Insights into extrinsic foot muscle activation during a 75 min run using T2 mapping

Abstract

The extrinsic foot muscles are essentially for controlling the movement path but our knowledge of their behavior during prolonged running is still very limited. Therefore, this study analyzed the time-course of muscle activation using T2 mapping during 75 min of running. In this prospective study, 19 recreational active runners completed 75 min of treadmill running at a constant speed. Interleaved T2 mapping sequences were acquired and segmented at timepoints 0, 2.5, 5, 10, 15, 45, and 75 min. ANOVA for repeated measurements followed by a Tukey post hoc test and Pearson correlation between running speed and initial signal increase at 2.5 min were calculated. All muscles showed a significant signal increase between baseline and 2.5 min (e.g. medial gastrocnemius: + 15.48%; p < 0.01). This was followed by a plateau phase till 15 min for all but the extensor digitorum longus muscle and a significant decrease at 45 or 75 min for all muscles (all p < 0.05). Correlation between running speed and signal increase was negative for all muscles and significant for both gastrocnemii (e.g. medial: r = − 0.57, p = 0.0104) and soleus (r = − 0.47, p = 0.0412). The decrease of relaxation times times in the later running phases was less pronounced for faster runners (≥ 10 km/h). T2 relaxation times do not only decrease after cessation of exercise but already during prolonged running. The lesser initial increase and later decrease in faster runners may indicate training induced changes.

Muscle activity with 0.5 T upright MRI—DESS to measure T2 in biceps and triceps

“…In particular, our preactivity mean T 2 (biceps T 2 : 36 ± 11 ms, triceps: 34 ± 8 ms) was in line with previous studies at similar field strengths but different muscle regions 24,28 . However, our mean T 2 for the biceps during muscle activity (47 ± 21 ms, +31%) was slightly higher than mean T 2 values from previous exercise studies 3,4,9,17,24,28,29 . This could be due to previous work capturing T 2 after exercise, whereas this study measured T 2 during muscle activity.…”

“…Changes in muscle physiology can be measured by fluctuations in transverse relaxation ( T 2 ) signal before and after exercises, with disease, or with compensation due to injury 1–3 . Exercised‐based studies typically collect data immediately after activity, and consistently report increases in T 2 in muscle groups ranging from the spinal multifidus, erector spinae, thigh, quadriceps, calf, and foot 2,4–17 . It is generally thought that with activity an accumulation of osmolites (i.e.…”

The behaviour of T2* and T2 relaxation time in extrinsic foot muscles under continuous exercise: A prospective analysis during extended running

“…As this correlation between the initial increase and these parameters can only be shown for individual muscles, the clinical relevance here is questionable. Taking a closer look at the described correlations, a negative correlation between the initial increase in T2 relaxation time and running speed has described by our working group before, with a further description of a lower drop of T2 relaxation time during later running phases [ 25 ]. Some possible explanations would be an already altered muscle fibre composition and metabolism due to training effects or a more efficient motion pattern for better runners resulting in a reduced muscular strain [ 25 ].…”

“…Taking a closer look at the described correlations, a negative correlation between the initial increase in T2 relaxation time and running speed has described by our working group before, with a further description of a lower drop of T2 relaxation time during later running phases [ 25 ]. Some possible explanations would be an already altered muscle fibre composition and metabolism due to training effects or a more efficient motion pattern for better runners resulting in a reduced muscular strain [ 25 ]. A possible positive correlation between the initial increase of relaxation time and the subject’s weight can be explained theoretically as one can imagine that the acceleration of a larger weight is associated with a higher workload for the muscle with a consecutive increase in relaxation times, however, possible correlations have not been described in the literature so far.…”

“…This calculation ensures that the relaxation time for each slice is included according to its percentage of total muscle volume. The muscle volumes of the participants have previously been used by Willwacher et al [ 22 ] and Bratke et al [ 25 ].…”