Noninvasive Monitoring of Training Induced Muscle Adaptation with P31-MRS: Fibre Type Shifts Correlate with Metabolic Changes

Abstract EN

Purpose.

To evaluate training induced metabolic changes noninvasively with P31 magnetic resonance spectroscopy (P31-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 P31-MRS of the resting gastrocnemius muscle were performed.

Fibre type distribution was analyzed histologically and tested for correlation with the ratios of high energy phosphates ([PCr]/[Pi], [PCr]/[βATP] and [PCr + Pi]/[βATP]).

The correlation between the changes of the P31-MRS parameters during training and the resulting changes in fibre composition were also analysed.

Results.

We observed an increased type-II-fibre proportion after speed-strength and detraining.

After endurance training the percentage of fast-twitch fibres was reduced.

The progression of the [PCr]/[Pi]-ratio was similar to that of the fast-twitch fibres during the training.

We found a correlation between the type-II-fibre proportion and [PCr]/[Pi] (r=0.70, P<0.01) or [PCr]/[βATP] (r=0.69, P<0.01); the correlations between its changes (delta) and the fibre-shift were significant as well (delta[PCr]/[Pi] r=0.66, delta[PCr]/[βATP] r=0.55, P<0.01).

Conclusion.

Shifts in fibre type composition and high energy phosphate metabolite content covary in human gastrocnemius muscle.

Therefore P31-MRS might be a feasible method for noninvasive monitoring of exercise-induced fibre type transformation.