Critical Power and Maximal Lactate Steady State in Cycling: "Watts" the Difference?

From a physiological perspective, the delineation between steady-state and non-steady-state exercise, also referred to as the maximal metabolic steady state, holds paramount importance for evaluating athletic performance and designing and monitoring training programs. The critical power and the maximal lactate steady state are two widely used indices to estimate this threshold, yet previous studies consistently reported significant discrepancies between their associated power outputs. These findings have fueled the debate regarding the interchangeability of critical power and the maximal lactate steady state in practice. This paper reviews the methodological intricacies intrinsic to the determination of these thresholds, and elucidates how inappropriate determination methods and methodological inconsistencies between studies have contributed to the documented differences in the literature. Through a critical examination of relevant literature and by integration of our laboratory data, we demonstrate that differences between critical power and the maximal lactate steady state may be reconciled to only a few Watts when applying appropriate and strict determination criteria, so that both indices may be used to estimate the maximal metabolic steady-state threshold in practice. To this end, we have defined a set of good practice guidelines to assist scientists and coaches in obtaining the most valid critical power and maximal lactate steady state estimates.

Effects of acute simulated altitude on the maximal lactate steady state in humans

We sought to determine the effects of acute simulated altitude on the maximal lactate steady state (MLSS) and physiological responses to cycling at and 10 W above the MLSS-associated power output (PO) (MLSSp and MLSSp+10, respectively). Eleven (4 females) participants (means [SD]; 28 [4] yr; V̇o2max: 54.3 [6.9] mL·kg-1·min-1) acclimatized to ∼1,100 m performed 30-min constant PO trials in simulated altitudes of 0 m sea level (SL), 1,111 m mild altitude (MILD), and 2,222 m moderate altitude (MOD). MLSSp, defined as the highest PO with stable (<1 mM change) blood lactate concentration ([BLa]) between 10 and 30 min, was significantly lower in MOD (209 [54] W) compared with SL (230 [56] W; P < 0.001) and MILD (225 [58] W; P = 0.001), but MILD and SL were not different (P = 0.12). V̇o2 and V̇co2 decreased at higher simulated altitudes due to lower POs (P < 0.05), but other end-exercise physiological responses (e.g., [BLa], ventilation [V̇e], heart rate [HR]) were not different between conditions at MLSSp or MLSSp + 10 (P > 0.05). At the same absolute intensity (MLSSp for MILD), [BLa], HR, and V̇E and all perceptual variables were exacerbated in MOD compared with SL and MILD (P < 0.05). Maximum voluntary contraction, voluntary activation, and potentiated twitch forces were exacerbated at MLSSp + 10 relative to MLSSp within conditions (P < 0.05); however, condition did not affect performance fatiguability at the same relative or absolute intensity (P > 0.05). As MLSSp decreased in hypoxia, adjustments in PO are needed to ensure the same relative intensity across altitudes, but common indices of exercise intensity may facilitate exercise prescription and monitoring in hypoxia.NEW & NOTEWORTHY This study demonstrates the power output and metabolic rate associated with the maximal lactate steady-state (MLSS) decline in response to simulated altitude; however, common indices of exercise intensity remained unchanged when cycling was performed at the work rate associated with MLSS at each simulated altitude. These results support previous studies that investigated the effects of hypoxia on alternative measures of the critical intensity of exercise and will inform exercise prescription/monitoring across altitudes.

Agreement Between Maximal Lactate Steady State and Critical Power in Different Sports: A Systematic Review and Bayesian's Meta-Regression

ABSTRACT

Borszcz, FK, de Aguiar, RA, Costa, VP, Denadai, BS, and de Lucas, RD. Agreement between maximal lactate steady state and critical power in different sports: A systematic review and Bayesian's meta-regression. J Strength Cond Res 38(6): e320-e339, 2024-This study aimed to systematically review the literature and perform a meta-regression to determine the level of agreement between maximal lactate steady state (MLSS) and critical power (CP). Considered eligible to include were peer-reviewed and "gray literature" studies in English, Spanish, and Portuguese languages in cyclical exercises. The last search was made on March 24, 2022, on PubMed, ScienceDirect, SciELO, and Google Scholar. The study's quality was evaluated using 4 criteria adapted from the COSMIN tool. The level of agreement was examined by 2 separate meta-regressions modeled under Bayesian's methods, the first for the mean differences and the second for the SD of differences. The searches yielded 455 studies, of which 36 studies were included. Quality scale revealed detailed methods and small samples used and that some studies lacked inclusion/exclusion criteria reporting. For MLSS and CP comparison, likely (i.e., coefficients with high probabilities) covariates that change the mean difference were the MLSS time frame and delta criteria of blood lactate concentration, MLSS number and duration of pauses, CP longest predictive trial duration, CP type of predictive trials, CP model fitting parameters, and exercise modality. Covariates for SD of the differences were the subject's maximal oxygen uptake, CP's longest predictive trial duration, and exercise modality. Traditional MLSS protocol and CP from 2- to 15-minute trials do not reflect equivalent exercise intensity levels; the proximity between MLSS and CP measures can differ depending on test design, and both MLSS and CP have inherent limitations. Therefore, comparisons between them should always consider these aspects.

The Additional Effect of Training Above the Maximal Metabolic Steady State on VO2peak, Wpeak and Time-Trial Performance in Endurance-Trained Athletes: A Systematic Review, Meta-analysis, and Reality Check

BACKGROUND

To improve sport performance, athletes use training regimens that include exercise below and above the maximal metabolic steady state (MMSS).

OBJECTIVE

The objective of this review was to determine the additional effect of training above MMSS on VO2peak, Wpeak and time-trial (TT) performance in endurance-trained athletes.

METHODS

Studies were included in the review if they (i) were published in academic journals, (ii) were in English, (iii) were prospective, (iv) included trained participants, (v) had an intervention group that contained training above and below MMSS, (vi) had a comparator group that only performed training below MMSS, and (vii) reported results for VO2peak, Wpeak, or TT performance. Medline and SPORTDiscus were searched from inception until February 23, 2023.

RESULTS

Fourteen studies that ranged from 2 to 12 weeks were included in the review. There were 171 recreational and 128 competitive endurance athletes. The mean age and VO2peak of participants ranged from 15 to 43 years and 38 to 68 mL·kg-1·min-1, respectively. The inclusion of training above MMSS led to a 2.5 mL·kg-1·min-1 (95% CI 1.4-3.6; p < 0.01; I2 = 0%) greater improvement in VO2peak. A minimum of 81 participants per group would be required to obtain sufficient power to determine a significant effect (SMD 0.44) for VO2peak. No intensity-specific effect was observed for Wpeak or TT performance, in part due to a smaller sample size.

CONCLUSION

A single training meso-cycle that includes training above MMSS can improve VO2peak in endurance-trained athletes more than training only below MMSS. However, we do not have sufficient evidence to conclude that concurrent adaptation occurs for Wpeak or TT performance.

Is the maximal lactate steady state concept really relevant to predict endurance performance?

PURPOSE

There is no convincing evidence for the idea that a high power output at the maximal lactate steady state (PO_{_MLSS}) and a high fraction of [Formula: see text]O_2max at MLSS (%[Formula: see text]O_{2_MLSS}) are decisive for endurance performance. We tested the hypotheses that (1) %[Formula: see text]O_{2_MLSS} is positively correlated with the ability to sustain a high fraction of [Formula: see text]O_2max for a given competition duration (%[Formula: see text]O_{2_TT}); (2) %[Formula: see text]O_{2_MLSS} improves the prediction of the average power output of a time trial (PO_{_TT}) in addition to [Formula: see text]O_2max and gross efficiency (GE); (3) PO_{_MLSS} improves the prediction of PO_{_TT} in addition to [Formula: see text]O_2max and GE.

METHODS

Twenty-one recreationally active participants performed stepwise incremental tests on the first and final testing day to measure GE and check for potential test-related training effects in terms of changes in the minimal lactate equivalent power output (∆PO_LEmin), 30-min constant load tests to determine MLSS, a ramp test and verification bout for [Formula: see text]O_2max, and 20-min time trials for %[Formula: see text]O_{2_TT} and PO_{_TT}. Hypothesis 1 was tested via bivariate and partial correlations between %[Formula: see text]O_{2_MLSS} and %[Formula: see text]O_{2_TT}. Multiple regression models with [Formula: see text]O_2max, GE, ∆PO_LEmin, and %[Formula: see text]O_{2_MLSS} (Hypothesis 2) or PO_{_MLSS} instead of %[Formula: see text]O_{2_MLSS} (Hypothesis 3), respectively, as predictors, and PO_{_TT} as the dependent variable were used to test the hypotheses.

RESULTS

%[Formula: see text]O_{2_MLSS} was not correlated with %[Formula: see text]O_{2_TT} (r = 0.17, p = 0.583). Neither %[Formula: see text]O_{2_MLSS} (p = 0.424) nor PO_{_MLSS} (p = 0.208) did improve the prediction of PO_{_TT} in addition to [Formula: see text]O_2max and GE.

CONCLUSION

These results challenge the assumption that PO_{_MLSS} or %[Formula: see text]O_{2_MLSS} are independent predictors of supra-MLSS PO_{_TT} and %[Formula: see text]O_{2_TT}.

A critical review of critical power

The elegant concept of a hyperbolic relationship between power, velocity, or torque and time to exhaustion has rightfully captivated the imagination and inspired extensive research for over half a century. Theoretically, the relationship's asymptote along the time axis (critical power, velocity, or torque) indicates the exercise intensity that could be maintained for extended durations, or the "heavy-severe exercise boundary". Much more than a critical mass of the extensive accumulated evidence, however, has persistently shown the determined intensity of critical power and its variants as being too high to maintain for extended periods. The extensive scientific research devoted to the topic has almost exclusively centered around its relationships with various endurance parameters and performances, as well as the identification of procedural problems and how to mitigate them. The prevalent underlying premise has been that the observed discrepancies are mainly due to experimental 'noise' and procedural inconsistencies. Consequently, little or no effort has been directed at other perspectives such as trying to elucidate physiological reasons that possibly underly and account for those discrepancies. This review, therefore, will attempt to offer a new such perspective and point out the discrepancies' likely root causes.

Methodological Reconciliation of CP and MLSS and Their Agreement with the Maximal Metabolic Steady State

The critical power (CP) and maximal lactate steady state (MLSS) are operational surrogates of the maximal metabolic steady state (MMSS). However, their concordance and their agreement with MMSS remains variable likely due to methodological factors.

PURPOSE

To compare the concordance between CP and MLSS estimated by various models and criteria and their agreement with MMSS.

METHODS

After a ramp-test, ten recreationally active males performed four-to-five severe-intensity constant-power output (PO) trials to estimate CP, and three-to-four constant-PO trials to determine MLSS and identify MMSS. CP was computed using the 3-parameter hyperbolic (CP3-hyp), 2-parameter hyperbolic (CP2-hyp), linear (CPlin), and inverse of time (CP1/Tlim) models. In addition, the model with lowest combined parameter error identified the "best-fit" CP (CPbest-fit). MLSS was determined as an increase in blood lactate concentration ≤ 1 mM during constant-PO cycling from the 5th (MLSS10-30), 10th (MLSS10-30), 15th (MLSS15-30), 20th (MLSS20-30), or 25th (MLSS25-30) to 30th minute. MMSS was identified as the greatest PO associated with the highest submaximal steady state V[Combining Dot Above]O2 (MV[Combining Dot Above]O2ss).

RESULTS

Concordance between the various CP and MLSS estimates was greatest when MLSS was identified as MLSS15-30, MLSS20-30, and MLSS25-30. The PO at MV[Combining Dot Above]O2ss was 243 ± 43 W. Of the various CP models and MLSS criteria, CP2-hyp (244 ± 46 W) and CPlin (248 ± 46 W) and MLSS15-30 and MLSS20-30 (both 245 ± 46 W), respectively displayed, on average, the greatest agreement with MV[Combining Dot Above]O2ss. Nevertheless, all CP models and MLSS criteria demonstrated some degree of inaccuracies with respect to MV[Combining Dot Above]O2ss.

CONCLUSIONS

Differences between CP and MLSS can be reconciled with optimal methods of determination. When estimating MMSS, from CP the error margin of the model-estimate should be considered. For MLSS, MLSS15-30 and MLSS20-30 demonstrated the highest degree of accuracy.

Agreement of maximal lactate steady state with critical power and physiological thresholds in rowing

The aim of this study was threefold: (a) to compare the maximal lactate steady state (MLSS) with critical power (CP); (b) to describe the relationship of MLSS with rowing performances; and (c) to verify the agreement of MLSS with several exercise intensity thresholds in rowers. Fourteen male rowers (mean [SD]: age = 26 [13] years; height = 1.82 [0.05] m; body mass = 81.0 [7.6] kg) performed on a rowing ergometer: (I) discontinuous incremental test with 3 min stages and 30-s recovery intervals (INC_3min); (II) continuous incremental test with 60-s stages (INC_1min); (III) two to four constant workload tests to determine MLSS; and (IV) performance tests of 500, 1000, 2000 and 6000 m to determine CP. Twenty-seven exercise intensity thresholds based on blood lactate, heart rate and ventilatory responses were determined by incremental tests, and then compared with MLSS. CP (257 [38] W) was higher than MLSS (187 [25] W; p < 0.001), with a very large mean difference (37%), large typical error of estimate (14%) and moderate correlation (r = 0.48). Despite the correlations between MLSS and most intensity thresholds (r > 0.70), all presented low correspondence (TEE > 5%), with a lower bias found between MLSS and the first intensity thresholds (-12.5% to 4.1%). MLSS was correlated with mean power during 500 m (r = 0.65), 1000 m (r = 0.86) and 2000 m (r = 0.78). In conclusion, MLSS intensity is substantially lower than CP and presented low agreement with 27 incremental-derived thresholds, questioning their use to estimate MLSS during rowing ergometer exercise.Highlights MLSS was substantially lower than CP in rowing exercise with a mean difference of 37%, much larger than the difference commonly found in running and cycling exercise (i.e., ?10%).A clear disagreement was reported between MLSS and 27 physiological thresholds determined in different incremental tests.There is a positive association of MLSS with 500, 1000 and 2000 m rowing ergometer performance tests.

Exercise above the maximal lactate steady state does not elicit a V̇O2 slow component that leads to attainment of V̇O2max

There is a pervasive belief that the severe-intensity domain is defined as work rates above the power associated with a maximal lactate steady state (MLSS) and by a oxygen uptake (V̇O₂) response that demonstrates a rapid increase (primary phase) followed by a slower increase (slow component), which leads to maximal oxygen uptake (V̇O_2max) if exercise is continued long enough. Fifteen university students performed 5 to 7 tests to calculate power at MLSS (154 ± 29 W). The tests included 30 min of exercise at each of 3 work rates: (i) below (-2 ± 1 W) power at MLSS, (ii) above (+4 ± 1 W) the power at MLSS, and (iii) well above (+19 ± 8 W) power at MLSS. The V̇O₂ response in each test was described using mathematical modeling. Contrary to expectation, the response at the supra-MLSS work rates had not 2, but 3, distinct phases: the primary phase and the slow component, plus a "delayed" third phase, which emerged after ∼15 min. V̇O_2max was not attained at supra-MLSS work rates. These results challenge commonly held beliefs about definitions and descriptions of exercise intensity domains. Novelty: The V̇O₂ response at work rates that are too high to sustain a lactate steady state but not high enough to elicit V̇O_2max features not 2, but 3, distinct phases. There is no consensus on whether intensity domains should be defined by their boundaries or by the responses they engender.

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.

RESPOSTA FISIOLÓGICA E PERCEPTUAL NA VELOCIDADE CRÍTICA E PONTO DE COMPENSAÇÃO RESPIRATÓRIA

RESUMO Introdução: O ponto de compensação respiratória (PCR) representa a taxa metabólica durante um teste incremental máximo, a partir da qual se perde o controle do equilíbrio ácido-base. Entretanto, a velocidade crítica (VC) define o limite superior do domínio pesado do exercício, no qual a exaustão não está relacionada à perturbação metabólica. Objetivo: Comparar a resposta fisiológica (frequência cardíaca - FC, lactato sanguíneo - [La] e consumo de oxigênio - V̇O2) e perceptual (percepção subjetiva de esforço - PSE) durante o exercício na VC e no PCR, visando analisar as similaridades contextuais. Métodos: Dez corredores adolescentes (15,8 ± 1,7 anos) submeteram-se a um teste progressivo (incrementos de 1,0 km×h-1 por minuto, até a exaustão) para determinar V̇O2max, PCR e velocidades correspondentes. A VC foi estimada por três esforços, com tempo limite previsto entre 2 e 12 minutos. Os participantes realizaram dois esforços de sete minutos cada, em dias diferentes, na VC e vPCR. Foram registradas FC, PSE (escala 6-20) a cada minuto e [La] de repouso e após cada esforço. O V̇O2 foi analisado respiração a respiração durante os esforços. O teste de Mann-Whitney comparou as respostas de FC, [La], V̇O2 e PSE em VC e vPCR. A variância entre essas respostas foi analisada pelo coeficiente de dispersão (R2). O índice de significância foi P≤0,05. Resultados: Os valores máximos no teste progressivo foram 56,1 ± 5,5 ml×kg-1×min-1 (V̇O2max), 16,5 ± 1,7 km×h-1 (vV̇O2max), 202 ± 12 bpm (FCmax), 19,4 ± 1,3 (PSE) e 12,7 ± 3,1 mmol×L-1 ([La]). Não foram observadas diferenças entre VC (a 83,8 ± 3,6% vV̇O2max) e vPCR (a 86,5 ± 3,6% vV̇O2max) nas respostas de PSE (P = 0,761), FC (P = 0,096), [La] (P = 0,104) e V̇O2 (P = 0,364). Demonstrou-se haver correlações entre VC e vPCR nas respostas de [La] (R2 = 0,76; P = 0,011), PSE (R2 = 0,84; P < 0,01) e V̇O2max (R2 = 0,82; P < 0,01). Conclusão: Pode-se inferir que o exercício em PCR reproduziu uma resposta fisiológica e perceptual similar àquela em VC.

Maximal power output during incremental cycling test is dependent on the curvature constant of the power–time relationship

The aim of this study was to investigate whether the maximal power output (Pmax) during an incremental test was dependent on the curvature constant (W′) of the power–time relationship. Thirty healthy male subjects (maximal oxygen uptake = 3.58 ± 0.40 L·min−1) performed a ramp incremental cycling test to determine the maximal oxygen uptake and Pmax, and 4 constant work rate tests to exhaustion to estimate 2 parameters from the modeling of the power–time relationship (i.e., critical power (CP) and W′). Afterwards, the participants were ranked according to their magnitude of W′. The median third was excluded to form a high W′ group (HIGH, n = 10), and a low W′ group (LOW, n = 10). Maximal oxygen uptake (3.84 ± 0.50 vs. 3.49 ± 0.37 L·min−1) and CP (213 ± 22 vs. 200 ± 29 W) were not significantly different between HIGH and LOW, respectively. However, Pmax was significantly greater for the HIGH (337 ± 23 W) than for the LOW (299 ± 40 W). Thus, in physically active individuals with similar aerobic parameters, W′ influences the Pmax during incremental testing.

Prior heavy-intensity exercise's enhancement of oxygen-uptake kinetics and short-term high-intensity exercise performance independent of aerobic-training status

Prior high-intensity exercise can improve exercise performance during severe-intensity exercise. These positive alterations have been attributed, at least in part, to enhancement of overall oxygen-uptake (VO2) kinetics.

PURPOSE

To determine the effects of prior heavy-intensity exercise on VO2 kinetics and short-term high-intensity exercise performance in individuals with different aerobic-training statuses.

METHODS

Fifteen active subjects (UT; VO2max = 43.8 ± 6.3 mL · kg-1 · min-1) and 10 well-trained endurance cyclists (T; VO2max = 66.7 ± 6.7 mL · kg-1 · min-1) performed the following protocols: an incremental test to determine lactate threshold and VO2max, 4 maximal constant-load tests to estimate critical power, and two 3-min bouts of cycle exercise, involving 2 min of constant-work-rate exercise at severe intensity followed by a 1-min all-out sprint test. This trial was performed without prior intervention and 10 min after prior heavy-intensity exercise (ie, 6 min at 90% critical power).

RESULTS

The mean response time of VO2 was shortened after prior exercise for both UT (30.7 ± 9.2 vs 24.1 ± 7.2 s) and T (31.8 ± 5.2 vs 25.4 ± 4.3 s), but no group-by-condition interaction was detected. The end-sprint performance (ie, mean power output) was improved in both groups (UT ~4.7%, T ~2.0%; P < .05) by prior exercise.

CONCLUSION

The effect of prior heavy-intensity exercise on overall VO2 kinetics and short-term high-intensity exercise performance is independent of aerobic-training status.

Aptidão aeróbia e amplitude dos domínios de intensidade de exercício no ciclismo

INTRODUÇÃO: A determinação dos domínios de intensidade de exercício tem importantes implicações na prescrição do treino aeróbio e na elaboração de delineamentos experimentais. OBJETIVO: Analisar os efeitos do nível de aptidão aeróbia sobre a amplitude dos domínios de intensidade de exercício durante o ciclismo. MÉTODOS: Doze ciclistas (CIC), 11 corredores (COR) e oito indivíduos não treinados (NT) foram submetidos aos seguintes protocolos em diferentes dias: 1) teste progressivo para determinação do limiar de lactato (LL), consumo máximo de oxigênio (VO2máx) e sua respectiva intensidade (IVO2máx); 2) três testes de carga constante até a exaustão a 95, 100 e 110% IVO2máx para a determinação da potência crítica (PC); 3) testes até a exaustão para determinar a intensidade superior do domínio severo (Isup). As amplitudes dos domínios (moderado < LL; LL > pesado < PC; PC > severo < Isup) foram expressas como percentual da Isup (VO2). RESULTADOS: A amplitude do domínio moderado foi similar entre CIC (52 ± 8%) e COR (47 ± 4%) e significantemente maior no CIC em relação ao NT (41 ± 7%). O domínio pesado foi significantemente menor no CIC (17 ± 6%) em relação ao COR (27 ± 6%) e NT (27 ± 9%). Em relação ao domínio severo não foram encontradas diferenças significantes entre os CIC (31 ± 7%), COR (26 ± 5%) e NT (31 ± 7%). CONCLUSÃO: O domínio pesado de exercício é mais sensível a mudanças determinadas pelo nível de aptidão aeróbia, existindo a necessidade de que se atenda ao princípio da especificidade do movimento, quando se pretende obter um elevado grau de adaptação fisiológica.