The purpose of this article is to synthesize the literature on studies that investigate electromyographic activity of abdominal muscles during abdominal exercises performance. MEDLINE and Sportdiscus databases were searched, as well as the Web pages of electronic journals access, ScienceDirect, and Swetswise, from 1950 to 2008. The terms used to search the literature were abdominal muscle and the specific names for the abdominal muscles and their combination with electromyography, and/or strengthening, and/or exercise, and/or spine stability, and/or low back pain. The related topics included the influence of the different exercises, modification of exercise positions, involvement of different joints, the position with supported or unsupported segments, plane variation to modify loads, and the use of equipment. Studies related to abdominal conditioning exercises and core stabilization were also reviewed. Eighty-seven studies were identified as relevant for this literature synthesis. Overall, the studies retrieved lacked consistency, which made it impossible to extract aggregate estimates and did not allow for a rigorous meta-analysis. The most important factors for the selection of abdominal strengthening exercises are (a) spine flexion and rotation without hip flexion, (b) arm support, (c) lower body segments involvement controlling the correct performance, (d) inclined planes or additional loads to increase the contraction intensity significantly, and (e) when the goal is to challenge spine stability, exercises such as abdominal bracing or abdominal hollowing are preferable depending on the participants' objectives and characteristics. Pertaining to safety criteria, the most important factors are (a) avoid active hip flexion and fixed feet, (b) do not pull with the hands behind the head, and (c) a position of knees and hips flexion during upper body exercises. Further replicable studies are needed to address and clarify the methodological doubts expressed in this article and to provide more consistent and reliable results that might help us build a body of knowledge on this topic. Future electromyographic studies should consider addressing the limitations described in this review.

Nonrandomized control trial. To determine if the variations of speed and loading conditions during trunk flexion–extension could influence the times of occurrence and disappearance of the electrical silence of the erector spinae muscles, the degrees of lumbar flexion at those instants, and the relative lumbar motion time. It has been suggested that varying either the speed of movement or the load on the trunk during trunk flexion–extension movements may influence the flexion–relaxation phenomenon or the kinesiologic data. However, no study dealt with the simultaneous effect of the speed of movement on the spine rhythm and on the occurrence of the electrical silence of the erector spinae. A total of 22 pain-free volunteers performed a series of trunk flexion–extension movements varying the speed and load. The motion of the lumbar spine (°) and the integrated electromyography (μV) of erector spinae muscles were simultaneously recorded. Two measures were calculated: the percentage of the maximum lumbar spine flexion at the instants when changes of electrical activity represented the beginning and end of the electrical silence and the relative lumbar spine motion time during trunk flexion and extension movements. The increase in speed of movement significantly increased the relative lumbar flexion time and significantly reduced the relative lumbar extension time (t = 2.49 and t = 2.25, P < 0.05); furthermore, it significantly delayed the appearance of the electrical silence in the range of flexion (t = 3.52, P < 0.01). There was no significant effect from a change in load. The relative spine motion time differed depending on the direction of movement, being longer during trunk flexion and shorter during extension. The increase in speed of movement produced greater differences in the relative time between trunk flexion and extension; furthermore, it delayed the appearance of the electrical silence of the erector spinae muscles in the range of flexion.

Purpose The most relevant musculoskeletal problems are related with back health. Study instruments have been designed for adult patient population but not for school-aged children. The aim of this study was to develop and evaluate the psychometric properties of a questionnaire to assess adolescents’ level of back care knowledge in daily life physical activities. Methods Participants were 171 adolescents from secondary schools. The questionnaire was made up of 24 questions. A Delphi method was used for test validation. Cronbach’s alpha, test–retest, Wilcoxon signed-rank and Bland–Altman graph were used to evaluate the instrument reliability. Results Cronbach’s alpha (α = 0.82) showed a strong internal consistency. Test–retest was excellent for total score (0.76) and moderate to excellent (0.54–0.76) for seven score conceptual categories with good results of standard error of the mean and minimal detectable change. No differences were found between test 1 and test 2 except for the standing posture scores. Conclusion The questionnaire showed acceptable psychometric values. Results showed that this questionnaire is a good instrument to assess adolescent’s back care knowledge.