Method for detection of intracellular pH threshold; comparison between subjective observation and regression analysis

Area of Science:

• Exercise Physiology
• Biophysics

Background:

• Assessing metabolic changes during exercise is crucial for understanding muscle function.
• Intracellular pH (pHi) and phosphate compounds are key indicators of metabolic state.
• Objective and reproducible methods for determining thresholds of these parameters are needed.

Purpose of the Study:

• To evaluate the objectivity and reproducibility of intracellular pH threshold (pHT) detection.
• To compare visual (E) and regression analysis (linear, semilog, log-log) methods for pHT determination.
• To examine the threshold of the inorganic phosphate-to-phosphocreatine ratio (PT) using regression analysis.

Main Methods:

• Fifteen male subjects performed wrist flexion to exhaustion using a ramp protocol.
• Continuous 31P-MRS (phosphorus magnetic resonance spectroscopy) monitored muscle tissue.
• Intracellular pH and phosphate compounds were recorded minute-by-minute.

Main Results:

• Intracellular pH threshold (pHT) showed significant reproducibility across visual and three regression analysis methods.
• The inorganic phosphate-to-phosphocreatine ratio (PT) threshold was not reproducible.
• A clear threshold behavior was observed for changes in muscle pH.

Conclusions:

• Intracellular pH threshold (pHT) is a reproducible marker during exercise.
• The existence of a reproducible phosphate-to-phosphocreatine ratio (PT) threshold is questionable.
• These findings support the concept of a distinct metabolic threshold related to intracellular pH changes.