On Monday, April 20, the 130th Boston Marathon will roll through Hopkinton to Copley Square. Over 30,000 runners will then be at the starting line. What they do today, four days before, will determine their finish time more than the training blocks of the last three months. The science behind it is called Tapering – and it’s half physiology and half self-control.

The Science: What Really Happens in Your Body During Tapering

Tapering is not laziness with an excuse. It’s a physiological phase where your body reduces fatigue while preserving the adaptations from intense training. Inigo Mujika, a sports physiologist at the University of the Basque Country and one of the world’s leading tapering researchers, compiled over 180 studies in his widely cited 2003 meta-analysis. The greatest gains come from a volume reduction of 41 to 60 percent while maintaining training frequency and intensity.

For example, if you’ve been running 80 kilometers per week in marathon training, taper down to 40 to 50 kilometers. If you’ve been doing ten sessions in two weeks, reduce to eight to nine. What you should not do: skip the tempo sessions. Short intervals at marathon pace are crucial for maintaining VO2max and lactate threshold. Skipping these runs can leave you feeling tired and with fresh legs on race day – a feeling many Boston Marathon rookies know well.

Hormonally, remarkable changes occur during this phase. The ratio of anabolic to catabolic hormones shifts, with testosterone-to-cortisol ratios increasing. Simultaneously, muscle micro-injuries regenerate, immune system markers normalize, and heart rate variability improves. Studies on rowers (Neary 2003) show a performance increase of up to six percent in a three-week tapering phase, with significantly less training.

The most common mistake: The feeling during the taper week is often miserable. Your legs feel heavy, your head is foggy, and dreams become vivid. This is not a sign of poor form but of your body restructuring. Regeneration processes in the body are in full swing, which may not always feel great.

The Last 96 Hours: What to Consume When

The last training that really brings something is on Thursday. After Friday, it’s no longer about fitness, but about energy storage and body awareness. Here are the four days leading up to Boston, broken down according to what professionals like Eliud Kipchoge or Germany’s marathon trainer consistently recommend.

Boston has a peculiarity: the shuttle bus to Hopkinton leaves the Boston Common between 6:00 and 8:00 AM on race morning. The runners then stand for up to three hours in the Athlete’s Village in cool temperatures. Anyone who eats or drinks incorrectly during these three hours has already lost the race before it starts. Routines are part of the taper, not just the race day.

Two key differences from other major marathons are critical: First, Boston starts downhill, with the first six kilometers descending about 140 meters. Anyone who doesn’t have fresh legs from the taper and can’t maintain the pace from kilometer four on these first six kilometers ruins their thighs and pays for it on Heartbreak Hill at kilometer 32. Second, the race temperature is historically volatile, ranging from 7 degrees with rain (2018) to 31 degrees with sunshine (2012). The taper nutrition is adjusted accordingly – more electrolytes and fewer heavy carbohydrates on Sunday if it’s hot. Anyone who tapers without a weather plan is improvising on the shuttle bus.

The third point concerns the journey itself. Many European runners fly in on Wednesday or Thursday, losing two nights of deep sleep due to time zone changes and still start with a classic textbook taper. This doesn’t work. Anyone coming from Germany should either arrive earlier (six to seven days before) and incorporate the jet lag into the taper, or consciously accept that the sleep deficit is part of the equation. Melatonin dosage and light exposure then become part of the plan – not an afterthought.

Active vs. passive recovery: The debate on Sunday before the race

The most common question in Boston WhatsApp groups these days: Should I run again on Sunday or should I completely rest? The data is not conclusive, but here are the arguments from both sides, as discussed with two trainers who support athletes in Boston.

The consensus that emerged from both discussions: 15 to 20 minutes of very light jogging in the morning, with a maximum of three short accelerations, followed by strict rest. For those who suffer from race nerves and start to sweat just thinking about pace tables, a short run is almost more important than the physiological component. The body then remembers that running is normal – not an event. This is particularly true for Boston, as the days leading up to the race are already stressful with organizational tasks (boarding pass, bib check, shuttle). Other marathon routines from Berlin or Munich cannot be directly transferred.

What the taper discussion often forgets: the mental component is just as important as the physiological one. A taper that freshens the legs but puts the mind into panic is only half effective. The last 96 hours are also 96 hours of self-reflection – about why one has been training long runs, what the goal is, and how it will feel. Those who do not plan this often fall apart at kilometer 32, even though the body is still capable.

Cool-down

Click on a question to reveal the answer.

How many kilometers should I run this week?

About 40 to 50 percent of your peak weekly volume. If you’ve been running 80 kilometers a week, that’s about 35 kilometers in race week, including the actual marathon. Important: distribute over two to three sessions, not focus on one long run. Long runs right before the race bring nothing but fatigue.

My body feels off during taper. Is this normal?

Absolutely. Heavy legs, a foggy head, sudden cold symptoms without actual illness, strange dreams – all typical taper effects. Your body is building up, which often feels like stagnation. Most studies show: the actual race performance is better than the feeling the week before.

Carb-Loading: really 10 grams of carbs per kilo for three days?

Modern studies (Burke 2018) show: one to two days with eight to ten grams per kilo are sufficient for maximum glycogen storage. Three days don’t add anything but more gastrointestinal issues. More important than the grams is the implementation: low in fiber, easy to digest, spread over the day. Not a big pasta dinner Saturday night, but consistently over two days.

Strength training in taper week – yes or no?

Heavy strength training: no. It causes micro-injuries that you’ll carry into the marathon. Activation and mobilization: yes, but brief. One session on Monday or Tuesday with low intensity (50 percent of usual weights, few repetitions) is okay. Wednesday: only mobilization, fascia rolling, light stretching.

What if I’m nervous and can’t sleep?

The night on Saturday is more important than the night on Sunday. The body compensates for a poor night’s sleep right before the race without performance loss. Important: don’t try new sleep aids, no alcohol, room dark and cool, phone out of the bedroom. If thoughts are circling: get up, read for ten minutes, back to bed. This is better than lying awake for hours.

Source Title Image: Pexels / Roman Biernacki