Thames Path 100 training: a hundred flat miles where there is nowhere to hide

The Thames Path 100 runs from Richmond to Oxford on the river's towpath, a hundred miles with 1,900 feet of climbing, which for a hundred is none. It starts at nine on a Saturday morning in early May and gives you 30 hours, with a cut-off at every one of the twelve aid stations. Pacers join at Henley, mile 51, about where the dark begins. Two thirds to three quarters finish. It is the race people enter because it is flat, and the race that teaches them what flat costs.

For a runner over 40 it is the purest durability test in the library. There is no hill to walk, no descent to blame. The stride that fades at hour six fades in full view.

Flat is not easy

On a mountain course the terrain changes your gait every few minutes and the muscles share the load. On the towpath every step is the same step, for 25 hours, and the same tissues take every one. Calves, Achilles and the small muscles of the foot are the first to go, and the quarter of the course on tarmac makes it worse. So the preparation is long continuous running: back-to-back weekends, four and five hour runs on flat firm ground, calf and foot strength through the winter, and the long-run progression held inside the 30-day guardrail from the progression note, because a flat course tempts people into big jumps.

Fifteen before Henley, 117 after

Centurion's results list finishers only, so there is no full record of where people stop. The organiser's 2023 report is the exception. In a wet, muddy year only 15 runners stopped before Henley at mile 51. Between miles 51 and 89 another 117 did, and 207 finished, 61% of a record field. Drier years finish better: 216 of 300 in 2025, 200 of 300 in 2026. Other years' reports name only a few individual drops, at Cookham, Reading, Purley and Benson.

The pattern fits the course. The first half rarely stops anyone; the second half asks whether the stride still works. One 2023 finisher left Clifton Hampden at mile 85 and wrote: "When we left, I couldn’t run. Literally couldn’t, no choice in the matter." They walked the last 13 miles.

The night on the river

The second half falls mostly in the dark: the cold by the water, the flat monotony and a gut that has stopped. The night note is the block, and the fuelling plan from the carbs note is written for a full night of eating on the move, because on a flat course the calories are the pace. May can bring a warm afternoon and a 6°C night in the same race, so the layers are in the drop bag at Henley and the rehearsal includes putting them on.

Mud, water, road crossings

In a wet spring the towpath is bog and the organisers say so; in 2025 diversions for bridge works made the course 103 miles. Shoe choice is decided on the week's forecast, and the plan includes runs in mud so the first time is not race day. Road crossings are unmarshalled; navigation is yours, with acorn waymarks, pink ribbons and a GPX. None of it is hard. All of it is harder at 3 am.

Where durability shows up

The Thames Path gives the cleanest data of any hundred: flat, runnable, comparable from start to finish. What I read through a build is the second half of long runs against the first at the same heart rate, week on week, and the day-after cost of the long flat runs on the calves and feet. The pattern I want by April is a runner whose fourth hour looks like their first. Then I decide what the next block holds.

Twenty weeks to make the stride last

Entries open in the autumn. For a 1 May 2027 start I'd begin in mid-December, which gives 20 weeks.

The base is capped easy running and two strength sessions a week heavy on calves and feet: slow single-leg calf raises, bent-knee and straight, kept 48 hours clear of the long run. Then the long run becomes the key session: continuous running on flat firm ground, no walking breaks, growing about 10 per cent at a time against the longest of the last 30 days, and held for a week after three steps up. I read the second half against the first every time.

The towpath block adds three things. Back-to-backs, peaking at about five hours and three the next day, four weeks out. A night run on the river: start at six in the evening, run past midnight, eat on the move. And a carbohydrate ladder on every long run, up about 10 grams an hour every week or two, finishing two weeks out. Then a two-week taper. Heat preparation only if the forecast asks for it.

What I watch

• Pace at the same heart rate in the second half of long runs against the first.
• Calf, Achilles and foot soreness in the days after long flat runs, and how it changes across the build.
• The long-run jump against the longest run of the last 30 days, every week.
• Carbohydrate per hour through the night rehearsal, and the gut score.
• How the athlete copes with monotony: whether the effort drifts up when the ground stops changing.

Facts checked September 2026 against centurionrunning.com and the 2026 info pack, rules and crew instructions: 100 miles, 1,900 ft of gain, about 25% paved, a 09:00 start and 30-hour limit with cut-offs at every aid station including those above, pacers from Henley, crew at eight points only, the mandatory kit and the one-hour penalty per missing item, 300 first-come places with a 50-mile qualifier under 15 hours and a £225 fee, and finish rates of 67% in 2026 and 72% in 2025 from the organiser's race reports. The 2027 date is 1 May. Where runners stop was checked in October 2026 against Centurion's 2023 to 2026 race reports and results: the results list finishers only; the 2023 report gives 15 drops before Henley, 117 between miles 51 and 89 and 207 finishers (61%); the 2025 and 2026 reports give 216 and 200 finishers from 300 starters and name individual drops. The quote is from a 2023 finisher's blog race report. The build's phase lengths, long-run and carbohydrate steps, peak weekend and taper are coaching method translated to this race, not a tested protocol. Darkness hours are computed from sunrise and sunset data. Evidence level: the durability and fuelling physiology matches the field notes; the demands are the race's own.