Author(s): WU, F., BI, Z., LYU, M., ZHONG, Y., DAI, S., WANG, J., LI, Y., Institution: SHANGHAI UNIVERSITY OF SPORT, Country: CHINA, Abstract-ID: 2076

INTRODUCTION:
Maximal lactate steady state (MLSS) is the physiological boundary between heavy and severe intensity domains [1]. However, its determination typically requires multiple constant load tests (30 min each) over several days, often reducing participant willingness due to fatigue and time commitment. Alternatively, a method to calculate MLSS power based on individual maximal aerobic power (VO2max) and maximal lactate accumulation rate (VLamax) was proposed. This method simulates the dynamic equilibrium of lactate production and clearance, requiring only one ramp incremental test and one short sprint test [2]. While applied in athletes of varying endurance levels, VLamax determination relies heavily on the assumption of "alactic time interval" (t_alac), a parameter that remains controversial [2, 3, 4]. This study aimed to evaluate the validity of four calculated MLSS (MLSScalc) variations based on different t_alac settings against the rigorously tested MLSS (MLSStest).
METHODS:
Nineteen highly trained male athletes (wrestling, soccer, swimming, etc.) participated in this study. All participants completed: 1) A ramp incremental test for VO2max; 2) Two 15-s isokinetic all-out sprints separated by >7 days for VLamax (the average of the two trials was used for analysis); and 3) 2-5 constant load tests (30 min) to strictly determine MLSStest [1]. VLamax was calculated using four common t_alac settings [2, 3, 4]: Formula 1 (time to 3.5% drop from peak power); Formula 2 (time to peak power); Formula 3 (time to peak power and aerobic contribution); and Formula 4 (no deduction). These VLamax values were input into the standard metabolic simulation model to derive four MLSScalc values.
RESULTS:
Test-retest reliability for VLamax was good across all formulas (ICC: 0.737 to 0.866; CV: 5.28% to 8.12%). The mean MLSStest was 173.5 +/- 25.7 W. The mean MLSScalc values ranged from 193.4 W to 205.5 W. Although all MLSScalc variations showed significant correlations with MLSStest (r = 0.816 to 0.826, p < 0.05), paired t-tests revealed that all calculated results were significantly higher than measured values (p < 0.05). MLSScalc overestimated MLSS by +19.9 W (Formula 1) to +32.0 W (Formula 4). Bland-Altman analysis demonstrated wide limits of agreement (LoA) of approximately +/- 34 W regardless of the equation used.
CONCLUSION:
Despite satisfactory VLamax reliability, the calculation method based on VLamax systematically overestimates MLSS in highly trained mixed-sport athletes. The individual error range of MLSScalc is too large to meet the precision requirements for individual training prescription. This systematic overestimation suggests that current algorithms may not be fully applicable across different sports and endurance levels, and direct constant load testing remains irreplaceable.
REFERENCES:
1. Beneke R. Eur J Appl Physiol 2003;89:95.
2. Hauser T et al. Theor Biol Med Model 2014;11:1.
3. Yang WH et al. Front Physiol 2023;14:1147321.
4. Wackerhage H et al. Sports Med 2025;55:1853.