[Agility Lab] The Fundamentals of 180 Degree Turns

A 180-degree turn can be broken down into three different components:

1. An approach phase where the athlete accelerates up to an effective speed
2. An entry phase which is a maximal deceleration while the body begins rotation
3. An exit phase which is a maximal re-acceleration into the new direction

The Approach

The approach is simply acceleration, the important skill here is the athlete’s ability to moderate their speed to match their deceleration abilities. This is the concept of affordances. The athlete must know “how fast can I move within the space I have but still be able to decelerate and complete the task”. “How long can I afford to accelerate for?”.

The Entry Phase

The entry phase is where most of the important technical features exist and is where you want to focus your coaching time. Interestingly, it is the component which we know the least about as deceleration remains poorly understood. In the entry phase, if you are slow, performance suffers. If you are fast, but end up in a rubbish position, performance suffers.

This isn’t saying that the re-acceleration isn’t important, just that the effectiveness in the re-acceleration is difficult without a good competent entry phase. Unless you just go slowly, which isn’t useful for anything.

“The deceleration component should begin as late as possible, but as early as required to suit each athlete’s deceleration capabilities”

If someone is an effective decelerator, they will start the deceleration late, brake over a short distance and end up in an effective position at the plant step. This means they can accelerate for longer, getting up to a faster speed and save time. If they are a poor decelerator or they have approached from a long distance away, they will begin the deceleration component early to spread the required impulse over more steps. This might be decelerating over 7 steps instead of 5. Remember, as late as possible, but as early as required to end up in an effective plant step position.

When the deceleration phase begins, the early steps should provide some braking force and facilitate early changes in the centre of mass (COM) and base of support (BOS) relationship. The COM should lower, and the BOS should move in-front, allowing the production of a shin angle which points behind you.

One of the very first movements you’ll see as someone approaches these turns is a subtle drop or hang back of the inside shoulder. This is the start of the rotation, drop-in COM height and the BOS moving forwards. There are then steps between the first braking step and the last (the plant step) where these positions continue to be exaggerated. Once you start to identify this in athletes, you realise just how much impact having a pre-planned task has on early kinematics. It might be 6 or 7 steps away from the turn line the body starts to organise itself to optimise the movement. Hence why the time constraints in reactive movements are so impactful.

The COM and the BOS manipulation cannot be separated in our analysis. The main reasons we lower our COM is so our legs are able to reach different points on the ground and create greater direction-specific shin angles. The rotation component is important to help the later exit phase. Remember a key principle of the re-acceleration phase is to get to the sagittal plane fas early as possible. And the more rotation needed in the transverse plane at this stage, the harder that is to do. Once this entry phase has taken place where the COM has lowered, the BOS moved forwards and the body began to rotate towards the new direction, the athlete has a final ground contact before moving back into the original direction. This final ground contact is referred to as the plant step.

Remember that the role of each step in a change of direction such as this is to optimise the ability of the step following it to do its job. If the penultimate step (the final step prior to the plant step) doesn’t sufficiently reduce momentum (or the steps preceding it haven’t performed their role either), this will influence the position and loading of the plant step.

Four priorities to look for as the athlete enters the plant step:
1) Approximately 90 degrees or rotation (half of what’s required)
2) Lower COM height
3) Both legs with a shin angle facing the new direction

Once the penultimate step has maximised its braking force it may remain in contact with the ground and provide some vertical support to maintain COM height. This part of the movement is the only point within a 180 degree turn when the body will have support from both feet at the same time. This is because to optimise the shin angle of the plant step, the location of it must be outside the BOS where it cant effectively support the body mass. It is also logical for the penultimate step to remain in contact with the ground because the position which it requires to apply braking force, is similar to the position which it requires to optimise its role in propulsion. Therefore, this same leg, at times without leaving the ground acts at the final braking step (penultimate step) and the first re-acceleration step (propulsion step).

However, It is common for the penultimate step to lift slightly while the plant step is in contact with the ground. This is commonly seen in athletes whose COM has not been sufficiently lowered, insufficient rotation has taken place or the penultimate step location isn’t also optimised for re-acceleration potential.

If this leg executes its role effectively, the plant step can then occur with minimal stress and the transition between entry and exit is fast and effective. If this leg doesn’t effectively perform its role, the plant step is overloaded reducing the safety and the effectiveness of force application.
An effective plant step should be stiff, have a fast ground contact time and be the final step prior to the exit/re-acceleration phase. Anything that has been ineffective before that point will likely slow the ground contact time and reduce the effectivenes of force application.

Simplifying the role and muscular demand of each step looks like this:

Penultimate Step (Entry) = deceleration and an eccentric muscle action
Plant Step = final deceleration and initial re-acceleration with a more ‘isometric’ muscle action
Propulsion Step (Exit) = re-acceleration and concentric muscle action

The Exit Phase

The exit phase is simple. It is mainly going to be a product of your acceleration capabilities, the position you put yourself in during the deceleration phase and your ability to apply force effectively.

Summary:

In coaching it feels like there is loads to look at. But the simplest framework is to look at the plant step position as this is the outcome of everything that has happened before it. Once we have evaluated what we see, we can go back to the entry phase and see what the earliest issue is to start to plan out intervention.