’Tis the season for spring marathon training – especially if you’re preparing for a big-name event like the London Marathon. From first-time marathoners to world-class athletes, more than 56,000 participants are expected to take on this monumental race in April, which would make it the biggest marathon to be staged anywhere in the world, ever.
One 2025 London Marathon entrant who is both a first-time marathoner and a world-class athlete is Alex Yee – one of the most accomplished triathletes of our time. Still only 27 years old, the British star dominated the tripartite discipline in 2024, winning Olympic gold in the drama-filled men’s individual triathlon in Paris, followed by Olympic bronze in the mixed relay triathlon for good measure.
As if becoming an Olympic champion wasn’t enough, he then cemented his number one status by taking gold in the 2024 World Triathlon Championship Series, too.
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But this season, Yee is returning to his running roots. A former 10,000m specialist, who became the British champion over the distance in 2018, Yee is now ramping up the miles ahead of his first-ever marathon in London next month – and he won’t be holding back.
Thanks to data captured by his Coros Pace Pro running watch and Coros heart rate monitor, we’ve shared the stats from one of Yee’s hardest London Marathon training sessions – a 30km progression run – to show just what it takes to work at his level.
Warning: it’s impressive stuff.
The motivation to run the London Marathon
The London Marathon is a bucket list race for runners – and, indeed, non-runners – across the world. Yee, who hails from the London Borough of Lewisham, located only a few miles down the road from the London Marathon start line, is no exception.
‘The marathon is something that I’ve wanted to try for a while,’ says Yee, who, at the 2020 Olympic Games in Tokyo, also attained gold and silver medals in the mixed relay triathlon and men’s individual triathlon respectively.
‘There’s something so enticing about the distance,’ continues Yee, who usually runs about a quarter of the length of a marathon in race conditions. ‘Taking it on now just makes sense – it’s something different to mix things up and keep the motivation high. And what could be more motivating than running in my hometown?’
Yee’s marathon training mix
A master of swimming, cycling and running, it makes sense that Yee has retained all three sports as part of his London Marathon preparations. After all, he is still a professional triathlete by trade.
Although his swimming and cycling have been scaled back to make room for more run-specific sessions, they still feature in Yee’s weekly fitness routine and have helped him to build his aerobic base.
‘The start of 2025 has been a little up and down, but being able to see my data moving in the right direction is reassuring,’ says Yee, who, over the course of his marathon training, has been tracking and continuing to increase his ‘Base Fitness’ – a metric, provided by Coros, that takes a 42-day average of your training load to determine your aerobic fitness level. ‘I know my body and what it responds well to – and seeing those improvements in the numbers reinforces that I’m on the right track.’
As Yee exemplifies, incorporating non-running activities like cycling and swimming into your marathon training – in addition, of course, to all-important strength and conditioning – can enhance your overall endurance and work a wider suite of muscles while helping to keep injuries at bay. Plus, mixing things up keeps your mind engaged as you move toward your marathon 0r other long-term target.
Using data to define progress
Using Coros technology as a key training companion, Yee has been able to dial into the specifics to make sure that he can optimise his marathon preparations and continue to build from one session to the next. ‘Since working with Coros, I’ve been able to analyse different areas in my data that can be improved – it’s an exciting time in my career,’ he says Yee.
Just like most world-leading athletes, Yee closely monitors his heart rate – especially during key sessions, where he’s working at or above threshold pace – to make sure that he’s training efficiently.
‘Heart rate is a great metric to track across all aspects of my training,’ notes Yee, who uses a Coros heart rate monitor to capture all the right metrics. ‘Alongside how I feel, it helps me to understand how my body is coping with the workload.’
As for the workload itself? For Yee, this involves pumping out a threshold pace of around 3:02 min/km (4:53 min/mile), where his heart rate sits at 172-184 beats per minute (bpm). If he can sustain this for 26.2 miles, Yee is looking at a London Marathon finish time of around 2:08.
‘I’d love to run somewhere around 2:07 to 2:10,’ says Yee, whose marathon ambitions match the data predictions. ‘We are going into the unknown, so we will see – but I want to give it a really good go.’
Yee’s 30km progression run – in stats
Doing long runs and sessions at marathon pace helps to prepare both your body and your mind for the big 26.2-mile challenge ahead. Hence, Yee took on a testing 30km progression run as part of his marathon build, where he tried to replicate the physical and mental demands of race day.
Setting off at 9:35am, the same time that the elite men usually start the London Marathon, Yee clocked 17:21 for his first 5K, with a steady heart rate of 143 bpm. He then pushed on for the bulk of the session, covering the next 20km at an average pace of 3:04 min/km (4:56 min/mile). He completed this block with a heart rate of 172 bpm, which sits well within his threshold zone.
Despite being 25km in, Yee was still able to find more speed, completing the final 5K in 14:50 at a scorching average pace of 2:58 min/km (4:47 min/mile). All the while, his heart rate was still within his threshold zone at 177 bpm.
Overall, for this 30km run, Yee averaged a pace of 3:07 min/km (5:00 min/mile).
‘I’m really enjoying these longer sessions,’ says Yee. ‘Going from sessions like 6 x 2km as my maximum volume, to now running 30km continuously, is a big jump – but my body is responding well and, most importantly, I’m loving the challenge.’
Beyond the London Marathon
Although it will mark a pivotal moment in his already-glowing athletic career, racing this year’s London Marathon is by no means the be-all and end-all for Yee. Rather, it is a stepping stone to – it is hoped – even greater success in the realm of triathlon.
In fact, despite the accolades that he has attained so far, Yee believes that he still has more to prove as a top-tier triathlete.
‘I’m by no means a complete triathlete yet,’ he says, musing on his past and future Olympic performances. ‘I spent a lot of time working on areas that I needed to improve for Paris. With a few years until LA 2028, I want to see how much I can progress across all aspects of triathlon.’
In the meantime, that little old running race around London – his home – is calling.
To dive deeper into Yee’s training for the 2025 London Marathon, check out the Coros blog.
