Interval Training Overview

As nordic skiers, the vast majority (80-85%) of our training is done in low intensity zones. Zone 1 (1-1.5 mmol/L or 55-70% of Max HR) increases aerobic capacity and builds endurance, providing a critical fitness base for high-intensity training and racing. The other 15-20% of training is high-intensity in Zones 3 and above. Effective endurance training is a lot of easy aerobic base training and strategic high-intensity training. Note that this equation does not include much medium-intensity training, or Zone 2 (70-80 % of HR?) That is because training in this zone is a ‘no mans land’ where an athlete is training too hard to receive the benefits of low-intensity training (higher fatigue), and too easy to make the adaptations earned from high-intensity training. There are some benefits to this zone, such as increasing aerobic efficiency, but generally, we try not to spend too much time in this zone.

(Read this article for more on Training Zones).

For elite athletes, who train hundreds of hours year round, staying in your zones is important in order to maximize the benefits of a high training volume. For the more recreational skier who is just trying to improve their overall fitness, strict adherence to heart rate zones or lactate thresholds is less critical. Most people are somewhere in between recreational and elite, but the general rule for all remains the same: go EASY on the EASY days, HARD on the HARD days, and minimize the time spent awkwardly in between.

Because of the high physiological demand of intensity training, it is worth understanding the different types of intervals and why we do them so that we are getting the most out of each session. Starting with the obvious - we do intervals to get faster at skiing. You have to train fast to ski fast. We do intervals at different lengths and intensities to improve specific areas of fitness, but there are other benefits to interval training beyond the physical.

Improve Fitness

There are three basic categories of intensity training, Aerobic/Threshold (L3), Anaerobic/VO2 Max (L4), and Speed (L5) and each has a specific intention.

Aerobic Base Fitness (L3 ) These are the bread and butter intervals for endurance training, and the majority of interval training in done in this zone. These intervals are primarily done to increase endurance, stamina, and efficiency (higher lactate threshold) through sustained medium intensity efforts. Intervals range from 5 - 30 minutes in length, with the most common intervals being 8-15 minutes. Elite athletes will complete around 40-60+ minutes of “on-time” during a single session, while juniors or masters might be closer to 30-50 minutes total. The goal of aerobic interval training is not to go all out, but rather to purposefully stay in or slightly below your lactate threshold. L3 intervals are NOT a competition, and you will see better results by keeping them controlled.

Zone 3 Lactate: 2-4 mmol/L

% of Max HR: 80-90 %

Aerobic Intervals Examples:

6x6 minutes, 2 minutes recovery

5-8 x 8 minutes, 2-3 min recovery

3-6 x 10 minutes 3 min recovery

3-4 x 15 minutes recovery

This great chart is from Nordic Labs: 

Anaerobic and Vo2 Max Intervals (L4,L4+) Anaerobic intervals are much harder on the body than aerobic intervals, and therefore we don’t do them as often within a training plan. These intervals range anywhere from 90 seconds to 6 minutes and are shorter because we can’t maintain true anaerobic threshold for much longer than that without the quality or efficacy diminishing severely. Anaerobic (L4+) intervals increase muscular endurance, power application, oxygen uptake efficiency, and Vo2 Max. Typically, we start to add in shorter and harder intensity towards the end of the summer as we start to get closer to the start of the race season.

Zone 4 Lactate Range: 4 mmol/L - 15mmoL/L +

% of Max HR: 90-100 %

Workout Examples:

4-6x 4 min, 2 min recovery

2 x (5 x 90 seconds), 2 minutes rest between intervals, 10 minutes rest between sets.

L4 Ladder (1, 2, 4, 6, 4, 2,1) w. 1-2 min recovery

Speeds (L5+) Speeds are important for races of all distances and all skiers benefit from adding them to a training regimine. Speeds are important primarily for developing fast-twitch muscle fibers while simultaneously increasing the ability of your muscles to tolerate lactic acid. Speed workouts are also highly beneficial for enhancing neuromuscular coordination, mental focus, and agility. A standard speed workout is usuallythree speed stations [e.g. gradual uphill, gradual downhill, flat] with 5x20-30 second speeds at each station. Do all 5 speeds before moving on to the next station. Speeds can also be integrated into other intensity workouts to simulate surges during races.

Besides gains in our overall fitness, there are other physiological and mental reasons that we do intervals.

Technique at Speed

Another purpose of intervals is to practice strong and efficient technique at race speed. While the technique fundamentals remain the same, efficient glide and proper timing will feel different at L1 pace than it will at a sprint pace or a 10k pace. We need to practice skiing in every gear so that we learn how to apply power at different tempos, with the lowest energy cost.

Here are some workouts to practice

1. 6x6 min with the first 3-4 intervals normal L3, and the last 2-3 intervals on gradual downhill terrain. What is the purpose of this? Downhill intervals force us to ski in a more forward position, and maximize the glide on each ski and get comfortable skiing at speed for sustained periods of time.

1. L3 with fast finishes: 3-6 x 6 minutes @ L3 pace, with the last 30 seconds at your finishing sprint speed (or just below). This will help you practice skiing fast at the end of a hard aerobic effort.

1. Mid-interval surges: Similar to #2, during a L3/Threshold interval, add in 1-2 20 second speed surges. I recommend doing these during terrain changes to practice transitioning from one technique to another, pushing over the tops of hills into a downhill, etc.. which mimics how you would ski in a race.

Muscular Endurance:

Heart rate isn’t the only way to measure the effectiveness of an interval session, and different techniques will produce different heart rate zones.Other factors such as altitude and even hydration can play a role. For example, double pole intervals tend to produce a lower heart rate overall than running or striding. However, the muscular endurance demands of a double pole workout will likely be higher. It is entirely possible for your heart rate to be in your target intensity zone AND have a higher muscular load, but they don’t alway match, and that’s ok.

Similarly, as you increase the volume of your L3 training (in mid-late summer, elite athletes will often complete 50-75 minutes of ‘on-time’), the muscular load also increases. This is why skiers emphasize strength training, so that not only can we apply power in shorter races, but also so that we are able to maintain good technique even as we start to fatigue at the end of a long race or workout.

Mental Toughness

Lastly, intervals are the way we practice mental toughness and race day mental preparation. Every interval session should be hard, but not all of them will be as mentally taxing as others. For example, a controlled L3 session will probably be less difficult overall than a time trial or a hard L4 session that is meant to push your aerobic and muscular systems to the limit. That being said, there will always be intervals of every modality that just feel way harder than they should. You might be tired, sore, the conditions are bad, or you are not in the mood etc.. but you still need to go out there and do the work because you have a goal and you won’t reach it by backing off when things aren’t going well.

I call these days mental toughness days because they present you with a choice; you can either succumb to whatever it is that is making it hard for you to be mental and physically engaged in the workout, OR you can choose to view the workout as an opportunity to practice some of the mental strategies and tools to push through and complete a high quality workout. This is a quote from Rick Kapala that I think perfectly captures this approach: "You are as tough as you decide to be and being tough is a learned behavior. When you get out and do a challenging workout in tough conditions – the day is doubly successful."

When it gets hard is when the biggest mental gains are made. We don’t learn or grow by staying in our comfort zone and, at the end of the day, our mindset is the biggest barrier to reaching our full potential.

Obviously if you are sick, injured or mentally burned out, forcing mental toughness is not the move, and generally you know when it's time to take a break. Race day will not always be bluebird hard track skiing, so we need to practice pushing ourselves in all kinds of conditions. We race how we practice so we should practice how we want to race.

All of these ‘whys’ of interval training often occur simultaneously in a workout, and if you have been training for a while, the intent of each is natural or is assumed. Nevertheless, it is important to remind ourselves of the purpose of interval training, and continue to look for ways that we can extract more benefits, mental and physiological, from each workout.