The American College of Sports Medicine recommends training larger muscle groups first during a workout, followed by progressively smaller muscle groups. The logic is that the larger muscle groups require greater effort to fully activate. Despite this logic, there hasn’t been a lot of research looking at the effects of exercise order and muscle growth specifically.
University of Rio de Janeiro researchers examined the influence of exercise order on strength and muscle thickness in untrained men after 12 weeks of resistance training. The exercises were bench press, lat pulldown, machine triceps extension, and biceps curl with a straight bar. One group trained large muscle groups first (bench press, lat pulldown), and the other groups trained biceps and triceps first (biceps curl, triceps extension).
For strength, exercises performed at the end of a workout were negatively affected by exercise order. For muscle size, the smaller muscle groups grew more when performed at the beginning of a workout.
For size or strength, large muscle groups or small muscle groups, exercise order should begin with muscle groups and exercises that are particularly important for the training goals of a program.
Whatever muscle group you’re trying to bring up, train it first in your workout. But to avoid injury, be sure to adequately warm up any muscle group placed at the beginning of a workout.