The TEFR09 participants had to endure an immense physical exposure, leading to stress fractures, swollen feet, sometimes necessitating cutting away part of the running shoe in order to continue running,1
but 46 out of 67 (68.7%) were able to finish. Our study participants showed changes during the run with an increase of the AT diameter and intraosseous SI as well as subcutaneous oedema. Non-finishers displayed higher rates of soft tissue oedema.
We had hypothesised that runners will show increasing pathology of hind foot and ankle as well as AT during the run even if they are able to finish the TEFR09.
The literature up to date had been inconclusive as to the consequences of marathon training, including our own data15
that had shown little changes in MRI appearance of the hind foot and AT during training and participation of a (half) marathon. However, the TEFR09 with extended running load over 64 stages without any day rest is not comparable to other sporting events or normal leisure activities.
The results show a gradual increase of the diameter of the AT from a mean of 6.8 to a mean of 7.8 mm over the course of the run. This stands in contrast to reports linking AT diameter to disease21
or showing decrease of AT diameter with training.22
However, the results match with previous data on runners23
and healthy marathoners15
or reports stressing the relevance of AT SI24
or calcaneus oedema at tendon insertion25
for pathology. No significant correlation could be shown to tendon SI or lesions or calcaneus bone oedema at tendon insertion, further strengthening the point that the observed AT changes seem to be adaptive.
Furthermore, gradual increases over the run in osseous signal of the calcaneus as well as the maximal intraosseous signal in any foot bone and the number of bone lesions could be shown (see ).
The increased SI draws attention to reports on stress fractures,9
but the appearance of the recorded alterations in our study occurred early and did not coincide with stress fractures. Thus, the signal increase is thought to result from stress response12
as reported in asymptomatic runners.8
Sometimes diffuse bone oedema in nearly all end phalanges pointed to contusions because of tight shoes. However, bone oedema and lesions were not linked to abortion of the run (NF status).
Also, increases in subcutaneous oedema occurred over the course of the run (see ). Here, subcutaneous oedema at the time of the start of TEFR09 was rare with around 5% (see ), while it rose sharply at time point 2 (after a mean of 1068 km) to approximately 65% and increased only moderately to approximately 70% at time point 5 (after a mean of 3669 km). This corresponds to the sometimes grotesque swelling of runners' feet, necessitating cutting of running shoes to resemble crude sandals (see ).
Increase of leg volume and ankle oedema during prolonged exercise has been reported29
and has been attributed to endocrine dysregulation. However, recent studies postulate rather fluid overload as the source of the swellings,31
and total body water increase has been shown33
in long endurance athletes. Fluid intake had been shown to be positively correlated with the change of the volume of athletes' feet34
; furthermore, it has been shown that the total body water has increased over the course of multistage runs.35
So it can be assumed that the subcutaneous oedema is caused at least partially by excessive water intake.
We had hypothesised that bone oedema and the corresponding SI would decrease during rest (lying down). However, our data showed no correlation of the resting time to the SI. So the observed bone oedema seems to reflect true load effects and not simple hydrostatic changes.
We had expected to see more severe lesions in NF than in F and had hoped to find risk factors or predictive parameters for NF. Here, significant differences could be shown only for soft tissue parameters: At the beginning of the TEFR09, only the SI of the left plantar aponeurosis was significantly higher in NF, pointing to possible overload even before the start. During the run, NF showed significantly more subcutaneous oedema and oedema of the (right) plantar aponeurosis. This may indicate that soft tissue oedema is more relevant to the possible abortion of the run than the intraosseous changes described above or tendon problems. Especially the signal alterations in the plantar aponeurosis point to plantar fasciitis, a problem thought to be the main cause of inferior heel pain in runners and is detected easily by MRI.37
Considering clinical data on abortion of the run (see ), the stated soft-tissue-related causes refer mainly to the legs (mostly shin splint and perimyositis). These regions were not included in the current investigation. However, it is probable that oedema related to shin splint or perimyositis had spread along the lower legs to the foot, so that the visible subcutaneous oedema was not directly related to a pathology in the foot.
With λ values between 0.88 and 0.98, the inter-rater reliability can be rated as excellent.20
Strengths, limitations and implications for future research
This is the first study in history to report results from close observation of multistage ultra-marathon athletes by mobile MRI. Therefore, it is the first study to report changes in the musculoskeletal system in multistage ultra-marathoners. The chance to observe an event like the TEFR09 with a mobile MRI scanner had been great, but the difficulties of tight schedules of the athletes prohibited greater numbers.
Poor infrastructure and difficult local situations at the stage destinations sometimes made a nearby commissioning of the mobile MRI impossible. However, the strongest influence forcing the staff to change and adapt their research work daily was the athlete himself, with his individual personality and more or less daily changing mental and physical condition and necessities: pain, injuries, fatigue, fears, doubts, illness, regeneration programme and nutrition plan.
The stated radiological findings like subcutaneous or intraosseous oedema are important. Lacking additional data, our study cannot prove the cause for it (workload, endocrine imbalance or fluid overload, as discussed above). Therefore, additional data like fluid intake, electrolyte content of plasma and urine as well as hormonal factors should be sampled in future studies.
The inclusion of 22 runners permitted detailed examinations, but the number may have been too small to detect factors distinguishing NF. However, the study sample of 22 athletes had been randomised out of all participants, their biometric data show that they are representative of the whole group of TEFR09 participants. So their results may be generalised.
During the TEFR09 and under extreme stress, adaptive changes like the increase of the AT diameter could be detected with MRI as well as signs of soft tissue overload with swelling and oedema. The meaning of the SI increase of the foot bones is thought to resemble a stress response but is not correlated with abortion of the race or development of stress fractures during the observed transcontinental multistage ultra-marathon.