Legs or Lungs?
What is your limiting factor? Think back to your last interval workout or long effort. What was most fatigued when you finished? Where your legs burning or where you out of breathe?
Traditionally, most of the off-season training that we undergo is designed to increase your tolerance to pain. Lactate Tolerance is the official term. We try to improve our buffering system so that lactate does not slow us down so much. Expressions such as "go for the burn" and "push through the pain" are in every workout video and all coach's vocabularies. This approach does work well as the more you exposure yourself to lactate, the better you can handle hard intervals, racing and hill climbing. So, why ask the question "legs or lungs?"
What we have noticed over decades of coaching people is that there is a limit to your pain tolerance. The most popular measured pain thresholds are known as your bike Functional Threshold Power (FTP) and Running Threshold Speed. They both eventually hit a ceiling. This seems to happen year after year once you overcome the initial learning curve.
But, hold on!
Can we increase this limit that we keep hitting or is this all our DNA will allow us to do? We say "NO WAY!" The best example is right in front of us at the Beijing Olympics. It's amazing how the figure skaters are doing "quads" all over the ice and the snowboarders and freestyle skiers are now completing 1620s! This wasn't happening 5-10 years ago. So, we don't buy that DNA excuse!
We feel that athletes of all ages should take the big picture view of their training plan. Ask for a professional opinion. Are you balanced in your training approach? Do you cross-train? What is your weak limit? Why is your FTP the same as last year? Here is a list of questions to ask yourself with some potential solutions:
Legs Burn too much > more interval training
Lack of power > more strength training
Endurance > start aerobic training
Aerodynamics > flexibility in your hips and torso
Lungs > Altitude Training (hypoxia) to improve respiration
To answer the initial question, leg or lungs, the best answer is to find a way to work on your limiter. Simply training the same as you did last year will not improve your weakness. Re-schedule your plan to incorporate sessions that address the limiter. You will then see how good you truly can be without burning yourself out.
Questions? You should have at least one!