If you were asked to name the world's toughest marathon, you might plump for the Everest Marathon, and you would be correct, according to a recent survey carried out by PureGym. With over 450 gyms throughout the UK and nearly 700 worldwide, PureGym boasts more than 2.2 million members at its 24/7 access facilities, so when they conduct fitness research, it is well worth taking note.

As for the easiest marathon, surely London would top any such list given the recent exploits in the capital, with the first (and second) sub-two-hour performances achieved in true racing conditions? This time you'd be wrong. PureGym's survey ranks the Osaka Marathon as the easiest. London makes the top six, but only in the geographical sense, as that position is awarded to Battersea Park Marathon, according to PureGym's Marathon Difficulty Index.

Pure Gym analysed various performance and environmental data from 100 global marathons before concluding that the Everest Marathon is the toughest in the world. The health and fitness chain allocated each marathon a difficulty score based on factors that included maximum elevation gained, maximum altitude, average finishing times, typical race-day temperatures, average wind speeds, and overall physiological challenge.

With an index score of 90.72, the Everest Marathon in Nepal is in a class of its own. An average finish time of 8:50:35 speaks volumes, as does the peak altitude of 5,190m, and the total climb of over 2,500m! In contrast, the comparatively flat Osaka Marathon scored just 10.98 points.

The Beachy Head Marathon in Sussex was the hardest in Britain (55.37 points) due mainly to 1,698m of elevation gain, followed by the Eryri (Snowdonia) Marathon in Wales. Scotland's only top-ten ranked marathon in the hardest list is the Loch Ness Marathon in sixth place.

In the easiest marathon list, Battersea Park's multi-lap marathon course is followed by two northern events: Manchester Marathon and Blackpool Marathon are the runners-up. No Welsh marathons made this list, but Scotland was proudly represented by the Edinburgh Marathon in ninth place.

For the full list and detailed explanation, visit the PureGym Marathon Difficulty Index blog here.

For curated trips to many of the world's best marathons, visit Marathon Tours & Travel UK here.

Photo courtesy of Visit Eastbourne/Beachy Head Marathon