The lateral neck flexor endurance test: Normative values in the young adult population

Unilateral muscular deficits have been identified in individuals with neck pain, although no unilateral clinical tests have been described in the literature. Assessment of lateral neck flexor endurance may allow identification of abnormal unilateral muscle function. The lateral neck flexor (LNF) endurance test, where an individual holds their head parallel to the ground while side-lying, may be a clinical option. We sought to (1) determine inter-rater reliability of the LNF endurance test and (2) establish normative LNF values in healthy individuals.

Inter-rater reliability was assessed for four raters, working in pairs to assess a pilot sample of 20 individuals. Normative data was subsequently collected for 60 healthy adults, age 20-40. All participants completed the International Physical Activity Questionnaire to assess physical activity and the LNF endurance test was assessed once per side.

The LNF endurance test demonstrated excellent inter-rater reliability: ICC_(2,1) = 0.972 [0.941-0.987]. Left and right median LNF hold times were 122.0, 133.94 s for males and 97.42, 93.73 s for females, respectively. Individual median hold time ratios were 72.1% for males and 68.7% for females. There were no meaningful correlations between reported physical activity and LNF endurance.

The LNF endurance test is a reliable measure. Males generally displayed greater LNF endurance than females, although variability within groups was high. Based on the observed values in this healthy population, 120 s for males and 90 s for females with a 70% side:side ratio appear to be useful normative benchmarks although further research is required including clinical populations.