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Interval Training Explained: Training For Adventure

Boost your overall endurance in less time. Intervals for all outdoor athletes.
Interval Training For The Outdoors

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One of the best ways to improve overall endurance and athletic performance is by incorporating interval training into your workout program. 

Whether you are looking at climbing training programs, you are training for your next PCT through-hike, or maybe your first marathon, interval training is an easy and fun way to quickly improve your endurance and increase your lactate threshold (more on this later).

As we discuss further down, there are 3 main types of interval workouts; Interval or HIIT, Tempo, and Fartleks (yep that’s a real word). 

In this article ‘interval’ will be used as the generic term for all 3 types of workouts. 

A lot of advice you will read about interval training suggests the use of fancy devices like heart rate monitors or training masks, but you don’t need that stuff to realize the benefits.

Interval helps your body become more efficient but it also helps your mind get more in tune with your body.

Through consistent interval training, you will be able to identify when you are in the optimal zone through your breathing and effort.

Read on to learn more and find your new best performance level.

What Is Interval Training?

Interval training consists of alternating short high-intensity bursts of effort followed by slower-paced recovery phases. Essentially, you are working out in short intervals. 

One interval is followed by the other—high intensity followed by low intensity. This cycle repeats throughout the workout. 

The actual intensity of the high-intensity phase varies depending on your goals or plan. Following, the low-intensity phase is done at an easy to an extremely low level of effort. 

For example, an interval workout for long-distance runners might look like this: 

  • Warm-up
  • 2 minutes sprint – 3 minutes recover x 5 sets
  • 3 minutes sprint – 2 minutes recover x 3 sets
  • Cool down

Note: In this type of work out your ‘sprint’ would be whatever is the best pace you can maintain consistently for that 2 or 3 minutes. Your ‘recover’ periods are at an extremely–almost painstakingly slow pace. 

A different style, maybe for a mountaineer, might be done on an incline or hill and look like this: 

  • Warm-up
  • 5-10 minutes on – 5 minutes off x 10 sets 
  • Cooldown

Note: In this workout, hikers would maintain a pace for 5-10 minutes that is near their max but not quite. The ‘off’ periods would consist of continual hiking at a slow to moderate pace or a walk back down the hill. 

Specific interval workouts might be different, but the goal is always the same; increasing V02 Max and the Lactic Acid Threshold.

How Does Interval Training Work? 

Interval Training For Trail Running

Our bodies generate energy in two ways, aerobically and anaerobically. 

Aerobic means ‘with oxygen’ and refers to the absorption and transportation of oxygen to make energy. 

Anaerobic means ‘without oxygen’ and implies an effort where oxygen is not available or utilized for energy. 

Our bodies prefer to make energy with oxygen rather than without. However, aerobic energy production is not as fast as anaerobic production. 

When we push ourselves hard to the summit, in an interval workout, or a HIIT circuit, our muscles’ demand for energy outweighs our body’s ability to provide it aerobically. 

At this point, you start producing energy anaerobically through something called glycolysis. This is the process by which your body takes sugar (glucose) and turns it into usable energy for your muscles. 

In the presence of plenty of oxygen, glycolysis proceeds without a hitch. 

But when you don’t have enough oxygen, like when you are huffing and puffing through the crux of your project or you have been doing 8-count burpees for 3 minutes, glycolysis leads to lactate production. 

Lactic Acid 

Lactic Acid also referred to simply as Lactate, is important in the process allowing your body to create energy in the absence of oxygen. 

However, this process is only temporary. Lactate was designed to help us with fight or flight. Running from lions and tigers and bears oh my only lasts a few minutes; either you getaway or you get eaten. 

Lactate is the substance that allows your body to access quick energy when your muscles need it most. After a few minutes, though, lactate starts to build up in a process of self-regulation. 

Too much lactate cause acidity which is bad for your muscles. Higher acidity makes your muscles less efficient. This is the point where your muscles start burning and begin to feel like weights pulling you down. 

This causes you to slow down which in turn allows oxygen to return to the muscles so they can recover. 

Lactate Threshold

That tipping point where built-up lactate outweighs energy production is something called the ‘Lactate Threshold.’ During exercise, when lactate builds faster than it can be removed, you have reached your ‘lactate threshold.’ 

The most significant benefit of interval training is the ability to move this threshold further and further up. 

Take a look at this video from GU labs to learn just out lactate threshold is calculated in the lab and why it matters for you.

When you have a higher lactate threshold your body is more efficient at utilizing or getting rid of lactate. 

Remember, lactate is only made in anaerobic settings when you are pushing yourself to your max. So as your lactate threshold increases you will be able to maintain higher intensity exercise for longer periods of time. 

This is the beauty of interval training; by pushing yourself in short intense spurts of effort you can dramatically improve your ability to maintain muscular intensity for sustained long periods of time. 

How Does This Translate To Outdoors Activities? 

Say you want to through-hike the PCT in 2 months. Well, you are going to have to move fast. To maintain that level of intensity over time your body will need to be efficient at utilizing and moving lactate so your muscles don’t burn out. 

The people who set speed records have incredible lactate thresholds. They are able to maintain super-high levels of intensity without tipping over the lactate threshold. 

Looking to send your 40-meter overhanging project? You could read inspirational quotes all day long but improving your lactate threshold will help you stay strong longer so you can pull hard through the anchors instead of burning out mid crux. 


Before we move on to the list of benefits of interval training and look at some different types of interval workouts, there is one more important thing to mention; V02 max. 

V02 max is a measurement of the maximum amount of oxygen a person can utilize to produce energy during exercise before tipping into aerobic energy production. 

Put another way, V02 max measures how fit you are internally. This measurement doesn’t care how big your biceps are or what your abs look like. 

V02 max is a measurement of your heart’s ability to move oxygen around your body when you need it. Importantly, it is also a measure of your body’s ability to utilize the oxygen your heart feeds it.  

The higher your V02 max, the harder and faster you can push yourself during exercise before fatigue sets in. 

How It Is Measured

V02 max is calculated as milliliters of oxygen used per minute per kilogram of body weight. 

Calculations also take into account age and gender. There are a number of different methods of V02 calculation. One of the most accepted calculations is the FirstBeat method. ——links——

As an example, a good V02 max for a 30-year-old male would be 45 while an incredible max would be above 60. 

For a 30-year-old female good would be a V02 max of 35 and amazing would be a score above 50. 

This video from The Running Channel adds some key points about V02 max. Stay tuned to the end to get some great interval workout suggestions.

Interval Training Benefits

Now we know how it works and a bit about the benefits. But let’s take a deeper look at what interval training can do for you. 

Interval training has been the subject of clinical tests for a long time. The results are almost unanimous. Interval training or high-intensity interval training (HIIT) burns more calories and has a greater effect of lactate threshold and V02 max than continuous-intensity exercise. But that’s not all! 

Top Benefits Of Interval Training:

Types Of Interval Training

As we mentioned earlier, there are a few different types of interval workouts. The 3 interval workouts you will hear about most often are Tempo workouts, Fartleks, and Interval or High-Intensity Interval Workouts (HIIT). 

All three types of interval training, regardless of your level, ultimately provide the same physiological benefits; improved exercise capacity. 

HIIT or Interval

HIIT or Interval workouts tend to be the most structured of the three.

You will do high-intensity work for an exact period of time then rest for an exact period of time. This will be done for a specific number of sets. 

While interval or HIIT workouts are great for running, this is often the type of workout you might do in a boot camp or stationary-bicycle class. 

HIIT workouts are also highly adaptable to gym climbing or training for bouldering. 


During a tempo workout, you will keep a fast pace (but not near or above you max) for a longer period of time. 

Tempo training was popularized by the famous Olympic coach, Jack Daniels (not the whiskey), in his 1998 book entitled Daniels Running Formula.

According to Daniels, a Tempo run is a pace about 30 seconds slower than you average 5K pace. 

If you don’t know your 5K pace or you are not using this for running, there is an easier way to remember. 

A tempo interval is performed at a pace you can hold steadily somewhere very close to your all-out pace for at least 20 minutes. 


By far the best name for a training style, Fartleks are also fun to do. 

Fartlek is a Swedish word meaning ‘speed play.’ 

Unlike the other types of interval workouts listed above, Fartleks are unstructured and alternate between hard and moderate efforts.

During a fartlek run you might decide to go all out until the top of the hill, do a 2-minute recovery, then hit 3 minutes at your max pace. Keep doing this for a defined amount of time. 

The goal of a fartlek run is to constantly push yourself in different ways. 

For example: When I used to train for ultra-marathons I would train with a buddy on fire-access roads in the foothills. 

On our fartlek runs, after a warm-up, we would say ‘ok, 5 sets of 3 minutes on—2 minutes off.’ We would take off and run that phase then recover for 5-10 minutes with super-duper slow jogging. 

Then we would say, ‘ok, race you for 1 minute for 3 sets.’ We would do that then recover. 

Next, it might be 15 minutes at a tempo pace. Then an all-out push to the next hill top. Then another race. 

Point is, we interspersed different durations and intensities of high-intensity work throughout the run. This not only makes your training more fun but also helps your body, and most importantly your mind, adapt to different types of stress. 

That’s a fartlek. Bet you didn’t think you’d learn that word today?

Fartleks For Climbing

The point of this article is not only to explain what fartleks and interval training are but to show how they can apply to adventure sports. 

You can use fartleks to improve your endurance in rock climbing, paddling, surfing, hiking, mountain biking, and more. 

Heres an example of a fartlek workout for rock climbing endurance training that I used to train for long linkup days: 

  1. After warming up find a nice long route that is a few full grades below your onsight max. In the gym or at a stacked crag you might be able to find a few routes you could do off one anchor; even better. 
  2. Set a timer and climb as hard as you can for 5-10 minutes. 
  3. Rest 3-5 minutes then repeat. 

Ensure the route you choose is challenging but not too challenging. You want to be able to flow up but still break a sweat. 

If you are interval training on a hangboard, ensure proper warm up to avoid injury.

After your first interval, if it feels too easy, increase by a letter grade or two (i.e. 5.10a to 10b or c). 

To add more bang for your buck climb the last two minutes of the interval on a harder route than you did in the first 3-8 minutes. 

The more burn you can get and keep pushing the better results you will experience over time. 

Need some motivation? Watch hard-man Adam Ondra interval training on the boulder wall. You don’t have to wear a weight vest like him, but he is basically doing a HIIT workout. :


Training For Hiking

Interval training can be a great tool to help you get in shape for hiking.

Because intervals can be done just about anywhere, you can train for your summer hikes while at the gym during the winter. 

To train for hiking in the gym, simply hop on the treadmill, increase the incline and pump out some intervals just like the ones outlined above for running and climbing. 

Want to take your training to the next level? Cruise the treadmill with a loaded pack on. 

A winter of steep incline fartleks on the treadmill while carrying a pack will help condition your large muscles to perform better when fatigued. 

Come summer, when you’re switchbacking up the Whitney trail with a 50-pound pack passing other hikers sprawled out in the shade, your legs will thank you. 


Sometimes training is hard. It can be challenging to stay motivated, but it can also be difficult to see the big results we all aim for. 

Mix things up with interval training and you are sure to find more motivation and certain to start seeing dramatic results. 

Fartlek, a type of unstructured interval, literally means ‘speed play.’

Why not turn your workout into fun? Play with different durations and intensities of interval training to realize their full potential. 

Personally, interval training is my go-to for every type of sport. Intervals aren’t always easy (I might be a bit of masochist when it comes to training) but if you make them a regular part of your routine you will see incredible results. Period. 

Get out into your own personal crux range and go beyond the crux! 

What is your favorite interval workout? 

Have any tips or tricks to share? 

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