Yes, you can finish strong with guarantees by training three days a week, as long as you follow a well-balanced training plan. The first thing a marathoner should do is choose a training plan that spans several months; for beginners, my advice is to plan four months. This training plan I propose lasts 16 weeks, and if you adhere to it you will reach the marathon finish line without excessive suffering and with good sensations.
Before going into the four-month plan in detail, I’d like to share a few points I consider very important. At the end of each workout you should perform three abdominal exercises (15 to 25 repetitions each), two lower back exercises (10 repetitions), and six to eight stretching exercises (focusing on the area to stretch, pushing a bit and holding for at least about 12 seconds per exercise).
The paces for the easy runs should be slow to moderate. I provide some reference ranges within the plans that you can use as a guide. A common mistake among beginner runners is running the easy runs too fast.
A common question is whether you can change the order of the days to perform the workouts. You can, but avoid doing two workouts back-to-back. This is a key point to prevent the risk of injury.
Weights (or resistance bands) are fundamental in marathon preparation. I’m aware that the runner simply wants to go out running, but the gym is essential to avoid the “wall.” A runner tires out sooner muscularly than metabolically. It is very important to work very specifically the quadriceps (both eccentrically and concentrically), the abductors, the adductors, the calves, the soleus, the psoas, and the biceps femoris. You will perform much better and injure yourself much less. In the week of competition you should not do weights, nor in the three days prior to the marathon.
It is important to do ankle exercises once a week. They not only strengthen the ankles, but also improve the efficiency and effectiveness of your stride and greatly reduce the risk of injury (plantar fasciitis, tendinitis and/or periostitis).
16-week plan to finish the Marathon (in over 4 hours), suitable for beginners