Key result
Maximum mechanical power normalised to muscle volume and specific muscle contractile strength significantly correlated with the percentage area of type II fibres (r = 0.654, p = 0.002).
Why the study?
Fast twitch fibre percentage determines muscle mechanical power, but the invasive nature of muscle biopsy limits its practical application in training.
Cross-Sectional (n=20)
No
Effect estimate: r = 0.654
p-value: p=0.002
A novel non-invasive method combining MRI and dynamometry can predict 43% of the variance in type II muscle fibre area in the soleus muscle, offering a potential alternative to invasive muscle biopsies for performance diagnostics.
Association of normalized muscle power with type II fiber area is hypothesis-generating; leaves open causal influence on contractile function.
The percentage area of fast twitch fibres of a muscle is a major determinant of muscle mechanical power and, thus, an important biomarker for the evaluation of training processes. However, the invasive character of the assessment (muscle biopsy) limits the wide application of the biomarker in the training praxis. Our purpose was to develop a non-invasive method for the assessment of fast twitch fibre content in human soleus muscle. Maximum muscle mechanical power depends on the fibre composition, the muscle volume and muscle specific tension. Therefore, we hypothesised that the percentage area of type II fibres would show a high relationship with the maximum muscle mechanical power normalised to muscle volume and specific muscle contractile strength (i.e. plantar flexion moment divided by muscle cross-sectional area). In twenty male adults the percentage area of type II fibres, volume and maximum cross-sectional area of the soleus muscle as well as the maximum plantar flexion moment and the maximum mechanical power were measured using muscle biopsies, magnet resonance tomography, and dynamometry. The maximum mechanical power normalised to muscle volume and specific muscle contractile strength provided a significant relationship (r=0.654, p=0.002) with the percentage area of type II fibres. Although the proposed assessment-parameter cannot fully replace histological measurements, the predictive power of 43% can provide a relevant contribution to performance diagnostics in the training praxis.
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Winkler et al. (2019) conducted a cross-sectional in Healthy (sport-active) (n=20). Non-invasive assessment of maximum mechanical power normalised to muscle volume and specific muscle contractile strength vs. Muscle biopsy (histological measurement of type II fibres) was evaluated on Correlation with percentage area of type II fibres (r = 0.654, p=0.002). Maximum mechanical power normalised to muscle volume and specific muscle contractile strength significantly correlated with the percentage area of type II fibres (r = 0.654, p = 0.002).
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