An athlete’s aerobic capacity can be evaluated and improved upon via the implementation of maximal aerobic speed (MAS) training. MAS is a measurement of an athletes running velocity at the point their VO2 max was reached (vV02 max), or their maximal oxygen intake. More precisely, an athletes MAS is the lowest running velocity at which maximum oxygen intake occurred, as the athlete may be able to continue to run faster beyond this point before reaching their anaerobic threshold (Berthoin et al, 1992). An athletes MAS score can be quantified by having an athlete complete a MAS test, providing coaches with a 100% MAS score that is specific to that individual athlete. Once an athlete’s 100% MAS has been established, intervals can be programmed that are pre-set to a percentage of an athletes vVO2max or MAS. This includes sub-maximal (e.g. 80% MAS), maximal (100% MAS) and supra-maximal (120% MAS) maximal aerobic speed based intervals, which when periodised correctly, may lead to an improvement within an athlete’s aerobic capacity.

MAS Testing

An athletes MAS can be established in many ways, including incremental shuttle based running tests (e.g. Yo Yo IR1, Multistage shuttle test, Montreal Beep test, etc.) and linear continuous running tests set to a specific set distance (e.g. 1200m, 1500m, 2000m, etc.) or a specific time trial (e.g. 5-min, 6-min, 7-min, etc.). When implementing a shuttle based test, the demands of repeatedly decelerating, changing direction and re-accelerating places a greater demand on the aerobic bioenergetic system. The repeated recovery requirements between each intermittent high intensity effort places significant demands on the phosphocreatine system and therefore, an athlete’s ability to resynthesise phosphocreatine stores. A muscles oxidative capacity plays a key role within phosphocreatine resynthesis, as the process of replenishing muscle phosphocreatine stores is heavily oxygen dependent.

When implementing a shuttle based MAS test, the athletes MAS is established by recording the final running speed achieved within the last running shuttle before the athlete ceases to continue with the test. The final running speed established when using shuttle based tests will be recorded in km/hr, and will therefore need to be converted to m/s to allow MAS training distances to be easily calculated (Baker & Heaney). Therefore, when implementing shuttle based MAS testing coaches need to be aware that an athletes MAS score will most likely be lower when compared to a linear based MAS test result. This inaccuracy requires the athletes shuttle based MAS score to be corrected using the following equation (Berthoin et al, 1992):

(MAS=1.34*MSST final speed – 2.86)

Berthon et al (1997) previously demonstrated a significant relationship between an athletes MAS established via a 5 minute time trial and MAS established via an incremental treadmill test to exhaustion within a lab. Research by Chamoux et al (1996) previously demonstrated that a 5 minute time trial was the most suitable running duration when establishing an athletes MAS score. These findings demonstrate the validity of implementing a 5 minute continuous running time trial to establish an athletes MAS within intermittent high intensity based sports. When implementing a time trial or set distance MAS test, the athletes actual MAS score is simply calculated by dividing the distance covered (in metres) by the time taken to complete the test (in seconds).

MAS Training

The desired MAS percentages can then be calculated from the athletes MAS score and implemented within a program based on the desired intensity of that particular session (e.g. sub-maximal session at 80% MAS, maximal session at 100% MAS, supra-maximal session at 120% MAS). The percentage of the athletes MAS is then multiplied by the duration of the programmed interval (e.g. 15 seconds running at 100% MAS) before being marked out as the required distance to be covered per 15 second effort (e.g. 100% MAS = 4.2 m/s = 63m per 15 second run). This would then be repeated for a set number of efforts (e.g. 15 s work : 15 s rest @ 100% MAS x 8) with either an active recovery (for lower intensity MAS training) or complete rest (for higher intensity MAS training) between each interval. This block of work would then be repeated for a set number of sets.      

Dupont et al (2004) previously reported significant improvements in aerobic capacity and 40m sprint performance post 120% MAS training intervention in soccer players. These findings demonstrate the simultaneous aerobic and anaerobic benefits of supra maximal MAS training in team sport athletes and other sports that demand both aerobic and anaerobic capacity. It is clear that MAS training offers coaches with an effective means of evaluating and improving an athlete’s aerobic capacity, which in turn will benefit aerobic performance within intermittent sports, therefore providing practitioners with effective form of metabolic conditioning that can be included within the overall performance program. To easily calculate and set programs based on your MAS score, please visit the ‘MAS Calculator’ within the resources section.  

Multiple sports are intermittent in nature, requiring athletes to perform repeated high intensity efforts throughout the duration of the event (e.g. team sports, racquet sports, combat sports, etc.). Russell et al (2016) previously investigated the movement demands of premiership soccer players and reported that players covered a mean total distance of 9.5km, a mean high intensity distance of 487 m, and a total of 656 accelerations per 90 minute game. Spencer et al (2004) reported similar findings within competitive field hockey, with the mean number of repeat sprints performed being 4±1 sprints per high intensity bout. The authors also reported that 95% of the recovery phase during each repeated sprint was of an active nature. It is therefore evident that a major portion of the total distance covered per game is done so at a low intensity, with athletes being required to manoeuvre to a more advantageous attacking or defending position whilst recovering between each high intensity effort. Such active recovery based movement places large bioenergetic demands on an athlete’s aerobic capabilities, therefore requiring athletes to possess a sufficient aerobic capacity. 

Aerobic Adaptations that Favour Anaerobic Performance

Bogdanis et al (1996) previously demonstrated that aerobic metabolism significantly contributes to repeated sprint performance beyond the first performed sprint. The authors reported that aerobic metabolism demands increased from 31% to 50% beyond the first sprint effort when performing repeated 30 second maximal sprints. Hoff (2005) previously reported a reduction in the distance covered and the amount of repeated sprint completed during the second half of competitive games, suggesting a depletion in glycogen scores may contribute to such a reduction in performance. The authors further concluded that an improvement in an athlete’s aerobic capacity would lead to an improvement in stored fat utilisation, therefore reserving stored glycogen stores for more high intensity efforts. These findings demonstrate the need for aerobic capacity performance in athletes that require repeat high intensity effort capabilities, therefore enhancing high intensity aerobic metabolism contributions, recovery performance and glycogen reservation.

High-Intensity Interval Training

High-intensity interval training involves repeated high intensity efforts set to pre-determined work to rest ratios over specific durations, allowing athletes to accumulate a greater amount of time spent training at higher intensities. Another key benefit of high intensity interval training is that the repeated work to rest format allows an athletes aerobic and anaerobic capacity to trained simultaneously. Tabata et al (1996) previously demonstrated that high intensity intervals performed at reduced recovery periods and all out maximal activity concurrently improved aerobic capacity (VO2max) and anaerobic capacity performance measures. Helgerud et al (2001) previously reported significant improvements in aerobic capacity (VO2max), lactate threshold and running economy in elite junior soccer players post high intensity interval training intervention. Such simultaneous aerobic and anaerobic performance improvements would be beneficial for any sport that requires repeated high intensity efforts (e.g. team, racquet, combat and endurance based sports).  

These findings demonstrate the benefits of improving an athlete’s aerobic performance within intermittent high intensity effort sports, and how such favourable adaptations can be developed via the correct programming of high intensity interval training. Another effective form of metabolic conditioning based training is maximal aerobic speed (MAS) intervals, which is explored within the second part of this article series (see ‘Increasing Aerobic Performance Part II : Maximal Aerobic Speed Training’).   

Athletes who partake in combat sports involving repeated strikes to the head (e.g. boxing, Thai-boxing, MMA, etc.) require adequate neck strength to withstand the high impact forces of such strikes. When experiencing the whiplash effect immediately post head strike the neck flexors undergo a rapid eccentric contraction. Likewise, the lateral neck flexor muscles undergo a rapid eccentric contraction when the head is struck from a circular action (e.g. hook punch, spinning head kick, etc.). In addition to combat sports, certain collision sports such as rugby union / league require additional neck conditioning due to the high risk nature of collisions during tackle or contact during competitive play (e.g. ruck and mauls). It is therefore evident that the addition of neck conditioning is vital within combat and collision-based sports, ensuring athletes can effectively absorb the large impact forces experienced when receiving a strike to the head or during a collision.

Training Considerations

Lisman et al (2012) previously investigated the effect of an eight-week neck training intervention involving neck extension, flexion and lateral flexion based exercises on neck strength, girth, muscle activity (measured via EMG) and kinematic measures (peak linear and angular acceleration of the neck joint) experienced when performing a simulated tackle. The authors reported a 7 to 10% increase in neck extension and lateral flexion strength post training intervention. Later research by Hrysomallis (2016) reported a direct association between neck isometric strength levels and injury risk in professional rugby union players. These findings demonstrate the effectiveness of neck based strength training, and the importance of such training within collision based sports.  

Structural Balance

Due to the multi-directional functionality of the neck joint, it is paramount that any form of applied neck conditioning is implemented within a muscular structural balanced format. Research by Ylinen et al (2003) demonstrated the potential variability in neck strength between individuals. The authors measured the neck strength of elite Finnish senior and  junior wrestler’s vs general populations, and found individual strength differences in all directions within each group. The researchers also reported significant greater neck flexion strength vs extension and rotational strength within the elite senior wrestling group. These findings demonstrate the importance of ensuring any applied neck training is structural balanced and develops all neck muscularity equally.  

Strength and conditioning coaches working with athletes who require neck conditioning should implement training protocols that involve low loads and moderate training frequencies (e.g. two to three time per week), resisted in all neck movements for structural cervical spine balance and isometric holds. This should include an equal amount of neck flexion, extension, lateral flexion and anti-rotation based exercises in any neck injury prevention protocols. This can be achieved by programming resisted neck movements or loaded isometric holds. Lastly, any form of neck training should be carried out within a controlled manner, therefore avoiding any form of neck strain or injury.     

The cricket bowling action is a complex movement, involving the coordination of multiple body segments and the propulsion of a ball at high speeds (Ferdinands, 2011). This explosive throwing action involves a rapid circumduction of the arm at the glenohumeral joint, with the transfer of kinetic energy from the lower to the upper extremities. This translation of energy and high joint angular velocities at the glenohumeral joint places the dominant shoulder at a high risk of injury. Therefore, strength and conditioning coaches working within cricket performance need to be aware of the shoulder injury risks associated with the bowling action, and the mechanical principles that underpin these injury risks.    

Biomechanical Injury Mechanisms

Research by Green et al (2013) previously highlighted the high occurrence of shoulder injuries within elite cricket. The authors reported that the individual athletes who were currently suffering shoulder pain consistently presented a downward rotated scapula. Such a position of the scapula leads to increased forces acting on the subscapularis and glenohumeral joint as the shoulder undergoes rapid internal rotation during throwing actions. Furthermore, excessive internal rotation of the shoulder predisposes the athlete to supraspinatus impingement risk, whereby the supraspinatus tendon and long head bicep tendon become mechanically impinged within the sub-acromial space. Such a persistent mechanical impingement can lead to repeat acute shoulder pain and eventually result in chronic shoulder pain, thereby seriously debilitating the athlete.

Overuse & Underuse Injury Mechanisms

Interestingly, it would appear that both overuse and underuse of the shoulder via repeated bowling actions are both significant shoulder injury risk factors. Dennis et al (2003) previously reported that bowlers with an average of less than 123 deliveries per week or more than 188 deliveries per week were at a higher risk of shoulder injury. The authors investigated the relationship between shoulder injury rates and bowling load within elite fast bowlers and reported this high workload vs low workloads duality. Therefore, it is apparent that there exists an optimal ‘fast bowl maintenance workload’ that should be adhered to within practice. In addition, a lack of shoulder strength and rate of force development may contribute to the occurrence of shoulder injuries in fast bowlers who fall within the low threshold bracket. Likewise, the high workload group may have a lack of shoulder strength-power endurance.

Preventive Measures

Therefore, strength and conditioning coaches working within cricket need to be aware on the biomechanical demands of repeat bowling and throwing actions and the preventive measures that can be put in-place to manage the risk of shoulder injury. These preventive measures should include adequate shoulder external rotation strength relative to the athletes opposing internal shoulder rotation, adequate shoulder internal and external range of motion, scapular stability interventions that allows the anterior and posterior scapular muscularity to correctly co-contract and therefore stabilise the scapular during rapid throwing actions and unilateral shoulder strength and unilateral shoulder power based training (e.g. single arm overhead press variations and single arm med ball throw variations, respectively). Practitioners need to consider the overall bowling practice volume per micro-cycle, ensuring that an optimal volume of bowling practice is scheduled, therefore avoiding any potential overuse and underuse injuries. Finally, it is evident that the overall fast bowling workload needs to be accurately monitored across each individual player and not generically across the team.                                       

The movement demands of all sports are specific in nature. However, most sports require some form of change of direction, with varying levels of approach speed, body position, frequency, angle of direction, etc. The improvement and optimisation of change of direction performance is vital within strength and conditioning practice, and requires a thorough understanding of what optimal change of direction looks like (mechanically) and how it can be enhanced. This not only includes the programming of actual change of direction practice, but rather an integrated -training mode approach involving multiple training methods.  

When executing a rapid change of direction, an athlete is required to apply large ground reaction forces to propel themselves within the new desired direction (in conjunction with Newtonian mechanics). However, the time scale in which to apply such force is severely limited as the athlete is in locomotion and is therefore constrained to the duration of the foot contact when the force is being applied. Therefore, an athlete requires adequate force and power generating capabilities to enable them to effectively change direction.

Maximal Strength

The role of traditional strength training methods and change of direction performance has previously been debated within sport science, with the effectiveness of vertical plane strength based methods being called into question. However, a literature review completed by Watts (2015) concluded that maximal strength is a significant performance determinant within change of direction performance. Spiteri et al (2014) previously demonstrated that change of direction performance is positively correlated to maximal strength in conjunction with other strength qualities (isometric, concentric and eccentric strength).

Keiner et al (2014) reported similar findings when investigating the correlations between maximal strength and change of direction performance and the long-term effects of maximal strength training on the ability to effectively change direction. The authors reported that moderate to high correlations where present between maximal front and back squat performance and change of direction capabilities. Furthermore, the authors also reported that two years’ worth of strength training in elite youth soccer players (13 to 18 years of age) significantly improved change of direction performance. Nimphius et al (2010) reported consistent correlations between maximal strength and change of direct ability over the course of a playing season in softball athletes. These findings demonstrate the importance of maximal strength training and the improvement of change of direction ability, and why improving maximal strength and peak force capabilities in conjunction with other key qualities (power, RFD, optimal technique, etc.) is needed in athletes that require change of direction performance.

Unilateral Strength

As change of direction is both unilateral and multi-directional in nature, coaches need to ensure that some of the applied training modes closely resemble the kinematics and kinetics of change of direction performance. For example, unilateral squat variations (e.g. split squats, lunges, loaded step ups, etc.) more closely mimic the kinematic demands of unilateral based movements. Loaded movements that applying towing devices such as lateral sled drags effectively replicate the mechanics of lateral cutting movements. Such training modes can be programmed in combination with lateral based plyometrics (e.g. lateral and diagonal bounds), unilateral based plyometrics (e.g. multi-uni lateral hops, etc.) and other training methods that enhance stretch shortening capabilities and tendon stiffness within a frontal plane.

Plyometrics

Plyometric interventions aimed at improving change of direction performance (by increasing power production and musculotendon stiffness) have been most effective when the chosen plyometric modes have most closely replicated the kinematics of change of direction performance (e.g. movement within a frontal plane, lower centre of mass, etc.). McCormick et al (2016) investigated the effects of frontal plane vs sagittal plane plyometric training on change of direction performance in basketball athletes, and found that the frontal plane based plyometric intervention was more effective at improving change of direction performance. Brughelli et al (2008) reported similar findings, suggesting that horizontal jump based training and lateral jump training (in conjunction with actual change of direction practice) was most effective at improving change of direction performance.

Therefore, performance programs aimed at improving change of direction performance should include not only change of direction practice, but also maximal strength and plyometric based training methods. Lastly, strength and conditioning coaches should ensure that not the selected exercise methods occur within a sagittal plane, but rather involve frontal plane based plyometrics and unilateral strength training modes.

Tactical metabolic training (TMT) involves directly replicating the physiological metabolic conditioning demands of sports performance by specifically manipulating the applied work : rest ratios to match the bioenergetic demands of an athletes chosen sport. Furthermore, the movement demands of competition can be replicated, including sprint distances, sprint frequency and change of direction demands. Plisk and Gambetta (1997) previously suggested that TMT based training was more favourable than other conventional forms of metabolic conditioning based training, suggesting that transfer of training effects would be greater due to the specific nature of the implemented TMT method. Furthermore, the authors also highlighted that TMT training methods increased overall training time efficiency, as the technical and tactical skill elements of the actual sport can be practised whilst applying TMT methods.

Applied Tactical Metabolic Training

Lythe and Kilding (2011) previously reported that elite men’s field hockey players covered 34±12 sprints per game, lasting an average duration of 3.3 s. Furthermore, Spencer et al (2004) reported that 95% of the recovery between each repeated sprint was of an active nature (see previously detailed ‘metabolic conditioning demands of team sport’). Therefore, a field hockey TMT based training intervention could be based upon players completing 22 and 46 sprints (34±12) or more (as a form of supra-maximal training) with each sprint lasting over 3 s in length with a form of active recovery between each sprint effort. Such specific training would accurately replicate the demands of competitive elite hockey, therefore resulting in a greater transfer of training effects. 

TMT can be applied to any sport with the right level of sport science and movement demand knowledge. For example, Turner (2009) previously reported that Thai-boxing is predominately anaerobic in nature with only minimal aerobic bio-energetic contribution during periods of ring movement and recovery, and therefore recommended that strength and conditioning coaches should look to mimic these demands by applying a ‘‘5 s on 5 s off’’ protocol termed ‘‘Combat Intervals’’ within metabolic based training. Likewise, Kirk et al (2015) previously demonstrated the intermittent nature of mixed martial arts, reporting that the work : rest ratio within competitive mixed martial arts was (W:R) of 1:1.01. The research findings presented by these authors provides the necessary information for the correct application of TMT within combat sport athletes.     

Small Sided Games

Weaving et al (2017) previously demonstrated that the training load of small sided rugby league games that included physical contacts most closely replicated the demands of competition. Foster et al (2010) previously reported that the manipulation of player number per game generated physiological responses suited to the improvement of aerobic conditioning in elite junior rugby league players. Furthermore, Gabbett et al (2012) reported that small-sided games played on a larger pitch resulted in greater distances being covered at moderate, high and very high velocities in senior rugby league athletes. These findings demonstrate that the design and implementation of small sided games with added constraints (e.g. increased pitch size, added physical contacts, reduced player team sizes, etc.) can lead to an increase in specific performance qualities within team sport athletes. Such added constraints may result in an increased performance when applied to other sports when engineered around previously gathered sport science data. Therefore, the application and design of TMT and small sided games should be considered within the overall performance training plan, allowing for a greater bioenergetic transfer of training effects within sports performance.

Complex training (sometimes referred to as contrast training) applies a post activation potentiate training effect by enhancing the neuromuscular system, with the athlete firstly completing a resisted training movement before completing a plyometric based training activity. The theory being that the first resisted movement increases the level of motor unit recruitment, motor neuron firing rate frequency and intra-muscular calcium concentrations, all of which result in an enhanced performance of the proceeding plyometric based exercise. This enhanced training effect is referred to as post activation potentiation and is an area of current active research within sports science.

Complex Training Considerations

Smilios et al (2005) previously investigated the acute effects of complex training involving loaded half squats and loaded jump squats on counter movement jump performance at varying loads, and found that both loaded half squats and loaded jump squats significantly improved counter movement jump performance in athlete populations. The authors concluded that contrast loading of low to moderate loads can lead to short-term increases in vertical jump performance. Baker has previously highlighted the importance of load selection when implementing complex training methods, suggesting that practitioners should design complex-training training interventions that incorporate exercises from within the speed-strength range of the force-velocity curve profile followed by exercise situated at the high velocity end of the force-velocity curve (Baker and Newton, 2005). This ensures that the motor neuron rate coding is similar for both training modes as both exercises would be performed at high velocities.

Antagonist – Agonist Method

Another complex-training training approach suggested by Baker and Newton (2005) involves performing a movement that recruits the antagonist muscularity vs the proceeding agonist movement. The authors hypothesised that the weak antagonist muscles may limit the speed of movement and that strengthening the weak antagonist may lead to an increase in agonist muscle movement speed and power output. The authors reported that the participant group that performed bench pulls between a bench throw performance test demonstrated significant increases in power output. These findings demonstrate that both agonist-agonist (or same movement pattern) or antagonist-agonist complex training may be advantageous to increasing power production in athletes.

Intra-complex Rest Considerations  

Comyns et al (2006) previously highlighted the importance of adequate recovery periods between each complex exercise (intra-complex) and between each set (intra-set) was of great importance when implementing complex training methods. The authors suggested that the required rest intra-complex rest period may be athlete dependent and should be longer, rather than shorter in duration. Therefore, intra-complex rest periods of 3-4 minutes are recommended when performing complex training with athletes.  

Complex training offers an effective means of increasing power output in athletes, whilst utilising both speed strength and plyometric training within a short time scale, therefore making complex training a time efficient training mode within strength and conditioning practice. However, practitioners should be aware of the neuromuscular demand of complex training, and therefore consider how it is scheduled within the overall periodised training plan and the athletes overall training status.   

The need for replicating the specific ‘repeated sprint demands’ within strength and conditioning practice were previously explored within part one of this article series, including the beneficial adaptations associated with repeated sprint ability training (see ‘Repeated Sprint Ability Part I : Bioenergetic Adaptations). The training considerations when programming repeated sprint ability training is explored within part two of this article series.            

Linear Based RSA

Little and Williams (2007) previously reported that a repeated sprint protocol of 40x15m sprints with a work : rest ratio of 1:4 or 1:6 most closely replicated the repeat physiological demands of competitive soccer. However, the authors also reported that the reduction in sprint performance when implementing a 1:4 work : rest ratio was too great when applied with soccer athletes, suggesting that a greater rest period may be required between sets (e.g. 1:6 work : rest ratio). Furthermore, the authors also recommended that a supra-maximal repeat sprint protocol of 15x40m sprints (with a work : rest ratio of 1:4) may be applicable when periodised appropriately within soccer performance programs. These findings demonstrate the benefits of repeated sprint training protocols that replicate the specific physiological demands of sports performance, and how repeated sprint training can be programmed with the occasional aim of overreaching an athlete as part of an overall periodised plan.   

Change of Direction Based RSA

A potential limitation of such linear ‘straight-line’ repeated sprint protocols is the lack of change of direction during each completed sprint effort. Buchheit et al (2010) previously reported a 30% reduction in sprint performance when comparing 25 m linear sprint performance vs 2 x 12.5 m shuttle sprint performance with the inclusion of a 180 degree turn. Furthermore, the authors also reported variances in measured performance variables between both sprint protocols, with the greater (and therefore more demanding) scores being recorded during the shuttle sprint efforts. The authors suggested that the greater time taken to complete each sprint was a result of the athlete participants having less time to accelerate due to the shorter distance being covered, and the need to decelerate and perform a change of direction before re-accelerating.

The authors also suggested that the differences in sprint performance and the physiological performance variables observed were an indication that the change of direction requirement within the sprint shuttle protocol placed a greater physiological demand on the bodily systems when compared to the linear sprint protocol. Therefore, strength and conditioning coaches should consider implementing repeat sprint training methods that involve a change of direction when working with athlete’s who’s chosen sports involve repeated changes of direction, or as a form of progressive overload within an overall periodised plan.

Aerobic Capacity 

Bogdanis et al (1996) previously demonstrated that aerobic metabolism significantly contributes to repeated sprint performance beyond the first performed sprint. The authors reported that aerobic metabolism demands increased from 31% to 50% beyond the first sprint effort when performing repeated 30 second maximal sprints. The significant increase in aerobic contributions even occurred after a four minute rest period between each repeated sprint. These findings demonstrate that aerobic capacity contributes significantly to repeated high intensity performance, both in the form of recovery and high intensity performance, despite the anaerobic nature such explosive movements Hoff (2005) previously reported a reduction in distance covered and repeated sprint efforts during the second half of competitive games, suggesting a depletion in glycogen scores may contribute to such a reduction in performance. The authors concluded that an improvement in an athlete’s aerobic capacity would lead to an improvement stored fat utilisation, therefore reserving stored glycogen stores for more high intensity efforts.

These findings demonstrate the need for athletes that require repeat high intensity effort capabilities to improve their relative aerobic capacity before embarking on a repeated sprint training protocol, therefore enhancing their aerobic metabolism contribution levels, intermittent recovery performance and glycogen reservation.        

Metabolic conditioning can be considered as an overall umbrella term that encompasses all forms of aerobic and anaerobic based conditioning. Practitioners should ensure any applied metabolic conditioning based training matches the bio-energetic and sports specific demands of an athletes chosen sport whilst periodically training at a sub-maximal and supra-maximal level in-relation to these pre-determined sport demands. Metabolic conditioning based training comes in a variety of forms, one of which is repeated sprint ability.

RSA Demands of Sport

Russell et al (2016) previously investigated the movement demands of premiership soccer players and reported that players covered a mean total distance of 9.5km, a mean high intensity distance of 487 m, and a total of 656 accelerations per 90 minute game. Likewise, rugby league and union players are required to perform repeat high intensity efforts (acceleration, deceleration and changes of direction) including repeat high force collisions (tackles, scrums, etc.) (Till, Scantlebury and Jones, 2017). Spencer et al (2004) reported similar findings, with the mean number of repeat sprints being 4±1 sprints per high intensity bout within competitive elite field hockey. The authors also reported that 95% of the recovery during each repeated sprint was of an active nature.

Similar to the intermittent nature of team sports, racquet sports require athletes to perform repeat high intensity efforts throughout competitive play. However, the distance covered per sprint is reduced when compared to team sport movement demands due to the constrains of the size of the court.  Pluim (2004) previously described tennis as an intermittent exercise, involving alternating short bouts of high intensity exercises lasting 4-10 seconds with short recovery periods of 10-20 seconds with several periods of longer duration activity of 60 to 90 seconds (rallies). These findings demonstrate the repeat sprint demands of team sports and racquet sports, and the need to replicate these demands with training, allowing for the favoured metabolic based adaptations associated with repeated sprint training.

Hydrogen Buffering Efficiency

The accumulation of lactate acid is often referred to as the main factor in diminishing power output and athlete performance. However, it appears that lactic acid itself may be accumulating in an attempt to buffer the accumulation of hydrogen ions that occurs during the process of anaerobic metabolism. The accumulation of hydrogen ions and inorganic phosphates has previously been shown to be key factors contributing to muscle fatigue in repeated sprint performance (Glaister, 2005). Both hydrogen ions and inorganic phosphates inhibit calcium’s effect to activate tropomyosin, therefore reducing the myosin – actin binding mechanism and cross bridge cycle rate. Edge et al (2006) previously reported that athletes with a high level of repeated sprint ability demonstrate a superior ability to buffer the accumulation of hydrogen ions associated with glycolytic metabolism. Therefore, it appears the ability to buffer hydrogen ions is a trainable adaptation in athletes, in addition to an increase in muscle glycolytic enzyme content and activity.

Lactate Shuttling

During the performance of high intensity efforts, skeletal muscle lactate transporters situated within the muscle membrane assist in the reduction of lactate accumulation. In particular, monocarboxylate transporters are critical in the removal of lactate and hydrogen ions. Bishop et al (2011) previously suggested that the responsiveness of monocarboxylate transporters maybe responsive to anaerobic based training methods involving repeated high intensity efforts. Furthermore, previous findings suggest that the transported lactate out of a muscle cell during high intensity training can be oxidised by the adjacent muscle fibres and used as a substrate for energy metabolism (Brooks 2009). Such increase in monocarboxylate transporter adaptations would contribute to an overall reduction in lactate and hydrogen accumulation and increase an athlete’s ability to ‘tolerate’ lactate and muscle buffering capabilities.       

Enhanced Glycolytic Enzyme Activity

An athlete’s anaerobic capacity performance is dependent upon multiple factors, including glycolytic enzyme content and activity. This is due to the glycolytic demands of anaerobic based activity, which taxes the glycolytic energy pathways. Kubukeli et al (2010) previously suggested that the number and activity of glycolytic metabolism based enzymes increase in response to training that stresses an athlete’s anaerobic bio-energetic systems. Such anaerobic based adaptations would obviously favour an athlete’s repeated high intensity effort capabilities.

Such adaptations would favour athletes who require the ability to produce repeated high intensity efforts, therefore providing a sound rationale for the inclusion of anaerobic based training such as repeated sprint based training. The next article within this series will explore the programming of repeated sprint ability within sports performance and what factors should be considered when designing repeated sprint ability-based training (see ‘Repeated Sprint Ability Part II : Training Considerations).

The demands of long-distance running require athletes to apply large ground reaction forces over the course of the event. Endurance athletes are required to apply such forces within a very limited time scale (e.g. during the contact phase of a running stride) suggesting the forces are required to be applied quickly and repeatedly. A key performance parameter that is vital to this ‘repetitive force and power production’ process is musculotendinous stiffness.   

Tendon stiffness is the ability to produce rapid RFD within the shortest ground contact time possible, and therefore involves very little flexion at the ankle, knee or hip upon landing. As little change in joint angle occurs during tendon stiffness-based movements, most of mechanical work occurs within the tendon rather than the muscle. For example, upon landing from a drop jump plyometric, the muscles that plantar flex the ankle perform a quasi-eccentric-isometric contraction. This means the muscles are being held isometrically within the same position before being eccentrically lengthened under load and can therefore operate at the high force end of the force-velocity curve, whilst the tendon undergoes a rapid stretch-recoil action. The greater the level of tendon stiffness, the greater the RFD and energy economy of the movement, as less actual muscle work is occurring within the muscle itself. Such less energy demand obviously suits endurance-based sports, where muscles are required to produce sub-maximal force over the course of the entire event duration.

Plyometrics & Tendon Stiffness

Spurrs et al (2003) examined the effect of a plyometric training intervention on running performance, musculotendon stiffness and various performance measures. The authors reported significant improvements within the athletes 3 km performance, running economy, vertical jump performance and five bound distance tests. These findings clearly demonstrate the link between improvements in running performance and running economy, due to an increase in power production via musculotendon stiffness adaptations. It is evident that power output is in an important performance quality within endurance-based athletes and should therefore be trained accordingly in conjunction with other endurance-based training.  

Maximal Strength & Tendon Stiffness       

As an endurance-based athlete inevitably fatigues, the amount of force or torque generated will diminish, resulting in a reduction in overall performance. Therefore, the greater the level of force and torque generating capabilities from the outset, the lesser the effect on performance as the force and torque magnitudes decrease. Hence, an athlete will still be able to produce a greater amount of force / torque output when under fatigue, as the initial maximal force and torque levels were greater in the first instance. Ronald et al (1997) reported significant improvements in running economy in long-distance runner’s post strength training intervention. Hence, the favourable musculotendinous anatomical changes brought about by maximal strength training (e.g. an increase in tendon stiffness) in conjunction with speed strength training methods will result in an increase running economy. Aagaard and Andersen (2010) previously reported similar findings when reviewing the literature on strength training within endurance-based sports. The authors concluded that the enhancement in endurance performance is most likely due to increases in size of type IIA fibres, force generating capabilities, rate of force development and overall neuromuscular function.

It is evident that peak force, power production, and tendon stiffness are vital performance qualities within middle and long-distance running athletes. All of which will improve an athlete’s ability to produce repeated sub-maximal force / power output whilst under fatigue, therefore improving an individual’s overall running economy and overall running performance.