What ASR is, and what it is not

ASR is the speed range between an athlete’s maximal aerobic speed (MAS) and their maximal sprinting speed (MSS). In cycling, rowing and kayak the same idea is called the anaerobic power reserve (APR), using maximal aerobic power and peak power (Sandford et al., 2021).

An athlete with an MSS of 32 km/h and an MAS of 18 km/h has an ASR of 14 km/h. From these two field markers, coaches can estimate how well an athlete will tolerate efforts across the whole high-intensity range (Sandford et al., 2021).

Where the reserve sits. Below critical speed, the anaerobic contribution is small. Above critical speed, it rises sharply even before MAS is reached. Above MAS, performance depends on a blend of aerobic, anaerobic and neuromuscular or mechanical qualities, which is why it is so hard to measure directly (Sandford et al., 2021).

Common misconceptions. Sandford et al. (2021) set out four errors coaches should avoid:

What the research shows

The core finding is consistent: above MAS, the percentage of ASR used predicts tolerance better than the percentage of MAS.

%ASR explains time to exhaustion. In the first ASR study, Blondel et al. (2001) had athletes run to exhaustion at 90–140% of MAS. The percentage of ASR used explained 69% of the variance in time to exhaustion at 120% MAS and 88% at 140% MAS (as reported in Sandford et al., 2021). The lower the share of ASR used, the longer athletes lasted.

Speed–duration curves collapse onto one line. Athletes with different MAS and MSS show different times to exhaustion at the same absolute speed. When their speeds are expressed as a percentage of their own ASR, their speed–duration curves become very similar (Buchheit & Laursen, 2014, in Sandford et al., 2021). This held in running and cycling, which makes ASR a “generic” predictor of high-intensity tolerance whatever the mode or level of the athlete (Bundle et al., 2003; Weyand & Bundle, 2005; Sanders & Heijboer, 2019).

It carries over to team sport HIIT. During a typical HIIT session (8 sets of 10 × 4 s on, 16 s off), players who used a larger share of their ASR showed higher %VO2max and lactate responses. Players with a larger ASR also had less neuromuscular impairment and lower RPE (Buchheit et al., 2012, in Sandford et al., 2021). More use of the ASR means faster fatigue, which can affect coordination, decision making and technical execution.

%ASR reduces between-athlete variability. In rugby players and middle-distance runners, prescribing by %ASR rather than %MAS lowered the variation in blood lactate change and time to exhaustion between athletes (Julio et al., 2020, in Sandford et al., 2021).

Repeatability. Barros et al. (2025) argue that ASR and APR should be treated as a key determinant of repeatability, the ability to reproduce high-intensity efforts with little drop-off. They cite evidence that athletes with a larger APR show bigger decrements in mean and peak power over repeated sprints, because their high outputs rely more on non-oxidative energy. This sits alongside Hodgson et al. (2018), who found greater peripheral fatigue and lower muscle endurance in individuals with a small APR during step tests and repeated sprints (in Sandford et al., 2021). The two are not necessarily in conflict, since they describe different tasks, but coaches should not assume a large reserve always means better repeat-sprint fatigue resistance.

Absolute speed still matters most at the top. In elite male 800 m runners, faster athletes had a larger ASR driven by a higher MSS. Among athletes with similar MSS, MAS and ASR were not related to 800 m time (Sandford et al., 2019). In young soccer players, the best predictor of improved repeated-sprint ability was improvement in MAS, MSS and ASR together, not ASR alone (Buchheit & Mendez-Villanueva, 2014, in Sandford et al., 2021).

The gap in the evidence. Most of this work is cross-sectional or acute. Few training studies prescribe intervals as %ASR over weeks, so whether it produces more uniform adaptation across profiles is still an open research question (Sandford et al., 2021; Thron et al., 2024).

Measuring ASR properly

ASR is only as good as the two tests behind it. A systematic review of 58 studies (Thron et al., 2024) shows that test choice changes the numbers enough to change the training prescription.

Testing MAS

• Team sport players: a 1200–1500 m time trial. Thron et al. (2024) recommend shorter distances for team sport athletes, sprinters and less fit athletes.
• Endurance athletes: a 1500–2000 m time trial, which better reflects MAS in trained endurance athletes (Thron et al., 2024).
• Shuttle tests (e.g. Bronco): an alternative option for team sport players when a track is not practical. Treat the result as an estimate. Thron et al. (2024) found that the final speed of shuttle and incremental field tests could not be confirmed as valid measures of true MAS, and tests with passive rest such as the 30–15 IFT overestimated it.
• Gold standard: laboratory gas analysis (CPET), where the speed at the onset of the VO2 plateau best reflects true MAS (Thron et al., 2024).

Sandford et al. (2021) stress that MAS depends heavily on the protocol: stage length, step size and rest all change the end speed. Use the same protocol every time you re-test.

Testing MSS

• Use radar, laser or timing gates to assess a flying 20 m. Give a 30 m acceleration zone, with the first gate on the 30 m line and the final gate on the 50 m line.
• Radar, laser, timing gates and validated smartphone video showed good validity and reliability for linear sprints (Thron et al., 2024). Team sport athletes reach MSS within roughly 20–40 m, while trained sprinters may need 40–70 m.
• Avoid GPS for reliable data. Most GPS and LPS studies did not show acceptable validity against radar, and match or training peak speeds do not reach true MSS (Thron et al., 2024). Treadmill sprints also underestimate MSS.
• Record wind, temperature, surface and footwear, since all of them affect sprint speed (Thron et al., 2024).

Why test choice matters

Thron et al. (2024) give an example. A recreational runner has a true MAS of 15 km/h and an MSS of 28 km/h, so an ASR of 13 km/h. At 30% ASR, the target is 18.9 km/h. If MAS is taken from the 30–15 IFT instead (19 km/h), the ASR shrinks to 9 km/h and the target rises to 21.7 km/h. If MSS is taken from match GPS, the target falls to about 18.2 km/h. The same athlete gets three different sessions.

Profiling athletes: speed, hybrid and endurance

MAS and MSS together describe an athlete’s locomotor profile, and squads usually hold a wide spread of profiles (Sandford et al., 2021). Muscle fibre type is one major, though not the only, mechanism behind these differences.

Profile, fibre type and soccer roles are from Sandford et al. (2021). SRR cut-offs are from Colomer (Sportsmith).

The Speed Reserve Ratio (SRR)

The SRR tells you how many times faster an athlete’s top sprint is than their MAS.

Because it has no units, it lets you compare athletes of any calibre. A player with an MSS of 35 km/h and an MAS of 18 km/h has an SRR of 1.94, a speed profile. Colomer presents the cut-offs as useful benchmarks for football that are not validated across all sports. Note that the article does not place ratios between 1.7 and 1.8, so treat those athletes as a judgement call.

Use the SRR with care when re-testing. If it rises only because MAS fell, that is aerobic detraining, not progress. Sandford et al. (2021) make the same point for ASR: it can grow artificially through aerobic deconditioning.

Why profile matters for training and recovery

• Recovery time differs. Speed-dominant athletes had a bigger drop in knee extension power after Wingate efforts and took up to 5 hours to recover, compared with about 20 minutes for endurance-dominant athletes (Lievens et al., 2020, in Sandford et al., 2021).
• Volume tolerance differs. In an overload study, endurance-dominant athletes coped better with high volumes and adapted more, while speed-dominant athletes recovered more slowly and were at higher risk of overreaching (Bellinger et al., 2020, in Sandford et al., 2021).
• Squad organisation. Sandford et al. (2021) suggest grouping athletes by locomotor profile rather than by playing position only, because two players in the same position can have very different profiles.

Practical application for S&C coaches

Sandford et al. (2021) propose a three-step process: identify each athlete’s locomotor profile, select the training model that suits it, then individualise sessions and recovery by sub-group.

Step 1: Prescribe above-MAS work as %ASR

Colomer (Sportsmith) advises using ASR-based prescription only when the target is above 100% MAS. Below MAS, use MAS or other aerobic markers.

Worked example. These three athletes are from Fig. 2 in Sandford et al. (2021). The last two columns are calculated here.

At 120% MAS, Athlete A works twice as hard relative to their reserve as Athlete C. Prescribing 25% ASR evens out that relative stress.

Step 2: Choose the training model by profile

Sandford et al. (2021) rate how much each stimulus should feature for each sub-group (●●● major, ● minor):

Endurance profiles suit continuous, higher-volume programmes, including long HIIT, and tolerate overload and double days well. Giving that programme to speed profiles risks maladaptation or overreaching. Speed profiles develop aerobic fitness better with short intervals and repeated sprint training, which they tolerate well because of their fibre type and buffering capacity (Sandford et al., 2021). Short HIIT of 10–15 s work and 20–30 s rest at 100–120% MAS, about 5–10% ASR, gives a lot of time near VO2max with little lactate build-up (Sandford et al., 2021).

Step 3: Match the HIIT format and recovery to the profile

The formats below are from Colomer (Sportsmith).

Progress the dose. In Colomer’s hybrid preseason example, short-interval intensity rises from 15–20% ASR in week 1 to 28% ASR by week 4, while all-out efforts are added from week 3.

Other coaching considerations

• Develop both ends. Improving MAS and MSS together improves tolerance to repeated high-speed efforts and may protect against injury in dense fixture periods (Sandford et al., 2021).
• Endurance profiles who need more speed should prioritise strength, sprint mechanics and low-amplitude plyometrics over more intense conditioning (Colomer, Sportsmith).
• Mind the enjoyment factor. Sub-groups respond emotionally differently to the same stimulus, which is part of good session design (Sandford et al., 2021).
• Use MAS as a screening tool, especially when players return from the off-season (Colomer, Sportsmith).

Limitations to keep in mind

• Few training studies. The case for %ASR rests mostly on acute and cross-sectional data. Longitudinal studies prescribing HIIT as %ASR are limited (Sandford et al., 2021; Thron et al., 2024).
• Many team sport actions never reach the ASR domain. Accelerations over a few seconds often happen below MAS despite their high energy cost, so how ASR applies to these actions is still unclear (Sandford et al., 2021).
• MAS is not a fixed physiological landmark. The anaerobic contribution rises before MAS is reached, so MAS is a useful training reference rather than a true threshold (Sandford et al., 2021).
• Profile cut-offs are provisional. The SRR cut-offs are football benchmarks, not validated across sports (Colomer, Sportsmith).
• The test evidence is narrow. Most MAS and MSS validity studies used male participants, many had small samples, and 70% of MSS validity studies were rated inadequate or doubtful in quality (Thron et al., 2024).

Key takeaways

• ASR = MSS − MAS. Above MAS, the percentage of ASR used predicts tolerance better than the percentage of MAS.
• Test properly. Use a 1200–1500 m time trial for team sport players, 1500–2000 m for endurance athletes, or a shuttle test such as the Bronco as an alternative for team sport players. Measure MSS over a flying 20 m after a 30 m acceleration with radar, laser or timing gates, not GPS.
• Keep protocols identical across re-tests, or the changes you see may be test noise.
• Profile with MAS, MSS, ASR and SRR together, never ASR alone.
• Prescribe above-MAS work as MAS + %ASR × ASR to equalise relative stress across a group.
• Match the format to the profile: repeated sprints and short intervals for speed profiles, a mix for hybrids, longer intervals and more volume for endurance profiles.
• Plan recovery by profile. Speed profiles need more time between hard sessions.
• Develop both ends of the profile, and check that a rising ASR or SRR is not just a falling MAS.