15.2.4 Operational age adjustment of effective ROM

The ROM used in this procedure is not necessarily the base ROM of the biomechanical model. When calculating instantaneous postures, Ergoniza Intelligent applies an operational age adjustment to the ROM used as a reference:

\[{ROM}_{ef\ j,d} = {ROM}_{base\ j,d} \bullet F_{edad\ j,d}\]

Equation 73

where:

• ROM_base,j,d is the model's reference ROM for joint j and movement d;

• Fedad_j,d is the age-adjustment factor;

• ROMef_j,d is the effective ROM used solely to calculate relative proximity to the joint limit.

This adjustment neither changes the model's actual ROM nor prevents a particular posture from being adopted. It changes only the denominator used to calculate rj,d. Thus, for an older person, the same angle may represent greater relative proximity to the functional limit.

The age factors used for the shoulder, elbow, hip, knee, and ankle were derived from the ROM reference values published by Soucie et al.84F¹, using ages 20–40 as the reference group. Factors greater than 1 are applied to the under-20 group when the data show a higher mean ROM, and factors below 1 are applied to the over-40 group when the data show a reduction in ROM.

For the neck and trunk, for which the data from Soucie et al. do not provide equivalent coverage, operational factors are based on specific studies of age-related loss of cervical and lumbar mobility. Kuhlman et al.85F² describe different reductions in cervical ROM for flexion, extension, lateral flexion, and rotation in older populations, while Intolo et al.86F³ show that the effect of age on lumbar ROM is not uniform across movement planes.

The literature also indicates that age-related loss of mobility is joint-specific. Flexitest results87F⁴ from a large sample show that the shoulder and trunk tend to lose proportionally more mobility than the elbow and knee, supporting the use of different age adjustments for different body regions.

Based on these studies, Ergoniza Intelligent uses the following factors:

These values should not be interpreted as normative or universal, but as an ergonomic parameterization based on the literature. They may be adjusted in future versions as new experimental data become available.