Intervals vs fartlek: get more from your running training

By JuanPa, creator of TrainingForever · With the experience of Marc Bañuls, coach with more than 15 years of experience

Rapid response: series are repetitions at a fixed intensity and distance or time with controlled recoveries; fartlek ("speed game") alternates pace changes continuously and more freely, often depending on the terrain. The series allows better control of intensity for specific objectives (Billat, 2001; Buchheit and Laursen, 2013) and fartlek gives variety and work of pace changes. The usual is to combine them according to the season phase.

Introduction to series and fartlek

In the world of running, the variety in training is key to improving performance and maintaining motivation. Two popular methods that runners usually integrate into their routines are series and fartlek. Both approaches offer unique benefits and can be adapted to different skill levels and objectives. In this section, we will explore in detail what series and fartlek are, as well as the history and evolution of these training methods.

Series definition

Series, also known as intervals, are a training method that involves alternating between high intensity periods and recovery periods. This type of training focuses on improving the speed and anaerobic capacity of the runner. The series usually take place on a track or on a flat terrain where distances can be measured accurately.

Series training is usually structured in repetitions of a specific distance, such as 400 meters, 800 meters or even 1 kilometer, with a set rest time between each repetition. For example, a typical series training could consist of running 5 repetitions of 800 meters at a fast pace, with 2 minutes of rest between each repetition.

Definition of fartlek

The term "fartlek" comes from Swedish and means "speed game". This training method is more flexible than series and is characterized by pace changes during a continuous race. Unlike series, fartlek does not require a rigid structure or a specific environment, making it ideal for running in different terrains and conditions.

A fartlek training can include short and fast accelerations followed by slower jogging periods, all within a single race session. The duration and intensity of each segment can be adjusted according to the sensations of the runner and the terrain. For example, a runner might decide to speed up to the maximum to reach a tree in the distance, then slow down to catch his breath, and repeat this pattern several times during his race.

History and evolution of both methods

Series training has its roots in competitive athletics, where coaches looked for ways to improve the performance of athletes in mid- and long-range races. Over the years, the series have been refined and adapted to meet the needs of runners of all levels, from beginners to elites.

On the other hand, fartlek was developed in the 1930s by Gösta Holmér, a Swedish coach looking for a more playful and less structured training method than traditional series. Holmer introduced fartlek as a way to break the monotony of training and improve both aerobic and anaerobic endurance. Since then, fartlek has been adopted by runners around the world and has become a valuable tool for improving the versatility and adaptability of the runner.

Both methods have evolved over time, incorporating advances in sport science and technology. Today, runners can use activity tracking devices to accurately measure their intervals and pace changes, thus optimizing their series and fartlek workouts.

In short, both series and fartlek are effective training methods that can help runners achieve their goals. The choice between one or the other will depend on factors such as personal goals, level of experience and individual preferences. In the following sections of the article, we will explore the specific benefits of each method and when it is more appropriate to choose over each other.

Benefits of the series

The series are an essential component in the training of many runners, from beginners to elite athletes. This training method focuses on performing high intensity repetitions followed by recovery periods, allowing runners to improve various aspects of their performance. Below, we explore in detail the highlights of the series.

Speed improvement

Series training is a powerful tool for increasing race speed. By performing repetitions at a faster rate than the usual race pace, runners train their body to adapt to higher speeds. This type of training activates fast shrinking muscle fibers, which are crucial for fast running.

Speed improvement not only translates into faster times in short distance races, but can also benefit long distance runners by allowing them to maintain a faster pace for longer.

Development of anaerobic endurance

The series are also essential for the development of anaerobic endurance. This type of endurance is the ability of the body to withstand intense stress during short periods, mainly using the anaerobic energy system. During the series, the body is forced to work under oxygen deficit conditions, which improves the ability of the muscles to function under these conditions.

Anaerobic training increases lactate tolerance, which means that runners can maintain high intensity stress for longer before muscle fatigue becomes limiting. This benefit is crucial for events that require rapid pace changes or for the final sprint in a race.

Physiological adaptations

Series training induces a series of physiological adaptations that are beneficial to the runners. Among the most significant are:

• Maximum VO2 increase: Maximum VO2 is the maximum amount of oxygen the body can use during intense exercise. The series help to improve this parameter, resulting in increased aerobic capacity and overall performance.
• Improvement of metabolic efficiency: The series increases the efficiency with which the body uses muscle glycogen and fats as sources of energy. This is especially beneficial for long distance racing, where efficient management of energy reserves is crucial.
• Strengthening the cardiovascular system: The heart and lungs are forced to work harder during the series, which improves cardiovascular capacity. This translates into a stronger heart and better blood circulation, allowing for a more efficient supply of oxygen and nutrients to the muscles.
• Increase in capillary density: High intensity training promotes the growth of new capillaries in the muscles, which improves the delivery of oxygen and the elimination of waste products.

The series not only improves physical performance, but also strengthens the runner's mentality, teaching him to handle discomfort and persevere under pressure.

In short, series are a versatile and effective training tool that offers multiple benefits to racers. From improved speed and anaerobic endurance to a series of physiological adaptations, this training method is essential for those seeking to optimize their performance in running. By properly incorporating series into a training plan, runners can experience significant improvements in their ability to compete and achieve their personal goals.

Benefits of fartlek

Fartlek, a Swedish word that means "speed game", is a training technique that combines periods of rapid race with slower race intervals. Unlike the series, which are usually more structured, fartlek is flexible and adapts to the needs and sensations of the runner. Below, we will explore in depth the benefits that this method can bring to your running training.

Variety and fun in training

One of the main attractions of fartlek is its ability to introduce variety and fun in training. Being not subject to a rigid scheme, fartlek allows runners to adjust the intensity and duration of the intervals according to their physical and mental state of the day. This flexibility not only helps to avoid boredom, but also reduces the risk of overtraining, as brokers can adapt their sessions depending on how they feel.

In addition, by incorporating changes in pace and terrain, fartlek keeps the rider mentally alert and committed, which can improve motivation in the long term. This variability can also be especially beneficial for solo training runners, as it offers them a constant and dynamic challenge.

Development of aerobic and anaerobic endurance

Fartlek is a powerful tool for improving both aerobic and anaerobic endurance. By alternating between different intensities, the body learns to adapt to rapid changes in pace, which is crucial to improve performance in long distance races.

• Aerobic endurance: During the lower intensity intervals, the body works on its aerobic capacity, using oxygen to convert carbohydrates and fats into energy. This improves the efficiency of the cardiovascular system and increases the overall endurance capacity.
• Anaerobic endurance: High intensity intervals, on the other hand, train the anaerobic system, which is responsible for providing energy in the absence of oxygen. This is especially useful for improving sprint capacity and speed in short sections.

Adaptation to different terrains

Another significant advantage of fartlek is its ability to adapt to different terrains. Unlike series, which are often performed on flat tracks or surfaces, fartlek can be carried out in a variety of environments, from dirt roads to mountain trails. This adaptability not only makes training more interesting, but also prepares the rider for the unpredictable conditions that can be found in races.

• Variety land: Running on different surfaces and slopes forces the body to work differently, which can improve muscle strength and stability. For example, running uphill strengthens the muscles of the legs and improves cardiovascular ability, while running downhill can help improve technique and speed.
• Climatic conditions: The fartlek also allows the runners to adapt to different climatic conditions. Training in different conditions can increase mental and physical resilience, preparing the rider for any eventuality during a competition.

When to choose series

Choosing between series and fartlek in your running training can be a crucial decision to achieve your personal and competitive goals. Series are an essential component in the training of many racers, especially those who seek to improve their performance in specific races. Next, we will explore in detail when it is more appropriate to opt for the series, considering factors such as competition goals, preparation for specific races and improvement of personal times.

Competition objectives

The series are particularly beneficial for runners who have clear and defined competition objectives. This type of training focuses on improving speed and anaerobic capacity, which is crucial to perform to the maximum in short and medium distance races. If your goal is to compete in events like the 5K, 10K or even half marathon, the series can help you develop the speed and power needed to maintain a competitive pace.

Preparation for specific races

Preparation for specific races is another scenario in which series can be extremely useful. When you are preparing for a particular race, the series allow you to simulate the conditions of the competition, adjusting the distance and pace of repetitions to match the demands of the race. This not only improves your physical condition, but also helps you develop a mental strategy for race day.

For example, if you're training for a 10K, you could include 1,000 metre series at a slightly faster pace than your target race pace. This will help you get used to the intensity of the race and manage the effort needed to maintain that pace throughout the distance.

Improvement of personal time

For many runners, improving their personal times is a constant motivation. The series are an effective tool to achieve this goal, as they allow you to work on speed and race efficiency. By performing series on a regular basis, you can identify your strengths and weaknesses, and adjust your training accordingly to maximize your improvements.

A common approach is to perform a time test at a specific distance at the beginning of a training cycle, and then use series to work in areas that need improvement. For example, if you discover that your weak point is to maintain speed in the second half of a race, you could incorporate longer tempo series or intervals to improve your fatigue endurance.

In addition, the series allow you to measure your progress in a tangible way. By recording your times in each repetition, you can clearly see how your speed and endurance improve over time, which can be a great source of motivation.

In short, choosing series in your running training is a strategic decision that can help you achieve your competition goals, prepare for specific races and improve your personal times. By properly integrating series into your training plan, you can maximize your performance and enjoy the benefits of a structured, goal-oriented approach.

When to choose fartlek

Fartlek is a versatile and dynamic training technique that can be an excellent choice in various stages of your preparation as a runner. Unlike the series, which are more structured and specific, fartlek offers greater freedom and adaptability, allowing runners to adjust the intensity and duration of the intervals according to their needs and sensations of the moment. Below, we will explore in detail when it is most advantageous to incorporate fartlek into your training routine.

Initial phase training

In the initial stages of a training program, especially if you are a beginner or are returning to running after a break, fartlek can be an invaluable tool. During these stages, the main objective is usually to develop a solid basis of endurance and improve aerobic capacity without subjecting the body to excessive stress.

The fartlek allows runners to adjust intensity intuitively, which is ideal for those who do not yet have precise control over their pace. You can start with shorter intervals of greater intensity, followed by active recovery periods. This flexibility helps prevent early exhaustion and reduces the risk of injury, allowing a progressive adaptation of the body to physical exertion.

Improvement of overall endurance

Fartlek is particularly effective in improving overall endurance, as it combines aerobic and anaerobic training elements in a single session. By varying the intensity and duration of the intervals, the body is challenged in multiple ways, promoting physiological adaptations that improve both cardiovascular capacity and muscle efficiency.

This training modality is ideal for runners who seek to increase their ability to maintain a prolonged effort without falling into the monotony of the sessions of constant pace. In addition, fartlek promotes active listening to the body, allowing the effort to be adjusted according to the sensations and physical state of the day.

Active recovery

Fartlek can also be an excellent option for active recovery sessions. After intense workouts or competitions, it is crucial to allow the body to recover properly while maintaining a moderate level of physical activity. Fartlek, with its flexible and less structured approach, is perfect for this purpose.

During a recovery-oriented fartlek session, runners can opt for low intensity intervals, interspersed with gentle hikes or trots. This not only helps maintain blood circulation and eliminate accumulated lactic acid, but also contributes to mental recovery by providing a respite from structured and competitive training.

Conclusion

Choosing fartlek as part of your running training can offer multiple benefits, especially in the early stages of a program, to improve overall endurance and as an active recovery method. Its adaptable and less rigid nature makes it an attractive option for runners of all levels, allowing to customize training according to individual needs and day conditions. By integrating fartlek into your routine, you will not only improve your physical performance, but also enjoy a more varied and enriching running experience.

Good practices

Optimizing your running training, whether through series or fartlek, requires a structured and conscious approach. Below are some good practices that will help you maximize the benefits of both methods and avoid injury or overtraining.

Training planning

Planning is an essential component for any successful training program. Both series and fartlek should be strategically integrated into your weekly routine to ensure a proper balance between intensity and recovery.

1. Sets clear targets: Before you start, define what you want to achieve with your training. Are you looking to improve your speed, increase your endurance or just enjoy more of your races? Having clear goals will help you choose the right method and stay motivated.
2. Design a balanced calendar: Alternative between high intensity sessions and recovery days. For example, if you do series one day, consider doing a fartlek session or a smooth run the next day. This will allow your body to recover properly and reduce the risk of injury.
3. Incorporates variety: Although it is important to follow a plan, it is also crucial to introduce variety in your workouts. Changing distance, pace and terrain not only keeps training interesting, but also challenges your body in different ways, promoting more complete adaptations.
4. Evaluate and adjust regularly: Review your progress every few weeks. If you notice that you are not reaching your goals or that you feel constantly fatigued, you may need to adjust the intensity, volume, or frequency of your workouts.

Listen to your body

The human body is an incredibly adaptable machine, but it also has its limits. Learning to listen to your body is essential to avoid overtraining and injury.

1. Acknowledges signs of fatigue: If you feel constantly tired, irritable, or if you experience decreasing performance, these may be signs that you need more rest. Do not ignore these signs; rest is a crucial part of the training process.
2. Adapt intensity according to your physical state: Not every day is the same. If you feel particularly tired or have had a stressful week, do not hesitate to reduce the intensity of your training. It's better to have a lighter session than to risk an injury.
3. Prioritize Recovery: Make sure to include recovery techniques in your routine, such as stretching, massages, or yoga. These practices not only help prevent injuries, but also improve your overall performance.

Gradual progression

Gradual progression is key to improving performance without putting your health at risk. In both series and fartlek, it is important to increase the workload in a controlled manner.

1. Progressively increase the load: Increase the distance, intensity or frequency of your workouts gradually. It increases the load gradually; the well-known 10% rule is only indicative: in a trial with beginner runners it did not reduce injuries compared to a standard program (Buist et al., 2008).
2. Introduce changes one at a time: If you decide to increase the intensity of your series, keep the distance constant for a while. Similarly, if you are adding more kilometers to your fartlek, do not simultaneously increase speed. This allows your body to adapt to one change before introducing another.
3. Includes download weeks: Every three or four weeks, it reduces the intensity or volume of your workouts. These download weeks allow your body to recover and prepare for the next training cycle.
4. Listen to the experts: If you have the opportunity, consult with a coach or sports physiotherapist. They can offer you personalized tips and help you design a program that suits your needs and capabilities.

Common errors

In the world of running, both series and fartlek are highly effective training methods to improve performance. However, as with any training strategy, it is easy to make mistakes that can hinder progress or even lead to injuries. Below, we explore some of the most common mistakes runners usually make by incorporating series and fartlek into their routines.

Training overload

One of the most frequent errors among runners, especially those who are new in structured training, is training overload. This error occurs when the intensity or volume of training is increased too quickly, without allowing the body to adapt properly.

Overloading can lead to a number of problems, from chronic fatigue to overuse injuries, such as plantar fasciitis or stress fractures. To avoid these problems, it is crucial to follow a training plan that includes days of rest and active recovery. Also, it's important to listen to your body and adjust your workout if you feel excessive pain or fatigue.

Lack of variety

Another common mistake is the lack of variety in training. Some runners tend to focus exclusively on one type of training, either series or fartlek, without incorporating other methods. This can lead to stagnation in performance and less motivation.

The variety in training not only maintains interest and motivation, but also ensures a balanced development of different physical abilities. For example, while the series are excellent for improving speed and anaerobic endurance, fartlek offers benefits in aerobic endurance and adaptation to different terrains.

Do not adjust the intensity

The third common error is not to adjust the intensity of training according to individual needs and day conditions. Both series and fartlek require careful control of intensity to be effective and safe.

It is important to remember that the appropriate intensity can vary from day to day, depending on factors such as fatigue level, climate and terrain. Failure to adjust intensity can result in excessive effort, increasing the risk of injury and overtraining.

To effectively adjust intensity, consider using tools such as heart rate monitor or stress perception. These tools can help you maintain the intensity in the desired range, ensuring that each training session fulfills its purpose without compromising health.

In short, avoiding these common mistakes requires a conscious and planned approach to training. By doing so, you will not only improve your performance, but also enjoy a safer and more satisfying running experience.

Series or fartlek: comparative table

In one study, high-intensity interval exercise was perceived as more pleasant than moderate continuous exercise (Bartlett et al., 2011), something useful to maintain adherence.

"Fartlek is my way of teaching the runner to change pace without looking at the clock. The series I use when I need you to key a concrete pace." — Marc Bañuls, coach with more than 15 years of experience

Frequently Asked Questions

What's better, series or fartlek?

None is better in general: series control intensity for specific objectives and fartlek gives variety and pace changes. They combine according to the phase.

How many times a week do series?

It depends on the level and plan; it is usually one or two quality sessions per week, with the rest of mild days.

Does fartlek work for beginners?

Yes, it is a simple way to introduce changes of pace in a progressive and flexible way.

Can I combine series and fartlek in the same week?

Yes, it is possible and, in fact, it can be very beneficial to combine series and fartlek in the same week of training. The key is to plan properly to maximize the benefits of each method without falling into overtraining.

The series are structured workouts that focus on improving speed and anaerobic endurance through high intensity intervals followed by rest periods. On the other hand, fartlek is a more flexible training that allows you to play with the intensities and adapt to different terrains, which helps to improve both aerobic and anaerobic endurance.

• Monday: Rest or smooth run.
• Tuesday: Series (e.g. 5x800 meters at race rate with 2 minutes of rest between series).
• Wednesday: Race of recovery or active rest.
• Thursday: Fartlek (for example, 45 minutes alternating between 1 minute fast and 2 minutes soft).
• Friday: Rest or cross training.
• Saturday: Long run at steady pace.
• Sunday: Rest or light activity.

Which is best for beginners?

For beginners, fartlek is usually a better initial choice. This training method is less structured and allows runners to adjust the intensity according to their physical fitness level and how they feel on a given day. Fartlek introduces runners into the concept of varying speed and effort without the pressure to comply with strict intervals.

• Flexibility: It doesn't require a clue or a precise stopwatch. It can be done anywhere and adapted to the terrain.
• Less pressure: It allows runners to adjust the pace according to their comfort level, which reduces the risk of injuries and overload.
• Fun: The variety of paces and terrain can make training more entertaining, keeping motivation high.

How to adapt training to my needs?

Adapting training to your specific needs is crucial to maximize benefits and minimize the risk of injury. Here are some steps to customize your training plan:

1. Evaluate your goals: Define clearly what you want to achieve with your training. Are you training for a specific race? Do you want to improve your personal time? Are you looking to increase your overall endurance?
2. Know your level of fitness: Perform an honest assessment of your current physical condition. This will help you determine the correct training intensity and volume.
3. Plan the progression: Gradually increase the intensity and volume of your workouts. It increases the load gradually; the well-known 10% rule is only indicative: in a trial with beginner runners it did not reduce injuries compared to a standard program (Buist et al., 2008).
4. Listen to your body: Pay attention to signs of fatigue and pain. If you feel persistent discomfort, consider adjusting your plan to include more days off or reduce intensity.
5. Diversify training: It incorporates a variety of training methods, such as series, fartlek, long runs and cross training, to work out different aspects of your physical condition.
6. Consult a professional: If you have doubts about how to structure your training plan, consider consulting a running coach or sports physiotherapist.

By following these steps, you can create a training plan that suits your specific needs and helps you achieve your goals safely and effectively.

Read also

• Training for 5K and 10K
• VAM: what is and how to calculate it
• Stagnation in training
• Heart rate zones

Sources

1. Billat LV. Interval training for performance: a scientific and empirical practice. Part I. Sports Med. 2001;31(1):13-31.
2. Buchheit M, Laursen PB. High-intensity interval training, solutions to the programming puzzle. Part I. Sports Med. 2013;43(5):313-38.
3. Bartlett JD, et al. High-intensity interval running is perceived to be more enjoyable than moderate-intensity continuous exercise. J Sports Sci. 2011;29(6):547-53.
4. Buist I, et al. No effect of a appreciated training program on the number of running-related injuries in novice runners: a randomized controlled trial. Am J Sports Med. 2008;36(1):33-9.