Ask a Sampling of 100 lifters what muscle group they train their traps with and probably 50 will say back while the other 50 will say shoulders. That pretty much sums up the typical disagreement on the issue, but it would be a mistake to conclude that it doesn’t really matter. The truth is, it does.
The traps, though thought of as one muscle, really function as three different muscles with different movements.
“The upper traps, which make up the most mass of the overall muscle, primarily lift and rotate the shoulder blades upward, as when shrugging the shoulders,” says Jim Stoppani, Ph.D, M&F senior science editor and author of Encyclopedia of Muscle & Strength (Human Kinetics, 2006). “The middle traps primarily pull the shoulder blades together, and the lower traps rotate the shoulder blades downward.”
Although trapezius training can be paired with either your shoulder or back workouts, Stoppani points out that most bodybuilders train their traps after shoulders because their primary interest is in developing the upper portion of the traps, and this area is already involved in most shoulder exercises. Following that logic, it makes sense to train them after shoulders, since they’re warmed up and ready to go. Conversely, only the middle traps are involved in back exercises. For that reason, doing shrugs (upper traps) on back day might not be the wisest choice since they won’t be warmed up.
But all in all, if you want to make the best possible choice between training traps with shoulders or back, go with shoulders, Stoppani advises. Or if you want to take a slightly more complex route, divide your trap training between the two: Do shrugging moves with shoulders, and on back day (or in a separate stand-alone workout) hit your middle traps with rows or incline dumbbell shrugs and your lower traps with lying dumbbell Y-raises or overhead barbell raises to the front (which is like a front raise for delts, except you raise the bar completely overhead). We don’t need a poll to know that’s a great solution.