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Flexion-Relaxation Phenomenon in Children and Adolescents With and Without Nonspecific Chronic Low Back Pain

An Electromyographic and Kinematic Cross-Sectional Comparative Study

Tabard-Fougère, Anne MS∗,†,‡,§; Dayer, Romain MD; Armand, Stéphane PhD∗,§; Vuillerme, Nicolas PhD†,§,¶

doi: 10.1097/BRS.0000000000002621

Study Design. A cross-sectional comparative study.

Objective. This study aimed to investigate the flexion-relaxation phenomenon (FRP), in standing trunk flexion and slumped sitting tasks, by comparing children and adolescents suffering from nonspecific chronic low back pain (NSCLBP) with controls (CTRL).

Summary of Background Data. The absence of the FRP can accurately discriminate adults with NSCLBP from those without during standing trunk flexion and slumped sitting tasks. Even if the FRP has been extensively studied in adults with NSCLBP, only one study has evaluated the FRP in adolescents, during a slumped sitting task, and this suggested that the FRP was also present in adolescents with NSCLBP.

Methods. Thirty-seven children and adolescents with NSCLBP and 23 CTRL performed standing trunk flexion and slumped sitting tasks. All participants were equipped with surface electromyography (EMG) electrodes on the erector spinae longissimus (ESL) and multifidus (M) muscles and reflective markers on the spinous processes of C7, L1, and S1. Global (C7-S1), thoracic (C7-L1), and lumbar (L1-S1) trunk flexion absolute angle were measured. The FRP was reported using visual inspection and a flexion-relaxation ratio (FRR). A self-reference threshold was used to identify the time of FRP onset. Repeated-measures analysis of variance (ANOVA) was used to determine the main and interaction effects of task, group and muscle on FRR, and the relative maximal angle at FRP onset of the global trunk (C7-S1).

Results. Results showed three main findings: (1) the FRP's low sensitivity in discriminating between NSCLBP and CTRL participants in groups, tasks, or muscles; (2) similar observed maximal flexion angles in both groups during flexion tasks; and (3) similar observed relative maximal global trunk flexion angles at FRP onset in groups, tasks, and muscles.

Conclusion. These results are not consistent with the literature on adults and could lead to modified therapeutic management of NSCLBP in children and adolescents.

Level of Evidence: 3

Willy Taillard Laboratory of Kinesiology, Geneva University Hospitals and University of Geneva, Geneva, Switzerland

University Grenoble Alpes, AGEIS, Grenoble, France

Division of Paediatric Orthopaedics, Geneva University Hospitals and Faculty of Medicine, Geneva, Switzerland

§LAI Jean-Raoul Scherrer, University of Geneva, Geneva, Switzerland/University Grenoble Alpes, Grenoble, France

Institut Universitaire de France, Paris, France.

Address correspondence and reprint requests to Anne Tabard-Fougère, MS, Willy Taillard Laboratory of Kinesiology, Geneva University Hospitals, 4, Rue Gabrielle-Perret-Gentil, CH-1211 Geneva 14, Switzerland; E-mail:

Received 6 December, 2017

Revised 15 February, 2018

Accepted 19 February, 2018

The manuscript submitted does not contain information about medical device(s)/drug(s).

Medtronic (A1146936) funds were received in support of this work.

Relevant financial activities outside the submitted work: grants.

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