I blasted my pecs (chest muscles) on Monday, and my chest muscles are still very sore today (Friday).
You see, in recent years, I've only found time to work out once or twice a week, and I pretty much have time only to do ab-core, legs, and cardio in combination with physical-therapy type exercises. Since I only have time for one or two workouts each week, I can only do these. These are priority because of my lumbar (lower back) problems (which I have under control and I am pain free by doing these exercises) and also because of my foot injury two years ago (where the joint that was dislocated is still giving me problems and pain). That's why the mainly lower body exercises are priority, and working out only one or two days a week, lower body is all I usually have time for. It's not ideal, but it's good enough to keep me slim, healthy, pain free (or close to it), and still looking young at 40.
I rarely am able to squeeze in any upper body workout, but I did this past Monday. I worked both fast-twitch and slow-twitch muscles in my upper body includin the pecs. I also did martial arts type movements with upper body (from back in my martial arts days) which also worked the fast-twitch muscles of the pecs in addition to other muscles and other areas (such as upper body speed, agility and flexibility, and neuromuscular control).
Long story short, I really blasted my pecs on Monday and they're still very sore today (Friday). I really need to do more upper body regularly if only I have enough time. I shall figure out a way.
For my lessons on how to be slim, fit, and looking young, go to - http://spirfit.org/Academy/#fitness
Note: I tried to simplify the jargon already to make this not confusing. If it is still confusing, I am sorry but it's because I have a background in exercise science, nutrition, and health education (nutritions science degree from University of California with focus in Exercise Science, have working experience in science research, was certified for ~eight years by National Academy of Sports Medicine, teach occasional health and fitness workshops, and had trained clients and college athletes in the past. Currently, I am working in various areas of education (unconventionally and innovatively) including fitness and health education in addition to other areas of education.