Have you ever been in the middle of a ‘long’ run and suddenly your legs become wobbly and feel as though they may buckle underneath you? Or maybe you have seen footage of athletes such as David Wyeth in the 2017 London Marathon struggling to make it over the line as his legs seemingly gave up and began to collapse beneath him. Another well-known example of this is when Great Britain triathlete Alastair Brownlee helped his brother Jonny over the finish line in the World Series Finale in Mexico in 2016 when he appeared to have lost control of his legs. Footage of this race shows his legs looking ‘rubbery’ and unstable in a typical example of jelly legs.