Originally Posted by Derek Simonds
I can see that you pull hard then no tension then pull hard again but my heart rate is definitely not falling during that period of moving forward.
HICT isn't designed for cardiac adaptations. It could create positive cardiac adaptations in people new to endurance training though, and it could help maintain some cardiac adaptations for a while.
HICT is designed to make those middle range threshold fibers more oxidative-slow twitch and fast twitch, but not the highest threshold fibers. HRI (High Resistance Intervals) make your highest threshold fibers more oxidative. I did HRI only once prior to OCS, because I didn't have a sled or prowler or hills to run, and every hill totally trashed my legs.
Your heart rate is only an indicator of intensity level. It doesn't determine intensity, as just getting excited or looking at NASCAR drivers will show you. HICT is supposed to be done at about 10 BPM below your lactate threshold.
So, in other words, there's the supply side (heart) and the utilization side (muscles). HICT is primarily for the utilization side.
Also, when you guys play around with this stuff, you'll notice the different effects of speed vs. resistance level on your heart rate. Speed tends to elevate your heart rate more. In CrossFit terms, Fran will probably elevate your heart rate much more than Heavy Fran. It's easy to see this stuff on a bike, since you can change resistance levels rather easily.