Does 'bonk training' really work?

Fasted training is often considered a shortcut to improved endurance, but is almost cracking all it's cracked up to be?

Cyclist preparing for a morning ride (left), rider pouring water into bottle (right)
'Bonk training' is often slotted into a morning ride - but is it a good idea?
(Image credit: Future)

In our 'Will It Work?' series, Sports Science expert Hannah Reynolds investigates common fitness hacks, to determine if they're really any good for the time crunched athlete.  

Bonk training, also known as fasted training, is a well-worn concept that cyclists have been employing for decades. Most riders are familiar with the lightheaded feelings of ‘bonking’ or blowing up and generally bonking is something to avoid  as the consequences are an absolute loss of performance. Bonking occurs when your body has run out of its preferred fuel source, glucose, and becomes reliant on the much slower energy released from fat. 

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Hannah Reynolds

Hannah Reynolds interest in cycling began while studying for a degree in Sports Science at the University College Chichester and surrounded by elite level cyclists. She is now undertaking a PhD at Sheffield Hallam University investigating the use of e-bikes by older people. 

A committed dabbler whose passion outweighed her talent Reynolds has competed across all disciplines of cycling bar BMX. In the very distant past she has been south-east road race champion, southern cyclo-cross champion and finished third in the European 24hr Solo mountain-bike champs in 2011. She was also the Fitness Editor of Cycling Weekly for 15 years. 

Hannah Reynolds is author of several cycling books, France-en-Velo a guide to the ultimate 1000 mile cycle route from the Channel to Med; Britain's Best Bike Ride. LEJOG1000; A 1000 mile journey from Land's End to John o' Groats and 1001 Cycling Tips