Keywords:
Musculoskeletal soft tissue, MR physics, MR, Physiological studies, Segmentation
Authors:
S. Kaspar, J. Reinhardt, M. Gloor, C. Stippich, D. Fischer, A. Fischmann; Basle/CH
DOI:
10.1594/ecr2013/C-1294
Conclusion
This is the first trial evaluating the influence of training and exercise on fat fraction measurements using quantitative MRI.
Consistently to our previous results [6] we found a reduced fat fraction in the second scan.
However,
we did not detect any significant change in fat fraction over the training period.
One possible reason would be the short training period,
which lasted only 6 to 8 weeks.
However significant changes is muscle CSA were reported after a 6-week training period with 3 training sessions per week [9],
while we could not detect a significant change in CSA.
In one study,
a 12 week training period lead to a significant reduction of inter-muscular fat in healthy volunteers [10].
It is,
however,
unclear whether these results could be translated to our measurements of intra-muscular fat fraction.
As we were interested in the influence of training on muscle fat fraction,
to evaluate confounding factors in clinical trials,
we excluded fat along the muscular fascia from the ROIs to be evaluated.
Any changes in inter-muscular fat would therefore be missed by our measurements.
While we did not find any significant changes in fat-fraction at each leg before or after the training session,
there was still a non-significant tendency for a decrease in muscle fat in the trained leg.
In addition we found a discrepancy of fat fraction after exercise between the legs,
during the second scanning session.
A possible explanation lies in the exercise regimen: bilateral squats were performed until muscular fatigue was reached.
As the volunteers were able to increase the number of squats by up to 40 / set,
the single exercise session was probably limited by the untrained leg.
We therefore assume,
that the trained leg would have been able to achieve more squats,
resulting in a further reduction of the fat fractions.
We found no correlation of fat fraction and CSA,
however we did not evaluate body-mass index or weight loss of our volunteers,
neither was there any dietary restriction.
So far there only few trials examined the effect of training by measuring the cross sectional area (CSA) in healthy volunteers [11].
Variability in cross sectional area between muscles was low in our patient cohort.
Smeulders et al found excellent inter- and intra-reader correlation in the volume of small muscles of the arm and concluded that differenced below 7% could be reliably detected [12].
Differences in mean CSA in our patient group were below 2% with 95% confidence intervals below 5% in most cases.
All possible changes are therefore too small to be detectable.
Ono and Higashihara reported changes in CSA of 28.5% two days after a single exercise session [13]; a similar increase in CSA would have been detected in our population.
One possible explanation is their use of a different training regimen with 10 repeats per set,
while our volunteers performed up to 70 squats per training session,
putting more strain on oxidative muscle fibres.
This would be supported by the fact,
that other trials using 10 repeats per set at 75% of maximal force,
found significant changes after a six week training period with less pronounced increase with persistent training over longer periods [9].
In conclusion we found that muscle fat fraction is influenced by a single exercise session but not by moderate training.
For future studies these results imply that fat fraction can be a good follow-up parameter in neuromuscular disorders,
as it was not modified by moderate training,
as long as there is no exercise session right before MRI scanning.