with the 800-m specialists attaining a lower percentage of VO2max than the 400-m specialists. The 400-m specialists appear to compensate for a lower VO2max by attaining a higher percentage VO2max during a 400-m trial.

Relationship between maximal oxygen uptake and oxygen uptake attained during treadmill middle-distance running

Traditionally, it has been assumed that during middle-distance running oxygen uptake (VO2) reaches its maximal value (VO2max) providing the event is of a sufficient duration; however, this assumption is largely based on observations in individuals with a relatively low VO2max. The aim of this study was to determine whether VO2max is related to the VO2 attained (i.e. VO2peak) during middle-distance running on a treadmill. Fifteen well-trained male runners (age 23.3 +/- 3.8 years, height 1.80 +/- 0.10 m, body mass 76.9 +/- 10.6 kg) volunteered to participate in the study. The participants undertook two 800-m trials to examine the reproducibility of the VO2 response. These two trials, together with a progressive test to determine VO2max, were completed in a randomized order. Oxygen uptake was determined throughout each test using 15-s Douglas bag collections. Following the application of a 30-s rolling average, the highest VO2 during the progressive test (i.e. VO2max) was compared with the highest VO2 during the 800-m trials (i.e. VO2peak) to examine the relationship between VO2max and the VO2 attained in the 800-m trials. For the 15 runners, VO2max was 58.9 +/- 7.1 ml x kg(-1) x min(-1). Two groups were formed using a median split based on VO2max. For the high and low VO2max groups, VO2max was 65.7 +/- 3.0 and 52.4 +/- 1.8 ml x kg(-1) x min(-1) respectively. The limits of agreement (95%) for test-retest reproducibility for the VO2 attained during the 800-m trials were +/- 3.5 ml x kg(-1) x min(-1) for a VO2peak of 50.6 ml x kg(-1) x min(-1) (the mean VO2peak for the low VO2max group) and +/- 2.3 ml x kg(-1) x min(-1) for a VO2peak of 59.0 ml x kg(-1) x min(-1) (the mean VO2peak for the high VO2max group), with a bias in VO2peak between the 800-m runs (i.e. the mean difference) of 1.2 ml x kg(-1) x min(-1). The VO2peak for the 800-m runs was 54.8 +/- 4.9 ml x kg(-1) x min(-1) for all 15 runners. For the high and low VO2max groups, VO2peak was 59.0 +/- 3.3 ml x kg(-1) x min(-1) (i.e. 90% VO2max) and 50.6 +/- 2.0 ml x kg(-1) x min(-1) (i.e. 97% VO2max) respectively. The negative relationship (-0.77) between VO2max and % VO2max attained for all 15 runners was significant (P = 0.001). These results demonstrate that (i) reproducibility is good and (ii) that VO2max is related to the %VO2max achieved, with participants with a higher VO2max achieving a lower %VO2max in an 800-m trial on a treadmill.

Cardiopulmonary exercise testing in children and adolescents with asthma who report symptoms of exercise-induced bronchoconstriction

Patients with asthma often report symptoms of exercise-induced bronchoconstriction. We performed cardiopulmonary exercise testing to establish the cause of exercise limitation in patients with asthma, under treatment, who reported symptoms of exercise-induced bronchoconstriction. Ten of the 42 patients meeting criteria for inclusion in our study (24%) developed exercise-induced bronchoconstriction. Exercise limitation without exercise-induced bronchoconstriction was found in both obese and non-obese patients, suggesting that poor fitness is a problem independent of body habitus. Including cardiopulmonary exercise testing in the management of children with suspected exercise-induced bronchoconstriction would provide a better understanding of the etiology of their symptoms and facilitate more appropriate treatment.

Effects of low and high levels of moderate hypoxia on anaerobic energy release during supramaximal cycle exercise

The purpose of this study was to investigate whether hypoxia can alter anaerobic energy release during supramaximal exercise. Seven male subjects performed 12 submaximal cycling tests to establish the relationship between workload and O2 demand. The subjects also performed 40 s Wingate tests (WT) under normoxia (room air), two levels of moderate hypoxia of 16.4% O2 and 12.7% O2. We measured the power output and oxygen uptake (VO2) during each test and estimated the O2 demand, O2 deficit and percentage of anaerobic energy release (%AnAER). These data were analyzed for each 20 s interval. At all intervals, there were no differences in Pmean per body mass (BM)(-1), O2 demand per BM(-1) or O2 deficit per BM(-1) among the three O2 conditions. However, under hypoxia of 12.7%, VO2 per BM(-1) was significantly decreased and %AnAER was significantly increased in the late phase (20-40 s) of the WT, compared to normoxia (P<0.05). There were no such significant differences between normoxia and hypoxia of 16.4%. Thus, the present results show that the degree of hypoxia affects the magnitude of the hypoxia-induced increase in anaerobic energy release in the late phase of the WT and suggest that certain degrees of hypoxia induce significant increases in the amount of anaerobic energy released, compared to normoxia.

Physiological responses during submaximal interval swimming training: effects of interval duration

The aim of the present study was to determine the time sustained near VO2max in two interval training (IT) swimming sessions comprising 4x400 m (IT(4x400)) or 16x100 (IT(16xl00)). Elite swimmers (Mean+/-SD age 18+/-2 yrs; body mass 66.9+/-6.5 kg: swim VO2max 55.7+/-5.8 ml.kg(-1).min(-1)) completed three experimental sessions at a 50-m indoor pool over a one week period. The first test comprised a 5 x 200-m incremental test to exhaustion for determination of the pulmonary ventilation threshold (VT, m.s(-1)), VO2max, the velocity associated with VO2max (VO2max, m(s(-1)) and maximum heart rate (HR(max), b.min(-1)). The remaining two tests involved the IT(4x400) and IT(16xl00) performed in a randomised order. The two IT sessions where completed at a velocity representing 25% of the difference between the VT and the VO2max (delta25%) and in the same work to rest ratio. During the IT sessions VO2 as well as HR were measured. The duration (s) >90% VO2max, also the duration (s) >90% HR(max), were not significantly different in the IT(16x100) and IT(4x400). However, limits of agreement (LIM(AG)) analysis demonstrated considerable individual variation in the time >90% VO2max (mean difference +/-2SD = 222+/-819 s) and the time >90% HRmax (mean difference +/-2SD = 61+/-758 s) between the two IT sessions. This factor deserves further research to establish the characteristics of those athletes which influence the physiological responses in IT of short or longer duration repetitions.

Effect of Endurance Training on the &OV0312;O2???Work Rate Relationship in Normoxia and Hypoxia

PURPOSE

We postulated that the relationship between VO2 and work rate (VO2-WR relationship) during incremental exercise is dependent on O2 availability, and that training-induced adaptations alter this relationship. We therefore studied the effect of endurance training on VO2 response during incremental exercise in normoxia and hypoxia (FIO2=0.134).

METHODS

Before and after training (6 d.wk, 4 wk), eight subjects performed incremental exercises under normoxia and hypoxia and one constant-work rate exercise in normoxia at 80% of pretraining VO2max. The slopes of the VO2-WR relationship during incremental exercise were calculated using all the points (whole slope) or only points before the lactate threshold (pre-LT slope). The difference between VO2max measured and VO2max expected from the pre-LT slope (DeltaVO2) was determined, as was the difference between VO2 at minute 10 and VO2 at minute 4 during the constant-work rate exercise (DeltaVO2(10'-4')).

RESULTS

In normoxia, training induced a significant decrease in the whole slope (11.0+/-1.0 vs 9.9+/-0.4 mL.min.W, P<0.05). In hypoxia, training induced a significant increase in the pre-LT slope (8.7+/-1.2 vs 9.8+/-0.7 mL.min.W; P<0.05) and the whole slope (8.5+/-1.2 vs 9.4+/-0.5 mL.min.W; P<0.05). A significant correlation between the decrease of DeltaVO2 and the decrease of DeltaVO2(10'-4') with training was found in normoxia (P<0.01, r=0.79).

CONCLUSIONS

Taken together, these results indicate that adaptations induced by endurance training are associated with more efficient incremental and constant-workload exercise performed in normoxia. Moreover, training contributes to improved O2 delivery during moderate exercise performed in hypoxia, and to enhanced near-maximal exercise tolerance.

The V?O2 response for an exhaustive treadmill run at 800-m pace: a breath-by-breath analysis

Recent research in which data were averaged over 10 or 30 s suggests that the VO(2) response of aerobically fit individuals plateaus below VO(2 max) in an exhaustive square-wave run lasting approximately 2 min. To investigate this phenomenon we examined the breath-by-breath VO(2) response of trained runners to an exhaustive treadmill run at 800 m pace. Eight male competitive runners completed two treadmill tests on separate days: a ramp test to exhaustion and an exhaustive square-wave run at 800-m pace. For the ramp test, the breath-by-breath data were smoothed with a 15-s moving average and the highest of the smoothed values was taken as VO(2 peak) [mean (SD): 68.9 (5.6) ml kg(-1) min(-1)]. For the square-wave, the breath-by-breath data were interpolated to give one value per second and modelled using a monoexponential function. Following a delay of 11.2 (1.5) s, VO(2) increased quickly [phase-2 time constant of 10.7 (2.7) s] towards an asymptote that represented just 85 (6)% of VO(2 peak) from the ramp test. Expressed in ml kg(-1) min(-1), this asymptote was independent of VO(2 peak) (r=0.04, P=0.94). However, as a percentage of VO(2 peak) it was negatively correlated with VO(2 peak) itself (r=-0.96, P<0.001). It is concluded that in an exhaustive square-wave treadmill run lasting approximately 2 min the VO(2) of aerobically fit runners increases quickly to plateau at a level that is lower than, but independent of, VO(2max).

Influence of repeated isometric contractions on muscle deoxygenation and pulmonary oxygen uptake kinetics in humans

The purpose of the present study was to compare simultaneously vastus lateralis (VL) deoxygenation and pulmonary O(2) uptake (O(2)) kinetics during fatiguing knee extension exercise with minimal cardiac load. Eight healthy subjects realized an intermittent bilateral knee-extension exercise (3-s contraction/3-s relaxation) at 40% of maximum voluntary contraction for 10 min. VL deoxygenation was recorded by near infrared spectroscopy at 2 Hz (NIRO-300, Hamamatsu Photonics, Japan) and O(2) was determined breath-by-breath (K4b(2), Cosmed, Italy). After a time delay of 16 +/- 5 s, deoxygenation kinetics at the onset of exercise followed an exponential time course at a significant faster rate than O(2) (time constant of 5.4 +/- 4.0 s vs. 31.6 +/- 10.4 s, P<0.01) reflecting a mismatch between local O(2) consumption and perfusion. Thereafter, a rise in O(2) of 223 +/- 123 ml min(-1) (consistent with the mathematical model, 259 +/- 126 ml min(-1)) was observed between minutes 2 and 10. During the same exercise time, changes in tissue oxygenation index decreased significantly and were individually correlated with the corresponding increased O(2) (P<0.05), suggesting that the majority of the slow rise of O(2) arose from the exercising limbs. Averaged heart rate increased from 67 +/- 11 to 116 +/- 20 beats min(-1) during exercise. Knee extension exercise may be relevant to estimate the cardiopulmonary and deoxygenation of working skeletal muscle responses for assessment of exercise limiting factors in clinical settings or in the exercise physiology.