Hirotake Yokota

Background: This study aimed to examine whether the morphology of the articular surface of the first tarsometatarsal (TMT) joint, plantar tarsometatarsal ligament (PTML), and hallux valgus angle (HVA) were associated with plane‐specific TMT joint displacement. Methods: Nine Thiel‐embalmed cadavers (18 feet) were included. HVA was measured using a goniometer. The capacity for TMT joint motion (mobility) was operationalized as displacement of the first metatarsal relative to the medial cuneiform under manual stress, measured ultrasonographically in the dorsal, plantar, and medial imaging planes. PTML morphology (length, width, and thickness) and TMT joint articular surface morphology (type classification) were assessed, and their associations with plane‐specific TMT joint displacement were analyzed. Results: No significant differences in dorsal, plantar, or medial displacement were observed between Type III and the other articular surface morphologies after adjustment for multiple comparisons. Similarly, PTML length, width, and thickness were not significantly associated with displacement in any direction. Although HVA was positively associated with plantar displacement before adjustment, this association did not remain significant after FDR correction. Conclusions: In this small exploratory cadaveric study, no statistically significant associations were identified between first TMT joint displacement and articular surface morphology, PTML morphology, or HVA after accounting for within‐cadaver clustering and multiple comparisons. These findings should be interpreted cautiously because of the small sample size and limited range of HVA severity. Level of Evidence: Level IV, Descriptive laboratory study

Background: Reaction time is analyzed in various situations in sporting events and is reported to be so important that it can make the difference between victory and defeat. This study focused on teeth clenching resulting in remote muscle activation, and examined whether it improves performance of reaction time. This study examined the effects of clenching and clenching strength on the systemic simple reaction time. Methods: This study included 20 healthy adults with normal clenching and a right dominant foot. The task movement for the systemic simple reaction time measurement was a 30 cm forward step. The following three clenching conditions were used: no clenching without dental contact (no-bite condition), a condition in which the participants were instructed to clench with moderate strength (moderate condition), and a condition in which the participants clenching with maximum effort (max condition). The analysis items were release time, grounding time, soleus muscle (Sol) reaction time, and masseter muscle activity. Results: The max condition significantly reduced the reaction time compared with the no-bite condition. Sol reaction and grounding times showed a negative correlation between clenching strength under moderate conditions and the rate of change in reaction time under no-bite and moderate conditions. Release time exhibited no significant correlation between clenching strength under the moderate condition and the rate of change in reaction time under the no-bite and moderate conditions. The remote facilitation effect of clenching improved the systemic reaction time by producing immediate muscle activity. Conclusions: Clenching shortens the systemic simple reaction time. This finding highlights the potential importance of clenching in enhancing performance during sporting events.

This study aimed to (1) examine the acute changes in the glenohumeral range of motion (ROM) after repetitive pitching and (2) clarify whether arm speed during pitching is associated with changes in the glenohumeral internal rotation (IR) and horizontal adduction (HADd) ROM. Fifteen healthy college males with over five years of baseball experience participated. Glenohumeral ROMs of IR, external rotation, and HADd were measured using a digital inclinometer before, immediately after, and one day after completing 100 repetitive full-effort pitches. Arm speed during pitching was measured using wearable inertial measurement unit sensors. IR ROM significantly decreased immediately after (p < 0.001) and a day after (p = 0.043) the pitching task compared to the baseline values. HADd (p = 0.361) and external rotation (p = 0.935) ROM exhibited no changes between pre-and post-pitching. Changes in the IR ROM were associated with arm speed during pitching (β = -0.728, p = 0.002 for pre-post change; β = -0.645, p = 0.009 for pre-post one-day change). Our findings imply that reductions in the glenohumeral IR ROM may precede chronic adaptations of the throwing shoulder. Furthermore, arm speed during pitching was a predictive factor for the changes in the glenohumeral IR ROM.

Reciprocal inhibition is often diminished in elderly individuals and those with upper motor neuron disorders. This reduction in reciprocal inhibition can hinder smooth joint movement. For subjects who have increased muscle tone and a limited range of motion in the joints, we focused on visual kinesthetic illusions as an intervention to increase reciprocal inhibition. We aimed to investigate the effects of visual kinesthetic illusions on reciprocal inhibition and motor function in the ankle joint. Participants participated in two experiments measuring reciprocal inhibition, namely reciprocal Ia inhibition and D1 inhibition, as well as motor functions related to ankle dorsiflexion and plantar flexion. Visual kinesthetic illusion was induced by displaying an image of each subject’s foot on a monitor. Our results showed that the visual kinesthetic illusion enhanced D1 inhibition and improved motor function in the ankle joint by prioritizing agonist muscle activity. We also observed a correlation between reciprocal inhibition and the muscle activity ratio. These findings suggest that visual kinesthetic illusions may improve motor function by increasing reciprocal inhibition. This study is the first to demonstrate the effects of visual kinesthetic illusion on reciprocal inhibition, and we believe that these findings can be applied in rehabilitation.

Repetitive passive movement (RPM) enhances reciprocal inhibition. RPM is more effective when performed rapidly and at wide joint angles. However, patients with limited joint range of motion may not receive the most effective RPM. Therefore, having an alternative method for performing RPM in patients who cannot perform actual exercise due to limited joint motion is necessary. This study investigated the effects of RPM on spinal excitability using a visual kinesthetic illusion. Participants included 17 healthy adults (7 women). Measurements were taken before, during, and immediately after the intervention. We established two intervention conditions: the control condition, in which participants focused their attention forward, and the illusion condition, in which participants watched a video about RPM. F-waves from the tibialis anterior and soleus muscles were measured, and F-wave persistence and F/M amplitude ratios were analyzed. Under the illusion condition, compared with the preintervention condition, the F/M amplitude ratio of the tibialis anterior increased by approximately 44% during the intervention (p < 0.05), whereas the F-wave persistence of the soleus decreased by approximately 23% from the immediate start of the intervention (p < 0.05). This study suggests that a visual kinesthetic illusion can increase the spinal excitability of the tibialis anterior, whereas reciprocal inhibition can decrease the spinal excitability of the soleus.

Repetitive passive movement (RPM) is an intervention that alters brain activity and spinal cord function based on reciprocal inhibition enhancement. However, if joint motion is inhibited, RPM with effective kinetic parameters may not be available to the patient. Thus, for its clinical application, it is necessary to provide intervention in patients who are unable to perform real movements because of factors that inhibit joint movement. Therefore, the present study aimed to investigate the effects of RPM without real movement on spinal excitability, using a visual kinaesthetic illusion. Participants included 17 healthy adults (10 men and 7 women). Measurements were acquired before the intervention (PRE), during, immediately thereafter (POST). Two intervention conditions were used: a control condition and an illusory condition. The analysis items were F waves, used to measure spinal cord excitability, their persistence and the F/M amplitude ratios obtained from surface electromyograms applied to the tibialis anterior (TA) and soleus (Sol) muscles. In the illusory condition, the F/M amplitude ratio of the TA significantly increased during the intervention (p < 0.05) and the F-wave persistence of the Sol significantly decreased from intervention to POST (p < 0.05). The present study suggests that through a visual kinaesthetic illusion, RPM without real movement could increase spinal excitability in the TA, whereas reciprocal inhibition may decrease spinal excitability in the Sol.

Tactile perception is a complex phenomenon that is processed by multiple cortical regions via the primary somatosensory cortex (S1). Although somatosensory gating in the S1 using paired-pulse stimulation can predict tactile performance, the functional relevance of cortico-cortical connections to tactile perception remains unclear. We investigated the mechanisms by which corticocortical and local networks predict tactile spatial acuity in 42 adults using magnetoencephalography (MEG). Resting-state MEG was recorded with the eyes open, whereas evoked responses were assessed using single- and paired-pulse electrical stimulation. Source data were used to estimate the S1-seed resting-state functional connectivity (rs-FC) in the whole brain and the evoked response in the S1. Two-point discrimination threshold was assessed using a custom-made device. The beta rs-FC revealed a negative correlation between the discrimination threshold and S1–superior parietal lobule, S1–inferior parietal lobule, and S1–superior temporal gyrus connection (all P < 0.049); strong connectivity was associated with better performance. Somatosensory gating of N20m was also negatively correlated with the discrimination threshold (P = 0.015), with weak gating associated with better performance. This is the first study to demonstrate that specific beta corticocortical networks functionally support tactile spatial acuity as well as the local inhibitory network.