Why does every beginner programme say three days a week when I want to train six?

The second reason is that a beginner cannot yet generate enough fatigue to justify a split.

Body-part splits exist so that an advanced lifter can do a large volume of work for one muscle group and then leave it alone for a week to recover. That is a solution to a problem you do not have — your sets are light relative to what your body will eventually handle, and you recover from them quickly.

Six days of two body parts each also means a lot of your training time goes on isolation work for small muscles, which is the least productive thing a beginner can do. Three full-body sessions of compound movements cover everything with a fraction of the exercises.

And there is a practical point: three sessions is a schedule you can protect for years. Six is a schedule that survives until the first busy week, and the most common way beginners fail is not overtraining, it is stopping.

If the real motivation is that you want to be in the gym more often — which is a perfectly good motivation — there are ways to use the extra days without wrecking the programme.

• Add conditioning on the off days. Walking, cycling, rowing at an easy pace. Helpful for recovery and for body composition, and it does not compete with the lifting.
• Practise technique at light loads. Twenty minutes of squatting an empty bar is not a workout and is enormously useful in the first months.
• Work on mobility where you are restricted, which for most beginners is ankles, hips and shoulders.

That gives you six days of activity, three days of training, and a programme that still works. The mistake is turning the extra enthusiasm into extra hard sets.

There is a real reason, and it is not about your commitment. It is about how often each muscle gets trained, which is the opposite of what the day count suggests.

A six-day split hitting two body parts per day means each muscle is trained roughly once a week. A three-day full-body programme means each muscle is trained three times a week.

So the programme you were told to do trains everything three times as often as the one you proposed. It is more frequent, not less. That is the whole answer and it surprises nearly everyone.

Frequency matters for beginners because the response to a session lasts a day or two, and because most of the early progress is learning the movements. Squatting three times a week produces far better technique after a month than squatting once a week does, and technique is what lets you keep adding weight later.

One thing worth being honest about: three days a week is not a law, and plenty of people train four or five days as beginners and do fine.

What is close to a law is that each muscle group benefits from being trained more than once a week, and that early progress comes from repeating a small number of movements often enough to get good at them. Any schedule satisfying those two is reasonable.

So take the advice as being about structure rather than about the number, and if you want a fourth day, add one — as an upper/lower split rather than as a body-part split.