MPEs vs bursts – part 2

May 28, 2024 | ACADEMY

In part 1 of the article, we started exploring the nuances of high-demanding actions in football through the lens of metabolic and mechanical approaches. Let’s continue the analysis by answering the next question.

is there any link between MPEs and bursts?

The first point to stress is that both MPEs and bursts are expressions of high intensity but refer to different aspects of the performance (metabolic vs mechanical). For this reason, they should not be confused. Indeed, even if accelerations have an impact on both of them, moderate accelerations in combination with certain speeds lead to an MPE because of the high anaerobic energy required. However, a burst is performed only if the player is close to her/his ASP. As such, we can consider the bursts a subset of the MPEs family or “the most demanding MPEs”.

Everything can be graphically displayed starting from the ASP for a better understanding. Once the player’s ASP has been determined through a maximal sprint (Figure 2, left panel), the area where the bursts occur can be easily defined (Figure 2, right panel). All the combinations of velocity and acceleration that fall in the purple area are considered bursts. From this picture, it’s quite clear that a burst can be carried out regardless of a fixed acceleration threshold, whatever this threshold value is: to be close to the ASP a very high acceleration is required if the player starts from low speeds; on the contrary, if the starting speed is high, a burst demands a rather low acceleration. And this consideration shows that counting the accelerations above one fixed arbitrary threshold doesn’t make much sense.

Figure 2Left panel: time course of the speed during the maximal sprint test (green dots) and exponential function that best fits the raw data (purple curve). Right panel: ASP obtained via maximal sprint test (dark purple line); 80 % of the external power output (ASP₈₀) allows us to define the zone of high intensity from a mechanical perspective (light purple area).

To stress even more the difference between MPEs and bursts, let’s consider the following intermittent exercise: 20 seconds to cover the overall length of the football pitch (about 100 m) and 20 seconds recovering on the spot (Figure 3, left panel). Representing this intermittent exercise in the acceleration-speed graph it’s immediately clear that this workout is far from the intensities entering the ASP zone (Figure 3, right panel). This simple image immediately leads to a very interesting comment: according to the criteria of the fixed acceleration threshold, each repetition yields an acceleration event above 2.5 m⋅s⁻² as is indicated by the grey dashed line in Figure 3, right panel. Can we consider these accelerations interesting from the neuro-muscular perspective? Are these the accelerations we’d like to see in our report?

The answer is “probably not”! Indeed, the acceleration peaks from the intermittent runs (about 3 m⋅s⁻²), despite being above the acceleration threshold of 2.5 m⋅s⁻², are far below the maximal acceleration achieved in the maximal sprint test (about 5 m⋅s⁻²). Therefore, it does not make sense to consider these actions (requiring only 60% of the player’s maximum potential) as high-mechanical spells. However, it’s also true that the same acceleration performed starting from 10 km⋅h⁻¹, rather than from scratch, would be an action very close to the maximum. We definitely cannot hope to solve this issue by dealing with acceleration alone: both velocity and acceleration must be considered to detect the most demanding actions from a neuro-muscular and metabolic standpoint.

Figure 3 – Left panel: time course of the speed during the maximal sprint test (green dots) and three repetitions of a 20/20 intermittent exercise (red dots). Right panel: both exercises are represented on the ASP graph (dark purple line) and ASP₈₀ (light purple line). The horizontal grey dashed line indicates the acceleration threshold (2.5 m⋅s⁻²).

What about the metabolic load of intermittent exercise?

To figure things out, it’s helpful to always refer to the ASP (Figure 4). On this graph, the curve corresponding to the VO2max of the player (about 20 W⋅kg⁻¹ for an elite football player) is also represented (red curve in Figure 4). This makes it possible to highlight the zone where any activity can be carried out only thanks to the anaerobic energy supply (light red area in Figure 4). Of course, the ‘ASP zone’ includes the most intense activities performed thanks to the anaerobic energy stores (dark red area in Figure 4). From all this, it becomes clear that there is a multitude of activities, that are not necessarily ‘extreme’, performed at both moderate speed and acceleration with a metabolic power requirement greater than the VO2max. This state of affairs highlights the balance between work and recovery phases, a key component in team sports performance.

Figure 4 – As from Figure 3, besides the ASP and ASP₈₀, the couples of speed and acceleration corresponding to a metabolic power of 20 W⋅kg⁻¹ are indicated by the red curve. The anaerobic zone above 20 W⋅kg⁻¹ is highlighted in red (see text for more details). Maximal sprint and intermittent runs, as in Figure 3, are indicated by the green and red dots, respectively.

In conclusion, is the difference between MPEs and bursts clear?

We hope so… but we have just to keep the following points in mind: both MPEs and bursts are expressions of high intensity; the former refers to the energetic balance between high-demanding and recovery phases that characterise the intermittent nature of the performance in team sports (a kind of anaerobic/aerobic ‘equilibrium’); the others represent the most intense neuro-muscular efforts that are carried out thanks to the highest accelerations achievable (very high at low speed and the lower the higher the speed) that require ‘extreme’ increases in muscle activity.

Further scientific content on mechanical analysis is available within the gpexe academy for all users (access from the web app footer).  
Additional references:
P.E. di Prampero, “Mechanical and Metabolic Power in Accelerated Running-PART I: the 100-m dash” – PubMed
C. Osgnach, “Mechanical and metabolic power in accelerated running-Part II: team sports” – PubMed
C. Osgnach, “How easy is to stumble over acceleration and deceleration?
C. Osgnach, “The limits of acceleration” 
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