Originally Posted by RecceDG

Prologue: There is a fitness test used in the Canadian Army called the "EXPRES test" or the "beep test". It consists of a pair of lines on a gym floor 20m apart, and a tape recording of beeps that play at reducing intervals. You run back and forth between the lines, leaving on each beep - and if you don't make it to the far line before the next beep sounds, you are done. It starts very, very slow, and slowly ramps up to where it takes a fair run to cross the gap.

You get a score based on the number of times you cross the floor, and the purpose is to test VO2 Max.

I've done this test a few times, and at maximum, it feels like my lungs are going to explode. Heart is hammering, gasping for air... legs are fine, but it just won't go no more. So I know what it feels like to be "VO2 Max-ed"
OK, so I'm out with the Tuesday Night Group Ride group I've fallen in with. One of the rituals of this ride is that there is an optional sprint at the midpoint - there's a stop sign at the turnaround point that some guys sprint to. It's not very long, no more than 1000m at best.

The time comes for the sprint, and the couple of guys who are big sprinters start pulling away. I go down in the drops, slide out of the pack, and increase my cadence (don't think I changed gears) and reel them in. At this point, I'm breathing hard and my heart rate is up, but I feel fine and fresh.
As I pull even, the hammer is REALLY dropped, and it is on. I hang with them for a bit, maybe 100m, but then they start pulling away. I'm trying to hammer harder, but the legs just won't do it - they feel heavy, leaden, and just won't go.

And I can't even maintain that pace, and have to slack off.

Again, heart rate way up, breathing hard for sure, but I don't feel VO2 max-ed out like I have on the beep test. Legs, not lungs.So what is this? What factor am I lacking? And what's the best way to improve on it?

DG