Dynamometry for Achilles Tendinopathy

Guest SpotMay 27, 2024Last Updated: Jun 05, 2024

Achilles tendinopathy is a prevalent musculoskeletal (MSK) injury that commonly affects athletes, particularly those engaged in activities that involve high degrees of running and jumping, which apply large magnitudes of load to the Achilles tendon. However, it is important to note that this injury does not develop exclusively in active individuals; up to 65% of diagnosed cases in general practice settings are found to occur in individuals aged 41-60 years and are considered unrelated to sporting or high-intensity activities. ^{(18, 20)}

…up to 65% of diagnosed cases in general practice settings are found to occur in individuals aged 41-60 years and are considered unrelated to sporting or high-intensity activities.

My previous guest insight article explored a proposed battery of force plates tests for Achilles tendinopathy, aiming to improve our clinical decisions and treatment outcomes.

While the utility of ForceDecks is not exclusive to active populations, this test battery may be viewed as part of a “progressive functional test approach,” which may inform our clinical assessments and rehabilitation programming for those progressing toward the higher end of the functional spectrum.

Expanding on the progressive functional test approach described above, the purpose of this article is to explore the clinical utility of dynamometry for assessing the lower end of the functional spectrum, where we may be dealing with clients with a lower initial level of function, a lower capacity goal or those for who we need to isolate specific muscles to inform our clinical decisions.

Ideal Use Cases for Dynamometry

On the Move

When traveling (e.g., at-home treatment sessions, away games with sporting teams) and when larger devices can’t be easily transported.

Efficiency

When a wide range of tests must be performed in a short period of time by a single practitioner (e.g., upper extremity, lower extremity, range of motion (ROM) and more).

Single-Joint Testing

HHDs are best suited for single-joint tests, where forces are typically lower and positions can be easily controlled, either in fixed-point or handheld configurations.

Bed-Based Testing

When the patient must be tested on a treatment bed due to compromised mobility or surgical recovery.

Adaptability

When the test you wish to perform cannot easily be conducted with other isometric testing technologies, such as grip strength, pinch and finger assessments.

Low Force Tests

When the patient is not strong enough to overpower the practitioner or the test produces low forces, HHDs may be the most convenient testing solution.

Accuracy

While accuracy is always important, the added precision, reliability and features of more advanced technology are not always necessary for all users, tests and settings.

Budget Constraints

HHDs are typically the most affordable isometric testing technologies.

Firstly, in this article, “dynamometers” will refer to Fixed-Frame Dynamometers (FFDs), Fixed-Point Dynamometers (FPDs) or Handheld Dynamometers (HHDs).

Fixed-Point and Fixed-Frame Dynamometry

Prone Knee Flexion 90°

Prone Knee Flexion 60°

ISO 60

Handheld Dynamometry

Sidelying Hip Abduction

Seated Hand Grip Squeeze

Prone Hip Extension

Want to know more about the various types of HHDs?

Functional Assessment Progressions in Achilles Tendinopathy

The test continuum below expands on the previously described functional test battery for Achilles tendinopathy. Using dynamometry can greatly assist clinicians by isolating and identifying strength and functional deficits that may form part of an individual’s clinical presentation, not otherwise discernable when utilizing standard manual muscle testing (MMT) methods or more global functional assessments.

When it comes to assessing function in Achilles tendinopathy, the question isn’t “Should we do it?” it’s “What functional tests should we perform?”

Developing a framework for accurate assessments appropriate to an individual’s stage of recovery and clinical needs helps avoid the “floor and ceiling effect.” This approach ensures that our therapeutic interventions align with an individual’s current capacity and build towards their desired capacity. It’s one thing to know which functional tests we can perform as part of our clinical assessments; however, we need to understand why these tests matter.

It’s one thing to know which functional tests we can perform as part of our clinical assessments; however, we need to understand why these tests matter.

Common Functional Deficits and Assessment Methods Utilized in Achilles Tendinopathy Assessments

In both active and sedentary cohorts, muscle power, strength deficits and reduced DF are considered modifiable risk factors for the development of Achilles tendinopathy.⁽²⁶⁾

It is important to recognize that there is still conflicting evidence regarding the predisposing nature of these deficits and their link to developing Achilles tendinopathy in uninjured individuals. ⁽²⁸⁾ However, in the presence of pathology, assessing and addressing these functional deficits are considered important, especially when we identify deficits relative to normative values and asymmetry between limbs. ⁽³³⁾

Identifying and understanding strength or ROM deficits will influence the selection, timing, dosage and progression of our exercise and treatment interventions.

Deficit	Evidence	Assessment Method	Metric	Therapeutic Interventions & Clinical Decisions
Non-Weight-Bearing Ankle DF ROM ^{(5, 18)} Weight-Bearing Ankle DF ROM	Varied evidence regarding reduced ROM being a universal risk.	DynaMo HumanTrak DynaMo	ROM Asymmetry	Therapeutic Goals Improve ankle DF ROM. Interventions to work within ankle DF restrictions if the range is an irritant (e.g., temporary use of heel lifts). Clinical Decisions E.g., footwear recommendations, advice relating to hill walking, exercise selection and “dosage.” Improve ankle DF ROM.
Ankle PF Strength (Isometric) ^{(5, 6, 7, 9, 12, 13, 16, 18)}	Gastrocnemius may account for 3.7% to 11% of deficits. Soleus may account for 23.2% to 36.7% of PF strength deficits. ⁽⁵⁾	DynaMo ForceFrame ForceDecks	Peak/Max Force Rate of Force Development (RFD) Time to 80% Peak Force Asymmetry	Exercise interventions via the ability to isolate soleus vs. gastrocnemius muscle influence. Clinical Decisions E.g., prescribing seated calf strength exercises to target soleus strength deficits (isometric → isotonic → plyometric).
PF Dynamic Strength	PF 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 and tempo).
Hip Strength Hip Abductors Hip External Rotators Hip Extensors ^{(5, 12, 21)}	-	DynaMo ForceFrame	Peak Force Peak RFD (DynaMo) Peak Force Asymmetry	Exercise interventions to target and address hip muscle strength deficits – suitable for both early- and late-stage strength assessments: Low load/early-stage strength: Clams or glute bridges. Higher load/late-stage strength: Maximum voluntary contraction (MVC) isometric hip abduction or Trap-Bar Deadlift.

Deficit

Evidence

Assessment Method

Metric

Therapeutic Interventions & Clinical Decisions

Non-Weight-Bearing

Ankle DF ROM ^{(5, 18)}

Weight-Bearing

Ankle DF ROM

Varied evidence regarding reduced ROM being a universal risk.

DynaMo

HumanTrak

DynaMo

ROM Asymmetry

Therapeutic Goals

Improve ankle DF ROM. Interventions to work within ankle DF restrictions if the range is an irritant (e.g., temporary use of heel lifts).

Clinical Decisions

E.g., footwear recommendations, advice relating to hill walking, exercise selection and “dosage.” Improve ankle DF ROM.

Ankle PF Strength (Isometric) ^{(5, 6, 7, 9, 12, 13, 16, 18)}

Gastrocnemius may account for 3.7% to 11% of deficits.

Soleus may account for 23.2% to 36.7% of PF strength deficits. ⁽⁵⁾

DynaMo

ForceFrame

ForceDecks

Peak/Max Force

Rate of Force Development (RFD)

Time to 80% Peak Force

Asymmetry

Exercise interventions via the ability to isolate soleus vs. gastrocnemius muscle influence.

Clinical Decisions

E.g., prescribing seated calf strength exercises to target soleus strength deficits (isometric → isotonic → plyometric).

PF Dynamic Strength

PF 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 and tempo).

Hip Strength

Hip Abductors

Hip External Rotators

Hip Extensors ^{(5, 12, 21)}

DynaMo

ForceFrame

Peak Force

Peak RFD (DynaMo)

Peak Force Asymmetry

Exercise interventions to target and address hip muscle strength deficits – suitable for both early- and late-stage strength assessments:

Low load/early-stage strength: Clams or glute bridges.

Higher load/late-stage strength: Maximum voluntary contraction (MVC) isometric hip abduction or Trap-Bar Deadlift.

Dynamic and Functional Strength

For a comprehensive overview, please refer to this article: Assessing Achilles Tendinopathy with Force Plates.

Deficit	Evidence	Assessment Method	Metric	Therapeutic Interventions & Clinical Decisions
Stretch-Shortening Cycle (SSC) Function ^{(18, 9, 16)} Slow SSC Function >250ms	Symptomatic limb associated with lower CMJ height.⁽⁷⁾	ForceDecks CMJ	Jump Height – Impulse-Momentum (IMP MOM) P2 Concentric Impulse	Exercise selection and progression. Return to mid-load activities.
SSC Function ^{(18, 12, 9, 7, 16, 6)}	Side-to-side differences in drop CMJ height are significantly associated with Achilles tendon peak forces and average loading rates during running. ⁽⁷⁾	ForceDecks DJ	Reactive Strength Index (RSI) Peak Drive Off Force Asymmetry Jump Height	Exercise selection and progression. Return to higher-load activities (e.g., jumping, ↑ running pace).
Jumping Fast SSC <250ms	-	ForceDecks “Jumping” (Hop Test)	Average RSI Average Peak Drive Off Force Asymmetry Average Force Fatigue	Exercise selection and progression (↑ velocity of movement, etc.).
Hopping	Performance deficits of 16% to 35% in individuals with Achilles tendinopathy. ⁽⁹⁾ Average and maximal hop height deficits of 18% & 16% respectively. Reduced hopping quotient of 20% of symptomatic side. ⁽⁹⁾	ForceDecks Single Leg Hop Test	Average RSI Average Peak Drive Off Force Asymmetry Average Force Fatigue	Return-to-sport. Introduce higher-intensity running or jumping (e.g., pace, etc.).

Purpose of Progressive Functional Assessments and Rehabilitation

As mentioned earlier, when conducting clinical assessments, we must ensure that the methods by which we assess an individual align with their functional capacity and allow us to capture meaningful data. This data will inform our clinical decisions, for example, exercise prescription and loading advice.

Failing to recognize the strengths and limitations of potential assessment methods and clinical interventions, often demonstrated by the “floor and ceiling effect,” can sell our clients short of achieving their functional restoration goals.

“Ceiling or floor effects occur when the tests or scales are relatively easy or difficult such that substantial proportions of individuals obtain either maximum or minimum scores and that the true extent of their abilities cannot be determined.” Liu (2018)

This concept is recognized in current literature and clinical practice, where in 2022, we saw the introduction of the VISA-A (sedentary) patient-reported outcome measure (PROM) to cater to the floor effect experienced by sedentary individuals completing the standard VISA-A, as well as the TENDINS-A introduced in early 2024. ^{(24, 35)}

Recognizing the limitations of the clinical assessments and therapeutic interventions we utilize in clinical practice is a strength, not a weakness.

Recognizing the limitations of the clinical assessments and therapeutic interventions we utilize in clinical practice is a strength, not a weakness. The strength comes from knowing when, where and why an assessment or therapeutic intervention has utility and where its limitations lie.

In the context of performing isolated strength testing, MMT remains the predominant (strength testing) method in clinical practice. Despite several well-known limitations of this assessment method. ⁽²²⁾

…MMT remains the predominant (strength testing) method in clinical practice. Despite several well-known limitations of this assessment method. ⁽²²⁾

Demonstrated limitations in utilizing MMT for assessing lower extremity strength include: ⁽²²⁾

Inadequacy of MMT for measuring forces generated by larger muscle groups, especially in the lower extremity.
Ceiling effect in which many people attain maximal strength scores, despite sub-clinical deficits in strength, when assessing via MMT. Furthermore, the ceiling effect of MMT limits the ability to detect changes in muscle strength over time.

While using dynamometry is an appropriate next step to mitigate the issues of reliability and accuracy, it is important to note that not all dynamometry assessments are created equal. While assessments like the supine PF assessment have shown to be valid and reliable in some populations, the test results are drastically lower than that of fixed frame and force plate assessments, likely demonstrating a ceiling effect. ^{(36, 32)} If possible, fixed frame and fixed-point dynamometry assessments are encouraged to measure the true force-generating capacity of the plantar flexors.

Factors Contributing to Achilles Tendinopathy Injury Recurrence

Returning to sport too soon.⁽¹²⁾
Failure to address deficits in musculotendinous function. ⁽¹²⁾
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⁾

When we appreciate the strengths and limitations of manual clinical assessment methods and consider the often-modifiable factors listed above that may contribute to poor rehabilitation outcomes, the clinical utility of objective testing becomes clear.

Given the evolution of technology, evidence and best practices, the question is not so much, “Why utilize data-driven assessments in my clinical practice?” but “Which data-driven assessments best suit my clinical practice?”

Floor-Ceiling Concept for Clinical Assessment (i.e., Strengths and Limitations)

Test	Technology	Strength	Limitation/Weakness	Floor	Ceiling
MMT	Nil - manual	No cost	Poor inter- and intra-reliability. Tester individual strength.	Uncommon in these client groups.	The majority of patients score a 4-5/5 utilizing MMT. Unable to manually detect strength deficits.
Visual Observations of Quality of Movement (QOM) and ROM During Functional Tasks (e.g., CMJ or hopping tasks).	Nil Video recording Smartphone Apps	Low/no cost	May be user-dependent for the quality of data obtained.	Individuals are unable to perform movement due to functional capacity, pathology or pain.	Visual QOM assessments are highly subjective and may not be able to detect sub-clinical deficits.
Jump Assessments	Smartphone Applications Jump Mats	Low/no cost	Basic calculations of jump height via flight time. Do not capture QOM.	Require a base level of PF strength and Achilles tendon loading capacity to perform the test.
Dynamometry	Push HHD ForceFrame (FFD) DynaMo (Compression, Tension and FPD) App Enabled for Feedback	Good intra-tester reliability and validity assessing the RFD ^{(31, 32)}and measures of peak force⁽³²⁾ of the hip musculature. Moderate to good validity of ankle and knee RFD measures. ⁽³²⁾	Unable to obtain data that reflects the function of the SSC. May need greater load capacity depending on the strength of the subject: DynaMo Plus – load capacity of 1,000N (100kg/220lbs) (compression). DynaMo Max – load capacity of 10,000N (1,000kg/2,200lbs). ForceFrame – load capacity of 2,500N (250kg/550lbs).	Minimum force threshold can be as low as 5 newtons.	When DynaMo Plus and DynaMo Max reach their limit.
ForceDecks – Jumps: CMJ, DJ, Hop	App-Enabled, Computer Enabled	An affordable price point, a high load ceiling and can assess dynamic and static movements.	Unable to isolate muscle groups for contributions to function (e.g., soleus vs. Gastrocnemius and hip muscles).	Minimum level of capacity required to perform tasks.

Given the evolution of technology, evidence and best practices, the question is not so much, “Why utilize data-driven assessments in my clinical practice?” but “Which data-driven assessments best suit my clinical practice?”

Developing Frameworks for Individualization

While there is widespread recognition that we need to individualize our management programs and therapeutic interventions, achieving efficiency and accuracy in our program formulation is built upon a foundation of consistency in our assessment frameworks.

…achieving efficiency and accuracy in program formulation is built upon a foundation of consistency in assessment frameworks.

Successful frameworks apply our understanding of pathology and address the various risk and individual factors that may contribute to its presentation. They also recognize the common functional deficits that may develop and determine where an individual may land on the pathology spectrum. Within clinical practice, we have non-specific elements of our frameworks, which include (but are not limited to) our ability to identify clients:

Goals
Health literacy and understanding of a pathology
Motivators
Barriers

Additionally, we then have the specific elements of our frameworks that allow us to:

Understand a pathology, its various clinical presentations and treatment options.
Assess and address a person’s current functional capacity and presenting functional deficits.
Develop management plans that facilitate functional restoration and align with the client’s goals.
Review, revise, progress and regress a rehabilitation program based on patient response.

There’s no “one-size-fits-all” approach. Successful management plans are built on a foundation of assessment frameworks that allow for the capture of meaningful information that allows clinicians to assess and address the individual factors that are contributing to a person’s clinical presentation.

Expanding upon our grasp of the importance of thorough assessment and management frameworks, the visual representation below can assist in choosing the most suitable equipment and testing techniques based on your patient’s current capacity or rehabilitation stage. This will enhance your clinical assessments.

The question isn’t so much, “Should I use technology in my clinical assessments?” It is more so “Which technology should I use in my clinical assessments?”

Understanding the clinical utility of technology, the metrics it assesses and how it may influence your management plans, coupled with the client demographics you see and the goal activities you are often programming to return your clients to, will help answer this question.

In addition to data-driven assessments providing an avenue for better-informed clinical decision-making regarding exercise selection and loading decisions, the utilization of technology within clinical practice provides simple and effective ways to address numerous elements considered integral to exercise treatment adherence. These include: ⁽³⁰⁾

Facilitating the linking of the client’s goals to our therapeutic goals.
Providing real-time, tangible data to help educate clients and facilitate “buy-in” to a prescribed movement program.
Developing micro-goals to create “manageable goals.”
Longitudinally tracking changes in metrics.

In summary, the recommendation of data-driven approaches is not to replace existing validated methods of assessment, such as VISA-A, VISA-A (sedentary) and TENDINS-A; instead, it aims to enable a more proactive approach to management through more informed clinical decisions and facilitating the overcoming of common barriers that exist in our clients’ rehabilitation engagement.

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

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