Where a pre-existing degenerative condition is sufficiently common in the general population (here, 10-15% of persons aged 40-49), an employee with that condition falls within the normal range of health and strength for the purpose of assessing the employer's duty of care, and the risk of injury to such employees is foreseeable. The distinction between whether countermeasures would have prevented a condition from ever occurring and whether they would have prevented the acceleration of that condition is critical to causation analysis — the relevant injury is the acceleration, not the underlying condition.
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