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

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.

A modified step-ramp-step protocol to prescribe constant-speed exercise in treadmill running

PURPOSE

This study investigated whether a running-adapted version of the cycling-based "step-ramp-step" (SRS) protocol would improve prediction of V ˙ O2 in treadmill exercise compared to the traditional prescriptive approach.

METHODS

Fourteen healthy individuals (6 females; 25 ± 6 years; 66.1 ± 12.7 kg) performed a treadmill-based SRS protocol including a ramp-incremental test to task failure followed by two constant-speed bouts within the moderate-(MODstep-below estimated lactate threshold; θLT), and heavy-intensity domains (HVYstep-between θLT and respiratory compensation point; RCP). Using the uncorrected V ˙ O2-to-speed relationship from the ramp exercise, three constant-speed bouts were performed at 40-50% between: baseline and θLT (CSEMOD); θLT and RCP (CSEHVY); and RCP and peak (CSESEV). For CSEMOD, CSEHVY, and CSESEV measured end-exercise V ˙ O2 was compared to predicted V ˙ O2 based on the: (i) "SRS-corrected" V ˙ O2-to-speed relationship (where MODstep and HVYstep were used to adjust the V ˙ O2 relative to speed); and (ii) linear "uncorrected" data.

RESULTS

Average treadmill speeds for CSEMOD and CSEHVY were 7.8 ± 0.8 and 11.0 ± 1.4 km·h-1, respectively, eliciting end-exercise V ˙ O2 of 1979 ± 390 and 2574 ± 540 mL·min-1. End-exercise V ˙ O2 values were not different compared to SRS-predicted V ˙ O2 at CSEMOD (mean difference: 5 ± 166 mL·min-1; p = 0.912) and CSEHVY (20 ± 128 mL·min-1; p = 0.568). The linear "uncorrected" estimates were not different for CSEMOD (- 91 ± 172 mL·min-1; p = 0.068) but lower for CSEHVY (- 195 ± 146 mL·min-1; p < 0.001). For CSESEV (running speed: 13.8 ± 1.7 km·h-1), the end-exercise V ˙ O2 was not different from peak V ˙ O2 achieved during the ramp (3027 ± 682 vs. 2979 ± 655 mL·min-1; p = 0.231).

CONCLUSION

In healthy individuals, the SRS protocol more accurately predicts speeds for a target V ˙ O2 compared to traditional approaches.

Heart Rate Variability Thresholds: Agreement with Established Approaches and Reproducibility in Trained Females and Males

PURPOSE

To determine in trained females and males i) the agreement between the gas exchange threshold (GET), lactate threshold 1 (LT1), and heart rate variability threshold 1 (HRVT1), as well as between the respiratory compensation point (RCP), lactate threshold 2 (LT2), and heart rate variability threshold 2 (HRVT2), and ii) the reproducibility of HRVT1 and HRVT2 during 2-min incremental step protocols.

METHODS

Fifty-seven trained participants (24 females) completed a 2-min step incremental test to task failure. Nineteen participants (eight females) completed a second test to evaluate reproducibility. Gas exchange and ventilatory responses, blood lactate concentration, and RR time series were recorded to assess the oxygen consumption (V̇O 2 ) and heart rate (HR) associated with the GET, RCP, LT1, LT2, HRVT1, and HRVT2.

RESULTS

V̇O 2 -GET versus V̇O 2 -HRVT1 and HR-GET versus HR-HRVT1 were statistically different for females (29.5 ± 4.0 vs 34.6 ± 6.1 mL·kg -1 ·min -1 ; 154 ± 11 vs 166 ± 12 bpm) and for males (33.9 ± 4.2 vs 42.7 ± 4.6 mL·kg -1 ·min -1 ; 145 ± 11 vs 165 ± 9 bpm; P < 0.001). V̇O 2 and HR at HRVT1 were greater than at LT1 ( P < 0.05). V̇O 2 -RCP versus V̇O 2 -HRVT2 and HR-RCP versus HR-HRVT2 were not statistically different for females (40.1 ± 4.7 vs 39.5 ± 6.7 mL·kg -1 ·min -1 ; 177 ± 9 vs 176 ± 9 bpm) and males (48.4 ± 5.4 vs 47.8 ± 4.8 mL·kg -1 ·min -1 ; 176 ± 8 vs 175 ± 9 bpm; P > 0.05). V̇O 2 and HR responses at LT2 were similar to HRVT2 ( P > 0.05). Intraclass correlation coefficient for V̇O 2 -HRVT1, HR-HRVT1, V̇O 2 -HRVT2, and HR-HRVT2 indicated good reproducibility when comparing the two different time points to standard methods.

CONCLUSIONS

Whereas HRVT2 is a valid and reproducible estimate of the RCP/LT2, current approaches for HRVT1 estimation did not show good agreement with outcomes at GET and LT1.

Heavy-, Severe-, and Extreme-, but Not Moderate-Intensity Exercise Increase V̇o 2max and Thresholds after 6 wk of Training

INTRODUCTION

This study assessed the effect of individualized, domain-based exercise intensity prescription on changes in maximal oxygen uptake (V̇O 2max ) and submaximal thresholds.

METHODS

Eighty-four young healthy participants (42 females, 42 males) were randomly assigned to six age, sex, and V̇O 2max -matched groups (14 participants each). Groups performed continuous cycling in the 1) moderate (MOD), 2) lower heavy (HVY1), and 3) upper heavy-intensity (HVY2) domain; interval cycling in the form of 4) high-intensity interval training (HIIT) in the severe-intensity domain, or 5) sprint-interval training (SIT) in the extreme-intensity domain; or no exercise for 6) control (CON). All training groups, except SIT, were work-matched. Training participants completed three sessions per week for 6 wk with physiological evaluations performed at PRE, MID, and POST intervention.

RESULTS

Compared with the change in V̇O 2max (∆V̇O 2max ) in CON (0.1 ± 1.2 mL·kg -1 ·min -1 ), all training groups, except MOD (1.8 ± 2.7 mL·kg -1 ·min -1 ), demonstrated a significant increase ( P < 0.05). HIIT produced the highest increase (6.2 ± 2.8 mL·kg -1 ·min -1 ) followed by HVY2 (5.4 ± 2.3 mL·kg -1 ·min -1 ), SIT (4.7 ± 2.3 mL·kg -1 ·min -1 ), and HVY1 (3.3 ± 2.4 mL·kg -1 ·min -1 ), respectively. The ΔPO at the estimated lactate threshold ( θLT ) was similar across HVY1, HVY2, HIIT, and SIT, which were all greater than CON ( P < 0.05). The ΔV̇O 2 and ΔPO at θLT for MOD was not different from CON ( P > 0.05). HIIT produced the highest ΔPO at maximal metabolic steady state, which was greater than CON, MOD, and SIT ( P < 0.05).

CONCLUSIONS

This study demonstrated that i) exercise intensity is a key component determining changes in V̇O 2max and submaximal thresholds and ii) exercise intensity domain-based prescription allows for a homogenous metabolic stimulus across individuals.

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.

Evaluation of the "Step-Ramp-Step" Protocol: Accurate Aerobic Exercise Prescription with Different Steps and Ramp Slopes

PURPOSE

To assess whether: i) a lower amplitude constant-load MOD is appropriate to determine the mean response time (MRT); ii) the method accurately corrects the dissociation in the V̇O 2 -PO relationship during ramp compared with constant-load exercise when using different ramp slopes.

METHODS

Eighteen participants (7 females) performed three SRS tests including: i) step-transitions into MOD from 20 to 50 W (MOD 50 ) and 80 W (MOD 80 ); and ii) slopes of 15, 30, and 45 W·min -1 . The V̇O 2 and PO at the gas exchange threshold (GET) and the corrected respiratory compensation point (RCP CORR ) were determined. Two to three 30-min constant-load trials evaluated the V̇O 2 and PO at the maximal metabolic steady state (MMSS).

RESULTS

There were no differences in V̇O 2 at GET (1.97 ± 0.36, 1.99 ± 0.36, 1.95 ± 0.30 L·min -1 ), and RCP (2.81 ± 0.57, 2.86 ± 0.59, 2.84 ± 0.59) between 15, 30, and 45 W·min -1 ramps, respectively ( P > 0.05). The MRT in seconds was not affected by the amplitude of the MOD or the slope of the ramp (range 19 ± 10 s to 23 ± 20 s; P > 0.05). The mean PO at GET was not significantly affected by the amplitude of the MOD or the slope of the ramp (range 130 ± 30 W to 137 ± 30 W; P > 0.05). The PO at RCP CORR was similar for all conditions ((range 186 ± 43 W to 193 ± 47 W; P > 0.05).

CONCLUSIONS

The SRS protocol accounts for the V̇O 2 MRT when using smaller amplitude steps, and for the V̇O 2 slow component when using different ramp slopes, allowing for accurate partitioning of the exercise intensity domains in a single test.

Combining Near-Infrared Spectroscopy and Heart Rate Variability Derived Thresholds to Estimate the Critical Intensity of Exercise

ABSTRACT

Fleitas-Paniagua, PR, de Almeida Azevedo, R, Trpcic, M, Murias, JM, and Rogers, B. Combining near-infrared spectroscopy and heart rate variability derived thresholds to estimate the critical intensity of exercise. J Strength Cond Res 38(1): e16-e24, 2024-Critical intensity determination often requires costly tools and several testing sessions. Alternative approaches display relatively large individual variation. Therefore, simpler estimations with improved precision are needed. This study evaluated whether averaging the heart rate (HR) and oxygen uptake (V̇O 2 ) responses associated with the muscle deoxyhemoglobin concentration breakpoint ([HHb] BP ) and the heart rate variability (HRV) given by the detrended fluctuation analysis second threshold (HRVT2) during ramp incremental (RI) test improved the accuracy of identifying the HR and V̇O 2 at the respiratory compensation point (RCP). Ten female and 11 male recreationally trained subjects performed a 15 W·minute -1 RI test. Gas exchange, near-infrared spectroscopy (NIRS), and RR interval were recorded to assess the RCP, [HHb] BP , and HRVT2. Heart rate (mean ± SD : 158 ± 14, 156 ± 13, 160 ± 14 and, 158 ± 12 bpm) and V̇O 2 (3.08 ± 0.69, 2.98 ± 0.58, 3.06 ± 0.65, and 3.02 ± 0.60 L·minute -1 ) at the RCP, [HHb] BP , HRVT2, and HRVT2&[HHb] BP average (H&H Av ), respectively, were not significantly different ( p > 0.05). The linear relationship between H&H Av and RCP was higher compared with the relationship between [HHb] BP vs RCP and HRVT2 vs RCP for both HR ( r = 0.85; r = 0.73; r = 0.79, p > 0.05) and V̇O 2 ( r = 0.94; r = 0.93; r = 0.91, p > 0.05). Intraclass correlation between RCP, [HHb] BP , HRVT2, and H&H AV was 0.93 for V̇O 2 and 0.79 for HR. The [HHb] BP and the HRVT2 independently provided V̇O 2 and HR responses that strongly agreed with those at the RCP. Combining [HHb] BP and the HRVT2 resulted in estimations of the V̇O 2 and HR at the RCP that displayed smaller variability compared with each modality alone.

A Single Test Protocol to Establish the Full Spectrum of Exercise Intensity Prescription

PURPOSE

We aimed to test the extended capabilities of the SRS protocol by validating its capacity to predict the power outputs for targeted metabolic rates (V̇O 2 ) and time-to-task failure ( Tlim ) within the heavy- and severe-intensity domain, respectively.

METHODS

Fourteen young individuals completed (i) an SRS protocol from which the power outputs at GET and RCP (RCP CORR ), and the work accruable above RCP CORR , defined as W ' RAMP , were derived; (ii) one heavy-intensity bout at a power output predicted to elicit a targeted V̇O 2 equidistant from GET and RCP; and (iii) four severe-intensity trials at power outputs predicted to elicit targeted Tlim at minutes 2.5, 5, 10, and 13. These severe-intensity trials were also used to compute the constant-load-derived critical power and W ´ ( W ' CONSTANT ).

RESULTS

Targeted (2.41 ± 0.52 L·min -1 ) and measured (2.43 ± 0.52 L·min -1 ) V̇O 2 at the identified heavy-intensity power output (162 ± 43 W) were not different ( P = 0.71) and substantially concordant (CCC = 0.95). Likewise, targeted and measured Tlim for the four identified severe-intensity power outputs were not different ( P > 0.05), and the aggregated coefficient of variation was 10.7% ± 8.9%. The derived power outputs at RCP CORR (192 ± 53 W) and critical power (193 ± 53 W) were not different ( P = 0.65) and highly concordant (CCC = 0.99). There were also no differences between W ' RAMP and W ' CONSTANT ( P = 0.51).

CONCLUSIONS

The SRS protocol can accurately predict power outputs to elicit discrete metabolic rates and exercise durations, thus providing, with time efficiency, a high precision for the control of the metabolic stimulus during exercise.

A Perspective on High-Intensity Interval Training for Performance and Health

Interval training is a simple concept that refers to repeated bouts of relatively hard work interspersed with recovery periods of easier work or rest. The method has been used by high-level athletes for over a century to improve performance in endurance-type sports and events such as middle- and long-distance running. The concept of interval training to improve health, including in a rehabilitative context or when practiced by individuals who are relatively inactive or deconditioned, has also been advanced for decades. An important issue that affects the interpretation and application of interval training is the lack of standardized terminology. This particularly relates to the classification of intensity. There is no common definition of the term "high-intensity interval training" (HIIT) despite its widespread use. We contend that in a performance context, HIIT can be characterized as intermittent exercise bouts performed above the heavy-intensity domain. This categorization of HIIT is primarily encompassed by the severe-intensity domain. It is demarcated by indicators that principally include the critical power or critical speed, or other indices, including the second lactate threshold, maximal lactate steady state, or lactate turnpoint. In a health context, we contend that HIIT can be characterized as intermittent exercise bouts performed above moderate intensity. This categorization of HIIT is primarily encompassed by the classification of vigorous intensity. It is demarcated by various indicators related to perceived exertion, oxygen uptake, or heart rate as defined in authoritative public health and exercise prescription guidelines. A particularly intense variant of HIIT commonly termed "sprint interval training" can be distinguished as repeated bouts performed with near-maximal to "all out" effort. This characterization coincides with the highest intensity classification identified in training zone models or exercise prescription guidelines, including the extreme-intensity domain, anaerobic speed reserve, or near-maximal to maximal intensity classification. HIIT is considered an essential training component for the enhancement of athletic performance, but the optimal intensity distribution and specific HIIT prescription for endurance athletes is unclear. HIIT is also a viable method to improve cardiorespiratory fitness and other health-related indices in people who are insufficiently active, including those with cardiometabolic diseases. Research is needed to clarify responses to different HIIT strategies using robust study designs that employ best practices. We offer a perspective on the topic of HIIT for performance and health, including a conceptual framework that builds on the work of others and outlines how the method can be defined and operationalized within each context.

Effect of ramp slope on intensity thresholds based on correlation properties of heart rate variability during cycling

An index of heart rate variability (HRV), detrended fluctuation analysis (DFA a1) has gathered interest as a surrogate marker of exercise intensity boundaries. The aim of this report was to examine heart rate variability threshold (HRVT) behavior across different ramp incremental (RI) slopes. Seventeen participants completed a series of three RI (15, 30, and 45 W · min-1 slopes) with monitoring of gas exchange parameters, heart rate (HR) and HRV. HRVT1 was defined as the V̇O2 or HR at which DFA a1 reached 0.75 and the HRVT2 at which these values reached 0.5. HRVTs were compared by Pearson's r, Bland-Altman analysis, ICC3,1 , ANOVA, and paired t-testing. An excellent degree of reliability was seen across all three ramps, with an ICC3,1 of 0.93 and 0.88 for the HRVT1 V̇O2 and HR, respectively, and 0.90 and 0.92 for the HRVT2 V̇O2 and HR, respectively. Correlations between HRVT1/2 of the individual ramps were high with r values 0.84-0.95 for both HR and V̇O2 . Bland-Altman differences ranged between -1.4 and 1.2 mL · kg-1  · min-1 and -2 and +2 bpm. Paired t-testing showed no mean differences between any HRVT1/2 ramp comparisons. Cycling ramp slope does not appear to affect either HRVT1 or HRVT2 in terms of HR or V̇O2 .

Can the heart rate response at the respiratory compensation point be used to retrieve the maximal metabolic steady state?

The metabolic rate (VO2) at the maximal metabolic steady state (MMSS) is generally not different from the VO2 at the respiratory compensation point (RCP). Based on this, it is often assumed that the heart rate (HR) at RCP would also be similar to that at MMSS. The study aims to compare the HR at RCP with that at MMSS. Seventeen individuals completed a ramp-incremental test, a series of severe-intensity trials to estimate critical power and two-to-three 30-min trials to confirm MMSS. The HR at RCP was retrieved by linear interpolation of the ramp-VO2/HR relationship and compared to the HR at MMSS recorded at 10, 15, 20, 25 and 30 min. The HR at RCP was 166 ± 12 bpm. The HR during MMSS at the timepoints of interest was 168 ± 8, 171 ± 8, 175 ± 9, 177 ± 9 and 178 ± 10 bpm. The HR at RCP was not different from the HR at MMSS at 10 min (P > 0.05) but lower at subsequent timepoints (P < 0.05) with this difference becoming progressively larger. For all timepoints, limits of agreement were large (~30 bpm). Given these differences and the variability at the individual level, the HR at RCP cannot be used to control the metabolic stimulus of endurance exercise.

Functional threshold power is not a valid marker of the maximal metabolic steady state

Functional Threshold Power (FTP) has been considered a valid alternative to other performance markers that represent the upper boundary of the heavy intensity domain. However, such a claim has not been empirically examined from a physiological perspective.This study examined the blood lactate and VO₂ response when exercising at and 15 W above the FTP (FTP_+15W). Thirteen cyclists participated in the study. The VO₂ was recorded continuously throughout FTP and FTP_+15W, with blood lactate measured before the test, every 10 minutes and at task failure. Data were subsequently analysed using two-way ANOVA. The time to task failure at FTP and FTP_+15W were 33.7 ± 7.6 and 22.0 ± 5.7 minutes (p < 0.001), respectively. The VO_2peak was not attained when exercising at FTP_+15W (VO_2peak: 3.61 ± 0.81 vs FTP_+15W 3.33 ± 0.68 L·min^-1, p < 0.001). The VO₂ stabilised during both intensities. However, the end test blood lactate corresponding to FTP and FTP_+15W was significantly different (6.7 ± 2.1 mM vs 9.2 ± 2.9 mM; p < 0.05). The VO₂ response corresponding to FTP and FTP_+15W suggests that FTP should not be considered a threshold marker between heavy and severe intensity.

Time Course of Performance Fatigability during Exercise below, at, and above the Critical Intensity in Females and Males

PURPOSE

This study aimed to investigate the time course and amplitude of performance fatigability during cycling at intensities around the maximal lactate steady state (MLSS) until task failure (TTF).

METHODS

Ten females and 11 males were evaluated in eight visits: 1) ramp incremental test; 2-3) 30-min constant power output (PO) cycling for MLSS determination; and 4-8) cycling to TTF at PO relative to the MLSS of (i) -15%, (ii) -10 W, (iii) at MLSS, and (iv) +10 W, and (v) +15%. Performance fatigability was characterized by femoral nerve electrical stimulation of knee extensors at baseline; minutes 5, 10, 20, and 30; and TTF. Oxygen uptake, blood lactate concentration, muscle oxygen saturation, and perceived exertion were evaluated.

RESULTS

Approximately 75% of the total performance fatigability occurred within 5 min of exercise, independently of exercise intensity, followed by a further change at minute 30. Contractile function declined more in males than females (all P < 0.05). At task failure, exercise duration declined from MLSS -15% to MLSS +15% (all P < 0.05), accompanied by a greater rate of decline after MLSS +15% and MLSS +10 compared with MLSS, MLSS -10 , and MLSS -15% for voluntary activation (-0.005 and -0.003 vs -0.002, -0.001 and -0.001%·min -1 , respectively) and contractile function (potentiated single twitch force, -0.013 and -0.009 vs -0.006, -0.004 and -0.004%·min -1 , respectively).

CONCLUSIONS

Whereas the time course of performance fatigability responses was similar regardless of exercise intensity and sex, the total amplitude and rate of change were affected by the distinct metabolic disturbances around the MLSS, leading to different performance fatigability etiologies at task failure.

Impairment in maximal lactate steady state after carbon monoxide inhalation is related to training status

NEW FINDINGS

What is the central question of this study? What is the effect of an elevated COHb concentration following carbon monoxide inhalation on the maximal lactate steady state (MLSS) in humans and is this effect dependent on aerobic fitness? What is the main finding and its importance? An elevated COHb concentration intensified physiological responses to exercise at the MLSS- including heart rate, ventilation, and peripheral fatigue-in all participants and reduced the MLSS (i.e., destabilized the blood lactate concentration) in trained but not untrained males and females.

ABSTRACT

This study investigated whether a lower effective [Hb], induced by carbon monoxide (CO) inhalation, reduces the peak oxygen uptake (V̇O₂ peak) and the maximal lactate steady state (MLSS) and whether training status explains individual variation in these impairments. Healthy young participants completed two ramp incremental tests (n = 20 [10 female]) and two trials at MLSS (n = 16 [8 female]) following CO rebreathe tests and sham procedures (SHAM) in random orders. All fitness variables were normalized to fat-free mass (FFM) to account for sex-related differences in body composition, and males and females were matched for aerobic fitness. The V̇O₂ peak (mean [SD]: -4.2 [3.7]%), peak power output (-3.3 [2.2]%), and respiratory compensation point (-6.3 [4.5]%) were reduced in CO compared with SHAM (P < 0.001 for all), but the gas exchange threshold (-3.3 [7.1]%) was not (P = 0.077). Decreases in V̇O₂ peak (r = -0.45; P = 0.047) and peak power output (r = -0.49; P = 0.029) in CO were correlated with baseline aerobic fitness. Compared to SHAM, physiological and perceptual indicators of exercise-related stress were exacerbated by CO while cycling at MLSS. Notably, the mean blood lactate concentration ([La]) increased (i.e., Δ[La] > 1.0 mM) between 10 min (5.5 [1.4] mM) and 30 min (6.8 [1.3] mM; P = 0.026) in CO, with 9/16 participants classified as unstable. These unstable participants had a higher V̇O₂ peak (66.2 [8.5] vs. 56.4 [8.8] mL·kg FFM^-1 ·min^-1 , P = 0.042) and V̇O₂ at MLSS (55.8 vs. 44.3 mL·kg FFM^-1 ·min^-1 , P = 0.006) compared to the stable group. In conclusion, a reduced O₂ -carrying capacity decreased maximal and submaximal exercise performance, with higher aerobic fitness associated with greater impairments in both. This article is protected by copyright. All rights reserved.

Lactate Thresholds and the Simulation of Human Energy Metabolism: Contributions by the Cologne Sports Medicine Group in the 1970s and 1980s

Today, researchers, practitioners, and physicians measure the concentration of lactate during a graded exercise test to determine thresholds related to the maximal lactate steady state (maxLass) as a sensitive measure of endurance capacity. In the 1970s and 1980s, a group of Cologne-based researchers around Wildor Hollmann, Alois Mader, and Hermann Heck developed the methodology for systematic lactate testing and introduced a 4 mmol^.L⁻¹ lactate threshold. Later, they also developed the concept of the maxLass, and Mader designed a sophisticated mathematical model of human energy metabolism during exercise. Mader`s model simulates metabolic responses to exercise based on individual variables such as maximum oxygen uptake (V˙O_2max) and the maximal rate of lactate formation (ν_La.max). Mader’s model predicts that the ν_La.max reduces the power at the anaerobic threshold and endurance performance but that a high ν_La.max is required for events with high power outputs in elite athletes. Mader’s model also assumed before the millennium that the rate of fat oxidation is explained by the difference between glycolytic pyruvate synthesis and the actual rate of pyruvate oxidation which is consistent with current opinion. Mader’s model also simulated the V˙O_2max slow component in the mid-1980s. Unfortunately, several landmark studies by the Cologne group were only published in German, and as a result, contributions by the Cologne group are under-appreciated in the English-speaking world. This narrative review aims to introduce key contributions of the Cologne group to human metabolism research especially for readers who do not speak German.

Decoupling of Internal and External Workload During a Marathon: An Analysis of Durability in 82,303 Recreational Runners

Aim

This study characterised the decoupling of internal-to-external workload in marathon running and investigated whether decoupling magnitude and onset could improve predictions of marathon performance.

Methods

The decoupling of internal-to-external workload was calculated in 82,303 marathon runners (13,125 female). Internal workload was determined as a percentage of maximum heart rate, and external workload as speed relative to estimated critical speed (CS). Decoupling magnitude (i.e., decoupling in the 35–40 km segment relative to the 5–10 km segment) was classified as low (< 1.1), moderate (≥ 1.1 but < 1.2) or high (≥ 1.2). Decoupling onset was calculated when decoupling exceeded 1.025.

Results

The overall internal-to-external workload decoupling experienced was 1.16 ± 0.22, first detected 25.2 ± 9.9 km into marathon running. The low decoupling group (34.5% of runners) completed the marathon at a faster relative speed (88 ± 6% CS), had better marathon performance (217.3 ± 33.1 min), and first experienced decoupling later in the marathon (33.4 ± 9.0 km) compared to those in the moderate (32.7% of runners, 86 ± 6% CS, 224.9 ± 31.7 min, and 22.6 ± 7.7 km), and high decoupling groups (32.8% runners, 82 ± 7% CS, 238.5 ± 30.7 min, and 19.1 ± 6.8 km; all p < 0.01). Compared to females, males’ decoupling magnitude was greater (1.17 ± 0.22 vs. 1.12 ± 0.16; p < 0.01) and occurred earlier (25.0 ± 9.8 vs. 26.3 ± 10.6 km; p < 0.01). Marathon performance was associated with the magnitude and onset of decoupling, and when included in marathon performance models utilising CS and the curvature constant, prediction error was reduced from 6.45 to 5.16%.

Conclusion

Durability characteristics, assessed as internal-to-external workload ratio, show considerable inter-individual variability, and both its magnitude and onset are associated with marathon performance.

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.

Comparing muscle VO2 from near-infrared spectroscopy desaturation rate to pulmonary VO2 during cycling below, at and above the maximal lactate steady state

Muscle oxygen uptake (V̇O_2m) evaluated from changes in the near-infrared spectroscopy oxygen desaturation slope during a 5-s arterial blood flow occlusion has been proposed as an estimation of the actual V̇O_2m. However, its correspondence with pulmonary oxygen uptake (V̇O_2p) during exercise remains unknown.

PURPOSE

to investigate the V̇O_2m and V̇O_2p relationship in females and males in response to prolonged constant-load cycling exercise at different intensities.

METHODS

Eighteen participants (8 females) visited the laboratory on six occasions: 1) ramp incremental test; 2-3) 30-min constant power output (constant-PO) exercise bout to determine the maximal lactate steady state (MLSS); 4-6) constant-PO exercise bouts to task failure at (i) 15% below MLSS (MLSS_-15%); (ii) MLSS; (iii) 15% above MLSS (MLSS_+15%). V̇O_2m was estimated at baseline, at min 5, 10, 20, 30, and at task failure. V̇O_2p was continuously recorded during the constant-PO bouts.

RESULTS

V̇O_2pand V̇O_2m significantly increased from min 5 to min 30 in MLSS condition (all p < 0.05) and from min 5 to min 10 in MLSS_+15% condition (all p < 0.05). V̇O_2pand V̇O_2m were correlated (r² adj range of 0.70-0.98, all p < 0.001) amongst exercise intensities in both females and males. Additionally, both variables were also correlated when expressed as percent (r² adj range of 0.52-0.77, all p < 0.001).

CONCLUSION

V̇O_2p and V̇O_2m responses were similar when exercising below, at, and above the MLSS independently of sex. Most importantly, V̇O_2p andV̇O_2m were correlated regardless the exercise intensity and sex of the participants.