Non invasive investigation of the underlying cause of differences in metabolic capacity along the length of the tibialis anterior muscle using Magnetic Resonance

During skeletal muscle exercise the level of the energy buffer phosphocreatine
(PCr) decreases. The recovery of the PCr level after exercise is considered to
be a measure for the oxidative capacity of the exercising muscle. These PCr
changes can be observed in vivo by 31P MR spectroscopy. The rate of PCr
recovery varies between subjects (e.g. trained vs. untrained, elderly vs.
young) and also between muscles. In recent years it has become clear that
individual muscles are not a homogenous entity. For instance, we observed for
the first time that the PCr recovery rate after an isometric exercise can also
vary along the length of a muscle, i.e. in the tibialis anterior (TA). The
reason for this apparent strong gradient in the PCr recovery rate may be
because of a variation in oxidative capacity along the TA, for instance due to
variable fibre type composition, but also because of differences in
end-exercise pH and oxygen supply. Since our previous study showed no
difference in end-exercise pH along the TA, the gradient in PCr recovery rate
is either controlled by variable oxygen supply or by differences in true
oxidative capacity, which may be due to a variable fibre type distribution.
Therefore, we propose to investigate if fiber type composition and/or oxygen
supply play a role in the PCr recovery rate variation along the length of the
TA. During exercise the peak for inorganic phosphate (Pi) in the 31P MR
spectrum may split in two components which are assumed to reflect the dominant
fiber types. Tissue perfusion can be assessed by so-called IVIM diffusion and
blood oxygenation by T2* MRI and NIRS.

To investigate if difference in fiber type and/or oxygen supply are the
underlying cause for the difference in PCr recovery along the length of the
tibialis anterior muscle.

Cross sectional study where we investigate the acute effect of muscle
contraction within regions of the tibialis anterior on PCr recovery and muscle
perfusion.

The proposed study is fully non-invasive. Therefore, burden and risk is
minimal. The maximum duration of the MR experiment is 1,5 hour. Furthermore,
the subject has to perform 3 times muscle contraction until exhaustion, which
can be experienced as difficult. Both the duration of the MR experiment and
muscle contraction are, according to our own experience, well tolerated by
young healthy volunteers.