Energy, Thresholds and Zones in Running (Part 3)

Previously, in part one, we looked at energy systems used in running. Then, in part two, we looked at thresholds; what they are and how to calculate them.

Finally, in part three we’ll look at our calculated zones and how to incorporate them into an ongoing training regime.

What are zones?

Zones, as used in run training, are ranges of metrics targeting specific performance levels. Zones can be calculated using metrics such as speed, pace, power, heart rate and perceived effort. Major zones are demarcated using threshold values.

In this series of articles, we have been working with critical pace, so we’ll continue to use that metric here.

Zone Systems

The simplest format is a 3-zone system, demarcated by the primary thresholds. These wide margin zones can then be sub-divided, narrowing down specific areas of training focus. It is common to use 7-zone systems, which I use in my coaching with Optimal Running.

The 7-Zone System

Using zones calculated from our previous test sessions, we will look at each one in a little more detail.

Zone 1 — Recovery & Very Easy

This zone is mainly used for active recovery, following more difficult work. It is helpful to use recovery runs rather than taking full rest days, increasing volume with low level stress.

We can use this zone as return-to-training, after longer lay-offs.

We can also use the zone to complete a low-level block of aerobic training. By avoiding any higher intensity work, we ensure that the focus is purely aerobic.

Zone 2 — Easy

The higher end of this zone is our measured aerobic threshold. Plenty of volume can be built within this zone, due to the low levels of stress placed on the body. Similar to the previous zone, the work is almost completely aerobic. Run durations can be increased greatly, working on endurance development for longer events.

Zone 3 — Steady

The lower limit of this zone is now above our aerobic threshold. We start to use more carbohydrate for fuel as paces increase. This can also be classed as the ‘moderate-heavy’ zone, with the higher zone limit at close to Critical Pace. The majority of runners will find their ‘marathon pace’ somewhere in the low end this zone.

Zone 4 — Critical Pace (lower)

Critical Pace is sub-divided as it can be difficult to pinpoint an accurate value.

Work in this lower zone marks the transition from ‘moderate-heavy’, to ‘heavy-severe’ intensity. We will often hear this level referred to as ‘tempo’. Duration of training sessions will be shorter due to the increase in intensity. Energy derived is almost exclusively from carbohydrate.

This zone can be used for specific race preparation sessions, targeting narrow pace ranges. Over time, sessions can also be used to PUSH up our Critical Pace threshold from below, consequently lifting all associated zones.

Zone 5 — Critical Pace (higher)

Training intensity above Critical Pace is now classed as ‘severe’. Sessions at this level need to be broken down into interval and recovery phases, due to the breakdown in physiological/metabolic systems.

Training in this zone is used for longer interval work, mostly around specific race preparations.

Zone 6 — VO2max

VO2max marks the upper limit of the aerobic energy system. It is the maximum effort that can be sustained for ~2.5mins. Beyond here, anaerobic metabolism is increasingly called upon to support continuation of exercise; duration to exhaustion is short.

Training in the lower end of the zone can be used more regularly to maintain, or improve, aerobic capacity. This is where we can PULL up Critical Pace from above, again lifting all associated zones.

Training in the high end of the zone should be used more sparingly unless your focus is on middle distance type events such as 800/1500/3000m races.

Zone 7 — Anaerobic/Glycolytic

Depending on your focus, time spent in this zone is minimal. Work is divided into shorter intervals, needing longer recovery, due to depletion of fuel stored in the working muscles. Anaerobic means without oxygen, so turnover of fuel/energy is rapid, but limited.

Training in this zone can be used at both the start and/or finish of a longer training schedule towards a specific race or event. Fitness gains tend to happen quickly, but can easily be lost if persisting for too long. We need to use this type of training prudently.

Types of training sessions include sprints, short hill-sprints and shorter track type work such as 200/400/800 metre intervals.

So that completes our exploration of ‘Energy, Thresholds and Zones’ in running. I hope you found some useful advice to help with your own training.

As always, if you would like any personal guidance or coaching, you can subscribe to Optimal Running services on my Ko-fi page.

Until next time… keep running!