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XNRG 2022 events now open for booking!

This event is scheduled to go ahead, with some differences. Read our Covid-19 policy

No. of days 1 day

Distance 31 mi

Ascent gain 979 m

Accom. no

Food no

NEW Half ultra:

Distance 16 mi

Ascent gain 558 m

Choose from either a 50km ultra marathon or 25km half ultra in the picture-perfect Chilterns in aid of funding life-changing operations for children in developing countries.

The ideal 50km introduction to ultra marathon running. Escape to the Chilterns, an area of outstanding natural beauty. What's more, it's FREE to run, if you commit to raising funds for Humanity Direct.

Latest results


  • Transport to and from Princes Risborough station
  • Free parking at Princes Risborough School
  • A fully recced and marked route
  • Full medical cover throughout
  • A quality finishers T-shirt and medal
  • Checkpoint food and water at regular intervals
  • Free tea, coffee and cake at the finish
  • Prizes and trophies for overall and category winners
  • A great atmosphere and a fun but challenging day out
  • Action photos en-route, free to download

The winners, runners up and age group winners will receive fantastic prizes or vouchers from our sponsors.


The well-marked circular route will start and finish at Princes Risborough School. Using National Trails and Footpaths, there are clear signposts and post discs, as well as our signs and confidence tape.

We recommend familiarising yourself with the route before the start of the race.

Showing route for:



Minibus pick up starts from Princes Risborough Station


Registration opens.


Walkers rolling start (for full distance)


Runner medium paced rolling start (for full distance)


Elite runners start - target time below 6 hours (for full distance)


Rolling start for 25km distance


Refreshments available.


Minibus to the station running all afternoon


Entry for ultra


Entry for half ultra




The entry fee will be donated to fund a vital operation, or alternatively enter for FREE, if you commit to raise funds for Humanity Direct.

If you're fundraising book now through our system, then visit Humanity Direct's website to register yourself.

Please note: a 2.5% service charge, levied by the registration software, will be added to your total. We are using a new entry system that takes payment through the secure system Stripe. No payment information is retained by Extreme Energy, or our entry system tool.

Email us on if you have any questions about your options.

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If for some reason you are not able to make the event you have entered. The XNRG refund policy is that we will give you 70% refund of your entry fee up to 1 month before the start date of the event. You also have the option (1 month before the date of the event) to get a 100% transfer credit to another one of the other Humanity Direct 1 day events, or you can donate your entry fee to the charity. All entry fee money goes directly to the charity and directly to helping children with life changing operations. These options you can execute on your Ultrabritain entry page.

After this time we are sorry there will be no refunds or transfers to future events. Refunds will be to your booking credit card.

Race-day Preparation

Kit List

The only compulsory kit is a fully charged mobile phone and a minimum 500ml of water, but it's worth taking a look at our recommended kit list.

Other equipment may be made compulsory by the race director depending on the weather.


The event is supported by a Course Manager and a fully qualified medical crew will be in attendance. We strongly recommend taking a moment to read our medical page before booking.


We've answered a range of common questions in our FAQ. For other questions, say hello on

More Information

This popular race is especially good for those looking for a supportive event for their first ultra within easy reach of London. And for those wishing to build experience to gain entry to UTMB we can now also offer 2 ITRA points (for full ultra distance only)!

As with all of our events, everything is taken care of at the Chiltern Challenge so you can focus on the experience! We’ll provide transfers from the station, free parking, free photos, changing facilities and heaps of tea and cake.

The XNRG Chiltern Challenge is a unique chance to get a place on an amazing one day ultra for FREE if you fundraise for a Humanity Direct patient, or alternatively donate £65 for the full distance or £38 for the half ultra option.

Humanity Direct

In 2019 Humanity Direct raised £24,000 through the three Humanity Direct Ultras, which helped fund life saving and life changing operations for 35 children and we are hoping to raise even more in 2023.

So, how does it work?

It's simple. The entry fee is donated to fund a vital operation or, if you prefer, you can enter for FREE and start a fundraising page instead and raise as much as you can, with a minimum of £65.

“The support we’ve had from XNRG has been phenomenal. Thanks to you we’ve rolled out a vital eye-testing programme for children in rural Uganda with over 600 children receiving free glasses so far. Your donations and dedication have also helped us continue to provide life-saving and life-changing surgery for children whose families are live on less than a $1 a day and who would never be able to afford the medical care they need.  XNRG ultras truly do change lives!"

- Nick Swift, Humanity Direct’s Founder


Entries will close one week before the event (or when full). A waitlist option will be available if the event becomes fully booked.

Navigation and Support

Stretching from the River Thames in Oxfordshire to Hitchin in Hertfordshire, the Chiltern Hills are a spectacular Area of Natural Beauty boasting some of the finest protected countryside in the UK.

The well-marked circular route will start and finish at Princes Risborough School (HP27 0DR), incorporating four checkpoints for the full ultra distance, approximately 10km apart, and two at the half ultra.

Using National Trails and Footpaths, there are clear signposts and post discs, as well as our signs and confidence tape. We recommend familiarising yourself with the route before the start of the race.

Aid stations

There will be checkpoints at regular intervals with water and food - please bring your own cups. For the full ultra distance there will be four checkpoints and the half ultra will have two.

Due to the risk of cross contamination, we cannot provide checkpoint food to suit all dietary requirements. If you require special food or snacks to suit any allergies or vegetarian/vegan diets, can you please bring your own. Put them in containers, marked with your name and checkpoint number and give them to the checkpoint teams at the start of the race.

Trees Not Tees

As part of your entry fee you will get an event T-shirt, or you can choose not to have the T-shirt and the money we would pay for the T-shirt will go to Trees not Tees and a tree will be planted instead.

For more details visit their website -

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Hi, I don't usually respond to organisers after an event. I just wanted to say thanks for organising such an amazing first ultra. The race was superbly organised , well planned , Marshall ands food stops were excellent. I can assure you I will be running in your events again and recommend them to others. Thank you and your team for making the chilterns ultra such a great run.

Hi everybody I would like to congratulate XNRG on a superbly well run event in the Chilterns. It was a fabulous day out in stunning countryside. Everything went like clockwork, registration, briefing and the course was marked perfectly with tape, signs and sometimes quite elaborate pictograms sprayed on the ground making the maps supplied only necessary as an overview of the route. I find it quite mind boggling that you can plot and mark such a varied and interesting course in 31 miles of countryside, check it and then clear up afterwards. It made the entry fee worth it alone.

Just wanted to say thank you to everyone who helped with this event yesterday. It was my first ultra and I absolutely loved it! The fantastic organisation meant all I had to do was concentrate on getting myself round the distance! The malt loaf and coke at the checkpoints were a much needed treat! Thanks again.

We can't wait to see you there! Questions? Say hello on

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