I have mild asthma and if I don't use my inhaler "before" physical activity - I experience cramping in my legs. I'm guessing it is a lack of oxygen supply to the muscles in my calves (especially). If I use my inhaler 10-20 mins. before activity of any kind - I'm fine. Could it be something like this?
"Things look different from the seat of a bike carrying a sleeping bag with a cold beer tucked inside." ~Jim Malusa
2009 Trek 520-Brooks B-17 Special in Antique Brown
2010 Surly Long Haul Trucker-Brooks B-17 Standard in Black
1983 Fuji Espree Single Speed-Brooks B17 British Racing Green