The last time I did the Fraser Valley Gran Fondo 160km in July I had a sudden lock of the hip joint which caused cramping at the 100th kilometer mark that sparked off a chain reaction to the lower back.
This caused pain in my lower back because of the repetitive motion of pedaling for 5 hours continuously causing the hips to overwork and legs to cramp forcing me to stop on the side for 5 minutes to stretch the hip flexor and hydrate.
I have since identified a common trend among some of the cyclists, runners and triathlon athletes whereby they come to the clinic complaining of extensive lower back pain. Once I have assessed them, I often discover that they recently participated in a repetitive long-haul event such as a 100K elevated bike ride, running or iron man event.
The lightbulb went on that this mysterious lower back pain was not the source of the problem, but instead the overworked hip flexor was the root cause.