Unlike a superset, which typically has you pairing up two exercises for separate muscle groups (like chest and back), a compound set doubles down on the same muscle group, hitting the group from different angles to achieve total exhaustion.
Here's a great compound set for chest:
- Barbell Bench Press: 8-10 reps
- Rest: 15 Seconds
- Pec Deck Flye: 12-15 reps
The chest and triceps work as synergists for pressing patterns, so starting off with a bench press in a horizontal pattern will expose the sternal pectoralis to plenty of good muscle damage.
Following that bench with a flye pattern using a fixed machine like the pec deck does a few interesting things:
- First, sitting upright (compared to doing dumbbell flyes on a flat bench) changes the angle of the stress placed on the shoulders so you don't have to endure too much overkill and can rather focus on the chest stimulation alone.
- Second, the triceps don't act as synergists here but antagonists. That means even more emphasis on the chest.
- Third, the larger lever arm you create at the start position of the flye opens up the chest for a deep stretch, optimizing the length-tension ratio during the second half of the compound set. Many top bodybuilders will agree that the latter is a top tier directive for hypertrophy training and shouldn't be neglected.
- Lastly, doing the pec deck flye creates constant tension through a different force angle. In other words, the chest doesn't get to "relax" at any point during the lift.