Fig. 1

Schematic overview of methods. a Clinical 3 Tesla MR scanner with ²³Na knee-coil for lower leg muscles placed in. b ²³Na knee-coil with four calibration phantoms containing solutions of 10, 20, 30 and 40 mmol/L NaCl. c After dynamic reconstruction of the data based on a dedicated plugin, regions of interest (ROI) were drawn in Horos on MR images for all lower leg muscles and all calibration phantoms. d Signal intensities of ROIs (measured in arbitrary units) were translated to sodium content in mM using a linear trend analysis. Finally, sodium content of muscle tissue was assessed over time after exercise