Tag: Lactate Threshold

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.

What’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.