But yesterday it happened on a 17-mile training ride where my average heart rate was 90% of my maximum and I hit my max on two of the climbs - i.e., I was working really hard. When it happens, it feels like the front of my torso is slightly chilled - I feel like I am on the verge of being cold. Originally I wasn't really sure if it was really cold until I felt my flesh after I got home and stripped.
Your blood goes to where's it needed - to the legs where you're working hard. You're restricting the flow to the rest of the body like your chest.