The Anaerobic Speed Reserve (ASR) is defined as the range between Maximal Sprint Speed (MSS) and Maximal Aerobic Speed (MAS – or Velocity @VO2Max if assessed in a laboratory setting) which in turn represents an individual’s neuromuscular and anaerobic capacities (1). Anaerobic capacity can be explained and characterised as higher intensity/speed exercise that diminishes with duration as a result of the finite metabolic resources available (2). Additionally, MAS represents the highest/critical speed that can be sustained for a prolonged period of exercise and provides a distinct point of separation for practitioners to identify the differences between aerobic and anaerobic systems during exercise. To better understand variations between the group and individual ASR profiles, the Speed Reserve Ratio (SRR) calculated as MSS/MAS, filters this into a single tangible variable that can be more effectively used by practitioners, a popular tool within Middle Distance Running. Recent insights that have emerged through ASR research in middle distance running, have challenged traditional aerobically dominant physical preparation strategies and highlight the importance of assessing anaerobic capacity and MSS. Sandford, Allen, Kilding, Ross and, Laursen (1) set out to establish the relationships between ASR and MSS within 800M middle distance performance, reporting that ASR (as a product of greater MSS) resulted in the strongest correlations with 800M performance and is even capable of differentiating between 800M athlete profile types. Similarly, Bachero-Mena, Pareja-Blanco, Rodríguez-Rosell, Yáñez-García, Mora-Custodio, González-Badillo, J. J. (3) have also reported large relationships with 800M performance and all-out MSS efforts over short distances. However, this should not discourage the value of MAS, particularly considering that the participants involved in this research display high MAS scores, which may not be a key trait amongst less elite groups. Instead, these findings should emphasise the shared contributions of each system to elite performance, a relationship the ASR and SRR illustrate.
Figure 1. Example of the Anaerobic Speed Reserve differences between two athletes.
Despite the broad contrasts in sport, tactics, and time-motion characteristics between Team Sports and Middle Distance Running the importance of the aerobic and anaerobic system to sporting performance is coherent across both. As Team Sports continue to evolve the presence of high-speed running has remained influential to performance and continues to increase significantly (4–6). These actions are more commonly termed as ‘Repeated Sprint Ability’ (RSA), due to the proximity of repeated high-speed runs/efforts dispersed by 15 – 30 seconds of active or passive recovery, which also reflects the intermittent nature of Team Sports. High-Speed Running and RSA account for a considerable proportion of scoring situations and is also a key differentiator between competition levels, only further affirming the need to develop this quality in Team Sport Athletes (4,7–9). Given the intensity and temporal factors of High-Speed Running and RSA, it would seem the energetic demands are more applicable to anaerobic metabolisms as oppose to aerobic processes. There is a clear need for assessing/understanding RSA capacity amongst Team Sports athletes, yet the commonly selected method of assessment is the RSA test as opposed to the ASR (10).
…So can the ASR replace RSA tests in Team Sports?
ASR VS RSA: What are we really assessing?
The RSA test involves 6 – 12 maximal sprints (≤ 10 seconds) interspersed by short active or passive recovery periods (῀ 30 seconds). With many variations with regards to sprint distance, recovery activity and repetitions, varying based upon the sporting context, many RSA tests still present with good validity and reliability (10). Additionally, the ability for the RSA test to discriminate between, positions and competition levels also provide high ecological validity for team sports (11), therefore a logical method of assessment of anaerobic capacity over the ASR in Team Sports. Variables of RSA performances are expressed as Fatigue Index (performance drop off between best and worst sprint) or Speed Decrement (percentage decrement score by comparing actual performance with theoretical performance), demonstrating the ability to resist fatigue (12). Anaerobic capacity has been shown to facilitate RSA performance predominately through contributions to initial sprint performance, those with greater initial sprint speed also showing higher RSA and anaerobic capacities (glycolytic rate) (12,13). Comparatively other studies have identified that anaerobic metabolism only contributes to 40% of the initial sprint in repeated sprint performance, deteriorating significantly with increasing repetitions (14). Because of this, it would be questionable to attribute RSA solely to increased anaerobic capacity or even as an assessment of true anaerobic capacity. Bishop et al (11) present an alternative to this, outlining that the key determinants of RSA are initial sprint performance and the ability to recover between sprints. Greater levels of initial sprint performance consistently correlated with greater total sprint performance amongst RSA tests which are largely dependent upon phosphocreatine stores and neuromuscular abilities to produce high force in short periods (14,15). Whereas the abilities to recovery between sprints are supported by phosphocreatine resynthesis, muscle buffering, and high aerobic fitness levels. This can be explained by 1) Increasing contribution from aerobic metabolism in the latter stages of repeat sprint performance 2) Phosphocreatine dominates the energetic demands throughout repeat sprint performance 3) Hydrogen accumulation/decreased muscle buffering capacity from high-intensity exercise negates repeat sprint performance by inhibiting ATP production and muscle activation. More recently Bishop’s et al review conclusions have been supported specifically amongst team sport populations, whereby similar relationships between aerobic fitness, initial sprint performance, and RSA were shown (16).
Figure 2. Determinates of Repeat Sprint Ability (19).
With this considered the RSA test only truly provides an accurate indication of one of the two key determinates outlined by Bishop et al, that being initial sprint performance. The RSA test is redundant in presenting a valid measure of aerobic fitness making it challenging to understand how well an individual can recovery between sprints. Although fatigue index and speed decrement scores may give some broad indications to aerobic capacities, the challenge to accurately determine aerobic fitness levels and/or the limiting factors to RSA remains. The ASR, however, is comprised of exactly these two variables, an advantage over more common RSA tests, allowing for a more accurate understanding of the mentioned determinants of RSA. It could be argued that ASR as a function of MAS and MSS does not provide an understanding of the phosphocreatine resynthesis as it is based on single sprint performance, but research has shown a close link with this also has a strong link with aerobic capacity (17).
ASR VS RSA: Informing Interventions?
Identifying RSA amongst Team Sport athletes provides the opportunity for more informed interventions to improve upon RSA and thus overall sporting performance. Interventions used to improve RSA are far-ranging from resistance training to small, sided games each with a firm underpinning physiological rationale. More commonly compared and contrasted is the use of repeated sprint training, single sprint training, and interval training, all of which individually have shown positive effects on RSA (18,19). What is less clear within the research is whether any one type of training intervention has a greater effect on improving RSA than another. This is likely a product of multifactorial contributions that make up good RSA, with each intervention targeting either the metabolic or neuromuscular determinants of RSA and a combined approach may yield the most potent solution to developing RSA (19). Considering this the ASR may prove more suitable in the prescription of either intervention, due to the ability to better establish the specific strengths and areas for improvements using MAS and MSS to target RSA determinants (20). This was reflected well in Julio et al (20) study which investigated the use of ASR to better prescribe high-intensity interval exercise amongst rugby players and distance runners. Using 25% and 50% of ASR participants were able to achieve significant improvements in aerobic fitness and muscle buffer capacity, two qualities vital for recovery between repeat sprinting. This research also exhibits another advantage of the ASR, with greater scope to individualise speed zones and quantify external load for Team Sport athletes (21,22). RSA test, on the other hand, does not have the same prescriptive function for different interventions beyond single and repeated sprint training. With percentage (fatigue index and speed decrement and/or mean and total sprint distance the key variables derived from the RSA test, proving challenging to decide upon intensity (speed), volume, and recovery time for sub-maximal (≥ MAS) interval training. Irrespectively, much like interval training, repeat sprint training has been shown to improve aerobic capacity alongside positive changes to single sprint performance (19). Therefore, despite the difficulties in training prescription from fatigue index/speed decrement and mean/total sprint distance from the RSA test, using this assessment to prescribe repeat sprint training may be sufficient for the appropriate adaptions to improve RSA.
ASR VS RSA: Other Considerations
Beyond the assessments and interventions of RSA, the RSA test presents a unique opportunity to evaluate the kinematic changes to linear sprinting under the constraints of fatigue. The negative impact fatigue imposes on the neuromuscular, and biomechanical factors of sprinting are well reported, which in turn will have implications for injury predispositions (23–25). Consequently, the RSA test could be used as a screening tool to identify changes in sprint performance (e.g. pelvic tilt) that may be of injury risk, so that they may be addressed. However, this can only be achieved through additional biomechanical analysis that would require technological resources which may be both time-consuming and costly in the field.
Reviewing the advantages and disadvantages of both the RSA test and ASR that are presented in this discussion, it would prove that the ASR is a suitable replacement for the RSA test in Team Sports. Ultimately this decision is dictated by the information practitioners in the field are in pursuit of, as each method present slightly different insight and advantages. However, there must be an acknowledgement of the determinates of repeat sprint performance as this will influence the effectiveness of our decision-making process with regards to conditioning interventions.
References
(Display Cover Image Credit - Photo by Quino Al on Unsplash)
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