Test-retest repeatability of strength capacity, aerobic power and pericranial tenderness of neck and shoulder muscles in children - relevant for tension-type headache

Birte Tornøe,^1,2,5,6 Lars L Andersen,³ Jørgen H Skotte,³ Rigmor Jensen,⁴ Gunvor Gard,¹ Liselotte Skov,² Inger Hallström<sup>1

1</sup>Department of Health Sciences, Lund University, Scania, Sweden; ²Children's Headache Clinic, Department of Pediatrics, University of Copenhagen, Herlev Hospital, Herlev, Denmark; ³National Research Centre for the Working Environment, Copenhagen, Denmark; ⁴Danish Headache Center, Department of Neurology, University of Copenhagen, Glostrup Hospital, Glostrup, Denmark; ⁵Department of Physiotherapy and Occupational Therapy, University of Copenhagen, Glostrup Hospital, Glostrup, Denmark; ⁶Department of Physiotherapy, Medical Department, University of Copenhagen, Herlev Hospital, Herlev, Denmark

Background: Frequent or chronic tension-type headache in children is a prevalent and debilitating condition for the child, often leading to medication overuse. To explore the relationship between physical factors and tension-type headache in children, the quality of repeated measures was examined. The aim of the present study was to determine the test-retest repeatability of parameters determining isometric neck and shoulder strength and stability, aerobic power, and pericranial tenderness in children.
Methods: Twenty-five healthy children, 9 to 18 years of age, participated in test-retest procedures within a 1-week interval. A computerized padded force transducer was used for testing. The tests included the isometric maximal voluntary contraction and force steadiness of neck flexion and extension, and the isometric maximal voluntary contraction and rate of force of the dominant shoulder. Pericranial tenderness was recorded by means of standardized manual palpation, and a submaximal cycle ergometer test predicted maximal oxygen uptake (VO₂ max). The measurements were evaluated in steps, using the intraclass correlation coefficient (ICC); changes in the mean between the two test occasions; the levels of agreement, visualized in Bland-Altman Plots; and by quantifying the variability.
Results: The results showed an acceptable test-retest repeatability of isometric maximal voluntary contraction (ICC 0.90-0.97). The force steadiness measurements revealed a trend of systematic changes in the direction of neck flexion and need further examination in both healthy and ill children. The rate of force development, Total Tenderness Score, and prediction of VO₂ max showed repeatability, with ICC 0.80-0.87.
Conclusion: The measurements of strength capacity, aerobic power, and tenderness provide acceptable repeatability, suitable for research in children.

Keywords: muscle strength, intratester reliability, cardiovascular fitness