42.54 km. 2:37:34. What the data showed after.
By Robin Decottignies
The finish line is a threshold. Not the end of the effort, but the beginning of something else entirely: the physiological bill arriving.
I ran the Antwerp Marathon on 18 October 2026 in 2 hours, 37 minutes and 34 seconds. This post is not about the race. It is about what happened to my body in the 72 hours after, and what the data on my wrist confirmed in real time.
If you coach endurance athletes, train for long-distance events, or simply want to understand the relationship between effort and recovery, this is worth reading.
What a marathon does to the body
A full marathon is not a hard workout. It is one of the highest physiological stress events the human body can experience outside of illness or trauma.
In 2:37, my body burned an estimated 2,800 kcal. Core temperature climbed toward 39.5 degrees Celsius. Muscle fibres in the legs experienced microtears across nearly every motor unit. Cortisol and adrenaline flooded the system to sustain output. Glycogen was depleted from muscle and liver. And the immune system, overwhelmed by the demand for repair, entered a suppressed state for 24 to 72 hours post-finish.
This suppression window is sometimes called the "open window" in sports immunology. Your defences go down precisely when the body needs to redirect every available resource toward recovery. It is not weakness. It is prioritisation at the cellular level.
Understanding this changes how you approach the days after.
The preparation: what made the result possible
A 2:37 marathon does not happen on race day. It is the output of months of accumulated, deliberate work. Here is what the training block looked like.
August: the base.
August was not marathon-specific. It was broad. 44 hours of total training across 43 sessions and 29 active days. 353.8 km of running. 317.5 km of cycling. 6 strength sessions. Nearly daily movement.
The combination of running and cycling was intentional. Cycling adds aerobic stimulus without the impact load of running. It builds the engine while protecting the machine. Over a full training block, that distinction matters: you can accumulate more total volume when not every hour costs the joints the same price.
The 80/20 model: most of it was easy.
The majority of training volume sat in Zone 1. Easy pace. Conversational effort. That is not accidental and it is not a shortcut. It is the polarized training model, supported by decades of research on elite endurance athletes.
The principle is simple: most amateur runners train too hard on their easy days and not hard enough on their hard days. They end up stuck in a grey zone that is too intense to recover from fully and not intense enough to drive meaningful adaptation. Polarized training pulls the distribution to the extremes. Zone 1 for base, genuine intensity for the hard sessions, nothing in between.
Race-specific work in the final weeks.
In the final four weeks before Antwerp, total running volume was 297.2 km, averaging 74.3 km per week. Speed zones 2 and 3 dominated: not sprinting, not jogging, but running at and around marathon pace long enough that the body stopped treating it as a threat. The nervous system adapted to the rhythm before the race asked for it.
Three prep races. Three answers.
Three races in the preparation block served as checkpoints, not just fitness tests.
PK Dadizele (10 km). Windy conditions, a strategic race, won at 3:29 per kilometre pace. The legs were there.
Ten Miles Geluwe. Also windy, also strategic. Won it at the same pace. The pattern was becoming clear.
Halve Marathon Kuurne (21.1 km). Same pace again, different circumstances. Full dress rehearsal: gels, gear, pacing strategy, all confirmed.
Three races, the same pace, three wins. And a feeling that kept building race by race: well rested, fresher each time, more in control.
The goal of a prep race is not to perform. It is to remove uncertainty. You do not discover your race on race day. You confirm it.
Form on race day: CTL, ATL, TSB.
The Performance Management Chart told the final story before the start line. Fitness (CTL) had been built steadily from August through October. Fatigue (ATL) spiked during the hard training blocks and dropped during the taper. Form (TSB) was positive on race day.
The goal of a taper is not rest for its own sake. It is to let fatigue clear while keeping fitness in place. When TSB is positive on race day, you have managed the balance correctly. The body arrives fit and fresh rather than fit and depleted.
Nutrition: the quiet variable.
I eat very healthily year-round with a strong focus on carbohydrates as the primary fuel for training. In the final days before the race I adjusted by lowering fibre and fat intake to reduce gastrointestinal load on race morning, while keeping carbohydrate stores topped up.
On a supplementation level: vitamin D, omega-3 and magnesium are daily staples. Creatine was part of the preparation block. If I feel illness coming on, I add zinc. Nothing exotic. All evidence-backed.
The running mechanics: what the numbers said during the race
Before looking at recovery, it is worth looking at what the race itself produced in terms of biomechanical data.
Cadence: 177 steps per minute. The benchmark coaches and researchers use is 180 spm. At 177, I was right at the efficient threshold, maintaining low impact forces and avoiding the overstriding that slows runners down and loads the joints unnecessarily.
Stride length: 1.51 metres. This is not a number to chase in isolation. The calculation: 177 x 1.51 equals roughly 267 metres per minute, which translates to 3:44 per kilometre pace. The math aligns perfectly with the finish time.
Vertical oscillation: 9.9 cm. This is the one metric with room to improve. The most efficient runners operate below 8 cm. Oscillation measures how much energy goes upward rather than forward. At 9.9 cm, a small percentage of each stride is wasted on vertical movement. In training, the cue is simple: "push back, not up."
Vertical ratio: 6.5%. This relates oscillation to stride length and sits in the efficient range of 6 to 8%. The closer to the lower bound, the more energy is translated into forward motion.
Ground contact time: 215 milliseconds. Below 220 ms is the target for competitive runners. Shorter ground contact means more elastic energy return from the Achilles and fascia, and less braking force on each landing.
Total steps: approximately 27,789. Across 42.54 kilometres and 157 minutes of racing.
Four of five metrics were in range. Vertical oscillation is the one lever.
The stamina chart: the cleanest possible data story
Garmin's stamina metric tracks how much aerobic and anaerobic capacity remains in real time, based on heart rate, pace and VO2max estimates. It starts at 100% at the gun.
At the finish line: 4%.
That number sounds alarming until you see the graph. The decline from 100% to 4% was a perfectly straight line over 2 hours and 37 minutes. No early spike. No sudden collapse. No second-half implosion.
A straight line in stamina is the data signature of controlled pacing. It means the effort was distributed evenly across the distance, that the early kilometres were not run faster than the body could sustain, and that the body was never pushed into a reserve-depleting crisis.
4% at the finish is the ideal number. It means nothing was wasted and nothing was left.
The Stamina Potential line, shown in grey on the chart, ran almost parallel to the actual stamina line for the entire race. This means I was operating at or near my maximum capacity for each moment of the effort, without crossing into a zone that would have caused an accelerated collapse.
Pacing a marathon correctly is harder than it sounds. The physiological data confirmed that the approach worked.
Race day: the biological bill
My Body Battery at race start: 88 out of 100. Garmin classifies this as High. The body was rested, recovered and primed.
At the finish: 5 out of 100.
That is an 83-point drop in a single morning. The Body Battery timeline on race day showed a classic pattern: a steady decline through the race, followed by persistently high stress levels in the hours after the finish.
Those post-race orange stress bars are not psychological stress. They are physiological. Elevated heart rate at rest, inflammatory markers, cortisol still circulating, the immune and repair systems running at full capacity. Garmin's HRV-based algorithm reads all of it as stress, because it is.
Stress level at the end of race day: 39. The watch labelled it a demanding day.
The only recharging mechanism the body has in this state is sleep. The graph confirmed it: the Body Battery flatlined from finish to bedtime. No recovery was possible while the repair processes were active.
The recovery: three days in data
I did not train in the three days after the race. I walked, slept and ate. The data showed why this was the right decision, not a passive choice.
Day 1 after the race. Body Battery recovered to 76. Stress dropped to 16. The body had done a significant amount of repair work overnight. The first sleep post-marathon is the most productive recovery window available.
Day 2. Body Battery 90. The watch simply said: Easy. HRV was trending back toward baseline.
Day 3. Body Battery 95 out of 100. Resting heart rate 47 bpm. HRV between 86 and 95 milliseconds, back within my personal normal range.
Three days for the wearable metrics to return to baseline.
The metrics, however, are surface-level indicators. Full physiological recovery from a marathon takes three to four weeks. Muscle fibre repair, glycogen resynthesis, hormonal normalisation and immune recovery all operate on longer timelines than a Body Battery score can show. Returning to high-intensity training before this window closes is one of the most common mistakes endurance athletes make in the weeks after a major race.
What this means in practice
The data from this race and its aftermath confirms a few principles I work with as a coach:
The race is the stimulus. Recovery is where adaptation happens. The fitness gained from 18 weeks of preparation gets consolidated in the recovery period, not during the race itself. Cutting that period short interrupts the process.
Sleep is the primary recovery tool. Not ice baths, not compression, not supplements. Sleep is when cortisol clears, when growth hormone peaks, and when the immune system does its most productive repair work. Every other intervention is secondary.
The data does not lie, but it needs context. A Body Battery of 5 on race day is not a problem. It is the expected output of a well-executed effort. A Body Battery of 5 on a Tuesday during a training block is a different signal entirely. The same number carries a different meaning depending on what produced it.
Vertical oscillation is the next mechanical target. The other four running metrics were in range for a 2:37 performance. Bringing oscillation from 9.9 cm to 8 to 8.5 cm over the next training cycle would improve efficiency at the same effort level, translating to either a faster time or a lower cost for the same pace.
The numbers, together
| Metric | Value | Context |
|---|---|---|
| PREPARATION | ||
| August training volume | 44 hours | 43 sessions, 29 active days |
| Running (August) | 353.8 km | |
| Cycling (August) | 317.5 km | Aerobic load, no impact cost |
| Strength sessions | 6 | Running economy focus |
| Final 4-week running | 297.2 km | 74.3 km/week avg |
| Zone 1 share | ~80% | Polarized model |
| Prep races | 3 | Dadizele, Geluwe, Kuurne |
| Form (TSB) on race day | Positive | Fit and fresh |
| RACE | ||
| Finish time | 2:37:34 | |
| Estimated kcal burned | 2,800 | |
| Stamina at finish | 4% | Linear decline from 100% |
| Body Battery race day | 88 to 5 | 83-point drop |
| Cadence | 177 spm | Benchmark: 180 |
| Stride length | 1.51 m | Matches pace perfectly |
| Vertical oscillation | 9.9 cm | Target: below 8 cm |
| Vertical ratio | 6.5% | Efficient range: 6 to 8% |
| Ground contact time | 215 ms | Target: below 220 ms |
| Post-race stress | Level 39 | Physiological, not psychological |
| Day 3 Body Battery | 95/100 | Back to baseline |
| Day 3 resting HR | 47 bpm | Back to baseline |
| Day 3 HRV | 86 to 95 ms | Back within personal range |
| Total steps | 27,789 |
A necessary disclaimer
What is described in this post works for me. It will not work for everyone, and I want to be clear about that.
I thrive on frequent racing and near-daily running in the final weeks before a marathon. Most runners need more recovery time, fewer races and more conservative volume. My body has adapted to this pattern over years of consistent training. Trying to replicate this approach without that base is a reliable path to injury or burnout.
The same applies to nutrition and supplementation. What I eat and take is built around my own biology, bloodwork, training load and daily life. There is no universal protocol.
The principle transfers. The exact protocol does not. Use this as a reference point, not a template.
Final thought
The finish line at Antwerp was a moment. The data tells a longer story: 18 weeks of preparation, 157 minutes of controlled execution, and three days of disciplined recovery before the body was ready to begin again.
Sport as foundation. Energy as system.
If you work with athletes or are building your own endurance base and want to understand what the data actually means for training and recovery, that is exactly what I do at robindecottignies.com.
Robin Decottignies is a performance coach working with endurance athletes and leaders. More at robindecottignies.com.