Röijezon U.1, Jull G.1,2, Djupsjöbacka M.3, Hodges P.2
1Luelå University of Technology, Health Sciences, Luleå, Sweden, 2University of Queensland, School of Health and Rehabilitation Sciences, Brisbane, Australia, 3University of Gävle, Occupational and Public Health Sciences, Umeå, Sweden
Background: Use of unstable surfaces is common in fitness training and for prevention and rehabilitation of movement dysfunction in musculoskeletal and neurological disorders to improve balance, stability, neuromuscular control and proprioception. Previous research has shown changes in neuromuscular activation patterns, including increased muscular activation and co-contraction, when using unstable compared to stable conditions. No previous study has investigated the effects of unstable cervical motor skill tasks on the neuromuscular activation of the deep and superficial cervical muscles.
Purpose: To examine the effect of a dynamically challenging task compared to a stable control condition on neck muscle activity, and how the degree of difficulty influences the activity of the deep and superficial cervical muscles in the unpredictable dynamically challenging neck co-ordination task.
Methods: Participants included nine healthy individuals, three female and six male, with mean age 31 (range 25 to 60) years. Participants were sitting and a plate with a rim was fixed to their head. The task was to control the movement of a metal ball on the plate from a starting position to the centre of the plate and hold it still for 3 seconds. Participants had a visual view of the ball and plate via a stand with two mirrors. Five different surfaces, from high to low rolling resistance were compared to a control condition where the ball was fixed in the centre of the plate. Fine-wire or surface EMG was recorded for the right cervical muscles: rectus capitis posterior major (RCPM), obliquus inferior (OI) semispinalis cervicus (SMC), multifidus (MF) which are considered deep muscles; and splenius capitis (SPC), sternocleidomastoid (SCM), scalenus anterior (SA) and upper trapezius (UTR), which are considered superficial muscles. Non-parametric repeated measures analyses where used to compare the fixed condition and the five different surfaces for each muscle, and for pooled data for the four deep muscles and four superficial muscles, respectively.
Results: The relative EMG activity was significantly higher when the ball was free (movable) on the plate than during the control condition (p 0,05) for all muscles except RCPM. The deep neck muscles (pooled data RCPM, OI, MF and SMC) showed a large increase in muscle activity when changing from fixed to a movable ball condition (p 0,05), but no significant changes in muscle activity when comparing smallest to higher rolling resistance. The superficial neck muscles (pooled data SPC, SCM, AS and UTR) showed a gradual stepwise increase in muscle activity with decreasing rolling resistance conditions, including a significant difference when comparing smallest to higher rolling resistances (p 0,05).
Conclusion(s): The nervous system has different strategies regarding activation of deep versus superficial neck muscles during unstable tasks. When comparing the pooled data there is a clear picture that the deep muscles activate as soon as any instability is introduced, while the superficial muscles are activated relative to how dynamically challenging the task is, i.e., there is a stepwise increase.
Implications: Using unstable systems may be useful to increase activity of deep local muscles of the cervical spine when small dynamic challenge is introduced.
Funding acknowledgements: The Swedish Insurance Society - Land och Sjöfonden, Sweden.
Topic: Musculoskeletal: spine
Ethics approval: Medical Research Ethics Committee at the University of Queensland, Brisbane, Australia.
All authors, affiliations and abstracts have been published as submitted.
