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Chapter 6
The absence of evidence for activation of the tongue musculature is somewhat surprising in view of the results of Kraaijenga et al., who found a significant increased tongue strength in healthy volunteers (n = 10) as well as chronic dysphagia patients (n = 18) after an SEA training period of six weeks (18, 35). Also, Clark et al. reported increased tongue pressures in healthy participants (n = 40) after a training period of four weeks including the cES exercise (43). This contradiction might be because the effects of the single ES+ as well as the single conventional exercises on tongue muscle strength are so small that they can only be measured after a long-term training period. However, the contradiction might also be due to the fact that the exercises in this study were performed in supine instead of upright position, with tongue retraction possibly being accomplished easier due to gravity. Testing in supine position in the present study, however, was unavoidable given the direct decrease of T2-values after exercise with a half-life of approximately seven minutes (24). Performing the exercise outside of the MRI and repositioning the subject in the MRI would take over five minutes. Therefore, despite the fact the T2 mapping acquisition only takes four minutes, at least almost half of the effect of exercise on T2-value would be gone.
The SEA exercises were based on the conventional exercises and were hypothesized to target the same muscles but with greater extent due to the use of progressive load. Our results, although explorative, suggest that the SEA exercises activated the same muscle groups as the conventional swallowing exercises plus the lateral pterygoid muscles (Figure 10). The lateral pterygoid muscle, an important jaw opening muscle, is a quite relevant target to prevent trismus, which is highly prevalent in patients after treatment for head and neck cancer (12).
Of the conventional swallowing exercises, especially the Shaker exercise has shown to be effective in improving swallowing function (13, 14). However, the disadvantage of this maneuver is that it has to be performed in supine position. This position is not feasible for a substantial proportion of head and neck cancer patients due to their physical condition including stiffness of the neck musculature. To avoid this supine position, Mishra et al. have developed a variant of the Shaker exercise in 45° reclined position (44). However, evidence of effectiveness of this exercise in head and neck cancer patients is not available yet. The SEA also avoids supine position, to increase feasibility and thus compliance to the exercises (19). Our results suggest that all muscles activated by the Shaker exercise (i.e., suprahyoid muscles, infrahyoid muscles and sternocleidomastoid muscles) were also activated by the SEA exercises indicating that the goal to find a substitute for the Shaker with a more feasible position is accomplished. Thus, application of the SEA both seems to targets more muscle groups, and likely increases compliance due to the more feasible upright position in which the exercises can be performed (19).
MfMRI with T2-maps is a non-invasive method to visualize muscle activation patterns during exercise. T2-mapping values are strongly correlated with results of electromyography, an invasive method to assess muscle activity (21-24). The hypothesis regarding the mechanism of increased T2-values after exercise, is that during exercise water shifts to the intracellular space