ABC of Football Medicine® Lesson 8: Athletic Development role in the muscle injury prevention – Part 2

Let’s dive into the Part 2 – Assessment:

(Click here if you didn’t read the Part 1 on: Athletic Development role in the muscle injury prevention)

Having identified the domains that should be taken into account in the players’ athletic capacity (strength and strength-specific manifestations as well as the energetic systems and its different capacities and domains), the next step is to characterise the necessities of the football athlete in order to serve as a guide in our preparation for the assessment process.

When selecting the tests to be used, it is crucial to value if these tests are valid (does the test assess what it is supposed to assess?) and if they are reproducible (is the test consistent?). After taking both these factors into account, we’re ready to select the tests that will be fitting to the context along with guaranteeing the quality of the assessment.

The Maximum Strength is the basic quality that directly influences the expression of muscle power (Wisloff 2004, Peterson 2005), with gains in strength associated to the optimization of relative strength (relative to the body weight) and also inducing significative gains in power actions, such as jump height or sprint velocity (Wisloff 2004, Styles 2015).

When considering strength manifestations, the Rate of Force Development is one that deserves special attention, since it is possible to be assessed by interpreting the strength-time curve and, from this, infer the muscular function in a given time frame. This fact has a particular importance due to the nature of the sport’s actions, characterised by occurring in time frames shorter than 250ms. Being so, characterising the athlete’s profile in terms of strength/time is a good indicator to guide the training process (Hernandez 2014).

Regarding Power, its importance to football is easily understood; many are the studies that found a positive relationship between higher performance indexes and athletes with higher power levels. This correlation is sustained by the amount of actions in football that directly depend on the capacity for generating higher power outputs in order to be successful (Turner 2011, Hoff 2004).

The Reactive Strength is another of the manifestations to be taken into account, given the positive impact in sports performance, namely in actions consisting of running, jumping and changes-of-direction (Brazier 2014). Besides the positive effect on performance, there is also an indication that the development of the reactive strength (and, consequently, the muscular stiffness), may have a positive impact in the injury reduction (Brazier 2014).

Having reviewed how each of the strength components impacts the performance in football and given the nature of high intensity action in a match, the assessment of each of these qualities is considered mandatory. This is proposed in the table below.

Table 1. Needs Analysis for the different capacities/actions in football, related to different playing positions

Having reviewed these needs, we understand what we have to pay attention to when assessing a certain player, playing in a certain position. This assessment will not only provide an athletic profile but will also point out the gaps that should be trained to perfect the Strength and Power profile of each player.

Assessing Strength and its different Manifestations

There are several tests described to assess the different qualities and, as we’ve introduced, selecting the test is a key part of this process. This choice may be dependent on several factors, such as: 1) the available equipment; 2) the number of athletes to be tested; 3) the level of the athletes and if they are familizared with the chosen tests or not. 

A simple assessment model proposed (taking into account constraints that most clubs face), could include the following tests:

  1. Squat Jump;
  2. Countermovement Jump;
  3. Drop Jump – Reactive Strength Index OR Triple Leg Hop
  4. 1RM Half Squat

With these 4 tests, the athleticism level of each player becomes clear (regarding the strength and power profile). This short and efficient test protocol allows the identification of the qualities that should be worked on.

Applying these tests, we now are able to run a critical analysis of the athletic level of each player, comparing the values with team peers or with other normative values published in the literature.One example of a intra-team comparison is showed below:

Table 2: Results of Strength and Power Profile Assessment (normative data based on Strength Diagnosis in soccer, published by Football Medicine)

Athlete comparison allows to: 1) identify the strengths and weaknesses of each team; 2) compare the needs of each player, comparing with other team players, depending on their playing position or not.

After identifying these needs, a specific goal of the training process can be created which fits the individual. Taking the example of three of these athletes, we can identify different needs.

In athlete 3, we see an overall underdevelopment of the maximal strength; according to what we explored before, since this is the basis for the remaining manifestations of force, the focus for this athlete would be the development of the maximal strength.

In athlete 9 we see that the maximal strength levels are good but a below-average reactive force and power indexes is observed; for this athlete, the training focus would be training the power and reactive strength.

Regarding athlete 25, we see that his assessment of the strength and power profile shows adequate results at all levels; this points us to a goal of maintaining the maximal strength levels and working, when possible, on enhancing the power and reactive strength.

Besides this global assessment, this profile could also include tests such as:

  • Unilateral strength/power tests – useful to assess the explosive strength qualities asymmetries between limbs, that may be considered as risk factors for injury, like single leg hop or single leg drop jump, for example;
  • Unilateral Strength Endurance tests – useful to assess asymmetries in strength endurance profile and fatigue resistance. These tests can include exercises for time or for maximum repetitions, such as the Single Leg (SL) Hamstring Bridge, SL Calf Raise or Side planks, which will also assess asymmetries between limbs.

One way of using the strength tests in order to decide the type of training needed is described in a brilliant article by one of the Football Medicine team members, which you can find on the Football Medicine website entitled “Strength diagnosis in Soccer”


Assessing Energy Systems

Looking back at the needs for analysis made for the football athlete (Table 1), we see that the complexity of actions involved in this modality stands out. The energy system assessment is a crucial step to distinguish the different profiles of the athletes and, with the results in mind, adapt the training methodology and aim for performance optimization.

We can characterize each of the energy systems by categorizing two distinct qualities, namely the capacity and power of each system: the capacity of a system tells us the amount of work that the system is capable of withstanding; the power assessment represents the maximum amount of energy that the system can produce per unit of time.

When we talk about anaerobic capacity and power, we are 1) inferring what energy capacity the anaerobic system can produce to maintain work, that is, anaerobic capacity and 2) what is the maximum amount of work that we can produce through the anaerobic system in a given time, that is, anaerobic power. The same thing can be done for the aerobic system, characterizing the athlete profile taking into account these different qualities.

Football is characterized by repetitive high intensity short duration actions, as well as a repetition of sprints (1 to 7 sec); however, these characteristics also change between playing positions. According to the reference values available at the time of this literature, we see that full-backs, wingers and forwards are the positions that hold the highest number of sprints per match and are as well the ones that cover the highest distance at high intensities (Rampini 2007, Di Salvo 2010). In this way, an assessment of the ability to perform repetitive sprints is an important marker of sports performance (Rampini 2006), especially in players taking these roles. The use of tests that evaluate the assessment of several sprints, separated by short periods of rest is a good way of replicating the physiological needs required during these actions on a match.

A Running-Based Anaerobic Sprint Test (RAST) is a test that has the goal of assessing the capacity of producing work for short duration actions at high intensity involving, in this case, the repetition of 6 sprints on a 35 meter distance, with 10 sec recovery between sprints. This test allows us to assess two performance markers: Capacity and Anaerobic Power. These measures are retrieved by assessing the fatigue index (determined by the % of work decrease between the best and the worst repetition), the maximum velocity in the best repetition or by the mean velocity in the 6 repetitions (Zagatto 2009).

Image Source: Science for Sport. 

Besides the RAST, there are other tests proposed to access the athletes’ anaerobic capacity. For example, two other assessment models have been proposed (Meckel 2009), with either a short protocol (12x12m sprint with 20sec recovery) and a long protocol (6x40m sprint with 30s recovery). After comparing the results of these protocols, the conclusion was that the physiological responses differ, even when the total sprint distance achieved was the same; given the characteristics of football (with short high intensity sprint actions), the conclusion was that the short protocol was the most representative of the sports demands and, therefore, the best fit. Other protocols, like the Rampini proposal (which consists of a 40m [20m+20m] shuttle sprint protocol with 20sec recovery between reps), also include changes of direction.

It should be considered that there have been many other proposed models to assess this physical quality and that, given this vast range of options presented in the literature, the chosen test should be adapted to the clubs’ reality and should be suited to the capacities intended to be tested.

Besides the anaerobic profile assessment, an even more relevant assessment is the aerobic capacity of our athlete; as mentioned before, this represents the bigger portion of a football match, with around 98% of the energy produced arising from aerobic metabolism and only 2% arising from the anaerobic system (Hoff 2004). This matter is reinforced by the strong evidence of relation between higher achievers in aerobic fitness markers and performance outcomes such as distance covered, time with ball and average sprints during the game (Turner 2014, Rampini 2006). Besides these performance indicators, high aerobic indexes are also related to higher competitive levels, final classification of the team and the difference between being part of the first team or not (Turner 2011, Turner 2014).

Due to the difficulty associated with the implementation as well as the costs regarding the utilization of laboratory tests in the aerobic profile, the field tests have been proposed as alternative measurements, revealing themselves as practical, time-efficient and reliable, with strong correlations with the physiological parameters assessed in the lab (Bucheit 2009, Thomas 2006). One example of a marker that can be retrieved for field tests is the Maximal Aerobic Speed (MAS), which refers to the minimal velocity through which the VO2max is achieved. It is a useful marker to quantify the intensity of the work being done in an energetic point of view and, with this, guide the training process. At the same time, it is a marker correlated to sports performance, differentiating athletes of different competitive levels (see table below).

There are many field tests that are proposed to assess the MAS: the 30-15 test, the Yo-Yo Intermittent Recovery Test, the Bronco Test, among others. All of these are valid and reliable options, having been scrutinized by science both for its physiological answers but also for its relation towards performance measurements. These tests, however, present with some differences between each other: they can be incremental (30-15 and Yo-Yo) or continuous (Bronco) and they can be linear (Yo-Yo) or include changes of direction (30-15 and Bronco).

On a simple note, some suggestions are more attractive due to an easier application. The Set Distance time-trials or the Set Time distance-trials are tests that present as valid and viable to estimate de MAS from a linear and continuous setting (Baket 2011, Bellenger 2015). These tests have the following principles:

    1. Set Distance time-trials: Setting a given time and writing down the distance covered in this time (ideally around 4 to 6 minutes). Given the following example:
      1. 5 min trial test, distance covered 1300m. MAS= distance/time (in sec) = 1300/300; MAS= 4,33 m/s.
    2. Set Time distance-trials: Setting a given distance and writing down the time needed (ideally between 1200 and 2200 meters). The example follows
      1. 2000m test, time needed 6’50” (410 sec). MAS= 2000/410= 4.88 m/s.

The application of these tests allows us to calculate the MAS in a continuous, linear manner and reach some conclusions, not only by intra-team peer comparison as well as the comparison with normative reference data (see Normative data for maximal aerobic speed for field sport athletes: A brief review (2013) Baker, Dan; Heaney, Nathan).This allows us to identify the athletes that present the best or the worse aerobical fitness but, at the same time, to retrieve data needed to prescribe the training.

Besides the MAS, there are other interesting measurements that we may retrieve from these tests. One example is the Anaerobic Speed  Reserve (ASR), calculated as the difference between the Maximal Sprinting Speed (MSS) and the MAS. This measurement is equal to the work capacity that is capable on intensities above the MAS. This measurement is useful in assessing the anaerobic capacity and can be an alternative to the repeated sprint tests (Dardouri 2014), which are themselves time costly.

Given access to the MSS, we can calculate the ASR following the equation: ASR = MSS – MAS. Taking the last example of the 2000 meter trial test, if the athlete presents with 8,5 m/s MSS, we can conclude that the ASR is 3,62 m/s (8,5 – 4,88).

Below we present a table with the results of a time trial, with the MAS, MSS and ASR calculated (Table 4)

When analysing the data present on the table above, we see that the MAS values retrieved can be either compared to normative data but also used to compare between playing positions, correlating them to the performance markers on the field. Through this assessment, we can better characterize the fitness level of our athletes, both aerobically and anaerobically. Taken as an example, if through this evaluation we identify that an athlete has a good anaerobic profile but has some deficits from an aerobic point of view, it is possible that, when recruited for a longer activity, he enters an anaerobic regime too early, leading to the early induction of fatigue due to the inability of the anaerobic system in sustaining work for long periods of time. On the other hand, if a good aerobic base is lacking, the recovery between high intensity efforts will also be penalized and lead to an earlier onset of fatigue. 

Optimizing the MAS becomes one of the main goals of the training, in order to maximize the aerobic system capacities and enhance recovery between high intensity efforts.

The ASR marker analysis (not having any normative values described) should be made taking into account the team colleagues as well as the playing position. It is known that this marker correlates with the capacity of sustaining work above the MAS and is, for that reason, an anaerobic capacity marker that should not only be relevant for the assessment process but also to guide the training, specially in speeds above the MAS.

The ASR is intimately correlated to the maximum sprint velocity and the aerobic capacity and should therefore be developed in this continuum; this means 1) looking to optimize the maximum sprinting velocity (enhancing the anaerobic capacity; and 2) optimizing the recovery capacity between sprints/high efforts actions – enhancing the aerobic profile. 

On the other hand, if a deficit is identified when it comes to the ASR and the aerobic profile presents with optimal values, the training session should focus on this quality: focusing in the ASR limit; in other words, the need to develop the maximum sprint velocity as well as increasing the capacity of resistance to repeated high effort actions, both increasing this capacity and the reserve capacity of this system.

With this assessment, on the same line of thought as done with the strength and power profile, we’re able to create a energy system profile that includes the aerobic profile (through finding the MAS) and the anaerobic profile (by calculating the ASR). With this, we’re able to identify the athletes’ necessities and individualize the training process and goals.

Authors: André Mendes e Lucas Brink Carvalho

Ready for Part 3? Here we go!


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