There are considerable differences among individuals in the magnitude of improvement in
cardiorespiratory fitness in response to a standardized exercise program. Understanding why there
is human variability in the adaptations to training is of particular importance for personalized
exercise medicine applications and also for elite athletes motivated by the pursuit of sports
performance. The large inter-individual differences in muscle typology may explain, in part, the
divergent responses to exercise training. Slow twitch fibers have low fatigability and may adapt
optimally to high-volume contractions, whereas fast twitch fibers have high fatigability and need
longer to recover but may adapt optimally to high-frequency contractions. Therefore, the current
project will compare individual responses in participants with fast-twitch and slow-twitch typology
following both a one-fits-all training period and an individualized training period, in which
modalities are adapted to muscle typology. Interaction between muscle typology, training
modalities and training effects are rarely investigated because the only available method to
quantify muscle fiber type composition was histological evaluation of an invasive muscle biopsy.
Yet, we have recently developed a non-invasive method by proton magnetic resonance
spectroscopy. This now allows us to develop guidelines for adequate training programs in a
personalized and therefore more cost-effective manner.