Shigeaki Matsuo

Agonist contractions against electrically stimulated antagonists

OBJECTIVE To assess an exercise program that uses electrically stimulated antagonists to resist agonist muscle contractions. DESIGN In 1 limb, electrically stimulated antagonists resisted elbow flexion and extension. In the other, stimulation occurred without volitional muscle contraction. SETTING A biomechanics laboratory in Japan. PARTICIPANTS Twelve men between the ages of 19 and 24 years. Subjects served as their own controls. INTERVENTION Subjects trained 3 times a week for 12 weeks. Each session consisted of 10 sets of 10 elbow flexor and extensor contractions. MAIN OUTCOME MEASURES Isokinetic elbow extension and flexion torques. Biceps and triceps brachii cross-sectional areas. RESULTS Elbow extension torques increased (32.85% at 30 degrees/s, 27.20% at 60 degrees/s, 26.16% at 90 degrees/s; all P<or=.02) over the training period in limbs that trained against electrically stimulated antagonists. Control limb extension torque increases were smaller (8.52% -14.91%) and did not reach statistical significance. Elbow flexion torques improved in both groups, but the changes did not reach statistical significance. Cross-sectional areas increased in all muscles but were most marked in the antagonist stimulated limbs: triceps 16.20% versus 4.25% (P=.01) and biceps 16.65% versus 7.00% (P=.005). CONCLUSIONS Exercises that use electrically stimulated antagonist muscles may be effective in increasing muscle strength and mass.

Biomechanical effect and clinical application of the hip joint moment reduction brace

A new brace, the hip joint moment reduction brace, has been designed and constructed. The basic construct of the brace incorporates only the thigh, and it minimally restricts ones activities of daily living. The concept of the brace is to reduce the frontal plane moment of the applied force against which the abductor muscle must contract to balance, and this reduction of the frontal plane moment results in reduction of the abductor muscle force. The brace uses the mechanism of the ischial weightbearing and lessens the abductor moment by transmitting load from the ischium through the condyle of the femur. In gait testing, the maximum ischial load taken up by the brace was 36.9% of the ground reaction force in the late stance phase, and the integrated electromyogram of the abductor muscle was reduced by 32.6% during the whole stance phase using this brace. These findings confirmed a reduction in the frontal plane moment of the hip joint and the potential for reduction in the load on the hip joint. The hip joint moment reduction brace is recommended as effective conservative management of hip disorders, such as coxarthrosis, that are caused or worsened by biomechanical insufficiency.

Evaluation of Impact on Human Body at Heel Contact.

Impact created by the heel striking the floor leads to problems among athletes or patients having artificial joints. The impact force was evaluated using the ellipsoid of impact force and simple models. As the ellipsoid of impact force is derived from a kinematic relation between momentum immediately before and after striking the floor, it is easily applicable to other types of walking such as on steps or slope. The concept of equivalent mass and the center of impact force was also introduced. The mass is determined by the configuration of the leg at heel contact or the heel landing style of a runner. The center of impact force depends on the acting point of the force on the foot and reduces the effect of impact force on the ankle joint. The ellipsoid of impact force suggested the following : the impact force on the distal point of the shank in footless model was remarkably reduced by the assumption of foot ; and some degree of flexion of the knee reduced the impact force and took a minimum value. Experimental results of walking on the floor showed that the transfer of acceleration of impact force to upper elements was greatly attenuated at ankle and knee joints corresponding to normal and fixed ankle walking, respectively. In a running test using shoes with a cushioning material at the heel, the muscle activity of rectus femoris increased as the material hardness increased.