For more than a year now, I've been lifting mostly on a full body routine, 3 times per week. My full body routine basically comprises of compound exercises that focuses on major or large muscle groups such as chest, shoulders, back and legs (hams and quads). I'd usually attack the smaller muscles such as triceps, biceps and calves at the end of the workout. Abs and cardio would be optional after all that is done. I've gotten some good gainsin terms of lean mass and strength, and lost some fat with this routine. These couple of months, I noticed that my gains were beginning to stagnate, workouts are more fatiguing and I've become more overtrained easily on certain weeks. I suspect that increasing the load (heavier lifts) during each exercise is beginning to take a toll on my body. The full body routine is great when you're just starting out and building initial lean muscle and strength. But as you progress and need to increase the load, intensity and volume, especially for each body part to further add strength and size, a full body routine can be very fatiguing and would stretch your workout session too long.
For this reason, beginning of last week, I've switched to a split routine that allows me to increase the load, intensity and volume, and focus on developing each body part further. The split routine that I've chosen is an isolated body part routine, 3-4 times per week focusing on different body parts.
My 4 day split routine:
Day 1: Chest & Forearms (optional).
Day 2: Shoulders & Triceps.
Day 3: Back & Biceps.
Day 4: Legs.
If 4 days is too tiring on certain weeks, I'd scale back to a 3 day split routine:
Day 1: Chest & Back.
Day 2: Shoulders & Triceps.
Day 3: Legs & Biceps.
(Abs and cardio would be optional at the end of each session, although I usually do my abs. On days when I don't lift, I'd either rest or do cardio).
I would include a major muscle group on each day and usually work those first with compound exercises, before working on smaller muscle groups. Compound lifts on large muscles require a lot more energy, so it's always best to put them at the beginning of the workout. Also, I would change up my split routine sometimes, either on muscle group combination or move them around to different days, depending on my schedule. However, I need to monitor my workout to make sure I don't over-train a muscle group and possibly injure myself. I have a tendency to challenge myself, which is always good but sometimes I could overdo it.
Isolated body part split routines are very commonly used by fitness competitors or bodybuilders and is usually meant for more advanced trainees. Beginners can use it as well but it's usually preferred for beginners to build a foundation of strength and some lean muscle with a full body routine first. Jumping into a split routine might cause some over-training on certain body parts and injury, due to lack of initial strength and conditioning of the muscle to support.