Ryo Hirabayashi

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

Sugai, N, Hirabayashi, R, Okada, Y, Yoshida, Y, Okouchi, T, Yokota, H, Ishigaki, T, Komiya, M, Sakamoto, K, and Edama, M. Teeth clenching improves selective response and shortens reaction time. J Strength Cond Res XX(X): 000–000, 2026—In sports, rapid decision making and quick reactions are vital for optimal performance. Enhancing reaction time in choice to respond, task-based tasks require efficient cognitive processing and motor output. This study examined the effects of teeth clenching and clenching balance on reaction time. Teeth clenching has been shown to boost muscle activity and cognitive function; however, imbalanced clenching between the left and right sides may negatively affect performance. Twenty-two right-handed subjects with normal occlusion and 28 or more teeth completed a forward stepping task under 3 clenching conditions: no clenching without dental contact (No-CL), moderate clenching (Moderate-CL), and maximal clenching (Max-CL). Reaction time was assessed through the soleus muscle (Sol) activity, including Sol reaction time, release time, and grounding time. Results showed significantly shorter Sol reaction, release, and grounding times under Moderate-CL and Max-CL conditions than under no-CL ( p < 0.05). In subjects with balanced clenching, all 3 measures improved significantly under clenching conditions ( p < 0.05). However, those with clenching imbalance showed improvement only in Sol reaction time ( p < 0.05). Furthermore, a significant positive correlation was found between clenching imbalance and changes in reaction time, particularly for release time and overall reaction time under clenching conditions ( r > 0.37, p < 0.05). These findings suggest that clenching can enhance spinal excitability and cognitive performance through activation of the locus coeruleus, potentially improving reaction ability in sports and daily life. However, clenching imbalance may limit these benefits, highlighting the importance of considering clenching balance in future research and performance strategies.

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.

Background: The Kerlan-Jobe Orthopaedic Clinic shoulder and elbow score (KJOC) is sensitive enough to detect subtle changes in the functional level of the shoulder or elbow in overhead athletes. However, a Japanese version of the KJOC is not yet available. Moreover, the original KJOC uses a visual analog scale (VAS) assessment format that requires a print version so that users can add a check mark along a horizontal line. The KJOC can be completed using online tools such as Google Forms if a 10-point scale format can be used with comparable results. Purposes: To (1) translate and cross-culturally adapt the KJOC into Japanese (KJOC-J) and assess its validity and (2) evaluate the correlation between a standard VAS format and a 10-point scale format (KJOC-J10). Study Design: Cohort study (Diagnosis); Level of evidence, 3. Methods: In total, 318 athletes participated in the validation study, 255 in the test-retest reliability study for the KJOC-J, and 273 in the validation study for the KJOC-J10. Internal consistency was evaluated using the Cronbach alpha. Validity was evaluated by calculating the correlation between the KJOC-J and the Disability of the Arm, Shoulder and Hand (DASH). Test-retest reliability was assessed using the intraclass correlation coefficient (ICC). The validity of the KJOC-J10 was evaluated by calculating the correlation between the KJOC-J10 and KJOC-J. Results: The Cronbach alpha was 0.914, indicating good internal consistency. The KJOC-J was moderately correlated with the DASH ( r = −0.581; P < .001) and had good test-retest reliability (ICC, 0.874). A strong correlation was found between the KJOC-J and KJOC-J10 ( r = 0.846; P < .001). Conclusion: The study results demonstrated good internal consistency, validity, and reliability for the KJOC-J, indicating that it is a valid assessment tool for shoulder and elbow functions in Japanese overhead athletes. Moreover, a strong correlation was found between the VAS and 10-point formats of the KJOC-J.

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.