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Schmid S1,2, Stauffer M1,3, Jäger J2, Bangerter C4, List R2,5, Lorenzetti S2,6
1Bern University of Applied Sciences, Department of Health Professions, Bern, Switzerland, 2ETH Zurich, Institute for Biomechanics, Zurich, Switzerland, 3Fios - Praxis für Physio- und Ergotherapie, Herzogenbuchsee, Switzerland, 4Physio Hildebrandt, Bern, Switzerland, 5Schulthess Clinic, Human Performance Lab, Zurich, Switzerland, 6Swiss Federal Institute of Sport Magglingen SFISM, Magglingen, Switzerland
Background: Low back pain (LBP) and pelvic girdle pain (PGP) are common problems in women after childbirth with an overall prevalence of 25%. The regular carrying of the infants, often by using sling-based carrying techniques, might thereby be a contributing factor for the development and progression of these conditions. However, the neuromechanical adaptations of the spine due to sling-based infant carrying are not sufficiently well understood.
Purpose: More specific information on spinal motion as well as knowledge on trunk muscle activity during sling-based infant carrying might provide valuable information towards a better understanding of LBP/PGP in this population, which is important for the development of evidence-based recommendations for carrying techniques as well as treatment and prevention methods. This study therefore aimed at investigating the immediate effects of different sling-based infant carrying techniques on spinal kinematics and trunk muscle activity during standing and walking.
Methods: Fifteen healthy young women were included in this cross-sectional study. Using a 22-camera optoelectronic motion capture and a wireless surface electromyography system, three-dimensional pelvis and spinal kinematics as well as bilateral activation patterns of lumbar and thoracic erector spinae, rectus abdominis and obliquus externus muscles were derived during upright standing and level walking without carrying a load and while carrying a 6 kg-dummy with a sling in front as well as on either side. Data were analyzed using the MATLAB-based spm1d-package for n-dimensional Statistical Parametric Mapping, allowing group comparisons of discrete parameters (standing) as well as continuous data (walking). To distinguish between clinically relevant and clinically not relevant kinematic findings, statistically significant differences were only considered in case of ≥5°.
Results: Carrying the dummy in front was mainly associated with increased lumbar lordosis (standing: Δ8.8°, p=0.006; walking: Δ≥8.2°, 1-100% of gait cycle [%GC], p 0.001), whereas increased thoracic kyphosis (standing: Δ5.3°, p≤0.003; walking: Δ≥5.6°, 1-100%GC, p 0.001) and less axial rotation away from the dummy (standing: Δ5.3°, p=0.003; walking: Δ≥5.0°, 46-58%GC, p=0.002) were observed when carrying on the preferred side compared to carrying no load. Differences in muscle activity were mainly observed for the erector spinae muscles, i.e. higher bilateral activity when carrying the dummy in front (thoracic: Δ≥9.5%maxMVIC, p≤0.003) as well as higher contralateral activity when carrying the dummy on the preferred (thoracic: Δ≥5.3%maxMVIC, p 0.001) and non-preferred sides (lumbar: Δ≥13.2%maxMVIC, p 0.001).
Conclusion(s): Carrying a 6 kg-dummy in front and on the preferred and non-preferred sides during upright standing and level walking resulted in different neuromechanical responses for each of the three conditions. Carrying the dummy in front was mainly associated with increased lumbar lordosis, whereas increased thoracic kyphosis and less axial rotation away from the dummy were observed when carrying on the preferred side. All three conditions entailed increased paraspinal muscle activity, although only unilaterally in side carrying. Prospective trials including postpartum women with and without LBP/PGP should be conducted to confirm this assumption and to establish evidence-based recommendations.
Implications: Carrying an infant alternating on the preferred and non-preferred sides using a sling might contribute to the prevention and reduction LBP in women after childbirth.
Keywords: Trunk, Kinematics, Electromyography
Funding acknowledgements: This work was unfunded.
Purpose: More specific information on spinal motion as well as knowledge on trunk muscle activity during sling-based infant carrying might provide valuable information towards a better understanding of LBP/PGP in this population, which is important for the development of evidence-based recommendations for carrying techniques as well as treatment and prevention methods. This study therefore aimed at investigating the immediate effects of different sling-based infant carrying techniques on spinal kinematics and trunk muscle activity during standing and walking.
Methods: Fifteen healthy young women were included in this cross-sectional study. Using a 22-camera optoelectronic motion capture and a wireless surface electromyography system, three-dimensional pelvis and spinal kinematics as well as bilateral activation patterns of lumbar and thoracic erector spinae, rectus abdominis and obliquus externus muscles were derived during upright standing and level walking without carrying a load and while carrying a 6 kg-dummy with a sling in front as well as on either side. Data were analyzed using the MATLAB-based spm1d-package for n-dimensional Statistical Parametric Mapping, allowing group comparisons of discrete parameters (standing) as well as continuous data (walking). To distinguish between clinically relevant and clinically not relevant kinematic findings, statistically significant differences were only considered in case of ≥5°.
Results: Carrying the dummy in front was mainly associated with increased lumbar lordosis (standing: Δ8.8°, p=0.006; walking: Δ≥8.2°, 1-100% of gait cycle [%GC], p 0.001), whereas increased thoracic kyphosis (standing: Δ5.3°, p≤0.003; walking: Δ≥5.6°, 1-100%GC, p 0.001) and less axial rotation away from the dummy (standing: Δ5.3°, p=0.003; walking: Δ≥5.0°, 46-58%GC, p=0.002) were observed when carrying on the preferred side compared to carrying no load. Differences in muscle activity were mainly observed for the erector spinae muscles, i.e. higher bilateral activity when carrying the dummy in front (thoracic: Δ≥9.5%maxMVIC, p≤0.003) as well as higher contralateral activity when carrying the dummy on the preferred (thoracic: Δ≥5.3%maxMVIC, p 0.001) and non-preferred sides (lumbar: Δ≥13.2%maxMVIC, p 0.001).
Conclusion(s): Carrying a 6 kg-dummy in front and on the preferred and non-preferred sides during upright standing and level walking resulted in different neuromechanical responses for each of the three conditions. Carrying the dummy in front was mainly associated with increased lumbar lordosis, whereas increased thoracic kyphosis and less axial rotation away from the dummy were observed when carrying on the preferred side. All three conditions entailed increased paraspinal muscle activity, although only unilaterally in side carrying. Prospective trials including postpartum women with and without LBP/PGP should be conducted to confirm this assumption and to establish evidence-based recommendations.
Implications: Carrying an infant alternating on the preferred and non-preferred sides using a sling might contribute to the prevention and reduction LBP in women after childbirth.
Keywords: Trunk, Kinematics, Electromyography
Funding acknowledgements: This work was unfunded.
Topic: Human movement analysis
Ethics approval required: Yes
Institution: ETH Zurich
Ethics committee: Ethics committee of ETH Zurich
Ethics number: 2016-N-60
All authors, affiliations and abstracts have been published as submitted.
