Validation of a free fall acrobatics intervention protocol to reduce neck loads during parachute opening shock

BACKGROUND Elevated neck pain prevalence among skydivers is associated with exposure to repeated parachute opening shock (POS). A study is planned to evaluate a preventive free fall acrobatics intervention, but prior assessment of the protocol is necessary given the complex and safety-critical study environment. AIM To validate an intervention protocol to reduce POS neck loads. METHODS A protocol was developed based on observational data and theoretical calculations. Six experts rated each component of the protocol on a four-point Likert scale, regarding relevance, simplicity/feasibility and safety, and responded to open-ended questions. Two iterations were made, each followed by consensus panel protocol revisions. The content validity index (CVI) was used to quantify ratings. A measure of universal agreement (CVI/UA) was computed as the proportion of components that achieved a rating ≥3 by all raters. For safety, a high-sensitivity CVI/UA was computed with a rating of no <4 (highest score) as acceptable. RESULTS CVI/UA for relevance increased from 0.80 in the first assessment to 1.00 in the second; for simplicity from 0.50 to 0.63; and for safety from 0.70 to 1.00. High-sensitivity CVI/UA for safety increased from 0.10 to 0.75. Responses to open-ended questions included safety concerns for free fall stability, altitude awareness and concerns over comprehensibility. CONCLUSIONS The proposed protocol has been improved in assessed relevance, simplicity and safety, and is considered validated for the start of the empirical trial. To what degree complex interventions should be preceded by open prevalidation is discussed.