Following the structure and guidance in Scott Johnston & Steve House’s books Training for the New Alpinism and Training for the Uphill Athlete, I’ve focused over the past year on consistently accruing hours of work below my aerobic threshold (AeT). The past six months, I’ve averaged just about five hours per week, with more regularity than in prior years. Overall, my workload is at a 250 hours per year pace.
These hours have been very skewed towards low-intensity aerobic. Excluding strength training, I’ve spent 97% of my training time over the past year at or below my aerobic threshold (AeT). 
I’m pleased with my progress, especially considering my volume of only ~18 miles per week. I have not gotten injured, and have took about one day off every ten days (with the exception of one bad cold). My heart rate at AeT has increased from ~170 beats per minute last June, to ~175bpm last December, to ~180bpm today. My anaerobic threshold (AnT) heart rate has remained remarkably consistent over the past four years, right around 195bpm. I don’t expect the gap between AeT and AnT to shrink substantially further, nor do I expect to see much movement in AnT heart rate. Improvement should come from being able to run faster at the same heart rate.
And my running speed has improved: my pace at AeT increased from ~9:05 pace last December to ~8:03 pace in May. That’s about a 13% improvement in speed, and is illustrated here as a rightward shift in the curve of heart rate versus speed.
Given the overall workload (miles, hours, etc.), this was probably much of the low-hanging fruit. Core strength has been another area of improvement, using Scott’s Killer Core Routine as a guide. But increasing volume is the next source of gains.
My plan for the summer is to keep focused on consistent (and perhaps more hours of) Zone 1 work, consistent strength training, and adding in something like one Zone 3-4 workout per week. I’ll continue to mix up strength training, and not be too rigid, focusing on core stability, single-leg and hip stability, and mobility.
- The zone definitions I use are:
- Bottom of Zone 1: light jog, heart rate starting to increase a bit above baseline
- Top of Zone 1 / bottom of Zone 2: aerobic threshold heart rate minus ~15 beats per minute
- Top of Zone 2 / bottom of Zone 3: aerobic threshold, blood lactate 2mmol/L
- Top of Zone 3 / bottom of Zone 4: anaerobic threshold, blood lactate ~4-6mmoL/L
- Top of Zone 4 / bottom of Zone 5: anaerobic threshold plus ~10bpm