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The present study aimed to clarify the development of motor unit (MU) firing properties and the association between those neural properties and force steadiness (FS)/neurological tests in 6- to 12-year-old children. Fifty-eight school-aged children performed maximal voluntary knee extension contraction, a submaximal FS test at 10% of maximal voluntary knee extension contraction, knee extension reaction time to light stimulus test, and single-leg standing test, and data from 38 children who passed the criteria were subject to analysis. During the FS test, high-density surface electromyography was recorded from the vastus lateralis muscle to identify individual MU firing activity. FS was improved with an increase in age (r = −.540, P <.001). The MU firing rate (MUFR) was significantly decreased with an increase in age (r = −.343, P =.035). MUFR variability was not associated with age. Although there was no significant correlation between FS and MUFR, FS was significantly correlated with MUFR variability even after adjustment for the effect of age (r =.551, P =.002). Neither the reaction time nor the single-leg standing test was correlated with any MU firing properties. These findings suggest that MUFR variability makes an important contribution to precise force control in children but does not naturally develop with age. [ABSTRACT FROM AUTHOR]

Purpose: Contributions of neural and muscular factors to muscle strength change with growth, but such changes remain unclear in young populations. This study aimed to clarify the association between muscle strength and neural and muscular factors in youth athletes. Methods: Maximal voluntary contraction (MVC) during isometric knee extension, the motor unit firing rate (MUFR), and muscle thickness (MT) of the vastus lateralis were measured in 70 youth male soccer players (mean [SD]; chronological age = 16.3 [0.6] y, peak height velocity age = 13.1 [1.0] y). MUFR and MT were measured with high-density surface electromyography and ultrasonography, respectively. Results: For MUFR and MT, correlations with MVC were calculated and the values of different MVC groups were compared. A significant correlation between MVC and MT (r =.49, P <.01) was noted, but not MUFR (r =.03, P >.05). There was also no significant correlation between MT and MUFR (r = −.33, P >.05). In addition, comparison among groups (higher-/middle-/lower-strength groups) revealed that MT in the lower-strength group was significantly lower than in middle-and higher-strength groups (P <.01). Conclusion: In youth athletes, muscle strength is associated with muscular factors, rather than neural factors, and muscular and neural factors may independently contribute to muscle strength. [ABSTRACT FROM AUTHOR]

PurposeTo study validity and reliability of a Japanese version of the Cumberland Ankle Instability Tool and to determine the optimal cutoff score.MethodsIn this study, the questionnaire was cross-culturally adapted into Japanese. The psychometric properties tested in the Japanese version of the CAIT were measured for criteria validity, internal consistency and test–retest reliability in 111 collegiate soccer athletes. We also established the questionnaire cutoff score for discriminating between individuals with and without CAI.ResultsThere was a significant correlation between the Japanese version of the CAIT and the Karlsson score (r = 0.604,p < 0.001). The questionnaire had a high internal consistency (Cronbach’sα = 0.833) and reliability [intraclass correlation coefficient (ICC) = 0.826, 95% confidence interval (CI): 0.732–0.888]. The optimal cutoff score was ≤25, which was consistent with previous reports.ConclusionsThe Japanese version of the CAIT has been shown to be a valid and reliable questionnaire for determining the presence of CAI. We expect that researchers and clinicians will use the Japanese version of the CAIT in Japan.Implications for RehabilitationChronic Ankle Instability (CAI), which not only increases recurrence rate of ankle sprain but also decreases athletic performance, is a residual symptom after ankle sprain.Cumberland Ankle Instability Tool, which has the reliability and validity to assess CAI, will be critically useful in assessment procedure for CAI.It is preferable for clinicians and researchers to use the native language version of the CAIT. [ABSTRACT FROM AUTHOR]

This study aimed to determine the difference in motor unit (MU) firing pattern between hypertensive and normotensive individuals, and the relationship between MU firing pattern and post‐exercise blood pressure (BP) response in older individuals. Fourteen older untreated (systolic/diastolic BP (SBP/DBP) ≥ 130/80 mmHg, 76 (5) years), 11 treated hypertensive (78 (4) years) and 14 normotensive (SBP/DBP < 130/80 mmHg, 71 (4) years) individuals were studied. Participants performed ramp‐up exercises until 50% of maximal voluntary contraction (MVC) of knee extension and five MVCs. During the ramp‐up exercise, high‐density surface electromyography signals were recorded and each MU firing rate (FR) and recruitment threshold was assessed. The slope of the linear regression between MUFRs and recruitment thresholds was calculated to assess the MU firing pattern. Pre‐ and post‐exercise blood pressure was measured. Change in (∆)SBP from pre‐ to post‐exercise was greater in treated hypertensive than untreated hypertensive individuals (P = 0.026). MUFR was lower in treated hypertensive than untreated hypertensive and normotensive individuals (P < 0.001). Although the slope was not significantly different between groups (P = 0.294), FRs of larger MUs were lower than those of smaller MUs in treated hypertensive and normotensive individuals (P < 0.05) but sustained in untreated hypertensive individuals. The FRs of larger MUs and slope were positively correlated with the ∆SBP only in hypertensive individuals (r = 0.768 and 0.715; P = 0.044 and 0.020). MUFR was lower in treated hypertensive than untreated hypertensive and normotensive individuals. Furthermore, MU firing patterns were associated with the ∆SBP after exercise in older untreated hypertensive individuals, but this relationship was not observed in treated hypertensive and normotensive individuals. [ABSTRACT FROM AUTHOR]