Week 10: The Big Deposit

This is it. Your final week of peak mileage before the taper begins. Think of this as your last major deposit into the fitness bank before you cash out on race day. The work you put in now will still be paying dividends at mile 23 when most runners are bargaining with their legs to keep moving.

Your long run this week should be your longest of the entire cycle, somewhere north of 20 miles but not more than 22. This is where your body learns, at a deep physiological level, what it feels like to keep going when glycogen is running low. Studies show that long runs of 20 miles or more increase mitochondrial density and improve fat utilization, which means your body becomes more efficient at using fuel during the marathon. That efficiency is what helps you push through the later miles instead of hitting the wall.

The Power of Mixed Intervals

This week is the perfect time to tap into mixed intervals. A short interval workout, such as 12 x 400 meters, sharpens your top‑end speed and activates your fast‑twitch muscle fibers. A long interval workout, like 3 x 2 miles or 2 x 5K, trains your aerobic system to sustain a hard effort for extended periods. According to sports physiology research, combining short and long intervals in the same workout improves both VO₂ max (your maximum oxygen uptake) and lactate threshold (your ability to run faster without fatiguing). In practical terms, you are training both your “final kick” and your “marathon engine” in one week.

The Midweek Progression Run

Your midweek tempo run now becomes a progression run. Start at a relaxed pace, then gradually accelerate every couple of miles until you are gliding at a comfortably hard effort. This simulates the late‑race feeling of needing to pick up the pace when your legs are already fatigued. Research has shown that progression runs improve running economy and mental resilience because you are forced to run efficiently while tired. Plus, they are surprisingly fun. There is a certain confidence boost that comes from finishing faster than you started, especially in peak training weeks.

Why This Matters

You are a high‑performing professional. You already understand that preparation is everything. This week is about doing the work that future‑you will thank present‑you for. It is about putting in the mileage, the intervals, and the tempos now so that when you line up on race day you know you have done everything possible to prepare.

Once you hit the taper, you will start to cut back and recover. But right now, lean in. Embrace the fatigue. Keep stacking the miles. Because the fitness you are building in Week 10 is the final layer of armor you will carry into your marathon.