Last night’s class at Endeavor Performance illustrated a point that I knew but hadn’t thought about in a while; the relationship between pedaling cadence and heart rate. We warmed up as usual for about 15 minutes at an easy 60% of lactate threshold, then started into short tempo intervals (80% of lactate threshold) of five minutes each.
Instead of doing the tempo intervals at a cadence of 95-100 rpm like the last four weeks, Todd instructed us to do the first five minutes at 80 rpm to focus on leg strength, and the second five minutes at 110 rpm to work on leg speed. It was obvious from perceived exertion that the leg speed portion of the intervals were much harder than the strength portion. The 80 rpm segments were easy and relaxed, where the 110 rpm segments required focus and really made me feel the effort. Keep in mind that the CompuTrainers were set to keep the wattage required the same regardless of the cadence being used.
The perceived exertion wasn’t the only difference visible. Looking at the heart rate info from the workout, it is clearly visible which part of the workout I was in at any time. As leg speed went up so did heart rate, even if the wattage stayed the same. 
I’ve read a lot about how low leg speed focuses on muscle strength while higher leg speed focuses on aerobic strength. I’ll admit that this is a fairly intuitive connection, but to have a workout demonstrate the point so clearly was good. It’s one thing to read it and it’s one thing to have your muscles learn it.
One Comment
John likes.
That’s why I try to do both (like you are obviously doing) to work both systems. There is definitely more efficiency at lower cadences which is great for shorter events. But on longer events muscle fatigue sets in. So it’s good to be able to draw on that aerobic system at higher power levels. I have trouble finding the correct balance sometimes.