1  Core Principles

1.1 Sub-Threshold Focus

The aim is to improve the speed you can sustain at a manageable effort. Quality sessions target an intensity below the second lactate threshold (LT2), with short recoveries between repetitions. Most weekly training remains easy, below the first threshold (LT1); roughly 20-25% of training time is sub-threshold work. Zone numbers vary between watches and training systems, so a label such as “Zone 3” is not enough to set the effort.

For 5k through half-marathon runners, this can be an ongoing training framework. It does not require a later block of VO2max workouts. Occasional races supply higher-intensity efforts, while most training stays repeatable.

1.2 Intensity Control

Start conservatively and judge a session by how well you recover for the next one. Use several observations together:

• Pace: Set targets from current race fitness, not a past personal best or goal time. The appropriate pace depends on repetition duration and recovery. Adjust for heat, humidity, wind and terrain before starting. The workout examples give starting ranges; slow down further if they are too demanding.
• Heart rate: Use an individual lactate threshold heart rate (LTHR) estimate as a guardrail. One field estimate is the average HR during the final 20 minutes of a well-paced, solo 30-minute maximum effort after warming up. A chest strap helps avoid measurement errors. Copeland describes early repetitions finishing about 10-15 beats below LTHR, with later ones approaching it from below. This is a useful pattern, not a target to chase: HR lags and drifts, and repeatedly exceeding LTHR suggests the pace needs reducing.
• Perceived effort: Breathing should be controlled and the work manageable, with enough left for another repetition. Finish the planned session rather than testing that reserve. If effort feels unusually high, reduce pace even when the watch numbers look normal.
• Optional measurements: Lactate testing can help establish your own response, but a fixed reading of 2, 3 or 4 mmol/L does not guarantee the right intensity. Interpret readings against your individual curve and their trend through the session. Running power can provide another consistent reference on familiar routes, but neither a device estimate nor a percentage of critical power directly measures lactate.

1.3 Easy Recovery

Easy runs should leave room to recover between quality days. Copeland uses an average of no more than about 70% of measured maximum HR as a conservative cap, often running below it. This is a ceiling, not a goal. He now prefers HR to his earlier 65%-of-maximal-aerobic-speed guideline, which can still lead runners to push too hard.

In mild conditions, look for fairly steady HR after warming up. Slow down or walk hills as needed. Heat can cause drift even at easy effort, so also check breathing and how you feel. Keep the long run easy too.

1.4 Consistency & Repeatability

Improvement comes from months of training you can absorb. Controlled intensity makes frequent sessions more manageable, but does not remove injury risk or guarantee progress. Persistent fatigue is a reason to adjust the load, not to force another successful-looking week.