The report presents a quantitative measure of the effects of energy absorber stroke length upon cumulative probability of injury. The response of a seated subject to a vertical deceleration pulse representing a helicopter crash was calculated for a given seat and clothing weight. The seat-man system was analytically supported by a square wave energy absorber selected to generate no greater than 23 G for a 5th percentile man. The calculated response, DRI, provides a probability of spinal injury for the seated occupant. Since all parameters necessary for response computations had known statistical properties, it was possible to calculate the joint probability of injury for a particular deceleration pulse and subject weight. By calculating the statistical values for many deceleration and weight combinations, sufficient to represent the total population of both, a cumulative probability of injury was generated. Stroke length of the energy absorber required for each combination of deceleration and weight was calculated. By examining the effects of a limited stroke length, it was possible to generate a curve of stroke length available versus cumulative probability of injury. The curve indicates that for a realistic stroke length 12 inches, the cumulative probability of injury is 0.119. By doubling the stroke available or by halving it, the cumulative probability is decreased or increased by 7 percent. Comparisons with previously reported data indicate that the injury potential of the square wave is significantly higher than is theoretically achievable.