Assessing Achilles Tendinopathy with Force Plates

Guest article – Talysha Reeve B.App.Sc.(Podiatry), Graduate Certificate in Clinical Rehabilitation, Cert IV Fitness.

Talysha is an internationally-recognized podiatrist and educator, having presented at both live and online educational workshops, seminars and conferences to health practitioners from around the world.

Talysha is the founder of The Progressive Podiatry Project and P3 Japan education platforms. She also provides academic lecturing and biomechanics clinical supervision at the University of South Australia. In addition to this, Talysha provides injury management consultancy and contributes to the operations of the Podiatry Board of Australia.

We invited Talysha to write the following article on assessing Achilles tendinopathy with force plates.

Achilles tendinopathy is one of the most common non-acute lower extremity musculoskeletal pathologies seen in clinical practice, presenting in both active and sedentary populations. There are relatively higher incidence rates in active populations compared to less active populations, in addition to active populations also experiencing concerningly high recurrence rates across various sporting populations.  

Other injuries (such as ACLs), in which similar problems relating to high incidence and injury recurrence rates, have turned to technology to provide further insights that can guide clinicians toward successful return-to-play decisions. Given the broad clinical utility objective data provides, force plates are becoming increasingly popular in musculoskeletal (MSK) research and clinical practice.     

This resource is designed to enhance a clinician’s understanding of functional deficits and relevant assessments in those with Achilles tendinopathy and share a proposed evidence-based test battery utilizing force plates, such as VALD’s ForceDecks, that can improve our clinical decisions and rehabilitation outcomes. 

Integrating a force plate testing battery into our clinical assessments can help: 

Save time in the development of our rehabilitation management plans.

Improve our ability to educate patients and key stakeholders.

Engage clients in their rehabilitation.

Make more informed clinical decisions for progressing clients.

Make clinically sound return-to-sport decisions.

As with other conditions that can affect such a broad demographic, it is important to recognize that the potential contributing factors are highly variable for each individual, consequentially the requirements for successful management and functional restoration programs need to be specific to the individual. Not only does the program need to be targeted to the individual’s presenting functional impairments, but it also needs to reflect their functional goals.  

...successful management and functional restoration programs need to be specific to the individual ...the program needs to be targeted to the individual’s presenting impairments and needs to reflect their goals.

Rehabilitation programs that lack this individualization often underpin many of the obstacles and setbacks patients face when attempting to return to their sporting activities. The lack of individualization often does not allow clinicians to be proactive and responsive to the diverse functional restoration requirements of each individual patient. 

Subsequently, this can result in insufficient rehabilitation, in addition to either underdosing or overdosing a prescribed exercise, leading to protracted recovery times, as well as seeing a potentially increased risk of injury recurrence.    

Specific and Targeted Rehabilitation 

A recent systematic review of athletes with Achilles tendinopathy conducted by Quarmby et al. (2023), identified a number of consistent biomechanical alterations and performance deficits resulting from the pathology that impact gait and other motor tasks involved in sporting activities. Many insights relating to these functions can be easily assessed via various clinical tests performed on ForceDecks. 

As previously mentioned, identifying and monitoring performance deficits allows clinicians to make informed rehabilitation programming decisions.  

New to Force Plates and want to know more?

The work of Seymore et al. (2024) highlights the importance of proactive assessments and management quite well. With the authors reporting up to 41% of individuals who have experienced unilateral Achilles tendinopathy may go on to develop bilateral symptoms, likely in part due to compensatory gait alterations that develop post-injury. 

…up to 41% of individuals who have experienced unilateral Achilles tendinopathy may go on to develop bilateral symptoms, likely in part due to compensatory gait alterations that develop post-injury.

Within this study, altered gait patterns and ground contact time (GCT) asymmetries were identified in those with Achilles tendinopathy, elements that can be difficult to assess in a clinical setting.  

However, the identified gait loading asymmetries were further correlated to poor Drop Jump (reported as Drop Counter Movement Jump in the article) performance, demonstrating the ability of in-clinic functional tests to provide clinicians with information relating to a patient’s functional performance in relation to activities they may be engaging in outside of a clinical setting. 

…gait loading asymmetries were further correlated to poor Drop Jump performance, demonstrating the ability of in-clinic functional tests to provide clinicians with information relating to activities they may be engaging in outside of a clinical setting. 

Early identification of sub-clinical loading compensations may provide clinicians with information that would otherwise be difficult to obtain or the information may only become apparent after these problems manifest into a related problem. This is often seen when bilateral symptoms present upon increased loading during a “return-to-activity" phase of rehabilitation. 

The above example reflects just part of the broad utility objective data provides that aids in informing our rehabilitation programming and guiding return-to-activity decisions. 

Assessing Achilles Tendinopathy in Active Populations with Force Plates  

When rehabilitating Achilles tendinopathy, clinicians will typically follow a progressive loading process. Often working towards building baseline capacities in range of motion, strength and endurance before adding velocity and cyclic loading.  

Previously, patient-reported data informed how an individual progressed through this process. However, with increasingly accessible technology, clinicians are afforded the opportunity to capture additional data beyond these subjective measures, which serves immense benefits for our informed clinical decision-making.

However, with increasingly accessible technology, clinicians are afforded the opportunity to capture additional data beyond these subjective measures, which serves immense benefits for our informed clinical decision-making. 

This proposed Achilles tendinopathy test battery can assist clinicians by:

1. Providing clarity and building confidence regarding clinical decisions, including, exercise selection and rehabilitation progressions or regressions.  
2. Providing instant feedback and easy-to-understand information to help facilitate client education, engagement and encouragement throughout their treatment. 
3. Reducing the risk of injury flares and reinjury occurring, due to the improved accuracy in understanding a client’s current load-tolerating capacity. 
4. Coaching and mentoring of team members on clinical reasoning based on the data collected. Is the intervention working? Are the clinical decisions correct for the presentation?   

The tests along the battery spectrum we select, in addition to our rehabilitation programming, will depend on the individual’s clinical presentation. This means that those with lower levels of self-reported function will typically start lower down the test battery spectrum.  

A test battery refers to a set of tests and measures that are designed to evaluate multiple elements of function and performance, that is, they are multi-dimensional assessments. ^{(16, 7)}

Conducting a test battery throughout the course of a client’s rehabilitation journey will assist in developing an individualized rehabilitation program for a client, as well as allowing a clinician to be responsive to changes in a functional capacity that may necessitate progression, regression and modification of the prescribed rehabilitation program. 

Conducting a test battery throughout the course of a client’s rehabilitation journey will assist in developing an individualized rehabilitation program …that may necessitate progression, regression and modification.  

The proposed battery of force plates tests for Achilles tendinopathy outlines test progressions, many of which clinicians will already be familiar with, that may align with a client’s load-tolerating capacity and inform our clinical decisions relating to; exercise selection and progression, activity guidance, therapeutic interventions and return-to-sport.

Subsequent sections of this article will further explore the additional data that can be obtained from performing these functional tests on force decks and their significance for improving both exercise rehabilitation programming and clinical decision-making. 

Current Deficiencies in Assessing Function in Achilles Tendinopathy 

Pain during and after loading, in addition to impaired functional performance are two hallmark deficits commonly observed in those with Achilles tendinopathy and certainly provide clinical utility. ⁽¹²⁾ The information provided by these self-reported measures is retrospective, typically resulting in a reactive adaption to a rehabilitation program if a flare in symptoms occurs.  

The information provided by these [pain and impaired function] self-reported measures are retrospective, typically resulting in a reactive adaption to a rehabilitation program if a flare in symptoms occurs. 

This is where we begin to see the gap in rehabilitation and functional restoration that exists, where successful progression through the later stages of rehabilitation can be marred by injury flares and setbacks, often by returning to too much load, too soon. This may be in part due to limitations of “analog” functional assessments in a clinical setting.  

Pain during and after loading is typically reported during the single leg calf raise, jumping or hopping tests, often informing “readiness” to return to higher load activities. However, these tests may not adequately reflect the functional capacity of the tissue for increased or prolonged load exposures. 

“Full recovery of symptoms does not ensure full recovery of muscle-tendon function in patients with Achilles tendinopathy. Persisting functional deficits may not only increase the risk of re-injury, but also put the athlete at risk for other injuries.” ^{(16, 13)} 

Further, the relationship between pain and functional performance is not strongly correlated. High degrees of pain do not always equate to high degrees of functional impairment and low levels of pain do not equate to a low level of functional capacity. 

High degrees of pain do not always equate to high degrees of functional impairment and vice versa, low levels of pain do not equate to a low level of functional capacity. 

“It appears that measures of pain during functional tasks may be useful for determining the status of recovery but provide little insight into tendon loading.” (Corrigan, 2022) 

Pain responses and clinical tests are often able to provide valuable information regarding an individual’s capacity in the earlier stages of rehabilitation, for example, utilization of the validated VISA-A or the more recent TENDINS-A outcome measures. However, relying on these assessment methods and tools alone as we progress through the later stages of rehabilitation and when making important return-to-activity decisions, risks the potential of loading advice not entirely aligning with the true load-tolerating capacity of an individual.

Why Objective Test Batteries? 

No single test is able to assess all relevant functional metrics that require consideration when making return-to-activity decisions.   

For example, plantar flexion isometric and dynamic strength outcomes will influence a clinician’s return-to-running decision. 

Whilst these tests provide information relating to strength deficits, a potential risk factor that certainly needs to be addressed in our clinical rehabilitation, it does not paint a clear picture of the overall load-tolerating capacity of the Achilles tendon, especially in relation to higher load activities that require efficient function of the stretch-shortening cycle (SSC) during running.  

“Relying on such unidimensional measures to quantify PF function may hinder the appropriate identification of functional deficits in AT, which may lead to inadequate rehabilitation and persistent symptoms.” McAuliffe et al. (2019) 

However, when performing a test battery, the combined sensitivity of results can provide a more reliable representation of the functional capacity of an individual (Silbernagel, 2006). 

Test batteries for assessing Achilles tendinopathy have existed for upwards of 20 years ^{(16, 7)}, but with advances in technology we have an opportunity to further enhance our clinical assessments and outcomes.

For us to truly add value to our clients and improve our injury management outcomes, we need to build our understanding of what we are assessing, why we are assessing it and how the information gained from our assessments will inform our clinical decision-making.  

Common Functional Deficits Identified in Achilles Tendinopathy   

At this point, we understand what tests may form our test battery and the importance of these in guiding our rehabilitation decisions, but we need to understand why they are important to assess.  

By understanding the potential deficits that may form part of an individual’s clinical presentation, how they relate to function and how we can assess them allows us to; 

1. Structure and plan our clinical assessments.  
2. Select the most appropriate tests to perform along the spectrum of function.  
3. Utilize the data provided from the results of our functional tests to inform our rehabilitation programming; exercise selection and dosage. 
4. Make informed return-to-activity decisions. 

A number of studies have reported several functional deficits commonly identified in active individuals presenting with Achilles tendinopathy, many of which relate to impaired energy recycling of the tendon, also referred to as the SSC. 

As mentioned earlier, when we are performing functional tests in the clinic without the use of ForceDecks, whilst they are certainly useful, we are faced with considerable limitations in the information we can obtain from these tests.    

For example, visual observation of the single-leg hop test may demonstrate notable deficiencies in hop height and the overall movement strategy on the symptomatic limb. However, there typically needs to be a relatively large deficiency or alteration in movement strategy present for this to be noticeable and require an exceptionally trained eye of the assessing clinician, both of which have their limitations.  

Not to mention there are measures that we simply have no method of obtaining without the use of a objectively measured assessment.   

While resourceful, savvy clinicians may attempt to replicate many of these tests with certain handheld dynamometers, smartphone applications or jump mats, it is important to understand the blind spots that may arise from these selections. 

• Handheld Dynamometers: The load capacity of many dynamometers, such as  VALD’s DynaMo will top out around 100kg (220lb) for compressive loads and 200kg (440lb) for tensile loads. Converted into force (N) that is 980N (compression) and 1,960N (tension). However, many athletes, especially those in Rugby and American football will have plantar flexion force production easily exceeding 2,000N. This makes the use of a force plate imperative for force assessments, due to its ability to assess incredibly high load capacities (2,000kg / 4409lbs, 20,000N). 
• Smartphone Applications and Jump Mats: In jump assessments, many app or mat-based tools calculate jump height via flight time, or the amount of time the athlete spends in the air. This is due to the ability to extrapolate height (meters) from the gravity equation 9.8m/s². However, athletes may unintentionally “cheat” the test by crouching or flexing at the hip, knee and ankle, during the landing phase to spend more time in the air. This not only creates a source of error but makes the error accrued exponentially as the time value (seconds) is squared.

It is at this point where we can merge our understanding of a progressive test battery, to the common functional deficits that may require targeted rehabilitation programming in active clients presenting with Achilles tendinopathy.  

The table below shows not only what tests we can perform in our progressive test battery, but the relevant performance metrics and data you can obtain from utilizing force plates and how it may better guide your clinical decisions.

Stage of Rehab	Test	Assessment of Physical Function	ForceDecks Metric	Influence on Clinical Decision-Making
Early	Seated & Standing Plantar flexion (PF) Isometric (ISO)	Plantar flexion Isometric Maximal Strength  (Cue: Push as hard as you can.)	Peak Force (Asymmetry)  Peak Force / BM	Treatment Decisions  E.g., adjunct therapies; program progression/regression.  Movement Programming E.g., isometric dosing (sets, seconds).
Early-Mid	PF Dynamic Strength   (test not performed on force plates)	Plantar flexion Isotonic Strength and Power. Limb symmetry (18)	Number of Reps (Asymmetry)  External Load	Treatment Decisions  E.g., tolerance for isotonic movements.    Movement Programming E.g., dosage (goal sets-reps & tempo).
Early-Mid	Seated & Standing PF ISO	Ankle PF Isometric Explosive Strength  (Cue: Push as hard as you can, as fast as you can.)	RFD (200ms) Asymmetry    Time to Peak Force Asymmetry	Treatment Decisions  E.g., clearance for higher loading introduction (e.g., jogging).    Movement Programming E.g., progression to a faster tempo, higher external resistance and concentric/eccentric bias.
Early-Mid	Countermovement Jump (CMJ)	Ankle plantar flexion ballistic strength    Neuromuscular strategy	Jump Height (IMP - MOM)     P2 Concentric Impulse Asymmetry	Treatment Decisions  E.g., clearance/progression to increase the duration of self-paced running (min/km, min/mile).       Movement Programming E.g., progression to higher-dose, faster-tempo isotonics and introduction of plyometrics.
Mid-Late	Single Leg Countermovement Jump (SL CMJ)	SL Jump Strategy	P2 Concentric Impulse (Asymmetry)     RSI mod	Treatment Decisions  E.g., clearance/progression to faster-paced (min/km, min/mile) running.  Potential introduction of speed/interval work (faster bouts of pace min/km, min/mile).    Movement Programming  E.g., progression of plyometric exercises.
Mid-Late	Drop Jump (DJ)	PF Reactive Strength	RSI      Peak drive off force Asym     Active Stiffness     Jump Height (IMP - MOM)	Treatment Decisions  E.g., clearance/progression to faster-paced (min/km, min/mile) running.  Potential introduction of speed/interval work (faster bouts of pace min/km, min/mile).    Movement Programming  E.g., progression of plyometric exercises.
Late	Hop Test	Average Reactive Strength	RSI Active Stiffness    PEAK Drive-off Force Asymmetry	Treatment Decisions  E.g., progression of speed/interval work and possible increases in exposure to modified training.       Movement Programming E.g., increase plyometric exercise dosage and frequency of return-to-run programming.

The proposed test battery does not serve to replace a clinical assessment of Achilles tendinopathy, but simply enhances it, by closing data gaps that may exist in current clinical assessments that may potentially be driving the relatively high injury recurrence rates in active populations. 

Benefits of Data-Driven Rehabilitation Programming and Clinical Decision-Making 

When discussing high Achilles tendon injury and injury recurrence rates, the data is from large sample sizes and is not limited to a small subset of patient outliers.  

Wang et al. (2022) reported that runners are ten times more likely to develop Achilles tendinopathy compared to inactive individuals. Other sporting activities also demonstrate an increased risk relative to inactive cohorts. ⁽¹⁰⁾

While the incidence rates of Achilles tendinopathy are certainly concerning, the long-term deficits and likelihood of Achilles tendinopathy recurrence present a unique problem for individuals with Achilles tendinopathy. Recurrence rates range from 27-44% ^{(12, 13)} and are generally population or sport dependent. This variability also poses a large need for a standardized and detailed framework for clinicians to maintain clinical consistency when managing these populations. 

A number of factors have been identified that may contribute to these concerningly high injury recurrence rates:    

1. Returning to sport too soon. ⁽¹²⁾  
2. Failure to address deficits in musculotendinous function. ⁽¹²⁾  
3. Unclear guidelines and criteria relating to return-to-sport decisions. ⁽¹²⁾  
4. Clinicians fail to formulate individualized rehabilitation programs, that address identified deficits relating to the presenting pathology and the physiological demands of the goal activities. ⁽¹³⁾

“Inadequate rehabilitation and returning to sport prior to full recovery are risks that might be minimised with appropriate guidance in the return-to-sport phase.” ⁽¹³⁾

Utilizing ForceDecks for Rehabilitation Progression and Clinical Decision-Making 

There are many circumstances in which a standard loading test in a clinical setting will not provoke symptoms, for example, single leg hops with a focus on pain response during late-stage rehabilitation.

The lack of pain during this functional test may be interpreted by a clinician that sufficient capacity has been achieved, leading to a clearance to progress to running activities or increasing the intensity of current running activities.  

The lack of pain during this functional test may be interpreted by a clinician that sufficient capacity has been achieved... However, performing the same hop test on ForceDecks/force plates can provide further insights into functional capacity that may not be identifiable otherwise.  

However, performing the same hop test on force plates can provide further insights into functional capacity that may not be identifiable otherwise. 

Was their ground contact time within a normal level of variation between limbs? Did they demonstrate adequate rate of development qualities? Did they show appreciable differences in the concentric or eccentric phases of the hop when compared to the uninjured limb? All of these questions and more can be answered instantaneously when using ForceDecks as a part of your testing battery. 

A clinical decision based on these results may include:

• More time focusing on exercise load exposures to improve SSC function. 
• Alterations in the return-to-activity recommendations, such as more time between higher load exposures to allow sufficient tissue adaptation or alterations in the cleared running paces may be recommended.  

In summary, by developing a framework for utilizing a force plate test battery for Achilles tendinopathy clinical assessments, we are able to gather meaningful data that can help proactively address the various factors that often contribute to poor rehabilitation outcomes and high reinjury rates, allowing us to create sustainable rehabilitation outcomes.  

If you would like to know more about the value of implementing technology into your organization, please reach out.

References

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