Full throttle allows your hero to convert their knowledge of throttling monsters into forward motion. The biomechanical principles behind this are still a mystery, but then again, scientists are still too busy unraveling the secrets of heroes' livers.
Level 1-5: The hero can recall childhood memories of vigorously cuddling and accidentally choking someone's cute and furry pet to death. The lingering embarrassment forces them to quicken their pace.
Level 6-10: The hero recalls how, at level one and without equipment, they were forced to throttle a significant otter to death in a struggle for life and death. The emotional thrill of that first bare-handed victory gives some extra spring to their step.
Level 11-15: The hero's adventures have given them a reasonable number of deaths-by-choking to look back at. The triumphant feeling makes them able to cross vast distances with large strides.
Level 16-20: The hero has killed many a monster with its bare hands, and is a veritable master in the fatal manipulation of the windpipes of any living creature. This confidence makes the hero bound rather than walk, speeding up travel significantly.
20-25: The hero recalls discovering where the Dreaded Gazebo's windpipe is located - and using that knowledge to throttle a wooden structure. This makes them feel proud enough to break into a gallop, looking around for more carpentry to obliterate.
25+: Your hero recalls all the confused and worried faces of Godville Admins they choked to death. Remembering how their eyes rolled away after the final spasms makes them feel invincible, and causes them to dash toward new adventures with incredible speed and disregard for danger.