Enhanced echo intensity (EI) on an ultrasound image of skeletal muscle indicates changes in muscle quality, including increases in intramuscular fibrous and adipose tissues. However, it is not known whether muscle quality assessed from the EI of computer-aided gray-scale analysis of an ultrasound image is associated with the muscle strength or body composition of a subject. The objectives of this study were to investigate whether muscle quality assessed from EI measured using gray-scale analysis is associated with muscle strength independently of age or muscle thickness (MT), and to examine the relationship between muscle EI and body composition. Ninety-two healthy women with a mean age of 70.4 ± 5.5 years (range, 51-87 years) dwelling in Kyoto, Japan, participated in the study. The MT, subcutaneous fat thickness (FT), and EI of the quadriceps femoris on the right extremity were assessed from transverse ultrasound images. Knee extensor isometric strength was used as a measure of the quadriceps femoris muscle strength. EI was significantly correlated with quadriceps strength independently of age or MT, and stepwise regression analysis revealed that MT and EI were independently associated with quadriceps strength. Importantly, EI showed no significant correlations with FT, percentage of body fat (%BF), or body mass index (BMI), while FT, BMI, and %BF did not significantly influence muscle strength. These data suggest that muscle quantity (i.e., MT) and muscle quality assessed from EI measured using computer-aided gray-scale analysis independently contribute to muscle strength in middle-aged and elderly persons.

Static stretching (SS) is commonly used to prevent or improve limited joint mobility. However, it is unclear whether the components of the muscle-tendon unit (MTU) are affected by 5 min of SS. This study investigated the acute and prolonged effect of SS on the mechanical properties of the MTU. The subjects comprised 15 male participants (mean age: 21.5 AE 1.6 years). MTU stiffness, muscle stiffness, tendon stiffness, and fascicle length of the gastrocnemius muscle were measured by ultrasonography and a dynamometer while the ankle was passively dorsiflexed. The measurements were performed prior to the 5 min of SS, immediately after the SS, and 10 min after the SS. MTU stiffness and muscle stiffness significantly decreased at both immediately and 10 min after SS, whereas no significant differences in MTU stiffness and muscle stiffness were found between immediately and 10 min after SS. Tendon stiffness immediately after SS was significantly higher than prior to and 10 min after SS. No significant change in the fascicle length occurred after SS. These results suggest that 5 min of SS affects MTU and muscle stiffness both immediately and 10 min after SS, which may be associated with a change in the connective tissue properties. ß

The purpose of this study was to clarify the difference in muscle coactivation during postural control between older and young adults and to identify the characteristics of postural control strategies in older adults by investigating the relationship between muscle coactivation and postural control ability. Forty-six healthy older adults (82.0±7.5 years) and 34 healthy young adults (22.1±2.3 years) participated. The postural tasks selected consisted of static standing, functional reach, functional stability boundary and gait. Coactivation of the ankle joint was recorded during each task via electromyography (EMG). The older adults showed significantly higher coactivation than the young adults during the tasks of standing, functional reach, functional stability boundary (forward), and gait (p<0.01). Postural sway area (ρ=0.42, p<0.05) and functional reach distance (ρ=-0.52, p<0.05) significantly correlated with coactivation during the corresponding task in older adults, i.e., muscle coactivation was significantly higher in the elderly with low postural control ability than in the elderly with high balance ability. Increased muscle coactivation could be a necessary change to compensate for a deterioration in postural control accompanying healthy aging. Further research is needed to clarify in greater detail positive and negative effects of muscle coactivation on postural control.

Static stretch is commonly used to prevent contracture and to improve joint mobility. However, it is unclear whether the components of the muscle-tendon unit are affected by a static stretch training program. This study investigated the effect of a four-week static stretch training program on the viscoelastic properties of the muscle-tendon unit and muscle. The subjects comprised 18 male participants (mean age 21.4 ± 1.7 years). The range of motion (ROM), passive torque, myotendinous junction (MTJ) displacement and, muscle fascicle length of the gastrocnemius muscle were assessed using both ultrasonography and a dynamometer while the ankle was passively dorsiflexed. After the initial test, the participants were assigned either to a group that stretched for 4 weeks (N = 9) or to a control group (N = 9). The tests were repeated after the static stretch training program. The ROM and MTJ displacement significantly increased, and the passive torque at 30° significantly decreased, in the stretching group after the study period. However, there was no significant increase in muscle fascicle length. These results suggest that a 4-week static stretch training program changes the flexibility of the overall MTU without causing concomitant changes in muscle fascicle length.

The purpose of this study was to analyze the validity of the newly designed functional ability test (FAT) for the normal population and patients with deficiency of the anterior cruciate ligament (ACL). The FAT consists of four tests: the figure-of-eight hop, the up-down hop, the side hop, and the single hop. Sixty control subjects and 50 patients with unilateral ACL deficiency were tested. In the control group, the values measured were significantly different between males and females in all of the tests. On the other hand, when left/right difference values were compared, no significant difference was found between males and females in any of the tests. More than 95% of control group exhibited symmetrical function in each part of the FAT, whereas in the ACL-deficient group, the percentage of patients who showed abnormal symmetry was 68% in the figure-of-eight hop, 58% in the up-down hop, 44% in the side hop, and 42% in the single hop. The percentage of ACL-deficient patients with functional asymmetry in at least one of the four tests was 82%. The FAT was found to be useful in evaluating lower limb function in ACL-deficient patients.