2014 Volume 9 Issue 3 Pages 14-00035
The objective of this study was to examine the applicability of the musculoskeletal model to the sit-to-stand (STS) motion, especially focusing on the time-varying muscle load of the Erector Spinae. The musculoskeletal model was previously developed in order to estimate the effect of mechanical unbalance induced by pregnancy, which was mainly due to the increase in weight of the uterus. An experiment was carried out in order to validate the musculoskeletal model. In the experiment, non-pregnant subjects wearing an artificial pregnancy jacket performed the STS motion at three speeds. The experimental and simulated results of the muscle load of the Erector Spinae were then compared. From the comparison for the time histories of the muscle load, it was found that the characteristic tendencies observed in the experimental data were also observed in the simulated data. This suggests sufficient capabilities of the developed musculoskeletal model to predict the time-varying muscle load during the STS motion. The average muscle load of the Erector Spinae during the STS motion in the artificially-pregnant condition became 11% higher than that in the non-pregnant condition both for the experiment and simulation. This consistency between the experiment and simulation suggests the sufficient quantitative capability of the developed musculoskeletal model to predict the muscle load. Through the validated musculoskeletal model, the muscle load of the Erector Spinae during the STS motion for the non-pregnant and pregnant conditions were compared. From the comparison between the non-pregnant, artificially-pregnant and pregnant conditions in the simulation for the same body motion, it was found that the muscle load of the artificially-pregnant condition was 16% higher than that of the non-pregnant condition, and the muscle load of the pregnant condition was 50% higher than that of the non-pregnant condition.