To improve the understanding of load-time traces observed during instrumented impact testing, analytical and experimental studies have been conducted to determine the effects of inertial loading. The first load discontinuity in a load-time profile has been found to result from the interaction of a rapidly decreasing inertial load developed by Charpy specimens as they accelerate from rest and the finite ability of the instrumented tup to react to very rapid load transients. A model is developed which quantitatively correlates initial portions of load-time profiles for A1203 and U-3/4Ti with rigid-body accelerations of these materials. In addition, the magnitude of the initial load discontinuity is related to the acoustic impedances of the tup and specimen and the initial impact velocity in agreement with theory drawn from elastic wave mechanics. Successful correlation of this theory for a large variety of materials has allowed a semi-empirical relation to be developed for the prediction of inertial loads. Control procedures are suggested to both identify and reduce the role of inertial loads in instrumented impact testing.