I've also suffered a few times. On Clough head descent (then all the way to the finish) on the "Lakes in a Day race" last year. Also the Lakeland 50 in 2015. Plus a few others. The common factors between all these bouts of cramp is not feeling great on the day, and setting off too fast. I'm starting to think it's an imbalance in the body's chemistry that triggers the brain which triggers the muscles to spasm. I think the pickle juice must resupply these imbalances, and so turns the brains signals to the muscles off, in terms of the spasms.

Mitigating cramp I believe is best done by, training in a relevant way for the race (remember L100/50 + many others require a pack weighing appx 2.5KG), resting well and feeling good (hard to guarantee) prior to the race. Setting off at a relatively comfortable pace, especially when doing a long race without doing a warm up. Eating and drinking little and often with a decent bit of salt too. Strength training.

I did the Lakeland 100 last weekend, trained with a 5kg weights vest + long hill runs + speed work, felt good before it (lucky me), set off very conservatively, ate and drank little and often used NUUNs. Never had any cramp at all, just extremely sore blistered feet after 70 miles and Finished in a decent time for me.