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sábado, 31 de agosto de 2013

Decelerations: relationship between velocity, acceleration and time

Approaches and level of analysis of the physical demonstration of professional soccer players. Level 4 (part 11).

And we finally arrive to the last post on this issue to let go to the next level of the approaches.
In it we present and (try to) explain a graph in which velocity, acceleration and time of some decelerations performed after a sprint arriving to a different velocity has been performed.

This decelerations has been performed by an Spanish veteran amateur soccer player, so we have to be analyze with caution this data, done the differences that can exist between this soccer player profile and younger soccer players and/or soccer players of higher level of performance.

In this graph you will see in the X axis the instant velocity data, and in the Y axis both the acceleration and time data.
Basically, it seems as if the time to demonstrate the maximum acceleration value during the decelerated sprint becomes higher with higher velocity values, and as if the acceleration demonstrated during those decelerated sprints become harder (higher deceleration values) with higher velocity values.

Hope you enjoy!!!


sábado, 24 de agosto de 2013

Decelerations using "raw data": relationship between time and acceleration

Approaches and level of analysis of the physical demonstration of professional soccer players. Level 4 (part 10).

As we have seen in previous posts, one of the problems we have when analyzing GPS data is the use of different filters, that in most cases we don't know which are and how they modify the original raw data.
That said, we also know that the filters are an invaluable tool when using this short of data, without which we can not work.

But in this case, the idea is to analyze if with the raw data we can see the same tendencies observed with filters (commented in previous posts) or there is some other questions that arise ...

The basic data you will see in the graphics is exactly the same used before, but in this case without applying any filter, and it comes from an veteran spanish soccer player, that has performed different exercises and specific tasks (sprints with different decelerations and CoD, and also data from some SSG), wearing a GPS unit working at 5 Hz.

Stay tuned,




domingo, 18 de agosto de 2013

Relationship between velocity and acceleration

Approaches and level of analysis of the physical demonstration of professional soccer players. Level 4 (part 9).

Directly related with last video post, you will see the relationship that is establish between velocity and acceleration demonstrated by soccer players, with data obtained during some analytic drills performed at different intensities and in different conditions (with or without CoD, and with different speeds prior the deceleration), by a spanish veteran soccer player or some professional swiss soccer players during training or games.

As you will see, it seems that the maximum value of acceleration when decelerating is shown with an average velocity value of around 2 and 5 m/s, but not more, what could be interpreted (in absence of more specific data) as if the subjects would need to "slow down" their velocity until they can manage all the mechanical load imposed in their body when performing this short of decelerations.

We have to think that decelerating abruptly with a high quantity of energy accumulated (as with high velocity previous the posterior deceleration) and specially when it is performed suddenly as a response of the needs imposed by the game (during training or matches) is really a hard task directly related with very high forces supported by the body and their main directly implicated systems (as osteoarticular and tendinomuscular systems) just with one leg (when planting the foot on the ground) and not always in a favorable situation (think on degrees of freedom of different articulations, position, ...).

Hope you enjoy it,


lunes, 12 de agosto de 2013

Relationship between time and decelerations

Approaches and level of analysis of the physical demonstration of professional soccer players. Level 4 (part 8).

We follow with some basic relationships between decelerations and, in this case, time for arriving to the maximum value of deceleration.

In default of more studies with large samples of soccer players, and specifically professional players, we observe that harder decelerations are performed in less time, so at first, this concept should be introduced when analyzing decelerations, especially when taking in account its intensity.

The data showed today has been obtained with a 5 Hz GPS unit, from a veteran spanish soccer player, when performing sprints with CoD in different conditions, changing the velocity prior to the CoD, changing also the way of performing the deceleration (hard, hard trying to apply more flexion on knees and hip, progressive, etc.), and when training using different SSG.

One very important thing that usually is forgotten is that the Hz of your units, but specially the filters used by the system - software used, modify this short of relationship between decelerations and time, so we have to be careful when doing this short of analysis done that this information is not used, not known by the users.

Enjoy,


martes, 6 de agosto de 2013

Relationship between acceleration, deceleration and impacts

Approaches and level of analysis of the physical demonstration of professional soccer players. Level 4 (part 8).

You know that actually one approach when analyzing the load that soccer players are experiencing during training and competition is related with the number of decelerations performed. We have been talking about some characteristics of decelerations, and their relationship, and also we have shared some data to better understand all this issues.
Despite we tend to relate decelerations with the eccentric muscular load experienced by players, we sometimes forget that there is also a relationship between decelerations and the load in joints, bones and tendons, which we can approach to its measure by the impacts (shock) count.
This is a very interesting approach to have in account specially with some injured players (when they are in their readaptation (rehabilitation) process.

Done that, you will see a simple example of a sprint with a CoD of 12m + 12m performed by a veteran spanish soccer player, with the relationship between the phases of acceleration and deceleration (also the CoD), and their relationship with the impacts performed.
Remember that the impacts are measured by a triaxial accelerometer working at 100 Hz, but the velocity (and  the acceleration derived) is measured by a GPS working at 5 Hz, but when exported to Excel, the data appears at 1 Hz ... (for further questions on this issue better ask directly for them, please). These are some of the problems that you have to, at least, know about the technology we are using (and this is one of the main brands on GPS for sports ...).

Enjoy,