Return-to-Work Readiness: Functional Capacity vs. Job Demand

Injury & Program

Injury severity Moderate

Weeks in rehab program 0 wk

Therapy intensity / adherence 60%

Target Job

Functional Capacity

Lift capacity

25 lb

% of pre-injury

25%

RTW readiness

—

Re-injury risk

—

How it works

Functional capacity is modelled as a bounded exponential recovery curve driven by weekly therapy dose:

C(t) = Cmax - (Cmax - C0) * e^(-k*t)
k = k0 + (intensity/100) * kmax
Cmax = 100 lb (pre-injury occasional-lift capacity)

C0 (starting capacity after injury) and k0 (base recovery rate) come from injury severity — mild starts higher and recovers faster, severe starts lower and slower. Higher therapy intensity/adherence raises the effective recovery-rate constant k, the same dose-response idea used in real graded-exposure and progressive-loading rehab protocols.

Job physical-demand levels follow the standard US Dept. of Labor / SSA occasional-lift classification used in vocational rehab and disability evaluation:

Sedentary ≤ 10 lb   Light ≤ 20 lb   Medium ≤ 50 lb
Heavy ≤ 100 lb      Very Heavy > 100 lb

Re-injury risk uses a logistic function of the capacity/demand ratio r = C(t) / demand:

risk(%) = 100 / (1 + e^(6*(r-1)))

At r = 1 (capacity exactly meets demand) risk sits at 50%; comfortably above 1 the curve drops toward a safe margin, below 1 it climbs toward near-certain re-aggravation — reflecting why vocational rehab targets a capacity cushion above the job's demand, not just a bare pass.

Attempt Lift Task runs a 3D lift with the selected job's load and rolls the risk model for a pass/strain/fail outcome, exactly as a Functional Capacity Evaluation (FCE) would score a real return-to-work test.

Worker Load crates

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