HENRY CLARK: Running at 11mph for 30 seconds broke me – these lot go faster than that for two hours!

There’s no such thing as that one Sunday a year when the capital’s streets are quiet, other than 15,000 yards pounding and thousands more supported from the sidelines.

Running a marathon is the ultimate test of fitness, endurance and character for all who take part – but it has always been the streets for me, the elite runners, that have fascinated me the most.

There’s something captivating about watching those athletes—who look like they could be blown over by a brisk breeze—perform at their peak and eat the 26 miles with such grace, poise, and tenacity.

I went to the lab at the Porsche Experience Center to find out what it would take to keep myself at the front of the pack.

On arrival I was greeted by the centre’s manager, Eliot Challifour, and his team, whose Bond villainous grin made me slightly unnerved.

I knew from experience that this meant they were about to throw everything at me.

I was told the day consisted of two tests. A blood lactate test, to measure how long my muscles can handle working at high intensity, and another VO2 max test, to find my physical breaking point. And now that there was no turning back, it was time to begin.

The human body is remarkably flexible, but running a marathon at serious speed takes its toll. Elite athletes can lose up to three liters of sweat per hour during a race, and losing more than two percent of total body weight will send the body into a state of shock.

“It was awful from 17 miles away,” former British track and field star Sir Mo Farah admitted after his first attempt at the London Marathon in 2014.

“I gritted my teeth and felt so wet and heavy — and the further I went, the heavier I felt. Everyone is talking about hitting the wall. I felt the way I did that day.”

What Farah was probably dealing with was the effects of his muscles and red blood cells producing lactate, which over time prevents the muscles from working at such intensities.

The top runners, through a combination of rigorous training and perfect pace, are able to control these levels to ensure they are not slowed down – and the first test was designed to measure how well I could do the same.

I ran on the treadmill at increasing speed for 25 minutes, getting my finger pricked at regular intervals and drawing blood to test how my lactate levels changed under increasing stress.

Fortunately, the sports scientists were on hand to avoid a scene reminiscent of a bloody horror movie carnage and instead brought up some interesting results.

Speed ​​demon Amos Kipruto (pictured) won the men’s marathon last year, finishing in two hours, 17 minutes and 26 seconds

At the lower speeds, there was almost no change in my lactate levels. But as the intensity increased, my levels spiked dramatically, meaning I had no chance of maintaining that pace over nearly a marathon distance.

And with pros racing negative splits—when the second half of the race is run faster than the first—I’d be left in a rumpled, cramped mess in the elite race. My soggy shirt served as a stark reminder of the dehydration risk of running a marathon. To counter this, the top runners have a carefully crafted hydration strategy to avoid disaster.

“The pros have aid stations every three miles and can hand in their own water bottles, so they have pre-filled water bottles with their own food,” says sports scientist Chris Harris of Precision Fuel & Hydration.

“You’ll see some bottles have a big loop of string on the top because they can just grab, drink and throw. That’s all they have to think about.’

While these plans are flexible to some extent, British weather can wreak havoc. Race day temperatures have dropped to 5°C, while runners endured a peak temperature of 24°C in 2018. Even if Sunday’s race turns out to be on the cold side, you’ll still see the elite runners heading for the aid station.

“There have been cases in marathons where runners have dropped their bottle, but they will take the time to stop and pick it up because it means more to them in the long run of that race, rather than just a bottle pick it up at the next aid station’, explains sports scientist James Hatton.

After a short water break for myself, it was time to hop back on the treadmill for the final assessment of the day: a VO2 max test, where I’m just against the treadmill, which is considered the best indicator of cardiovascular fitness.

I started at a comfortable pace and initially focused on establishing a rhythm with both my stride and my breathing.

But as the speed increased by 1 km/h every minute, my brain suddenly couldn’t concentrate on the technical details. Instead, every source of energy from both body and mind was channeled into simply staying on the treadmill.

Every step forward forced every tendon to strain and my legs grew heavier and heavier – it felt like I was dragging two tombstones with me.

My deep, oxygen-filled breaths soon became more and more shallow, useless pants and it wasn’t long before I was forced to wave the white flag in relief from the aching wreckage of my body.

My breaking point came after just 30 seconds of running at 18 km/h (11 mph), the same speed maintained by eventual winner Yalemzerf Yehualaw in last year’s women’s race.

Reigning women’s champion Yalemzerf Yehualaw ran at an average speed of 18 km/h last year

Male winner Amos Kipruto’s cruise control speed of 21 km/h (13 mph) on his way to victory in a ridiculous time of 2 hours and 04.39 minutes was simply unfathomable.

My VO2 max score (a calculation of how much oxygen my body can absorb during exercise) of 57 would be blown away by both Yehualaw and Kipruto, who would achieve scores of around 80.

And with my dreams of one day sprinting out of the pack through the final corner at Buckingham Palace and sliding down the Mall to get the tape shattered, it was time to go home.

Maybe I’ll stick to my local parkrun after all.