Real athletes are not voluminous.

There is a tendency of people to misjudge volume with actual exercise proof. The reality it is just proof of hypertrophy(heavy and concentrated weight lifting with few repetitions.)

The athelte will have a more

slim appearance, in fact nobody will notice he/she is an athlete unless shirtless or wearing shorts. Well shaped limbs and concave waist are part of the body of the athlete.

So to achieve such body and to have muscular definition, the best way that I know of is the Spartacus workout, which is 1 minute of a repeated exercise followed by 15 seconds of rest. 10 times in a row.
Depending on the types of exercises, this varies from difficult to overwhelming.

Push-ups, squats and sit-ups are tough, but the toughest exercise is the burpee. I will create an article just to address that specific exercise and why it is so effective(and devastating, because it works cardio and some variations really work all the main muscles in the body.)

I can assure you, you will hate 50 burpees in a row. It is tough, exhausting, detestable, irritating, humbling and despairing. But that's why it works. Done well, produces no damage to the articulations.

Bare in mind that the most effective exercises are the most exhausting and swelling. At 30 repetitions, My reward system starts to shun me and convince me to give up. It will happen to you as well, but you must continue up to the limit you have set yourself from the beginning, hopefully as much as your cardio resistance allows you to(this is when a pulse meter is handy.)

It is also time efficient because it only takes ~12 minutes, and if you want you can do three rounds with 2 minute rests in between for a total of ~ 45 minutes. All of it without any equipment, just your body and 4 square meters.