Abstract. [Purpose] To quantitatively investigate whether the muscle grades of the Curl-up (CU) and Double-leg-lowering (DLL) test show any electromyographic changes in the upper and lower rectus abdominis (RA) as trunk flexors.[Methods] The muscle activities of both the upper and lower RA in thirty healthy young males were recorded during each muscle grade task of two tests. The percentages of maximum voluntary contractions (%MVC) of the upper and lower RA were compared between each muscle grade and test. The %MVC ratios of the upper and lower RA were calculated to investigate the contribution of each muscle site in two tests.[Results] Although there were significant electromyographic differences among muscle grades in the CU test, there was no significant difference in the DLL test. The %MVC from both sites in the CU test were significantly larger in all muscle grades than in the DLL test. However, the %MVC ratio was consistently ~1.0 in both tests and the contribution of each muscle site did not differ. [Conclusion] These findings suggest that the three grading tasks used in this manual muscle testing procedure may be insufficient to objectively detect muscle weakness in the trunk flexors. The grading criterion for trunk flexors may need remediation.

[Purpose] To understand stair ascent and descent motions, we examined the muscle activities of the vastus medialis (VM) and vastus lateralis (VL) and the ground reaction force (GRF) in the supporting leg of eight young healthy males. We also compared these data with level walking data.[Result] The muscle activities of VM and VL during the ascent motion were the highest among the three tasks. The muscle activity ratios of VM and VL during ascending and descending differed from that during level walking. The VM contribution increased in the ascent and descent tasks compared with level walking. There was no significant difference for the vertical GRF among the tasks. Although the anterior-posterior GRF during the ascent motion was similar to that during level walking, the anteriorposterior GRF during the descent motion was different from that of the ascent motion and level walking. Further, the medial-lateral GRF during ascending and descending were different from that during level walking.[Conclusion] The results of this study suggest that the increased VM contribution of the supporting leg may be related to the change of medial-lateral GRF during ascent and descent. This finding will add knowledge to the rehabilitation and physical therapy of ascent and descent motions for elderly people and patients with motor disorders.

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Abstract.[Purpose] The aim of this study was to quantitatively investigate gender differences in trunk muscle strength and activity and to verify the two proposed fi eld tests for screening the muscle strength of trunk flexors by use of surface EMG (sEMG). [Subjects and Methods] Fifty-four healthy young volunteers participated in this study and RA strength was evaluated using the curl-up (CU) and doubleleg-lower (DLL) tests. All muscle activity that occurred in the upper and lower RA sites during the two tests was recorded using sEMG. The sEMG data were then normalized using the maximum voluntary contraction. To investigate the validity of the two tests, the ratio of muscle activity between the upper and lower RA sites was calculated.[Results] The reliability of the CU and the DLL tests were estimated using the intraclass correlation coefficient and the values ranged from 0.84-0.96 and 0.93-0.98, respectively. Muscle activity was signifi cantly higher in females than in males in all tests except one of the DLL tests. The activity ratio with respect to each muscle grade was constant between the CU and the DLL tests. [Conclusion] Our results indicate that trunk muscle activity is affected by gender, and the tests should be selected according to purpose.