Final 5km Acceleration Strategy in Running: Energy Reserve Management for a Positive Split in the Latter Half

Introduction

There’s a saying among marathon runners: “The first half is a warm-up; the second half is the race.” Within that second half, the final 5 kilometers (37–42km) are a microcosm of the entire race—your performance on this stretch often determines whether you hit your goal, and whether today’s run feels like a triumph or an ordeal.

A negative end split means running the final 5km faster than your average pace for the preceding distance. This isn’t just a technical matter; it’s a matter of energy reserve management that begins from the very first kilometer.

Why the Final 5km Is So Hard

After the 37km mark, runners face multiple physiological challenges:

To accelerate in the final 5km, you need to build up an “energy reserve” over the preceding 37km, minimizing the impact of these factors.

Three Levels of Energy Reserve Management

1. Pace Reserve: Don’t Overdraw Your Aerobic System

Runners who can accelerate in the final 5km never go out too fast in the early stages. The rules are simple:

• Run the first half 5–10 seconds/km slower than your target pace
• After entering the 25km mark, you should feel “a bit tired but still in control”
• At 30km, your perceived exertion should not exceed RPE 7 (on a 10-point scale)

Many runners feel great at 20–25km and speed up—this is the most common mistake. Feeling “good” at 25km is normal, but that “good” feeling will quickly evaporate after 30km.

2. Glycogen Reserve: Precise Execution of Your Fueling Strategy

• Consume one energy gel (about 25g of carbs) every 45 minutes throughout the race
• Take it with water (not sports drink) to ensure absorption
• Take your final energy gel at 30–35km; it takes 10–15 minutes to take effect
• If you use caffeinated gels, consider taking one at 30–32km to provide a late-race kick

3. Mental Reserve: Setting Segmented Mental Goals

• Divide the marathon into four 10km segments plus a final 2.1km
• The goal for the first three 10km segments is “save fuel”; the goal for the fourth 10km is “hold steady”
• The final 2.1km is when you “give everything”
• At 37km, tell yourself: “5km to go—each kilometer is the final 1/42nd of the marathon’s effort”

Executing the Final 5km

Entering the final 5km, how do you judge whether you have the conditions to accelerate:

• Is your pace still close to target (not fallen off by more than 15 seconds)?
• Is your heart rate within an acceptable range (not spiked above 98% of max HR)?
• Do your legs feel “sore but able to run” (rather than completely numb)?

If all three conditions hold, you can adopt a progressive acceleration strategy:

• 37–39km: Speed up 5 seconds/km from your previous pace
• 39–41km: Speed up another 5–8 seconds/km
• Final 1km: Go all out (let your body tell you where your limit is)

How Training Builds Your Ability to Accelerate in the Final 5km

Whether you can accelerate late in the race depends on the following training habits:

• Progressive long runs: In each 25–28km long run, deliberately accelerate in the final 5km to your target pace, teaching your body to “switch gears while fatigued”
• Back-to-back long runs: After a Saturday long run, do a 10–12km easy run on Sunday to build your ability to run under accumulated fatigue
• Practice fueling in training: Fully rehearse your fueling schedule during long runs to ensure your stomach won’t cause problems on race day

Practical Tips

• Taiwan race specifics: The Taipei Marathon has some uphill sections in the final kilometers, while the Kaohsiung Marathon’s final stretch is relatively flat—design your final 5km acceleration strategy around the course
• Visual target method: In the final 5km, pick “the runner ahead” as your chase target, locking onto a new one every 500m—this isn’t just psychological stimulation, it also helps maintain your cadence
• Use the aid stations: The last aid station is usually around 40km; grab a cup of water and splash it on your face to cool down—this small gesture can make you feel more alert for the final 2km

Conclusion

Accelerating in the final 5km isn’t a spur-of-the-moment decision on race day—it’s a carefully laid plan that begins at the first kilometer. Conservative pacing, precise fueling, segmented mental management—every detail is fuel accumulated for that final push before the finish line. When you still feel “there’s something left” after the 37km mark, that moment of joy is worth far more than the agony of having sprinted too early and fallen apart.

Related Reading

• The Finish-Line Sprint: Energy Conservation and Acceleration Strategy for the Final Kilometer
• Negative Splits: The Golden Marathon Strategy
• Marathon Race Tactics: Pace Management from the Start to the Final 10K
• Negative Splitting in Marathons: Why Running the Second Half Faster Than the First Is the Right Strategy