So, my legs have been staging a pretty vocal protest after the volume I threw at them last week. Clearly, a proper rest day was in order. And what better way for a “Seamus-style” rest day than a cheeky 15km run, right? (Yes, I know, the irony isn’t lost on me – it’s a classic move, and some of you have come to expect these kinds of shenanigans!)
Despite the “rest day” label, today’s 15km run on Monday, May 26th, 2025, had a very specific purpose: maintain Zone 2 heart rate throughout and continue building that crucial aerobic base. This kind of session is a cornerstone of my training, especially with Hyrox Toronto on the horizon.
The Goal: Zone 2 and Aerobic Base Building
The primary intention for this run was to spend quality time in Zone 2. This wasn’t about speed or pushing the pace; it was about sustained, controlled effort to enhance my aerobic capacity. This type of training is fundamental, and I want to explain why it’s so beneficial, particularly for endurance events like Hyrox.
The Power of Zone 2 Training for Hyrox (and Beyond!)
Many athletes fall into the trap of thinking every run needs to be hard and fast. While high-intensity work has its place, the vast majority of your endurance training should actually be done at a lower intensity – this is where Zone 2 training comes in.
What is Zone 2? It’s a conversational pace, an effort level where you can comfortably hold a conversation. For most, it corresponds to about 60-70% of your maximum heart rate.
The 80/20 Running Principle: This popular training philosophy suggests that about 80% of your weekly running volume should be at a low intensity (like Zone 2), with only about 20% dedicated to moderate and high-intensity efforts. Why? Because this approach builds a massive aerobic foundation with less risk of injury and burnout.
Benefits of Zone 2 Long Runs for Hyrox Training:
- Improved Mitochondrial Density & Function: Mitochondria are the powerhouses of your cells. Zone 2 training increases their number and efficiency, meaning your body gets better at producing energy aerobically.
- Enhanced Fat Utilization: Training in Zone 2 teaches your body to become more efficient at burning fat for fuel, sparing precious glycogen stores for higher intensity efforts during a long race like Hyrox.
- Increased Capillary Density: More capillaries mean better blood flow and oxygen delivery to your working muscles.
- Stronger Cardiovascular System: Your heart becomes more efficient at pumping blood.
- Improved Lactate Threshold: While higher intensity work directly pushes your lactate threshold (the point where lactate accumulates faster than it can be cleared), a strong aerobic base built through Zone 2 work allows you to sustain efforts closer to that threshold for longer. It also helps with lactate clearance and recovery *between* high-intensity efforts (like Hyrox stations).
- Better Recovery: Low-intensity work promotes blood flow and can aid in recovery from harder sessions.
- Mental Toughness: Spending extended periods in Zone 2 also builds mental discipline and the ability to stay focused for long durations – invaluable for a Hyrox event.
For Hyrox, where you’re constantly switching between running and demanding strength stations for over an hour (or much more!), having a deep aerobic well to draw from is non-negotiable. Zone 2 training builds that well.
My “Rest Day” 15km Run Experience
As mentioned, my legs were definitely complaining when I started out today. The goal was a steady Zone 2 effort. The first 8km went pretty smoothly, keeping my heart rate and pace where I wanted them. However, around the 9th kilometer, my watch decided to have one of its characteristic glitches (a recurring theme, it seems!), and the data feed went a bit haywire. I had to slow down considerably for a bit to try and get it working again, which explains the significant drop in pace and heart rate you’ll see for lap 9 in the data below.
Once that was sorted (as much as it could be), I settled back into a rhythm for the remaining kilometers. The overall average pace was **6:48 min/km** for the **15.02 km**, which took **1 hour, 42 minutes, and 3 seconds**. Given the initial leg soreness and the watch drama, I was content with maintaining a predominantly Zone 2 effort and just getting the time on my feet.
Why This Run Matters for Hyrox
Even on a “recovery day,” a run like this serves multiple purposes for Hyrox preparation:
- Reinforces the aerobic base necessary to sustain effort through all 8km of running in a Hyrox race.
- Trains the body to recover efficiently between bouts of higher intensity (simulating recovery between stations).
- Builds mental resilience for longer events.
- Provides an opportunity to practice pacing and listen to your body.
Building Your Aerobic Engine for Hyrox?
Understanding how to effectively build your aerobic base with training like Zone 2 runs is crucial for Hyrox success. As a certified Hyrox Performance Coach, I can help you structure your running and overall conditioning to conquer the October Hyrox in Toronto. Let’s build an engine that doesn’t quit!
Get in TouchWhat’s your favorite way to build your aerobic base? Do you incorporate much Zone 2 training? Share your thoughts in the comments!
Run Summary (May 26, 2025)
- Activity Name: Georgina Running
- TOTAL TIME: 1:42:04
- MOVING TIME: 1:41:39
- DISTANCE: 15.02 km
- AVG PACE: 6:48 min/km
- AVG HR: 133 bpm
- MAX HR: 164 bpm
- CALORIES: 1184 C
- AVG POWER: 288 W
- NORMALIZED POWER: 292 W
- VO2 MAX: 51
- TRAINING EFFECT: Aerobic Base (Aerobic: 3.3, Anaerobic: 0.0)
- AVG CADENCE: 155 spm
- ELEVATION GAIN/LOSS: 85m / 85m (approx)
Detailed Lap Data (1km Laps)
Lap Time Avg Pace (min/km) Avg HR (bpm) Max HR (bpm) Avg Power (W) Avg Cadence (spm) Ascent (m) Calories 1 6:02.4 6:02 133 147 316 161 1 74 2 6:18.5 6:19 146 150 309 159 3 80 3 6:23.3 6:23 146 157 307 158 10 79 4 6:34.5 6:34 146 153 302 156 8 79 5 6:48.3 6:48 147 154 298 155 6 82 6 6:53.5 6:54 152 155 299 148 12 87 7 6:54.9 6:55 153 159 290 156 7 83 8 6:46.6 6:47 159 164 301 156 11 88 9 7:18.1 7:18 89 97 260 149 7 79 10 6:44.4 6:44 115 128 269 157 0 76 11 6:52.2 6:52 126 131 278 156 3 75 12 6:52.0 6:52 127 135 278 156 1 77 13 7:16.7 7:17 118 125 277 155 9 77 14 7:09.5 7:10 120 126 270 154 6 73 15 6:59.2 6:59 117 126 275 156 1 73 Note: Lap 16 (0.02km) omitted from lap table for brevity but included in overall summary.







