The Truncation Error: How Half a Century of Misquoted Research Created a Flawed Standard for Recreational Pack Weight

v5.3 (June 18, 2026): OSF pre-registration reference corrected from informal URL citation to DOI-minted formal citation (10.17605/OSF.IO/Z46VS) with correct authorship attribution. ABSTRACT Background: The widely circulated guideline advising outdoor recreationists to limit pack weight to 10% of body weight lacks robust empirical foundation in the recreational trekking context. A historical trace of this figure reveals that it represents a simplified derivative of military load-carriage research conducted on young, physically fit soldiers — a population whose musculoskeletal and metabolic profile differs substantially from the middle-aged and older adults (ages 46–65+) who now constitute the demographic majority on long-distance pilgrimage trails such as the Camino de Santiago. This paper acknowledges that a recent plantar pressure study (Chicharro-Luna et al., 2026) provides biomechanical support for the 10% threshold in long-distance hikers generally; the present analysis argues that this finding, while valid for plantar loading outcomes, does not address the body-composition-adjusted skeletal load capacity problem that motivates this framework. Objective: This paper examines the propagation of the 10% guideline through the recreational trekking community, identifies the mechanism by which clinical precision was lost during transmission (herein termed the Truncation Error), proposes a body-composition-adjusted framework for pack weight calculation, and explicitly maps the strongest arguments against its premises, addressing each with preemptive evidentiary language. Methods: A critical literature synthesis was conducted across three domains: (1) the historical provenance and mathematical properties of four major IBW equations (Devine, 1974; Robinson et al., 1983; Miller et al., 1983; Hamwi, 1964), with verification against the universal body weight equation of Peterson et al. (2016); (2) load-carriage biomechanics literature including contradictory evidence (Knapik et al., 1996a, 2004; Birrell et al., 2007; Simpson et al., 2011; Chicharro-Luna et al., 2026; Hudson et al., 2024; Matur et al., 2025; Sturdy et al., 2025); and (3) NIH/NHANES anthropometric data for population-level body weight distributions. A parametric optimization was performed to identify percentage pairs producing a clinically defensible gradient across the adult height-weight spectrum. Results: The 7.7%/8.3% pairing produced the most consistent tier separation across the height range of 4'6" to 6'6" for both sexes. Systematic coefficient drift was identified in secondary-source propagation of the Robinson formula, with rounded coefficients (49/1.7) producing up to 2.73 lbs divergence from original published values (48.67/1.65) at 6'6". Contradictory evidence from recreational hiking research is reviewed and its population-validity scope distinguished from the present framework's intended application. Conclusions: The 10% guideline fails to account for the discrepancy between actual weight and skeletal load capacity in overweight individuals. A five-tier body-composition-adjusted array framework represents a theoretically defensible alternative, pending empirical validation through the pre-registered Silver Majority Camino Survey (SMCS-1; OSF: osf.io/n5uxc). This paper explicitly acknowledges the hypothesis-generating rather than evidence-confirming nature of its central claims. Keywords: pack weight, ideal body weight, Camino de Santiago, load carriage, body composition, Devine formula, Robinson formula, BMI, pilgrimage trekking, Factor of Safety, skeletal load capacity, evidence synthesis Version History: v1 (May 2026): Initial upload. v2 (June 2026): Citation corrections. v3 (June 2026): Added Hudson et al. (2024), clarified BMI 21.7 derivation, resolved Knapik dual-citation. v4 (June 2026): Added Chicharro-Luna et al. (2026) plantar pressure contradiction analysis; expanded pre-emptive rebuttal sections 2.4, 6.8, 6.9, 6.10; added Table 5 (peer review challenge map); reformulated Phase 2 epistemological framing. v5 (June 2026): Citation forensic corrections — (1) misattributed Rother et al. (2010) corrected to Simpson, Munro & Steele (2011) in all four body locations; (2) non-existent Knapik et al. (1996b) entry deleted from reference list and all body locations; (3) Section 2.1 rewritten to reflect single 1996 Knapik load-carriage paper; (4) IRB language updated to reflect exemption determination; (5) OSF pre-registration reference updated. Corrections documented in P1-D10-C1 Citation Investigation Results v1.0 (June 10, 2026). v5.1 (June 11, 2026): Pilgrim completion figures updated to verified 2024 (499,239) and 2025 (530,919) data per Oficina del Peregrino (P2 Audit C2-A). Oficina del Peregrino (2025) reference entry added. v5.2 (June 16, 2026): IRB determination date corrected to June 16, 2026 (wet signature date); IRB Self-Determination Memorandum reference updated to SMCS1-v1.4.