Objective: This study was performed to investigate the effects of the skeletal muscle index (SMI) of the whole body and lower limbs (as estimated by bioelectrical impedance analysis using an body composition meter) and the quadriceps muscle thickness and echo intensity (as measured by an ultrasound imaging system that can be easily used in clinical practice) on the knee extensor strength in healthy young adults.

Methods: The SMI of the whole body and lower limbs, the muscle thickness and echo intensity of each quadriceps muscle, and the knee extensor strength were measured in 120 legs of 60 healthy young adults.

Results: A significant relationship was found between the knee extensor strength and SMI of the whole body and lower limbs and between the knee extensor strength and the muscle thickness and echo intensity of each quadriceps muscle. Multiple regression analysis suggested that the SMI of the lower limbs, muscle thickness of the vastus medialis, and sex affected the knee extensor strength.

Conclusion: Multiple regression analysis suggested that the SMI of the lower limbs, muscle thickness of the vastus medialis, and sex can be used to estimate the knee extensor strength in healthy young adults.

Objective: When performing rehabilitation for post-orthopedic patients, it is necessary to evaluate and treat abnormal muscle tone. In recent years, ultrasonic measuring devices have often been used for simple evaluations of skeletal muscles and soft tissues in clinical practice, and they have been suggested for muscle activity measurement. The objective of this study was to clarify whether the low-intensity muscle contractions can be evaluated by measuring muscle bundle length, using an ultrasonic measuring device.

Method: The subjects were nine healthy people and 16 limbs. The task was an isometric knee extension of 30% or less of the maximum voluntary contraction. Using a surface electromyogram and an ultrasonic measuring device, the relative values of the EMG integrated value and of the amount of change in muscle bundle length were measured. The relationship between muscle bundle length and muscle activity was determined using curve regression analysis.

Results: The result of the curve regression analysis was r² = 0.736 (p < 0.001), and it strongly suggested that the relative value of the muscle bundle length increased, while the relative value of the EMG integral value increased.

Conclusion: It was suggested that the ultrasonic measurement of the muscle bundle length could be used to evaluate low-intensity muscle contractions for the vastus lateralis.

Purpose: In this study, we investigated the effect of motor imagery after exercise on precision pinch force control and excitability of spinal motor neural function.

Methods: We analyzed 13 healthy participants (mean age 20.3 ± 0.5 years). F-waves were recorded at rest, the pinch force was adjusted to 50% maximum voluntary contraction (MVC), and the error between the specified and actual 50% MVC values were calculated in the pinch task. After that, F-waves were recorded in kinesthetic- and first-person visual imagery on different days in random order, and the pinch task was performed again. The amplitude F/M ratio was used as a measure of the excitability of spinal motor neural function, and the absolute error in 50% MVC was used as a measure of the accuracy of the movement.

Results: There was no change in the amplitude F/M ratio or in the absolute error improvement in 50% MVC between the imaging strategies.

Conclusion: The similarity between first-person visual imagery and kinesthetic imagery in terms of motor imagery from a first-person perspective resulted in the same degree of increased spinal motor neural function excitability and maintained precision pinch force control.

Objective: The purpose of this study was to determine the sex- and age-specific normative data for single leg hop (SLH) after anterior cruciate ligament reconstruction (ACLR).

Method: A total of 687 patients who underwent primary ACLR participated in this study. The SLH for distance and SLH for distance normalized to body height (%body height) of both knees (involved and uninvolved) were examined retrospectively at the time of return to sports. We determined the average values of SLH for distance and %body height by sex and age (10s, 20s, 30s, 40s, 50s). In addition, the difference in SLH normative data by age for men and women was also examined.

Result: Sex- and age-specific normative data for SLH for distance and %body height of both knees (involved and uninvolved) were clarified. The age-adjusted normative data for SLH were higher in the 10s and 20s than in the 30s, 40s, and 50s.

Conclusion: The normative data defined by this study may be used to evaluate bilateral ACLR patients or contralateral ACL injury, who it is difficult to evaluate the limb symmetry index.