the most effective way to burn fat and keep muscle is HIIT, keto and AAS combo.
Lift more reps, minimum rest inbetween sets, then hit the nearest track and do 50-100yd sprints
The only "runners" that are scrawny are marathon runners. Olympian sprinters, running backs, boxers/ wrestlers who run everyday religiously, guys like lebron james who run around all game etc are very much jacked.
You can absolutely do cardio and retain muscle bud. Hell you can burn fat, not workout, eat like shit and still keep muscle if you talk to a guy named DNP. Lol