Flexion-rotation trunk test to assess abdominal muscle endurance: reliability, learning effect, and sex differences.

Trunk endurance tests are generally performed in sagittal or frontal plane. However, trunk field tests that measure the endurance of the rotator muscles are lacking. In view of this situation, we developed a flexion-rotation trunk test (FRT test) to assess the oblique abdominal muscle endurance. This new field test consists mainly in performing the maximum number of upper trunk flexion and rotation movements (reps) possible in 90 seconds. The objectives of this study were to analyze the FRT test reliability and to examine the effect of both the repetition and sex on test results. Fifty-one recreationally trained men (n = 35) and women (n = 16) completed 4 trials of the FRT test (T1, T2, T3, and T4), separated by 7 days each. The scores increased significantly between T1 and T3 (p < 0.001), showing a clear learning effect, but the increase between T3 and T4 was only 4.25% (p = 0.108). The intraclass correlation coefficients (ICCs) between trials were ≥0.83 and the standard errors of measurement (SEMs) ≤7.54 reps. The ICCs between trials increased, and SEMs decreased with test repetition, reaching an ICC of 0.94 and an SEM of 6.46 reps between T3 and T4. The comparison between sexes showed a higher abdominal endurance in men when compared with that in women (p = 0.003), and also a higher learning effect in men, especially at the beginning of the study. These findings suggest that, the FRT test is a reliable field protocol that differentiates between the abdominal endurance of men and women. However, it is necessary to perform an extensive familiarization period before testing (at least 3 trials of practice) to make learning effect negligible.

Trunk muscle activation during stabilization exercises with single and double leg support.

The aim of this study was to analyze trunk muscle activity during bridge style stabilization exercises, when combined with single and double leg support strategies. Twenty-nine healthy volunteers performed bridge exercises in 3 different positions (back, front and side bridges), with and without an elevated leg, and a quadruped exercise with contralateral arm and leg raise ("bird-dog"). Surface EMG was bilaterally recorded from rectus abdominis (RA), external and internal oblique (EO, IO), and erector spinae (ES). Back, front and side bridges primarily activated the ES (approximately 17% MVC), RA (approximately 30% MVC) and muscles required to support the lateral moment (mostly obliques), respectively. Compared with conventional bridge exercises, single leg support produced higher levels of trunk activation, predominantly in the oblique muscles. The bird-dog exercise produced greatest activity in IO on the side of the elevated arm and in the contralateral ES. In conclusion, during a common bridge with double leg support, the antigravity muscles were the most active. When performed with an elevated leg, however, rotation torques increased the activation of the trunk rotators, especially IO. This information may be useful for clinicians and rehabilitation specialists in determining appropriate exercise progression for the trunk stabilizers.