Endurance Training: Intervals, Altitude and Circuits

Endurance training can use intervals, altitude exposure and circuits, with different demands and tradeoffs. There is no single best approach for every sport or athlete. Training history, recovery and the task matter when comparing benefits, fatigue and performance.

How does endurance support different sports?

Endurance is one of the vital components of athletic performance. Whether an athlete wishes to run a marathon, become a world-class 400-meter dash runner or engage in team activities, endurance is an important part of training.

The possibilities of improving an athlete’s endurance are wide ranging, and there are many training methods available to help maximize endurance performance.

We will compare and contrast which approach to endurance training can support an athlete’s performance in their sport.

What changes with endurance training?

We first need to understand what endurance training can do at the cellular level.

Endurance training can improve muscle oxidative capacity, including the function of Type-I fibers (Slow Twitch). This does not mean the number of those fibers always increases.

These fibers help sustain longer, lower-intensity efforts, such as a marathon.

Morici and colleagues’ 2016 review, hosted by the National Library of Medicine, states “A recent meta-­analysis including studies on the effects of running in sedentary healthy adults confirmed that BMI, body fat, resting heart rate and triglycerides decreased, while maximal oxygen uptake and high-density lipoprotein cholesterol increased, especially when regular training was prolonged over time.”

Attending to all the benefits derived from endurance training are important for athletes actively competing in high endurance sports.

Regular training helps maximize performance and resist phasing out during long periods of physical activity.

How does interval training work?

One of the most popular forms of endurance training is High Intensity Interval Training (HIIT).

Fitness examples include Orangetheory Fitness, F45 and Row House; the intensity and recovery used in classes can vary.

Interval training alternates harder work with easier activity or rest. HIIT uses high-intensity efforts, which need not all be maximal sprints.

An example would be doing a full sprint for 30 seconds and then walking briskly for a minute.

According to Nike “This type of interval workout strengthens your heart and lungs to handle the demands of longer races. Training at a high intensity will also help your muscles better handle lactic acid, a chemical byproduct of anaerobic respiration.” Nike’s explanation uses a simplified lactate model. Lactate alone is not a complete explanation of fatigue or burning; acidity and other factors also matter.

One factor that attracts many athletes to HIIT is that it can effectively and quickly boost cardiovascular fitness by working harder (Intensity) instead of longer (Duration).

The cited 2021 Harvard article discusses small, short-term studies with possible blood-pressure and blood-sugar benefits. It also cautions that varied protocols and participants make generalization difficult.

A 1-hour HIIT session is not automatically equivalent to a 3-hour run for VO2 max, resting heart rate or sport preparation. Outcomes depend on the program and athlete.

Although HIIT has its benefits it also needs to be approached with caution.

According to the fitness blog, Physiomove London, “Because the goal of HIIT is to push the body to its physical limits, there is often little or no consideration for form and technique and, as a result, you can often perform exercises incorrectly in a way that your body may not be able to cope with. The result of this can be misalignment of the joints, leading to excess pressure and strain on the wrong parts of the body, causing injuries.”

This is a warning about poor practice, not a requirement of HIIT: intervals do not require abandoning form and technique.

What can altitude training change?

Some athletes will go to environmental extremes to help improve their endurance.

Colorado is one setting used for altitude training, but suitability depends on the athlete and training context.

Due to the decrease in pressure at higher altitudes, less oxygen is available to the lungs.

Altitude training can improve some endurance outcomes, but adaptations and performance benefits vary.

There are three ways to approach high altitude training.

The first is Train High, Compete High.

Athletes will spend time living and training at the same elevation at their competitions location in order to adapt.

The next approach is to Train High, Compete Low.

Athletes train at high altitudes when a competition is set to take place at sea level.

Additionally, athletes may train at high altitudes during the off season to improve endurance for the upcoming season.

The final approach is Live High, Train Low.

The approach includes research by Levine and Stray-Gundersen published in 1997.

The cited Polar article illustrates living and light training above 8,000ft and harder training below 4,000ft; these are examples, not universal cutoffs for every athlete.

According to Bronwyn Griffiths, “Along with improving oxygen flow, high-altitude training can also boost your VO2max. Measuring your oxygen intake during intense exercise, a higher result of this metric indicates a better capacity for endurance. Your tolerance to lactic acid, which contributes to muscle fatigue, also improves, meaning you can go longer without tiring.” This is Griffiths’s published explanation, not a guarantee. Lactate is not simply a waste product that directly causes all fatigue, and altitude responses vary.

These great benefits also include some disadvantages “It’s hard to judge your rate of perceived exertion at a new elevation. Difficulty breathing, tired muscles, and decreased speed don’t signify it’s time to stop at a higher altitude, so while you may stop sooner, you could also easily overtrain if you keep pushing yourself.”

The quoted warning is not permission to ignore worsening symptoms. CDC guidance treats altitude illness as a health issue, rather than something to push through for performance.

Overtraining is a serious problem for many athletes.

It can stop many athletes from competing and slow down the recovery time after exercise.

An example of the advantages of high-altitude training may be seen with the Denver Broncos.

When watching a Broncos game, the opposing team will often be seen wearing oxygen masks while on the sideline.

Altitude can affect visiting athletes, but sideline oxygen-mask use alone does not establish why a team tires or prove a home-team advantage.

How can circuits support endurance?

A common misconception of endurance training is that it is one dimensional.

When someone mentions endurance training, thoughts of running on a treadmill or doing endless laps in the pool may come to mind.

Circuit training offers another approach for endurance athletes.

Circuit training involves workouts that involve rotating through various exercises that target different parts of the body.

In a repetition circuit, each set is completed for a chosen number of repetitions.

The athlete then moves to another activity, with repetitions and rest planned for that circuit.

The sequence of exercises forms a circuit; rest can vary with its purpose.

Because movement through the circuit of exercises occurs relatively quickly, a circuit session may fit into 30–45 minutes, although duration depends on the plan.

The time efficiency of circuit training attracts many endurance athletes.

Which circuit formats are discussed?

Four circuit formats discussed here are repetition, timed, competition and sport-specific circuits.

Repetition circuit has an exercise performed for a prescribed number of repetitions and then moved to the next exercise.

In timed circuit training, an exercise is performed for a prescribed duration before moving on.

Competition circuit is similar to a timed circuit, but the athlete does as many repetitions as possible in that time.

Sport-specific circuit training is meant to improve movements involved in a specific sport, such as practicing jumps, kicks, turns, and tumbling skills for gymnastics.

Kristen Gasnick describes circuit training’s cardiovascular demands: “With little to no rest between exercises, circuit training helps to improve heart health by enhancing your endurance as your heart has to pump harder to supply your muscles with oxygen-rich blood.”

Time efficiency and variety of these workouts has intrigued athletes and has become a popular way to train for endurance.

Poorly managed circuit training can strain joints and muscles when technique breaks down or recovery is inadequate.

A circuit need not use full effort with minimal rest in every exercise.

How can athletes compare training approaches?

Choosing an endurance approach depends on the sport, athlete, recovery and preferences, rather than personal preference alone.

Every human, athlete, or casual gym goer will react and adapt differently to endurance exercise.

It is important to realize that it can take several months and even years for athletes to find the proper training regimen.

Even then, it could change as more research reveals new exercises to be offered to athletes.

The endurance exercises discussed are just some of the more popular.

Athletes may avoid HIIT, Circuit, and high-altitude training in favor of some other option.

Regardless of what they are training for, endurance exercises cross a wide range of sports.

Athletes in football, basketball and soccer, as well as world-class marathon runners and cyclists, understand the importance of endurance training.

They know how it can improve heart health as well as maximize their overall athletic performance.

Even in sports that do not require a lot of cardiovascular output, endurance training remains a key component of a comprehensive athletic training regimen.

References:

Morici, G., Gruttad’Auria, C. I., Baiamonte, P., Mazzuca, E., Castrogiovanni, A., & Bonsignore, M. R. (2016, June). Endurance training: Is it bad for you? Breathe (Sheffield, England). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4933620/#C11 https://doi.org/10.1183/20734735.007016

How to increase stamina and endurance for running. Nike.com. (2021, December 3). https://www.nike.com/a/increase-stamina-endurance-for-running#

Corliss, J. (2021, December 1). High-intensity exercise and your heart. Harvard Health. https://www.health.harvard.edu/exercise-and-fitness/high-intensity-exercise-and-your-heart

Corliss, J. (2021, December 1). High-intensity exercise and your heart. Harvard Health. https://www.health.harvard.edu/exercise-and-fitness/high-intensity-exercise-and-your-heart

HIIT: Possible negative effects on body. Physiomove London. (2023, May 26). https://physiomove.com/2021/07/19/does-hiit-training-cause-more-harm-than-good/

Kristen Gasnick, P. (2023, September 10). Circuit training: Purpose, benefits, and how to get started. Verywell Health. https://www.verywellhealth.com/what-is-circuit-training-5224393

Dreckett, D. (2022, February 1). Here are some advantages and disadvantages of circuit training. We R Sports. https://wersports.com/blogs/sports-health/here-are-some-advantages-and-disadvantages-of-circuit-training

Griffiths, B. (2023, March 28; updated April 17). Why Training With Altitude Can Give You the Competitive Edge. Polar Blog. https://www.polar.com/blog/high-altitude-training/

Girard, O., Levine, B. D., Chapman, R. F., & Wilber, R. (2023). Living High-Training Low for Olympic Medal Performance: What Have We Learned 25 Years After Implementation? International Journal of Sports Physiology and Performance, 18(6), 563–572. https://doi.org/10.1123/ijspp.2022-0501

Lactic acidosis: implications for human exercise performance. (2025). Review indexed in PubMed. https://pubmed.ncbi.nlm.nih.gov/40088272/

Hackett, P. H., & Shlim, D. R. (2025, April 23). High-Altitude Travel and Altitude Illness. CDC Yellow Book, 2026 edition. https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/high-altitude-travel-and-altitude-illness.html

“Regular training helps maximize performance and resist phasing out during long periods of physical activity.”

“In a repetition circuit, each set is completed for a chosen number of repetitions.”

“Although HIIT has its benefits it also needs to be approached with caution.”