It depends on where you are at in your training. There are three stages to training:
learning,
balancing, and
strengthening.
What is the purpose of a split routine? It's for when you can push your muscles so hard that it takes them 3-6 days to recover. If you work out on Monday and are still sore on Friday, perhaps you need a split routine; if you're better by Wednesday then you don't.
Learning (1-3 months)
In the first 1-3 months you're not really increasing muscle, you're just learning the movements. For example, I have more muscles than Ricky Ponting, but he can bowl faster than me, simply because he knows how to best exert his strength for the bowling effect. Likewise with lifting a bar with plates on it.
In those first 1-3 months you simply can't work out with the intensity that'll make you still sore days afterwards. You're still learning how to exert your strength for best lifting effect.
Balancing (3-6 months)
After then, that's when real muscle growth starts. But there are a zillion different muscles in our body, and they work together to do lifts. Problem is, before we lifted we had all these muscle imbalances. For example, office workers usually have weak backs and legs, because they don't use them. But when we bench press, even though we're not working the back directly, it does support us.
So that the first muscle growth is just correcting the imbalances we had. These are best corrected by big compound movements like squatting. It's very common, for example, for people's front thigh (quadriceps) to be much stronger than their back thigh (hamstrings).
On a split routine I have to do lots of isolation exercises, like leg extensions and leg curls on machines. I'll push my quads to their limit and they'll get stronger, and push my hams to their limit and they'll get strong - t
he imbalance will still be there.
But if I squat, then my strong quads will get to relax, and my weak hamstrings will be worked very hard until they become balanced with the quads. Then the two can both be worked hard, and grow stronger
together.
This period of getting generally stronger and correcting imbalances will last another 3-6 months at least. It can be made longer - even years - if the trainee decides to be Mr Chest & Biceps, or to never train legs. So together with the learning phase, we have at least 4-9 months of using big compound movements.
Strengthening (6-12 months)
Is it time to do split routines yet? For some, yes, for most, no. If the person started off naturally strong (eg they have years of sport or martial arts behind them) then at this stage they'll be able to work with great intensity, and maybe they're still sore four days later, so splits will be good for them.
However, most people have years of being sedentary behind them, so they still need time to get stronger and build up their workout intensity. Thus there's another 6-12 months in which they can get good growth from big compound exercises. No splits.
There might be some isolation exercises here, but just to bring up some lagging bodyparts - not true imbalances, just something you want to focus on, perhaps because of a sport you're doing. But still not split routines.
Altogether, from start of training to being ready to do splits, we're looking at 10-23 months.
These are rough times of course, some people adapt more quickly, others more slowly. Some are coming back to training from a long break, they'll be quicker than those entirely new to it. Others as I mentioned slow themselves down by "I don't want to do legs" or "I don't like a scheduled workout, I just do whatever I feel like" or someone has them spend a lot of time on Swiss balls doing tricep kickbacks, and that slows them down.
But most people will need 1-2 years of good solid training on the big compound lifts in full-body workouts before splits will make any sense. Are you there yet? Can you do lifts like benching and rowing your bodyweight, squatting x1.75bw, and so on? If not, then you probably aren't ready for split routines.
If so, then full-body with compound lifts, 2-3 times a week.
If you
are ready for split routines, congratulations! You're far above me and I can't advise you, ask someone more experienced
