Dr Will’s Running Power Training Zones

Updated: Aug 24

Here we go again, training zones!


It feels like every scientist/coach wants their own personal training zone system, and I’m no different!

"Ah Will, can’t you just use someone else's training zones and make them work?"

I’ve tried, but I’ve found it too frustrating and confusing for myself and the athletes I work with.


Training zones are designed to be a common language for training intensity prescription, a way of incorporating the many factors driving the purpose of a particular session or effort into a set of simple terms that can be communicated easily. For example, if a coach wants to prescribe a moderate intensity, long duration, marathon-specific run session, they can simply instruct the athlete to run in “zone 3”. With this one simple term, the athlete is given specific boundaries for completing the workout without needing to know the scientific basis of the prescribed session.


However, training prescription does not involve a list of rules to follow, and different coaches will have different opinions on how best to categorize the physiological processes and adaptations occurring during training into a set of 5-7 zones. As an athlete or coach, it doesn’t matter whether you choose an existing set or zones or establish your own; the most important thing is that both coach and athlete have a mutual understanding of what each zone represents.


As an example, here’s a brief explanation of the power zones I use with my athletes and my rationale for defining them in this way. I classify these zones in relation to critical power, a term describing the highest workload that can be sustained without using the anaerobic reserve—in other words, the transition point between anaerobic and aerobic work.



Dr Will's training zones for running power.
Dr Will's 7 training zones for running power.

Zone 1 (<75% critical power)


I consider zone 1 running to be low intensity exercise but not necessarily recovery/walking, as defined by Jim Vance. Once a large base of aerobic fitness has been established, it should be possible to run easily without having to leave this zone.


Zone 2 (76–87% critical power)


The aim of zone 2 is aerobic endurance development. Because I work with a lot of ultra and trail runners, I set the lower limit of this range slightly lower than others to account for the significant upward drift in heart rate that occurs after multiple hours of exercising. Over a long period of time, or due to the typical undervaluing of power outputs during trail running, running at a power output of >80% may be more strongly associated with the physiological demands of zone 3.


Zone 3 (88–94% Critical power)


Zone 3 is typically described as “tempo”, an ambiguous term which, to me, describes exercise conducted at physiological lactate threshold 1 (LT1). Often misunderstood as the lactate turn point (LTP) or the onset of blood lactate accumulation (OBLA), LT1 actually refers to the initial point at which lactate increases above baseline levels, typically to a concentration of 1 -2 mM. This is a very important reference point for marathon and ultramarathon runners because there is such a high level of correlation between LT1 and physical performance over events lasting multiple hours.

Therefore, in agreement with Vance, I set the upper end of zone 3 to 94% to ensure that training conducted at zone 3 remains below LT2. In contrast, Stryd and Steve Paladino both set the upper end of zone 3 as 100-101% of critical power, meaning that zone 3 efforts may incorporate a significant proportion of anaerobic work, particularly as the duration reaches >10 min. These coaches will have their own reasoning for doing so, and Paladino splits his zone 3 into 3a & 3b to ensure runners stay below 95% of critical power (typically the upper limit of marathon power) during particular efforts. This highlights why it is important to choose the set of zones that fits your training philosophy and stick to them.