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The current study was undertaken to verify appropriateness of muscle endurance test at three different angles (30。 , 40。 , 50。) of isometric contraction position, and to sought valid and reliable testing method that provide an alternative to sit-ups. Total 92 young and healthy subjects (68 males and 24 females) were recruited, and the following results were obtained. 1. A low correlations in males, but a high correlations in females was found when the comparisons were made between aerobic and muscle endurance capability. 2. Measuring tolerance time, by using isometric contraction was showed a significant correlation with the repetition numbers of sit-ups. 3. The highest correlation was found at 40 inclined degrees of plane, and the lowest correlation was drawn from 50 inclined degrees of plane. Based on these results, it was concluded that measuring tolerance time during maintaining an isometric contraction at 40 inclined degrees of plane is a valid and effective tool for measuring abdominal muscle endurance, and it can be used as an alternative way of sit-up, which potentially risky for inducing many back-associated injuries. Further studies need to be undertaken to determine for optimal angles, that can safely be applied for people of various age groups and physical conditions.

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The aim of this study was to investigate the changes of contraction patterns and the differences of activities in trunk muscles during dynamic balance (multidirectional tilting exercise). Methods: Eight physically active male subjects participated in the study. Tilting exercises were included by four directions (i.e., forward, backward, left, and right side), and were undertaken at three different tilting degrees (i.e., 10º, 20º, and 30º). They performed two occasions of tilting exercise, separated by 6-week time interval. Surface electromyography system was used for record of any signals produced by muscles which normalized as percentage of maximum voluntary isometric contraction. Results: There were no statistically significant different interactive effects in any of muscles between two factors (time vs. degree). However, we identified significant main effects of degrees (among 10 o , 20 o , and 30 o ) in muscle activations during maintaining with forward tilting (left and right longissimus, multifidus), backward tilting (left and right rectus abdominis, external oblique), left side tilting (right rectus abdominis, external oblique, longissimus, multifidus), right side tilting (left rectus abdominis, external oblique, longissimus, multifidus). Conclusion: Findings from this study allow the multidirectional tilting exercise to be considered as suitable for ameliorate muscle balance by inducing co-contraction in trunk muscles.