Physiological Responses to Linear/Non-Linear Soccer Simulations.

Phys Responses JSCR

Our recent study investigated the Loughborough Intermittent Shuttle Test (LIST) (Nicholas et al., 2000) and it’s effects on neuromuscular fatigue when adjusted.

The problem with this ‘gold standard’ simulation is that, though it mimics the demands of a typical soccer game, it’s ecological validity was to be questioned.. how could it mimic the demands of a soccer game if the testing was completely linear (running in one straight direction)? Nonlinear running is frequently performed during soccer matches, with professional players completing 727 (+/-) 203 swerves and turns within a single match (Bloomfield et al., 2007). Such swerves require a great deal of rapid changes of direction and decelerations.

But to successfully complete these actions in soccer, repetitive demanding muscle contractions are necessary, particularly those of an eccentric nature and the cumulative effect of performing these type of contractions ultimately leads to fatigue, less efficient movement patterns (Small et al., 2009) and an increased risk of injury (Greig & Seigler, 2009). Research has also suggested that nonlinear running induces greater heart rate (HR), perceptual, and metabolic responses than straight-line (linear) running (Dellal et al., 2010), but this has also been questioned in recent studies, where they found similar drops in jump performance regardless of the type of running (Hader et al., 2016).

JSCR Infographic

Summary of study. Credit to Adam Johnson @PreventionPhys

The aim of our study was see if a modified version of the LIST could be incorporated mimic the demands of soccer while also achieving a similar amount of swerves and turns as reported in Bloomfield’s paper. The modified LIST allowed for the inclusion of 6 x 90degree and 1 x 180degree changes of direction (COD) per run. This meant that there was a total of 720-1008 COD’s within the whole protocol without altering total simulation time or activity time during the simulation.


8 university football/rugby athletes too part measures including blood lactate, heart rate (maximum and average), jump height, peak landing and isometric force, and perceived fatigue were measured across the testing period. The running was monitored through Global Positioning System (GPS) trackers attached to each participant.


Though participants found the modified LIST harder through perceived fatigue and heart rate measures, it portrayed no changes to jump height and isometric/landing forces. The modifed LIST did not change the total distance covered in the LIST but did change the amount of decelerations and the high speed running (HSR) distance. However,  greater HSR distances were directly related to reductions in isometric hamstring force.

What does this mean?

COD’s do seem to induce higher ratings of perceived fatigue but HSR distance plays a role in hamstring fatigue, indicating how important this GPS variable is for sport scientists and coaches alike when it comes to monitoring training load and managing fatigue. It also allows for changes to training (particularly related to small sided games or metabolic conditioning) by incorporating COD’s which could reduce HSR distance but still lead to higher or similar metabolic demands.


The modification to the LIST was based on multi-directional running at 1.5x the timing of the maximal effort run timing of each participant. The COD’s were positioned in a manner that did not alter total distance covered by the original LIST. However, such timings and COD positionings may have given participants enough time to run and change directions at a pace which did not require a great deal of side cutting mechanics but full body turns following lesser speeds of running.

The study would ideally have aimed to recruit a larger sample size of professional athletes to see if these results reflected the larger population of professional soccer players.

Full study available here:

An Introduction to Concussion within Combat Sports (Part 1)

All of these animals have shock absorbers built into their bodies. The woodpecker’s tongue extends through the back of the mouth out of the nostril, encircling the entire cranium. It is the anatomical equivalent of a safety belt for its brain. Human beings? Not a single piece of our anatomy protects us from those types of collisions. A human being will get concussed at sixty G’s. A common head-to-head contact on a football field? One hundred G’s.

From the film ‘Concussion’ in 2015 based on some real life events and people.

Now while the whole film, let alone the quote, may not be completely scientifically accurate (or even about concussions). It is a profound statement allowing us to recognize the amazing intricacy of design for each and every organism, yet how fragile and dependent we are upon these designs.

The brain sits in a pool of cerebrospinal fluid without any connection to the skull. As shown in the quick movie clip; the example of an apple in a slightly filled jar of water gives us a parable of how the brain moves with each impact to the skull (in this case, the jar). With each impact to the jar, it leads to the loss of integrity of the apple, eventually causing it to crack. In the case of the brain? It’s a lot more complex than that.. a neatly packed piece of jelly with specific functions, hitting onto the cranium and causing the jelly to be stretched and sheared at a microscopic level.

SO what is a ‘Concussion’?

Concussion, also known as Mild Traumatic Brain Injury (mTBI), is an injury through impact to the head (brain) which causes temporary losses in brain function.

It has been previously described as “a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces” (Quality Standards Subcomittee, 1997)

It makes up 80-90% of TBI cases but is notably distinguishable from other forms of TBI because, there are no gross pathologies such as a hemorrhage or identifiable damage of the neural structure through conventional neuroimaging techniques such as MRI (Noble & Hesdorffer, 2013). This means it is quite difficult to diagnose and has many generic symptoms which can easily make it a condition which is misdiagnosed or more importantly, ignored or unnoticed.

How does it happen/What causes it?


Concussion is caused by acceleration, deceleration and rotational forces applied directly or indirectly to the head, leading to the damage of brain tissue. These forces can occur from direct or indirect impacts, hence concussions are not only the result of impact to the head, but from impact to the body resulting in head movement (e.g. car accidents involving a whiplash {coup-contrecoup})

(Note: The amount of movement in the picture above is not an accurate representation of brain movement within the cranium, but gives us an idea of the acceleration/deceleration forces on the brain during impact that leads to stretching of brain tissue)

Image result for concussion

The principal causes of head trauma in combat sports include straight impact blows to the face (e.g. jabs and front kicks) leading to linear acceleration of the head or impact from an angle (e.g. roundhouse kicks, hooks and uppercuts) leading to rotational acceleration (Unterharn-scheidt, 1995). High incidences are also seen within sports such as American Football, Hockey, Rugby, Football (soccer) and Basketball (Harmon et al., 2013). These are the results of head on head collisions and collisions with the ball or ground.

Image result for concussion sports

The movement of the brain within the skull can lead to shearing of cells along with stretching and disruptions at the structure of the neurons within the brain. The stronger the impact, the larger the stretch and deeper it may affect the brain. It is said that a 15% stretch of the neuron length will result in biochemical changes (such as membrane depolarization and deregulated release of neurotransmitters) resulting in an acute failure of neurons leading to a concussion (Gaetz, 2004). 

Through studies observing biomechanical forces to the brain, severity of impact to the brain has been observed to increase with weight class. In addition, it has been reported that the punch of a professional boxer may generate forces on impact that are equivalent to a 6kg bowling ball rolling at 20mph (Athaet et al., 1985)

Some studies have suggested changes in neural function even after standard header practices within soccer, which may suggest that with each exposure to head impact, there is an increased risk of concussion.

How prevalent is it?

The Centre for Disease Control and Prevention (CDC) reports an estimate of 135,000 patients per year to arrive at emergency departments with concussions from sports or recreational activity (Laker, 2011).

Within combat sports, particularly boxing and kickboxing, concussions account for approximately a third (33%) of injuries experienced by fighters . Similarly, 28.3% of fight stoppages within MMA have been reported due to head trauma with a rate of 15-16 concussions per 100 bouts (Curran-Sills & Abedin, 2018; Hutchison et al., 2014; Buse, 2006). It is most frequently observed in American football, especially linemen and linebackers, who are reported to be exposed to more than 1000 impacts per season (Crisco et al., 2010).

Even the sport of soccer/football has been observed to have significant rates of concussion with reports of 1/5th of injuries within high school games to be due to concussion (Kerr et al., 2018)

What are the symptoms?

Typically, clinical symptoms straight after a concussion include:

  • Headaches
  • Nausea
  • Loss of consciousness,
  • Blurriness
  • Fatigue
  • Loss of motor control (balance/coordination)
  • Loss of memory, concentration and attention
  • Change in mood states

(McCrory et al., 2012; Ropper & Gorson, 2007; Hall et al., 2005).

Most recover within days to weeks. However, 10-15% may experience persistent issues even after a year (Hall et al., 2005; Sterr et al., 2006).

Though loss of consciousness (e.g. Knockouts) is generally attributed to concussion, it is important to note that this is only known to occur in 10-20% of cases (Giza & Hovda, 2001), indicating it still may occur 80-90% of the time, regardless of an obvious sign.

However, even if these symptoms are eventually not apparent.. or concussion is not diagnosed..

with newer electro-physiological techniques, researchers now question has the brain actually recovered? Yes, the symptoms can cease to exist, but are there any unknown/residual effects?

Short answer: We’re not quite sure yet!

Less shorter answer: The risk of further concussions and musculoskeletal injuries have been reported to increase in athletes with previous concussions (Guskiewicz et al., 2003; Herman et al., 2016; Nordstrom et al., 2014), which suggests that some of these concussion-related changes to the brain have not yet truly healed. Some research also suggests that in some cases, the brain to muscle pathway still portrays signs of disrupted neural pathways even after 9 months post concussion (Lewine et al., 2007; Huang et al., 2009; Lewis et al., 2017).

Therefore the question is: How much do we still not actually know about the effects and potential causes of concussion in sports, let alone the sports which involve which involve repetitive head impact?


  • Part 2: Concussion diagnosis tools and management