On the existence of a lactate threshold during incremental exercise: a systems analysis

Area of Science:

• Exercise Physiology
• Systems Biology
• Biomedical Engineering

Background:

• The relationship between blood lactate concentration ([La]) and oxygen uptake (VO2) during incremental exercise is debated, with models suggesting either a smooth increase or an abrupt threshold.
• Understanding these dynamics is crucial for interpreting physiological responses to exercise.

Purpose of the Study:

• To investigate the dynamic characteristics of the physiological system governing [La] and VO2 responses during incremental exercise.
• To determine if the relationship between [La] and VO2 follows a continuous or threshold model.

Main Methods:

• Utilized system identification analysis techniques and a multivariate deterministic time series model.
• Fitted the model to simulated and experimental data of [La] and VO2 responses to incremental work rate changes.
• Employed a weighted recursive least squares algorithm to determine time-varying system response parameters.

Main Results:

• The developed model accurately fitted the experimental data.
• Identified two major transitions in model parameters at 53% and 77% of maximal VO2.
• These transitions indicate significant changes in the underlying physiological system's operational dynamics.

Conclusions:

• The exercise intensity range is divided into three distinct domains, each characterized by unique system dynamics.
• The findings suggest a multi-phase physiological response rather than a simple continuous or threshold model.
• Further research into this three-phase system can enhance understanding of [La] and VO2 regulation during exercise.