- I have never ingest caffeine regularly until the past year. Work/family things kept me from sleeping as much and I starting using caffeine more and more and I developed a mild addiction (if I don't have about 75 to 100mg in the morning, I get headaches), so I have been slowly reducing my caffeine intake to try to get back to zero. Additionally, since I was fasting for the blood draw, I hadn't had any caffeine that morning and the screening was at 10am. Since caffeine elevates your HR, does lack of caffeine drop it when your body is used to it?
- I have been doing really intense high-intensity interval training on the bike, taking my heart rate at high as 199bpm and regularly getting it into the upper 180s repeatedly in a workout. I've never done this kind of intensity regularly before. Maybe this has strengthened my heart?
- I recently re-started swimming regularly, but nothing crazy - 3000 yards 3x per week.
- Something else?
For context, I'm 40 years old, normally finish about at 10% in races (so in a race of 500 people, I normally end up about 50th), grew up swimming.