The present invention relates to inertial braking system for spring-loaded devices, such as block and tackle window balances incorporated in single and double hung window assemblies. In one embodiment, a block and tackle window balance includes a translatable block assembly disposed in a track including a pawl pivotally attached to the translatable block assembly. The pawl, in response to a rapid acceleration of the translatable block assembly, rotates about a pivot and frictionally engages the track, thereby wedging the translatable block assembly in the track. In another embodiment, the translatable block assembly includes a cam attached to the pawl and a brake shoe disposed between the cam and a cord seated within a pulley. Rotation of the pawl causes the cam to translate the brake shoe, thereby compressing the cord against the pulley.