UK's Fittest 65-year-old On Target For Fastest Marathon in 25 Years

Veteran endurance athlete Mark Kleanthous, 65, (above, in green) is on course to run his fastest marathon in 25 years in London next month, with a target time of sub‑3:20 – and he credits CurraNZ for his late‑career resurgence.

The runner from Leighton Buzzard is currently ranked in the top 16 in the UK for his age group, with an age‑grading of 83.47%, and is enjoying one of the most successful periods of his extraordinary running career.

With CurraNZ his go‑to performance tool, he has been a constant fixture on the podium over the last four months and now heads into London with exceptional form and confidence – aiming to run 16 minutes faster than last year’s London Marathon.

Primed after Standout Cambridge Half Marathon performance

As part of his London Marathon build‑up, Kleanthous produced a standout performance at the Cambridge Half Marathon last month, finishing almost four minutes faster than in 2025 and closing faster than any of the podium placers, despite being roughly twice their age.

He clocked 1:29:35, his first sub‑90‑minute half marathon in 16 years, having last broken the 1:30 barrier at age 49.

In a field of over 14,000 finishers and 14,500 entries, Kleanthous finished first in the 65+ age group (out of 115), winning by 3 minutes 45 seconds – almost a kilometre ahead of second place. In the event’s virtual head‑to‑head rankings, he passed more than 300 runners between 5km and the finish.

CurraNZ: central to his late‑career peak

Having competed in over 1350 events worldwide - including 545 triathlons, 48 Ironman triathlons, plus many 5K, 10K, marathons and ultra-marathons, the endurance coach has swum, biked and run over 283,000 mile down the years - the equivalent of circling the globe 11 times.

He says: "CurraNZ hasn't powered every step, but it's made a massive difference in the last 11 or so years - and particularly when I started double dosing."

This combination of better recovery, muscle function and superior fuel management helps explain why athletes like Mark are experiencing some of their best results in years while using CurraNZ.

Kleanthous is clear about the role CurraNZ has played in his performances.

“Without doubt, CurraNZ made a big difference. Not only does it help me sustain a high level of intensity, but it also allows me not to slow down, which in the latter stages of a marathon is often where all the time is lost.

“CurraNZ helps me burn fat for fuel during training and racing. I am a leaner athlete with more muscle mass and less fat when loading and taking CurraNZ on a regular basis.”

He takes one CurraNZ capsule daily as a baseline; two capsules a day for seven days before key races as a loading strategy; and two capsules with breakfast on race morning, plus one capsule 90 minutes before the start.

He reports that pre‑race loading helped him “cruise” at around 4:24/km early on, while the final capsule “kicked in” over the last 5km, supporting his strong negative split and fastest final kilometre.

Low‑mileage, high‑performance – and a string of podiums

Despite being a “low‑mileage runner”, averaging just 35–40km per week, Kleanthous focuses on consistent marathon‑length, race‑specific workouts rather than volume, and is routinely running faster than many of his age‑group rivals.

Since incorporating CurraNZ consistently into his routine, his results in the 65+ category over the last four months include: Beachy Head Marathon age‑group win, Dirt Half Marathon age‑group win, Beds County Cross Country Championships age‑group win and third overall in the cross‑country series age‑group standings.

These results, coupled with his Cambridge performance, underpin his current world‑class age‑group metrics and show a clear upward trajectory as he builds towards London.

Building towards London Marathon 2026

Kleanthous will line up at the London Marathon on 26 April with a clear goal: to run 16 minutes faster than his 2025 time and deliver his quickest marathon performance in a quarter of a century.

“I ran quicker at London in 2025 than in 2024, and it’s looking incredibly likely that 2026 will be faster again – and my best marathon in 25 years,” he says.

With his blistering age‑grading and UK ranking, and a meticulous training and nutrition strategy centred on CurraNZ, Kleanthous approaches the iconic race in the best shape he has enjoyed in decades – proving that high performance is possible well into the masters years with the right approach and support.

Follow Mark on Instagram: @ironmatemark