Well to start, why is one person's "comfortable pace" different than someone else's? Physiology and physics. There are a myriad of determining factors that help define how fast one person will be than another. But most of us compete in "endurance races" being a 5k or longer, and thus most of us are focused on the endurance end of the spectrum. That comes down to a few key things (but not exclusively): VO2max, lactate threshold, running economy, mitochondrial volume/density and stride efficiency. Here's something I wrote a while back which still mostly adheres with my thoughts on the subject:
Eureka! The Quintessential Running Post
I've worked with over 100 different runners in the last 3.5 years. One of the 20 questions I ask them is:
19) If I told you to run as slow as you can, how fast would you be running? This would be at a pace where you're barely breathing differently than normal walking. It feels like you're barely trying.
And over 90% of them say the same thing. They tell me a pace that is about 20% slower than what I estimate their Marathon pace to be. They don't have to want to run a marathon. That person could be training for a 5k. They could be a newbie or a seasoned vet. Yet, regardless of all that, that "slow as you can run which feels like you're barely breathing" almost always comes back at 20% slower than marathon pace race equivalency. So in my experience, that "comfortable pace" is very relative to that person's personal fitness and a simple calculation. I first ask what their recent PRs are to assess fitness. But I use question #19 to assess how close I am to that assessment.
Here's another excerpt from another thing that's more relevant to the second question: Can I just run what I want and that become the new normal?
The short answer is yes, you could do that. But the risk of injury/overtraining is far far higher. Thus, let's say there were two runners. One trains faster than their physiological pacing (i.e. uses 10k pace for long run pace) and the other trains at or near their physiological pacing. The runner who trains faster will improve faster. The runner who trains at/near will improve slower. But eventually (no guarantee though) the runner who is training too fast will succumb to overtraining/injury and need to take time off or back off. The at/near runner will continue slowly making gains. The other runner will come back from injury and bust out some serious pacing again to make up time. They'll make gains, and then get injured again. Take time off. So over the course of a year, the at/near runner will probably have improved by a greater margin that did the other runner who constantly had to adjust. The story of the tortoise and the hare comes to mind.
Train where you are, not where you want to be.
Most runners set goals for themselves. Whether that is a new distance or a faster time. But often I see runners extend themselves with the pacing too far. What was once marathon tempo pace becomes their 10k pace. But it's my belief that training where you are (with current fitness physiological pacing) is the best long term strategy. You'll make gains, and potentially can stay injury free for longer. You're working at appropriate paces, rather than paces of where you want to be. I made this image to illustrate this concept.
Let's say "current" is what we believe to be your current fitness pacing spectrum. Let's say that you have a new goal of lowering your half marathon time by 5 minutes. Some may say, well let's type in your new goal half marathon pace and come up with a new pacing scheme. This is where I'd argue you've chosen a "too fast" pacing spectrum. So what happens? Well potentially what was suppose to be "easy" is now a mixture of "easy" and "long". That's not a huge deal. You've made the "easy" just slightly harder, but things are still falling into those large zones of pacing at the slower end of the spectrum. But as you move further down the pacing spectrum you start to see issues. What was once your "10k" pace is now your "HM pace" for the purpose of workouts. So while you limited the 10k workouts to 20 min a single bout and having recovery intervals of 1 min for every 5 min of running, suddenly you're choosing to follow the HM rules for a workout at that same intensity. So instead of a 5:1, now suddenly you're looking at a duration cap of 60 minutes with no required rest breaks. That's a huge difference between how your body will perceive these workouts. In one case, you're making sure you don't do more than 20 min, but in the other case, you're suddenly allowing yourself to go all the way to 60 min. Could you complete the workout? It's certainly possible. But how your body reacts, adapts, and recovers from that workout is likely going to be completely different than was intended when following a training plan. You'll start to fall into a pattern where you'll always be trying to recover from the workout instead of reaping the benefits of it. It's what I call, "Don't Survive the Training, Thrive because of it". Just because you can, doesn't mean you should.
On the opposite end, you can see that little harm will be done if you train just slightly too slow. So I always try to impress upon my runners, train where you are and not necessarily where you want to be. With consistent training, you'll get where you want to be. A runner who can put in lots of good efforts without getting injured can become consistent and make consistent gains. But a runner who is striving beyond their current fitness and consistently ends up injured is likely to stunt their improvement over time.
For a more personal example:
I used a "PR the day" type mindset from when I started in 2012 through mid-2015. I went out and ran hard every day. If wanted to be faster, I had to train at faster paces endlessly. So, in the 3 years prior to switching my mindset, this was my improvement progress. I did about 2700 miles in those 3 years, was never seriously injured and trained rather consistently.
5k – *35:00 to 23:36 (33% improvement)
10k – 51:45 to 49:49 (4% improvement)
HM – 2:01:00 to 1:49:24 (10% improvement)
M – 4:50:26 to 4:20:34 (10% improvement)
After 18 weeks of Hansons training with going slow, reducing the long run, increasing the training load and physiologically relevant pacing:
10k – 49:49 to 49:22 (1% improvement) *Occurred during the 2nd half of the marathon
HM – 1:49:24 to 1:46:00 (3% improvement) *Occurred during the 2nd half of the marathon
M – 4:20:34 to 3:38:53 (16% improvement)
After 3 years (7750 miles, but roughly the same timeframe) of going slow, reducing the long run, increasing the training load and physiologically relevant pacing:
5k - 23:36 to 19:27 (18% improvement)
10k - 49:49 to 39:54 (20% improvement)
HM - 1:49:24 to 1:30:35 (17% improvement)
M - 4:20:34 to 3:14:05 (26% improvement)
Every couple years, I'll do a race to have something for PoT and I despise every second of it and swear I'll never do it again. Running is my "me" time, my time to engage in an activity that makes me feel good without any pressure to perform, so if it's ever not fun, I'll stop doing it. That said, I was able to get a PR and have fun at a couple Disney races, so it is possibel to mix the two, especially when one's PR isn't exactly difficult to reach, lol!
