AN EMG INVESTIGATION OF ERECTOR SPINAE MUSCLE ACTIVITY DURING THE TIMED LOADED STANDING TEST IN PEOPLE WITH VERTEBRAL OSTEOPOROSIS

Newman M.¹, Hughes T.¹, Lascurian I.², Vadher K.³, Barker K.^1,4

¹Oxford University Hospitals Foundation Trust, Nuffield Orthopaedic Centre, Oxford, United Kingdom, ²University of the Basque Country, Biscay, Spain, ³University of Oxford, Centre for Statistics in Medicine, Oxford, United Kingdom, ⁴University of Oxford, NDORMS, Oxford, United Kingdom

Background: Vertebral osteoporosis, osteoporotic vertebral fracture (OVF) and hyperkyphosis are all associated with reduced back extensor muscle strength and endurance. Exercise programmes that train back extensor muscles can be of benefit. Despite this, clinical assessment tools are lacking. The Timed Loaded Standing (TLS) test measures arm and back muscle endurance. It records how long someone can stand holding a 1kg dumbbell with arms extended and shoulders flexed to 90 degrees. Previous work TLS is reliable and correlates with relevant impairments but the contribution of key thoracic errector spinae (ES) muscles to TLS remains unclear.

Purpose: To investigate differences in thoracic ES muscle activity during TLS compared to quiet standing (QS) in people with symptomatic vertebral osteoporosis.

Methods: A cross-sectional observational study of adults with vertebral osteoporosis, different numbers of OVFs and back pain. Information was collected about bone health, spinal curvature (Flexi-curve ruler) and back pain (0-10 pain rating scale). TLS time and stop reason was recorded. Surface electromyography (sEMG) was used to measure thoracic ES muscle activity bilaterally at the level of T3 and T12 in QS and during TLS. Fatigability of the ES muscles was evaluated using the median frequency of the sEMG signal.

Results: There were 28 participants: 2 men, 26 women, aged a mean 70.4 (SD 8.7) years, with a mean thoracic kyphosis angle of 43.2 (SD14.7) degrees, mean number of 2.75 (SD 2.9) OVFs and mean 4.75 (SD 2.5) back pain rating. TLS time ranged from 9 to 250 seconds; mean 62.4 (SD 56.9). Nine (32%) participants reported stopping due to pain, 19 (68%) due to fatigue. Muscle activity across the thoracic ES was consistently low during QS, and increased significantly in TLS (p 0.0001). During TLS activity was significantly greater in the lower compared to the upper part of the thoracic ES with activity highest on the participant’s dominant side (p 00001). The change in median frequency over time throughout TLS varied considerably between participants. Individual median frequency plots displayed mixed evidence of fatigue.

Conclusion(s): The TLS test is a good proxy measure for back extensor strength; the thoracic ES muscles significantly increase activity to meet the demands of the TLS test. Activity of the lower thoracic ES on the participant’s dominant side may contribute most to producing back extension torques. Evidence for ES fatigue during TLS was weak and differed between individuals. Perhaps because the relative demand of the1kg load varied between individuals or because of factors such as pain, shoulder pathology, motivation or lumbar ES fatigue.

Implications: The TLS test is feasible with people with symptomatic vertebral osteoporosis and an indicator of thoracic ES muscle activity. Further work could investigate the contribution of the lumbar ES during TLS and consider whether adapting the TLS e.g.; varying the 1kg load, providing encouragement, links ES fatigue and test time more closely.

Funding acknowledgements: Funded by the National Institute for Health Research Health Technology Assessment programme (HTA 10/99/01).

Topic: Musculoskeletal

Ethics approval: Approved by NHS South Central ethics committee reference: 12/SC/0390

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