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Swing Phase Preparatory Loading
Are you consciously helping your clients to load their limbs correctly? The final stage of the swing phase has a lot to do with how the hoof/paw strikes the ground. Through exercises which deliberately target the swing phase we can influence and improve impact with the ground and therefore the forces that are transferred through the limb joints.
During assessment we tend to focus on how the limbs are moving and landing. It is easy to get hung up on the stance phase because this is what we are trying to influence, right? If we can influence how our patients bear weight then we can influence the forces that are transferred up the limb? Well yes this is right but are we also paying enough attention to the swing phase and the preparation of loading?
Think: Think about your assessment routine. Do you look at the swing phase and consciously consider how it is linked to how the limb strikes the ground? If the ground strike is suboptimal do you look backwards in the stride to see where perhaps you might be able to influence the movement of the limb through the air and therefore the way it lands?
What affects swing?
During the swing phase of the stride we would like to see the limb moving through a good range of movement. As well as maximal protraction and retraction we should also be considering the flight arc. A low flight arc, where the limb travels low to the ground or even drags, is undesirable. This can be a sign of pathology and pain but also weakness or poor motor control. During the rehabilitation phase, once the primary issue and pain is controlled, the animal is often left with a poor swing phase which we need to retrain.
Elastic energy contributes to the initial protraction of the limb during the first part of the swing phase but in walk especially, there is significant muscle contribution required for the limb to reach its highest point and produce a nice flight arc. Therefore, lack of muscle strength and control can lead to a low flight arc. In my experience this can be overlooked as a possible cause of ‘toe drag’ and it is often assumed that this clinical sign must be linked to an underlying pathology.
Peak flexion of the limb joints occurs during swing so it makes perfect sense that a lack of range of movement (ROM) will affect the swing of the limb. Range of movement may be restricted through pain, joint instability, muscle imbalance, poor motor control and feedback. If the limb can’t ‘fold up’ effectively, due to any of the above then there will be a lower or altered flight arc and probably some cheat strategies going on further up (that’s for another day).
As the limb moves into the final part of the swing phase, it starts to prepare for loading and this is where I think we could pay more attention. The focus in rehab can often be on improving ROM and positive (concentric) muscle strengthening. This is all great work and increasing flexion and power is essential but are we thinking enough about deceleration and the negative contraction and limb control? You can have lots of power in push off and optimal flexion of the joints but then what happens to the limb in preparation for ground strike? Is there too much control? Or not enough?
Swing phase retraction
The final part of the swing phase is ‘swing phase retraction’. This is where the limb is pulled backwards prior to landing. This reduces the horizontal velocity and preps the hoof/paw to land in the right place, optimising the forces that travel up the limb. Let me provide a few examples of how irregularities in this stage of the swing phase may present:
A dog who has suffered hip pain or a horse with heel pain may be overactive in this phase. This will present as a shortened stride, causing ‘toe first’ landing and affecting the forces through the limb joints. Addressing the primary problem will not always see a full return to normal movement as these movement pathways have been well ingrained and this is where rehab comes in. In this example we want to increase protraction and the speed at which the limb travels forward and reduce the overactive retraction to a normal level.
At the other end of the spectrum some patients have lost control over this phase. This can be due to protractor retractor muscle imbalance and weakness in the retractors (also core strength, but that’s another day another nibble). It is not always so obvious to see in these cases but this lack of controlled swing retraction and therefore loading, can lead to variable hoof/paw placement and what I call a foot slap (literally where the hoof/paw slaps the ground rather than being placed nicely). Due to the lack of reduced horizontal velocity, these cases can also commonly slip and slide especially on a non-grip surface. In this example, we want to promote controlled swing retraction.
Think: Can you think of some cases that have either been overactive in swing phase retraction or lost control of it? Can you see how these movements have altered the way the limb has been prepped for loading?
What can we do to influence this stage of the swing phase and better prepare the limb for loading?
It is less about learning any new magic exercises and more about being intentional about prescribing the exercises we already use with the aim of influencing this phase. Some examples of exercises that can be used to influence swing phase preparatory loading are:
Leg weights – it’s common to consider leg weights for strengthening of the hip and elbow flexors but they also have the added benefit of increasing negative (eccentric) work to help control the movement of the limb. The weights increase forward momentum of the limb so there is extra effort required to pull the limb backwards to the ground. Therefore, careful and appropriate use of leg weights may be useful in patients who have trouble controlling swing retraction (foot slappers!).
Cavalettis/poles – poles and cavalettis have become quite the trend in rehab and training but I would really like to encourage more considered use of these very valuable props! We really need to watch animals closely when setting pole work and evaluate how they are using their bodies to navigate through the obstacles. Quadrupeds are very good at cheating and it is essential we pay attention to HOW they get over the obstacles rather than just the fact that they can (or can’t). Poor pole or cavaletti work will just reinforce the poor patterns we are trying to break. Generally, those with overactive swing retraction will benefit from low poles but gradually moving the distances further apart to encourage reach. You can have closely spaced raised poles in one set and low poles which are spaced further apart in another set. Break this exercise down into smaller parts.
Resistance – using resistance training will help to increase force and speed of protraction in those who are retracting their limb too early in the swing phase. Resistance can be applied to dogs with resistance bands. Also, using the resistance of water is useful in these cases but the water needs to be deep enough so that they cannot step out and over it (consult a hydrotherapist).
Declines – walking downhill recruits the retractor muscles and relies more heavily on negative (eccentric) muscle strength and control. To progress this exercise, poles can be added on the hill and then steps down. These exercises require the animal to pull the limb back against the ground to counteract the increased gravitational forces, so are very useful for those who have a lack of control in swing retraction.
You can see by some of these exercises that you don’t always have to train the swing phase to improve the swing phase. For example, when walking downhill, it is the stance phase which develops the strength to improve the final part of the swing phase. With a little creative thinking, it is possible to develop exercises that can influence the way the limb moves through the air and therefore influences how it strikes the ground. Of course, there is more to add to this: abduction and adduction, flexion and extension of individual joints, core strength etc. But this is a good place to start!
Actions:
- Review your assessment protocol. You probably take a cranial and a lateral view but when you notice unbalanced loading what do you look at next? Utilise slo-mo video to take a closer look at swing phase retraction and see what is happening there.
- Review your exercise repertoire. Once you have added this extra perspective into your assessment, what steps will you take to address any problem you find? Have a think about what exercises you could use or add into your plan.
- Review your cases. During your treatments next week, have a look at swing phase retraction in your patients and see how it might be playing a part in the overall picture!