When Should You Do Intervals in a Zone 2 Workout?

Written by:

Adam Pulford

CTS Premier Cycling Coach

Updated On

May 12, 2025

Combining Zone 2 endurance rides with intervals is a powerful strategy, but timing matters. Should you incorporate high-intensity efforts right after warming up, schedule them mid-ride, or save them for the end when you’re already fatigued? It all depends on what you’re trying to accomplish.

If watching or listening is more your speed, there are video and audio versions of this content below:

Why the Timing of Intervals Matters

Interval training works by alternating between efforts at specific intensities with periods of easy recovery periods. They are a great way to accumulate more time-in-zone than you could sustain in a single effort. As you can read about here in more detail, there are 5 reasons we prescribe interval training:

1. More Work in Less Time
2. Target Specific Physiological Adaptations
3. Increase Durability
4. Develop Event-Specific Fitness
5. Entertainment and Motivation

How and when you perform intervals in a workout affects how much training stress is directed toward your aerobic and anaerobic systems. When you are fresh and rested at the beginning of a workout, you’re more likely to hit high power outputs and/or sustain high power efforts for longer. There are times, however, when it may be beneficial to accumulate fatigue from riding at an easy aerobic (Zone 2) intensity for one or several hours before incorporating intervals. These two scenarios will present different challenges and produce different adaptations

The Ideal Workout Structure: Intervals First, Endurance After

The most effective structure for most interval training sessions that incorporate efforts at or above lactate threshold is:

1. Warm-up (at least 10–20 minutes)
2. Intervals (Zone 4 or higher, or even Aerobic Tempo)
3. Zone 2 aerobic riding for the duration of your ride time

Why Early Intervals Are Often More Effective

• You’re physically fresher and can hit higher power numbers or sustain target power longer. You can accumulate more total work and time-in-zone at specific intensities, which is crucial for improving FTP and VO₂ max.
• You’re mentally fresher and can focus on sustaining high-quality efforts. For road sprints, time trial efforts, or MTB efforts on technical terrain, mental freshness is crucial for engraining proper technique (so you can sustain that technique when fatigued in an event).

Even if you’re planning a 2- to 3-hour ride, placing intervals in the first third or middle of the ride, after a thorough warm-up, is optimal for Zone 4+ efforts and even for tempo or threshold (Zone 3–4).

Benefits of Adding Zone 2 Endurance After Intervals

Riding in Zone 2 after intervals creates a unique training effect:

• Interval training generates lactate, and one of desired adaptations is improving your ability to reintegrate lactate into aerobic metabolism so it can be used as fuel. Riding Zone 2 after intervals helps muscles throughout your body to process more lactate more quickly. This improves performance long-term by accelerating your recovery after hard efforts, which allows you to repeat efforts more quickly.
• Training Stress Score (TSS) combines intensity and duration to “score” how strenuous your workouts are. But not all TSS points are created equally. Points from 0-100 TSS (e.g., the first 60-90 minutes, with or without intervals) require less strain than points from 101-200 TSS. These later points may be more influential on an athlete’s durability, whereas the early points may be more influential for high-power efforts. Intervals early on ramp up your TSS quickly, enabling athletes to accumulate higher point totals during the post-interval Zone 2 riding.

One criticism of riding Zone 2 after intervals is that intervals increase reliance on carbohydrate for fuel. Lactate, for instance, is created through the rapid breakdown of carbohydrate. One goal of Zone 2 exercise is to optimize fat burning by staying below the intensity where muscles must burn more carbohydrate to meet elevated energy demand. Critics of combining intervals and Zone 2 point out that tapping into higher rates of carbohydrate metabolism may hinder the desired adaptations for greater fat burning. At CTS, our contention is that endurance athletes are already great at burning fat, that fat oxidation is happening at all training intensities, and that harder efforts (fueled by more carbohydrate) are time-efficient and necessary to creating sufficient training stimulus to improve performance (speed, power, competitive results) as well as fitness (aerobic conditioning, fat/carbohydrate oxidation rates).

When You Should Do Intervals Late in a Ride

While doing intervals early is far more common, there are times when late-ride efforts are beneficial. Here are some of the specific scenarios that may apply to your training:

1. Race-Specific Prep

If your event includes decisive moments (e.g., a long climb or sprint) late in the race, it makes sense to simulate those scenarios in training. For example, if your 2- to 3-hour road race ends with a 10-minute climb, it’s important to practice executing that effort after 2–3 hours of riding. It is important to note, you’ll gain the power for this final climb during your shorter workouts with early intervals. You’ll gain the experience, pacing expertise, and resilience for the late-race climb by doing these intervals later in a ride. The same is true for sprints at the end of a criterium or a technical climb or descent in mountain bike race.

2. Fatigue Resistance Training (Durability)

Fatigue resistance or durability is your ability to sustain your power output later during long rides and race, and/or to repeat hard efforts at high power outputs after you already have lots of hours or miles in your legs. Particularly for the latter, it’s important to incorporate max or near-max training efforts after accumulating 1,500–2,500 kilojoules of aerobic work. The goal is to reduce the gap between your fresh and fatigued max efforts.

3. Logistical Constraints (e.g., Urban Riders)

Sometimes doing intervals in the middle of a ride is just necessary. If it takes 40-60 minutes to reach a safe and suitable location for interval training, you’ll naturally do intervals mid-ride. To have a great workout, go easy on the way out so you’re fresh for the intervals and top up your energy with a carbohydrate-rich gel or sports drink before starting the interval block.

Common Interval Scheduling Mistakes to Avoid

Incorporating interval training into Zone 2 rides is very common. Most athletes complete a few Zone 2-only rides each week, and then incorporate intervals into 1-3 rides/week. Working with thousands of athletes, we see athletes make the following mistakes:

1. Always Doing Intervals Late in the Ride
   They may hit the duration of intervals, but the power output is lower than it could be because of cumulative fatigue. For short efforts, like 15-second sprints up to 10- and 15-minute threshold intervals, maximizing the target power output for the interval duration is what drives the adaptation you’re looking for.
2. Skipping Fueling Before Intervals
   Whether you do intervals at the beginning, middle, or end of a workout, high carbohydrate availability (full glycogen stores and/or sufficient carbohydrate fueling during exercise) maximizes interval workout performance.
3. Neglecting Specificity
   The timing of intervals within an endurance ride can be adjusted to optimize your preparation for specific event demands. Athletes who only structure their interval workouts one way (i.e., always first, always later in rides) miss out on the specificity that interval timing can provide.

How to Decide Where Intervals Go in Your Workout

Use this simple guide: