How to stop my muscles from starting to atrophy when I can't make it to the gym for 4/5 days do to a crazy schedule? Are body weight exercises enough (pushups, pullups, situps and squats)
A mere 4–5 days away from resistance training is not nearly enough time for muscular atrophy to begin.
Most fitness professionals, myself included, agree that 10–14 days is the maximum time you can safely spend away from the gym before experiencing a noticeable drop in fitness level or muscle size and strength.
Of course, if you really need to keep exercising daily, my lord, there's a ton of routines you can do at home or in a hotel room, where you need no equipment. I've listed these many times here on Quora in similar questions. And yes, these are more than adequate for maintaining your fit level. Hell, some of these might even be better than stuff you do in the gym! Like burpees, Pull ups, and pushups. They're as good as ANY gym machine or free weight workout. ANY.
Incline and declined push ups.
Go for a run!
Side planks with leg lifts