Non‐Invasive Real‐Time Detection of Potassium Level Changes in Skeletal Muscles During Exercise by Magnetic Resonance Spectroscopy

Potassium is essential in cellular functions, with specific importance in muscle activity and cardiovascular health. It is the main intracellular cation in the human body, with 70% located in muscle. Traditional methods to measure potassium levels are invasive and lack specificity for intracellular concentrations. Recently, non-invasive in vivo investigation of K+ ion homeostasis has become feasible by using ³⁹K magnetic resonance imaging (MRI) and MR spectroscopy (MRS) at ultrahigh magnetic fields. However, studies demonstrating the sensitivity of ³⁹K MRI or MRS to detect potassium alterations in disease or upon intervention are sparse. This study utilizes ³⁹K MRS to non-invasively track real-time intramuscular potassium changes during exercise, providing an assessment of potassium dynamics and exploring the potential for technical artifacts in the measurements. Five healthy subjects (three males, two females) were recruited to perform standardized dynamic knee extensions inside a 7T MR scanner. Potassium levels were measured using a ³⁹K MRS protocol that included periods of rest, moderate, and heavy exercise followed by recovery. Additionally, possible measurement artifacts due to muscle movement or changes in coil position relative to the thigh were evaluated using ³⁹K MRS and ¹H MRI monitoring in separate sessions. The study revealed a consistent decrease in potassium levels during both moderate and heavy exercise, with an average decrease of 5%-6%. These changes were rapidly detectable and were reversed upon cessation of exercise, indicating effective in vivo monitoring capability. Possible experimental artifacts were investigated, and the results suggested not to be responsible for the detected potassium changes during exercise. The results of the non-localized ³⁹K MRS measurements during exercise correlated well with expected physiological changes based on previous literature. The application of ³⁹K MRS provides a valuable non-invasive tool for studying potassium dynamics in human skeletal muscle. This technique could enhance our understanding of muscle physiology and metabolic disorders. The ability to measure these changes in real time and non-invasively highlights the potential for clinical applications, including monitoring of diseases affecting muscle and cellular metabolism.