Evidence-Based Pack Weight Thresholds for Mature Recreational Trekkers: A Factor of Safety Synthesis for the Silver Majority Population

ABSTRACT Background: The global trekking community is witnessing a demographic shift toward the Silver Majority (adults aged 46–65+), a population highly susceptible to load-induced musculoskeletal injury. Current anecdotal pack weight guidance is derived from military load carriage research conducted on young adult males and has not been validated in older, predominantly female, civilian trekking populations. Real-world evidence from a 1,206-participant prospective cohort study (Stoltzfus et al., 2022) confirms that pack weight-to-body-weight ratio and BMI in the obese category are independently significant predictors of musculoskeletal injury. Objective: This paper synthesizes the available biomechanical and clinical evidence to derive conservative, evidence-informed pack weight thresholds for adults aged 46 and older engaged in multi-day recreational trekking, using a Factor of Safety methodology consistent with established occupational ergonomics standards. A secondary objective is to identify and operationalize the effect of ideal body weight deviation on load carriage risk — a variable absent from existing trekking guidance. Methods: Utilizing an iterative Factor of Safety methodology consistent with the NIOSH Revised Lifting Equation (Waters et al., 1994) and ISO 11228-1:2021, a high-fidelity evidence synthesis was performed, aligned with PRISMA 2020 reporting standards. Thirteen primary studies across six evidence categories were synthesized: load carriage metabolics and kinetics (Haisman, 1988; Knapik et al., 1996, 2004; Birrell Bastien et al., 2005; Dames Siragy et al., 2024), and comparative safety standards (Mackenzie et al., 2003; ISO 11228-1, 2021). Candidate load threshold pairings were evaluated using the Tri-Metric Reliability Score (TMRS), a composite scoring instrument developed to assess each pairing across metabolic, kinetic, and operational dimensions. Sensitivity analysis across six weighting schemes confirmed outcome robustness. Results: The 7.7%/8.3% pack weight-to-body-weight threshold pairing achieved the highest aggregated TMRS of approximately 93% (range: 92.6%–93.2% across six sensitivity analysis weighting schemes) and the highest precursor convergence score of 0.94. This pairing maintains pack weight within a range that does not measurably alter natural gait mechanics, by preserving a 0.2% safety margin below the 8.5% kinetic reference ceiling. Prospective cohort data (Stoltzfus et al., 2022) independently validates two primary theoretical constructs: the ratio-based load calculation model and the independent injury-predictive effect of excess body mass above ideal weight. Conclusion: A Factor of Safety evidence synthesis of 13 studies across six evidence categories supports pack weight thresholds of 7.7% (operational target) and 8.3% (authorized maximum) of actual body weight for mature recreational trekkers, with an additional ideal body weight gate for individuals whose actual weight materially exceeds their clinical ideal. All scoring instruments are internally derived and fully disclosed to support independent validation. A PROSPERO-registered prospective cohort study to empirically validate these thresholds in the target population is designated as the primary Phase II research objective. These findings represent population-level risk thresholds and do not constitute individual medical advice.