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Anaerobic Speed Reserve (ASR): A Smart Way to Prescribe HIIT

Updated: Aug 26

When it comes to prescribing high-intensity interval training (HIIT), one of the biggest challenges coaches face is how to individualize intensity. Two athletes may run the same interval at the same pace, but for one it could be submaximal, while for the other it might push them beyond their capacity.

This is where the concept of the Anaerobic Speed Reserve (ASR) comes in. ASR offers a practical, science-backed method to anchor HIIT prescription to each athlete’s unique physiology, bridging the gap between aerobic and anaerobic capacity.


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🔎 What is Anaerobic Speed Reserve?

ASR represents the speed difference between an athlete’s maximal aerobic speed (MAS) and their maximal sprint speed (MSS).

  • Maximal Aerobic Speed (MAS): the lowest running speed at which VO₂max is elicited (i.e., “aerobic ceiling”).

  • Maximal Sprint Speed (MSS): the fastest speed the athlete can reach in a short sprint (e.g., 30–50 m). The distance used to assess MSS depends on the sport.

👉 ASR = MSS − MAS

In simpler terms, ASR shows us how much “speed reserve” an athlete has above their aerobic limit. Some athletes are very endurance-oriented (small ASR, MAS closer to MSS), while others are more speed-oriented (large ASR, MAS much lower than MSS).

This matters because it influences how they tolerate and respond to HIIT.


⚡ Why is ASR Useful and Practical?

Traditional HIIT prescription often relies on:

  • %VO₂max

  • %MAS

  • %HRmax

While useful, these methods don’t account for the anaerobic contribution to exercise, which becomes critical in HIIT. Two athletes with the same MAS but different sprinting capabilities might experience completely different metabolic stress at the same target speed.

ASR solves this by:

  1. Personalization: It aligns interval speeds with an athlete’s physiological profile, balancing aerobic and anaerobic demand.

  2. Simplicity: Testing MSS (30–50 m sprint) and MAS (time trial or incremental test) is straightforward and field-friendly.

  3. Clarity for training zones: Instead of prescribing HIIT simply as “100–120% MAS”, coaches can anchor it to ASR fractions, making interval work more comparable across athletes.

  4. Bridging science and practice: ASR integrates principles of physiology into practical coaching tools without requiring lab equipment.


🏃 How Coaches Can Use ASR to Prescribe HIIT

Once MAS and MSS are measured, coaches can calculate ASR and use it to prescribe HIIT intensities as percentages of ASR.

Example:

  • Athlete A: MAS = 4.5 m/s, MSS = 9.0 m/s → ASR = 4.5 m/s

  • Athlete B: MAS = 5.0 m/s, MSS = 8.0 m/s → ASR = 3.0 m/s

At “50% ASR above MAS”, the two athletes would run at:

  • Athlete A: 4.5 + (0.5 × 4.5) = 6.75 m/s

  • Athlete B: 5.0 + (0.5 × 3.0) = 6.5 m/s

Even though Athlete A has a slower MAS, their higher sprint ability shifts the HIIT prescription upward. This ensures that the relative metabolic demand is more individualized (Figure 2).


Practical applications:

  1. Short intervals (15–60 s)

    • Use 40–70% of ASR above MAS.

    • Targets both aerobic and anaerobic systems, scalable for sprinters vs. endurance athletes.

  2. Long intervals/sets (1–4 min)

    • Use 10–30% of ASR above MAS.

    • Keeps intensity sustainable while still personalized.


  3. Mixed training

    • Coaches can design progressions by gradually increasing the %ASR contribution.

    • Example: Start with 20% ASR for aerobic athletes, move toward 40–50% for athletes needing more anaerobic emphasis.

      Figure 2. Here is an example of two athletes with the same MAS but different MSS, resulting in distinct ASR profiles and subsequently different HIIT prescriptions. *The graphic used is borrowed from the article of Sandford, Laursen, and Buchheit 2021.
      Figure 2. Here is an example of two athletes with the same MAS but different MSS, resulting in distinct ASR profiles and subsequently different HIIT prescriptions. *The graphic used is borrowed from the article of Sandford, Laursen, and Buchheit 2021.
How to organize a training session by using the ASR approach

A key principle of the ASR approach is using a work-to-rest ratio of 1:1, although this is not necessarily the only approach. WR should be adopted based on needs and goals.


For example:

15 seconds work: 15 seconds rest


The time to exhaustion (TTE) of an individual athlete is a crucial physiological determinant of this method. Therefore, TTE should be assessed for both short and long intervals/sets (see Figure 3).


Working Example

For 15:15 work intervals at 40% ASR, the TTE of Athlete A is approximately 120 seconds.


Calculation:

At 40% ASR above MAS, Athlete A would run 15 × 15-second intervals at:


4.5 + (0.4 × 4.5) = 6.3 m/s (22.7 km/h)


Short Intervals/SETS

  • Suggested structure: 3 reps (15s work + 15s light jogging recovery)

  • Total per set = 90 seconds (1.5 minutes)

  • Recommendation: Begin with a single set when introducing this method, then progress gradually toward the athlete’s upper limits.



Long Intervals/SETS

For longer intervals, the %ASR should be reduced.

Example: At 20% ASR above MAS, Athlete A would run 15 × 15-second intervals at:


4.5 + (0.2 × 4.5) = 5.4 m/s (19.4 km/h)


  • Suggested structure: 6 reps (15s work + 15s light jogging recovery)

  • Total per set = 180 seconds (3 minutes)


If you are aiming for long continuous intervals, applying an ASR of 5–10% would be the most appropriate approach.


Time-to-exhaustion trials with different prescription methods relative to MAS or ASR. The figure is adapted from Julio et al. (2020), published in the European Journal of Sport Science.
Time-to-exhaustion trials with different prescription methods relative to MAS or ASR. The figure is adapted from Julio et al. (2020), published in the European Journal of Sport Science.


✅ Pros of ASR

  • Personalization: Accounts for individual differences in aerobic and anaerobic capacity.

  • Fair comparisons: Equalizes training load across heterogeneous groups (e.g., sprinters vs. endurance players).

  • Simple testing: MAS (via 5–6 min TT) + MSS (30–50 m sprint) = all that’s needed.

  • Applied relevance: Especially valuable in team sports where players differ widely in fitness profiles.

  • Bridges aerobic–anaerobic spectrum: Ensures HIIT hits the intended physiological targets.


⚠️ Cons and Limitations

  • Testing errors: Accurate measurement of MAS and MSS is critical; poor test execution can misguide prescriptions.

  • Context dependence: ASR works best for running-based HIIT; adaptations may be needed for cycling, swimming, rowing or mixed-modality sports.

  • Complexity in communication: Some athletes may find %ASR confusing compared to simple “run at 4:00 min/km” instructions.

  • Not a magic bullet: Other factors (fatigue, recovery, tactical context) still shape HIIT effectiveness.

  • Limited research volume: While growing, ASR is less validated than traditional VO₂-based or HR-based methods.


🔧 Practical Takeaways for Coaches

  • Measure MAS and MSS regularly – it takes little time and provides big insights.

  • Use ASR to individualize HIIT prescription instead of one-size-fits-all %MAS.

  • Adjust %ASR ranges depending on training goals: aerobic development, anaerobic power, or mixed.

  • Educate athletes on the method to boost buy-in – simple analogies like “your speed reserve above VO₂max” help.

  • Combine ASR with other monitoring tools (RPE, HR response, recovery tracking) for a complete picture.


📌 Conclusion

The Anaerobic Speed Reserve is a powerful but practical concept that helps coaches tailor HIIT intensities to the individual. By bridging the gap between aerobic capacity (MAS) and maximal speed (MSS), it ensures interval training hits the intended targets without over- or under-shooting.

Like any tool, it has limitations and should be combined with sound coaching judgment. But in an era where personalization is key, ASR offers a valuable framework to make HIIT prescription smarter, fairer, and more effective.

For coaches working in endurance and team sports alike, this method represents a step forward in bringing science closer to the field. ✏️Author: Assist. Prof. Armin Paravlić, PhD

References used to shape this blog:

  1. Sandford GN, Laursen PB, Buchheit M. Anaerobic Speed/Power Reserve and Sport Performance: Scientific Basis, Current Applications and Future Directions. Sports Med. 2021 Oct;51(10):2017-2028. doi: 10.1007/s40279-021-01523-9. Epub 2021 Aug 16. PMID: 34398445.


  1. Tongwu Y, Jinghui Z, Chuanwei D, Zijian Z, Yuxiong X. Supramaximal interval training using anaerobic speed reserve or sprint interval training in rowers. Front Physiol. 2025 Mar 27;16:1516268. doi: 10.3389/fphys.2025.1516268. PMID: 40213147; PMCID: PMC11983448.


  1. Julio UF, Panissa VLG, Paludo AC, Alves ED, Campos FAD, Franchini E. Use of the anaerobic speed reserve to normalize the prescription of high-intensity interval exercise intensity. Eur J Sport Sci. 2020 Mar;20(2):166-173. doi: 10.1080/17461391.2019.1624833. Epub 2019 Jun 6. PMID: 31132025.

 

 
 
 

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