I thought I would stay in theme today. The past couple of days I talked about the importance of the slow run. Since I had a general aerobic run on the plan yesterday, I thought I would talk about that today. A general aerobic (GA) run is a little faster than a slow run. Not slow. Not fast. Just kind of half fast (cmon - say it quickly).
Honestly - how fast is "general aerobic"? To answer this we need to understand lactate threshold first. Lactate threshold (LT) is defined as the maximum pace you can run non-stop for one hour. It's usually right around your 10K race pace. So, the answer is somewhere between slow conversational pace and 10K pace. For those of us with heart rate monitors, this correlates to somewhere between 70% and 85% of max heart rate. The key to running aerobically is staying out of lactate threshold - above that pace your body will start accumulating acid that contributes to fatigue. Run at LT pace, and you will need to spend an extra day recovering.
The general aerobic run should form the foundation of your training program. These are the runs that build your overall fitness. They serve to help strengthen your leg muscles and improve your body's ability to transport oxygen from lungs to muscles. A typical training plan would include one day doing some speed work (intervals, tempo, etc.) and one long run day. Those constitute your "hard" workout days. The rest of your time is spent either in recovery or general aerobic range.
The last issue is the distance of a general aerobic run. According to the books, the distance can be anywhere between 3 and 10 miles. That's quite a range! Once again - the key is to make sure that you can handle the distance without stressing your body. These days, I have a little line that I use to determine whether a run should be a general aerobic run or a long/medium log run. Right now, that's right around 12 miles. Below 12 miles, I treat the run like a GA run and step the pace up a bit. Beyond 12 miles, I drop the pace and treat the run more like a long run. I find that right around 12 miles, my heart rate increases quickly, and to stay within the GA range, I need to start slowing my pace.
By the way, I think the best discussion of this can be found in the Competitive Runner's Handbook by Glover.
So, last night, I put in 9 1/2 miles. My average heart rate was 80% of max - so I managed to keep things aerobic. On tap today - rest. No rowing. No running. Just rest. Saturday - 15 miles. Things are starting to lengthen out - that's for sure.