Efficiency Evaluation: Ian Boswell's epic Unbound Gravel race win


After more than 10 hours in the saddle and 331 km in the legs, a double sprint between Ian Boswell and Laurens Ten Dam decided the Unbound Gravel 200 men's race winner.

Both were former WorldTour pros, well-known climbers and debutants in the Unbound Gravel race. Neither of them were known for their sprinting skills.

Boswell posted his ride on Strava in the days since the race, but we wanted more details. He was kind enough to share the performance data of his Wahoo Elemnt Roam headset and SRAM Force Quarq power meter with CyclingTips.

We took a long look at this performance file to see exactly what it takes to win such a grueling race.

And "grueling" is perhaps an understatement. The Unbound 200 is a real wear and tear, with the back door in the front group being a more important factor than stabbing attacks. But more on that later.

(This post discusses power-to-weight ratios. To put these numbers in context, read this article.)

Let's start with an overview of the entire trip. While the 247 watt average may not seem great for a gravel race, keep in mind that this 247 watt average can be used for 10 hours 14 minutes and from a rider weighing just 73 kg (3.38 W / kg ) applies. Add to that the really insane 32 km / h (20 mph) average speed for 10 hours on gravel roads! Mind you and really blown!

Some of the other summary numbers are just as amazing. 280 watt normalized power * (NP) (3.84 W / kg), 2,724 vertical meters, 9,107 kJ work (read: calories burned), all at an average daily temperature of 26 ° C (79 ° F).

(* Normalized force is the force the rider could have sustained if his performance had been constant throughout the exertion.)

A big day!

While WorldTour races like Milan-San Remo achieve the same 300km range as Unbound, speeds can be much higher due to the slick asphalt surfaces and team tactics. Therefore, sitting in the first five hours of MSR is usually much less physically demanding than an off-road group ride on Unbound.

The combination of difficult terrain, untreated surface and a greatly reduced slipstream effect of a smaller group means that the riders spend a lot more time performing at an event like Unbound.

Indeed, if we filter out the first 75-90 minutes of Unbound, when Boswell only had a few early attempts – presumably battling for position in the large group of starters – the numbers get even more impressive.

In the next nearly nine hours of racing (reading, tormenting), Boswell actually produced an average of almost 260 W (3.56 W / kg) or 286 W NP (3.92 W / kg). However, if you dig a little deeper into the performance file, we can see that the Boswell Index of Variability (VI – a ratio of NP to average performance) is only 1.11. Keep in mind that with such a long event the drivers would save energy and power whenever possible. Hence, this VI is another indicator that Unbound requires an athlete to be on the pedals for most of the day. Here practically zero roll-out.

For comparison, I looked at a Pro race from 2013 – I had a VI of 1.23. My Everesting (the fastest Everesting of all time – editor's note) had a VI of 1.14.

A little box with some big scary numbers.

Early selection

As mentioned earlier, the first 60-90 minutes of the race was a relatively quiet affair. Not surprising as the drivers had a full 10 hours (for the winner) of racing ahead of them.

The action began to warm up afterwards as the selection process began. In the next hour of the race, Boswell achieved peak performance for the race with exertions for 1 minute at 514 W (7.04 W / kg), 6 minutes at 354 W (4.85 W / kg), 10 minutes at 334 W (4th , 58 W / kg), 12 minutes at 328 W (4.5 W / kg), 20 minutes at 314 W (4.3 W / kg), 30 minutes at 302 W (4.14 W / kg) and 60 Minutes at 295 W (4.04 W / kg).

The fact that Boswell achieved so many top performances at this early stage shows that the race was really good. The back door of the front group could never close as the drivers seemingly kept falling out of the rear.

This one hour block of intense action was played over a mixture of steep hills, descents and hilly roads. The inclines were so steep that Boswell had slowed down to 12 km / h and mid-60s rpm, while on the other side he reached almost 70 km / h on some gravel descents.

Boswell appears to have kept a cool head as the race split up and that first pick was made. With such short steep climbs, it would be very easy to boil over the effort here, with potentially disastrous effects later in the race. Boswell peaked at one minute on this section, presumably in response to an attack, but his power file reflects that of a driver in complete control.

The top group maintained this tireless pace for the next two hours, averaging 32 km / h, while Boswell achieved a strong average of 268 W (3.67 W / kg). That is only part of the story, however, as more climbs, wind and attacks reduced this top group to just seven riders during that time.

What a group it was made up of former winners Colin Strickland and Ted King, former WorldTour riders Boswell, Ten Dam and Stetina, Lawrence Carpenter of Rally Pro Cycling and former UnitedHealthcare rider Eric Marcotte.

After a tireless three hours at a 277W average for Boswell, it was a climb as the riders tackled Little Egypt Road, which eventually edged out that group flawlessly and got a five-minute output of 363W out of Boswell – his peak of five Minutes for the day! If you think five minutes of exertion at 4.9 W / kg doesn't sound incredibly impressive, try after three hours at 3.8 W / kg. Crazy stuff.

Time out

Shortly thereafter, the group was reduced to just five as Marcotte and Carpenter were left behind (it's unclear whether this was due to fatigue or mechanics). At this point, the remaining five up front appeared to be declaring some kind of truce, perhaps given the fact that they still had 160 km to travel. They even agreed on a refreshment station.

For the next three and a half hours, the average speed dropped to 29 km / h. Boswell's average power for this section was 237 W (3.25 W / kg), for a welcome rest. However, the riders were now over 200km on the move and 7+ hours in the saddle, and it was unlikely that a drop in speed actually felt any easier.

The group of five huddled together over hilly gravel roads before there was finally a headwind in the last sections of the race.

The racetrack and the speed distribution. Perhaps more interesting, if not irrelevant, is this "Time over 40 km / h" diagram, which shows a whopping 1 hour 45 minutes and 80 km over 40 km / h.

It becomes clear

Few of the top group would want to risk a sprint in the finale of such a long and tough race. The race was a war of attrition up until then, with hundreds reduced to just five in the top group.

Stetina attacked around 40 km from the target. He drove free and Boswell responded with a series of efforts. The first was a 2:30 power at 350W (4.8W / kg) with a peak of 584W on Double D Hill, where Boswell actually won the KOM on Strava. This was immediately followed by a rapid descent into another short, sharp kick and another blow with almost 600 W (8.2 W / kg).

Eventually he put on a two minute effort on Kahola Hill and achieved 469 W (6.42 W / kg) with an average of 333 W (4.56 W / kg). At only 630 meters in length and 38 meters in altitude, this is not a climb that would normally split such an illustrious group of leaders, but it is unbound. After over nine hours of racing and a series of attacks, this would certainly have hurt a lot!

With a mixture of headwind and cross head for the last 40 km, the chances against a solo move were stacked. The chase group organized and after another series of driver exhaustions and mechanical misfortunes, only Boswell and Ten Dam were alone in the lead.

The two former WorldTour riders embarked on a time trial with two winners and achieved a mammoth 32 km / h and 264 W (3.62 W / kg) in the last 30 minutes of this 10:14 ride. Until, of course, they reached the last kilometer.

Then the cat and mouse began, none of the drivers wanted to start the sprint too early in what was surely the most agonizing sprint any driver would ever attempt. Even so, Boswell led the sprint and somehow managed to unleash a spike of 1,032 W (14.1 W / kg) with sustained 12 seconds at 938 W (12.85 W / kg) to stop Ten Dam and take the win the line to pick up.

It is this final spurt that is most impressive for me of the whole drive. I rode a 300km road race, 555km long distance race along the Irish Wild Atlantic Way, and completed three Everestings. From experience, I can tell you that sustained exertion is tough after seven, eight, or nine hours, but it is bursts of force, sharp accelerations, and sprints that become almost impossible.

While luck and avoiding mechanical problems undoubtedly play a role in Unbound's survival, Boswell and Ten Dam had the sheer strength of consistently blasting through the dirt for 10 hours. While none of the forces listed here would even come close to the best efforts of Ian Boswell, it is the sustainability and repeatability that are really impressive.

Boswell made exertions after nine hours very similar to what he did in the hard hours two and three. It is this endurance and resistance to fatigue that have earned him the highest level. Oh, and a healthy level of resilience, determination, calm and bike handling.


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