The second principle I mentioned in my first post is that aerobic fitness is rarely the limiter of speed. Again, I’m not a scientist but just stating what I learn through my own experience. If you happen to know of scientific evidence for anything I’m talking about (refuting or confirming) make note in the comments. Aerobic fitness does matter, it is just isn’t the be all end all.
In the past few months I’ve run the Portland Marathon (flat and on paved roads) and two 50K ultra-marathons (hilly and mostly off road). In these three outings, despite running them after just a few months of training after a long hiatus from running, I was never out of breath. There were a few times during the 50K’s when I was breathing super hard during steep climbs, but those were just a few isolated incidents. The majority of the time my lungs were not the limiter in any way. I was breathing fine, but still my perceived exertion was very high.
In the case of my Portland Marathon experience, after about 16 miles my legs just stopped working normally. I wasn’t aerobically fatigued in any way, but it felt like I just finished a billion reps of squats and my leg muscles just wouldn’t fire. During my 50K’s, I had a similar experience. My muscles were just exhausted, as if I finished a really demanding weight workout, but my cardiovascular system and lungs seemed fine. During The North Face 50K, there were plenty of long climbs on single-track trails. They took a lot of power to muscle up.
I wish I had worn a heart rate monitor during my races to prove this point. I bet my heart rate was right around 140 or so. Not super high. What also happened later in the races was that my form went to hell. I would slouch over and everything would just sag. My core and low back would tire. This would affect my stride and breathing.
My take away from these events is that muscular strength (across the whole body, not just legs) plays a massive part in endurance events. When I say strength I really mean power/weight ratio. Strength with a fairly lean overall mass. Strong core and strong back to support proper form over long distances. Strong posterior chain (calves, hamstrings, glutes, low-back) to support overall running form and power. Once a reasonable aerobic base is developed, it makes intuitive sense that working the other energetic and power-building pathways in the body is a smart thing to do.