this maybe

// Paste the below in your mapname.gsc

function increase_zom_sprint_speed()
{
    if( !isDefined( level._zombie_custom_spawn_logic ) )
        level._zombie_custom_spawn_logic = [];

    level._zombie_custom_spawn_logic[ level._zombie_custom_spawn_logic.size ] = &change_zom_anim_rate;
}

function change_zom_anim_rate()
{
    iprintlnbold( "^2Increased Move Speed Scale" );
    self ASMSetAnimationRate( 2.0 );
}

// add this in your function main

increase_zom_sprint_speed();