We researched aging of the LRB (Lead Rubber Bearing) installed in a base-isolated building which was constructed 15 years ago. The hardness of the cover rubber and the height were measured for 35 LRBs which were installed in the building. The compression test and combined compression shear test with monitor samples and actually installed LRB were performed to search changes in their hysteresis characteristics. The monitor samples were composed of 4 LRBs and 1 RB. Main results obtained were as follows: 1) The LRBs installed in the TC building crept approximately 1 (mm) during 15 years and did not changed during last 5 years. 2) The hardness of the cover rubber did not change against that of 15 years ago. 3) From the testing of the monitor samples, the compression stiffness increased approximately 17% and the shear stiffness increased approximately 5%, however the yield force changed quite a little during 15 years on average. As a result, the suitability of the design specifications of the LRB was confirmed.

Purpose During hopping, jumping and running, the musculoskeletal structure of the legs is often modelled with a spring-mass model, which consists of a body mass and a linear leg spring supporting the body mass 1 . In the model, the stiffness of the leg spring (leg stiffness; Kleg) is thought to be an important factor in musculoskeletal performance 2 . However, despite the fact that many athlete's activities are often measured, little is known about the regulation of Kleg in the elderly. Therefore, the purpose of the present study was to compare the Kleg between the elderly and young subjects in a range of hopping frequency. Method Fourteen elderly and eleven young subjects performed in-place hopping, matching metronome beats at 2.2, 2.6 and 3.0Hz. Based on the spring-mass model, Kleg was calculated as the ratio of maximum ground reaction force to maximum center of mass displacement at the midstance (Figure 1). Results & Discussion In both groups, the Kleg increased with an increase in hopping frequency, but was not significantly different between groups (Figure 2). Statistical analysis revealed the existence of a significant main effect of hopping frequency on Kleg. However, main effect of groups and interaction on Kleg were not observed. The results of the present study indicate that leg stiffness during hopping is invariant with aging. Since too high or too low Kleg is associated with musculoskeletal injury 2 , footwear and/or surface materials, impact on Kleg 2 should be considered for athletic environment in both master and young athletes. References

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