My Experience with Zone 2 Workouts

"You really need to take it easy for most of your long training workouts," explained Ken Mierke after my VO2 Max test back in October of last year. Turns out my body was switching from fat burning to carbohydrate burning fairly early, much earlier than what would be feasible in a race. In other words, my slow twitch muscle fibers were extremely under-trained. Ken being one of the most respected coaches in the area and in endurance sports, I stopped and listened... and changed my ways.

The science behind the above advice is solid. The human body has enough fat reserves to last any ironman distance. Even the top elite athletes with 5% body fat have enough fat on them to burn all day. Carbohydrate and glycogen reserves, on the other hand, are in limited storage and replenishment imperfect at best. There is simply no way for the body to absorb carbohydrates fast enough during a race to fulfill immediate performance needs. This eventually can lead to a "bonk" where the body stops responding and performance dips substantially. At that point there is nothing one can do other than slow down or stop.

Yes, this is what a bonk looks like

So what can one do in training? The key is that the body only recruits carbs as a source of energy under high intensity; for low intensity efforts the body primarily burns fat and uses the highly efficient slow twitch muscle fibers. The trick then is to train in a manner that raises one's aerobic capacity and effort threshold where the body starts recruiting fast twitch fibers. Here is where Zone 2 heart-rate training comes in. By training in this zone, an athlete can keep her powder dry for longer before having to make the big effort, hopefully much later than the competitors! 

So that in a nutshell is the science, hopefully I've explained it right.

I think I get it... wait.. doh! This was me some months ago

Practice however is hugely variant! Many people simply do not train in Zone 2 and go hard all the time. To be perfectly honest, prior to my test and Ken's advice, Zone 2 workouts made no sense to me either and in fact sounded counter-intuitive -- why would one train at low intensity when the purpose is to race at high intensity?

Clearly the answer is that one cannot and should not train in Zone 2 all the time. There is a need for mixing things up with intense workouts. But there is also a time and place for such workouts. In my training regimen, thats mid-week track for running and hill repeats (or trainer intervals) for biking.  The weekend low intensity workouts leave me significantly fresher to attack these intense workouts and maximize their fitness benefits.

After a few months of such focused training, a slow confidence has started building in me. I've had setbacks, both mental and physical, and have often doubted myself but the numbers are starting to show promise now. 
 
Two weeks ago I managed to knock out a mostly Zone 2 14 mile run at sub 8 min mile pace.. While this may not be fast in many books (surely, some people on my team run 7 min miles while texting on their cellphones), it represents significant progress for me. At the beginning of the year, I ran a 4 mile race at that pace going all out. Check out a report here. Now, I can run that pace in Zone 2 for 14 miles. The cool thing is that I knew I was holding back and could have gone faster.. great feeling!

Getting there.. ironically, slowly and steadily

Then just this past weekend I found myself alone out front on a Team Z ride with one fast dude on a bike, Ray Nancoz, a Swiss powerhouse. We climbed hills, rode some fast straightaways, blazed the downhills faster than cars, and even ended up in an impromptu drag race at the end (not in Zone 2 btw!). My legs felt alive, as if I've discovered an additional gear. My garmin felt the same way post ride.

Training schmaining... Here's what I want as my tri bike!

Being an economist obsessed with identifying causality, I obviously cannot attribute all my fitness gains to Zone 2 workouts alone. Indeed, I now weigh 148 pounds with single digit body fat, a full 27 lbs lighter than when I joined Team Z. So I'm sure throwing the spare tire out has a lot to do with my speed. Also, my nutrition has improved dramatically, thanks to the magic advice of Rebecca Mohning. Finally, mentally I am getting my head in the game with a keen focus on results oriented training.  

All these factors have a played a role. I'm eager to see if these improvements can show themselves in a race environment. Thankfully I don't have to wait too long as racing season is almost upon us... See you out there!