The relation between the flexion relaxation phenomenon onset angle and lumbar spine muscle reflex onset time in response to 30 min of slumped sitting
Introduction
In a large number of industries, occupational tasks require workers to sit for long periods of their workday (Shin, D’Souza, & Liu, 2009). Prolonged flexed postures have been suggested to induce changes in the tissue properties of the low back, which can lead to a possible low back injury (Sánchez-Zuriaga, Adams, & Dolan 2010). For instance, creep, a change in the length of viscoelastic structures, can result in biomechanical dysfunction by reducing the functional stiffness and responsiveness of reflexive activation of important postural muscles (Solomonow, Baratta, Banks, Freudenberger, & Zhou, 2003a). Sustained postures have been observed to induce these viscoelastic changes in the passive structures surrounding the spine, such as ligaments and tendons (Bazrgari et al., 2011, McGill and Brown, 1992, Larson et al., 2020). The increase in joint laxity due to creep can increase the trunk flexion range of a worker, heightening their risk of a hyperflexion injury (McGill & Brown, 1992). These injuries may cause or further exacerbate pain, which can limit or alter the daily functioning of an individual.
The changes that are induced by creep have been observed to influence the flexion-relaxation phenomenon (FRP) of the low back muscles as well as the onset of low back reflexes (LBR) (Howarth et al., 2013, Hendershot et al., 2011, Radebold et al., 2001). The FRP is a biomechanical phenomenon where back muscle activity turns off at a certain point in the flexion range (Howarth et al., 2013). This cessation in muscle activity is due to the passive tissues being able to withstand the load from the external low back moment of the torso without help from the muscles (Li et al., 2019). This typically occurs near the end range of flexion. It has been previously shown that prolonged spine flexion reduces the passive support of the spine (McGill & Brown, 1992), increasing the point during the flexion range where the low back muscles turn off (FRP onset) (Solomonow et al., 2003a, Howarth et al., 2013). The LBR is the activation of the trunk muscles in response to a sudden perturbation (Reeves, Cholewicki, & Milner, 2005). In cats, these reflexes have been shown to have a delayed response after the low back tissues have been passively stretched in a prolonged flexion posture, where creep is induced (Solomonow et al., 2003b). This delay in trunk reflexes is often found in people who experience low back pain (Radebold, Cholewicki, Panjabi, & Patel, 2000). Both the FRP and LBR provide important insights into the stiffness and function of the spine. In theory, if any lengthening occurs in spine tissues, this change should be reflected in increases in both the FRP onset point and LBR onset time.
Currently, the FRP and LBR measures are used in laboratory-based studies. Since they can indirectly assess viscoelastic changes in the low back, there may be potential to use them in the field to monitor injury risk in workers. If these measures are highly correlated, one could be used as a surrogate measure for the other. To our knowledge, this has yet to be investigated. Therefore, the primary objective of this research study was to determine if there is a positive correlation between the changes in the onset of the FRP and LBR following a 30-minute near-maximal flexion exposure. A secondary objective was to determine if there is a significant change in the onset of these measures in the lumbar multifidus (LM) and lumbar erector spinae (LS) muscles following the sitting exposure.
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Participants
Based on sample size calculations using previously published LBR and FRP data (and choosing the larger sample) we aimed to recruit 42 healthy participants from the general population for this study. Inclusion criteria were adults aged 18–69 with no low back impairments. Low back impairments were classified as a history of spinal tumors, back pain in the past 6 months, surgery, fracture, infection, or inflammatory arthritis (i.e., rheumatoid arthritis or ankylosing spondylitis). Participants
Participants
15 participants were recruited and included in the study. Participant characteristics were as follows: 6 males (20.83 ± 1.57 years, 184.49 ± 6.82 cm, 77.70 ± 12.11 kg) and 9 females (21.89 ± 1.59 years, 161.73 ± 7.19 cm, 60.64 ± 7.12 kg). The age range of these participants was 18–26 years.
Sitting exposure
During the sitting exposure, participants adopted an average lumbar angle of 87.53 ± 22.95% of maximum lumbar spine flexion.
FRP
Following the sitting exposure, a statistically significant increase in FRP onset
Discussion
The current investigation examined whether or not the change in the onset of the FRP and LBR are correlated following 30 min of near-maximal lumbar flexion. Additionally, the study aimed to determine whether the sitting exposure would significantly change the onset of the FRP and LBR compared to baseline measures. This study found no statistically significant correlations between the FRP and LBR measures for each muscle, a statistically significant increase in the angle of FRP onset in the RLM
Acknowledgements
The authors would like to thank Mona Frey for her assistance with the statistical analysis. This study was funded by an NSERC Discovery Grant (#20161771).
Sarah Mackey is a graduate student in the Faculty of Medicine at Memorial University of Newfoundland. She earned her Bachelor's Degree (Honours) in Kinesiology from the School of Human Kinetics and Recreation in 2020. Her research interests are the biomechanics of the low back, low back pain and physician postures during clinical procedures.
References (18)
- et al.
Frequency response of spine extensors during rapid isometric contractions: effects of muscle length and tension
J. Electromyogr. Kinesiol.
(1998) - et al.
Do flexion/extension postures affect the passive lumbar spine stiffness response to applied axial torque?
J. Biomech.
(2006) - et al.
Disturbance and recovery of trunk stiffness and reflexive muscle responses following prolonged trunk flexion: influences of flexion angle and duration
Clin. Biomech.
(2011) - et al.
Does prolonged seated deskwork alter the lumbar flexion-relaxation phenomenon?
J. Electromyogr. Kinesiol.
(2013) - et al.
Creep response of the lumbar spine to prolonged full flexion
Clin. Biomech.
(1992) - et al.
Muscle reflex classification of low-back pain
J. Electromyogr. Kinesiol.
(2005) - et al.
Flexion–relaxation response to static lumbar flexion in males and females
Clin. Biomech.
(2003) - et al.
Muscular dysfunction elicited by creep of lumbar viscoelastic tissue
J. Electromyogr. Kinesiol.
(2003) - et al.
Surface EMG electrodes do not accurately record from lumbar multifidus muscles
Clin. Biomech. (Bristol, Avon).
(2003)
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Sarah Mackey is a graduate student in the Faculty of Medicine at Memorial University of Newfoundland. She earned her Bachelor's Degree (Honours) in Kinesiology from the School of Human Kinetics and Recreation in 2020. Her research interests are the biomechanics of the low back, low back pain and physician postures during clinical procedures.
Jason Barnes earned his Bachelor's Degree (Honours) in Kinesiology from the School of Human Kinetics and Recreation in 2020. He is currently a physiotherapy student at Dalhousie University in Halifax, Canada.
Kristen Pike earned her Bachelor's Degree (Honours) in Kinesiology from the School of Human Kinetics and Recreation in 2020. She is currently a physiotherapy student at Dalhousie University in Halifax, Canada.
Dr. Diana De Carvalho is an Assistant Professor in the Faculty of Medicine at Memorial University of Newfoundland. She obtained her doctorate in 2015 from the Department of Kinesiology in the Faculty of Applied Health Sciences at the University of Waterloo. Dr. De Carvalho's research program focuses on the spine biomechanics of prolonged spine flexion, clinical low back pain and ergonomic/treatment interventions.