I have never run a marathon, but I have a good friend and members of his family who have. I have noticed two things in particular that teach me some things about spiritual formation.
First, as they run, they take advantage of water stations placed along the race course. Maps tell runners where these stations are located, so they can plan their race accordingly. Periodic hydration is essential; without it they cannot finish the course.
In a similar way, we need hydration stations as we run the race set before us. We need to map their locations into the course we set for ourselves. In spiritual formation we call this hydration a Daily Office, Liturgy of the Hours, Quiet Time, or some other name to mark those times and places where we find the Water of Life to continue running. We cannot finish the race without them.
But second, marathon runners know they must have something more than periodic watering; they must have sustained nutrition. In the broad sense, nutrition includes food, exercise, sleep, regular running, etc. These are the larger, infrastructural elements which keep them fit for a race whenever it occurs. Without these things, they could not hope to run a marathon.
In terms of spiritual formation, this represents the larger, foundational dimensions of the spiritual life. We call this a life of personal/social holiness, using the inward/outward disciplines (instituted and prudential means of grace) to provide the nutrients we need. And because the soul rides on Brother Donkey (as St. Francis said), we need the physical nutrition that proper food, exercise, and sleep provide.
Practically speaking, the hydration aspect means making use of whatever devotional materials you choose for daily formation. The nutrition aspect means having some ongoing practices that do not fluctuate or skip around from day to day.
With the combination of hydration and nutrition, we can be spiritually fit for the race God sets before us.