Noninvasive monitoring of training induced muscle adaptation with 31P-MRS: fibre type shifts correlate with metabolic changes.

Purpose: To evaluate training induced metabolic changes noninvasively with (31)P magnetic resonance spectroscopy ((31)P-MRS) for measuring muscle fibre type adaptation.

Methods: Eleven volunteers underwent a 24-week training, consisting of speed-strength, endurance, and detraining (each 8 weeks). Prior to and following each training period, needle biopsies and (31)P-MRS of the resting gastrocnemius muscle were performed.