One of the biggest changes I’ve seen in rehabilitation over the past decade is the increasing use of objective strength testing, which is a positive step … however, testing is often performed without detailed thought about why, which data you need/want and which decisions this data will help inform. So here we’re reviewing: using strength testing to guide rehabilitation decisions … getting to grips with the key details and at the end there’s a flow chart to help you appropriately deploy testing and interpret the results.
Objective assessment
Hand-held dynamometers (HHDs) are becoming more common in clinics. Isokinetic and custom-built dynamometers remain oft-used devices in many research settings. Force plates and wearable technologies are also becoming increasingly accessible. The use of objective testing in rehab settings is undoubtedly a positive step.
Objective measurements are generally more reliable than subjective judgement and allow us to track change over time. But owning a dynamometer, or any other testing device, doesn’t automatically make our rehabilitation more evidence-based.
The real value of strength testing isn’t the number. It’s the decision that number helps us make
Measuring isn’t the same as assessing
Imagine you test a patient’s quadriceps strength after ACL reconstruction and record a peak force of 310 N. What does that number actually tell you?
Well, on its own… very little. Without context, 310 N is simply a measurement. It doesn’t tell you whether the patient is ready to run, whether they’re progressing as expected, or whether their rehabilitation programme needs to change. A measurement only becomes clinically meaningful when it helps answer an important question.
For example:
- Is the patient improving?
- Are they strong enough for the demands of their daily life, work or sport?
- Is one limb substantially weaker than the other?
- Has rehabilitation plateaued?
- Is strength likely to be limiting function?
The purpose of testing is not to collect data. The purpose is to reduce uncertainty.
However, reducing uncertainty depends on the quality of the measurement itself. A strength test is only as useful as its ability to detect real changes in performance. Factors such as testing position, stabilisation, device characteristics, force onset detection and measurement error all influence whether an observed difference reflects a genuine change in muscle performance or simply variability in the measurement. These methodological considerations are often overlooked in clinical practice but become critical when objective data are used to guide rehabilitation or return-to-sport decisions. You can read more about that in my paper: [1]
Four questions to ask yourself when collecting data
The following might help you determine why you’re collecting strength (or any other) data. What decision are you hoping to inform once you have that data?
1. Attribution
Strength deficits can help identify impairments that may not be obvious during movement assessment alone. For example, persistent quadriceps weakness following knee injury or surgery is common and can contribute to reduced function, altered movement patterns and potentially slower recovery.
Strength testing here may help quantify the impairment rather than relying on observation or patient perception.
2. Monitor progress
One of the greatest advantages of objective testing is that it allows us to determine whether the rehabilitation / training / conditioning is effective. Patients can report feeling stronger before measurable changes occur, or indeed vice versa – feel no different despite substantial improvements.
Regular testing helps answer a simple question:
Is capacity improving?
If not, perhaps the programme needs to change.
3. Guiding rehabilitation
Suppose that a patient has excellent balance, good range of motion and minimal pain, yet through testing you note that their knee extensor strength remains 35% lower than the opposite limb.
That can immediately change the rehabilitation priorities. Rather than adding increasingly complex exercises, the focus may need to shift towards increasing muscle strength through appropriate resistance training.
Testing can help target limited clinical resources rather than simply documenting deficiencies.
4. Supporting return-to-activity decisions
Whether the goal is returning to work, recreational running or elite sport, rehabilitation ultimately comes down to matching physical capacity with task demands – trying to ensure that the person has the capacity and resilience to undertake their normal activities, ideally with ease.
Strength is only one component of readiness, but it is an important one. Objective measurements, including of strength, provide another piece of evidence to support decision-making rather than relying solely on time since injury or subjective confidence.
Data should inform, not dictate, clinical decisions
A misconception of strength testing in rehab is that there’s a single cut-off value, achieve this value and your patient is ‘ready’. Examples of this can be seen in ACL rehab; current guidelines recommend limb symmetry indices greater than 90% for a safe return to play (RTP) [2]. This is just part of the picture, not the whole. No single strength score determines whether or not someone is ready to return to activity. Of course know that RTP decisions need to take account of other factors, such as psychological, biomechanics etc, but let’s just look at the strength data and the ILS value of 90%. Indeed, if you have accurate testing procedures, it can show adequate symmetry and reassure a perhaps a safer RTP. However, what you don’t see with ratio data is the absolute strength performance. Performance of both limbs can often remain lower compared to baseline or pre-surgery values [3]; so whilst you may have great symmetry, you have weaker performance overall compared to pre-surgery. Not ideal for RTP. We need to consider the data in wider context.
To enhance the utility of your data interpret it alongside other things like:
- symptoms
- movement quality
- absolute performance (in instances of ratio data)
- training tolerance
- psychological readiness
- pre-injury / surgery data
- the demands of the individual’s goals
- relevant normative data (if available) etc…
Used in this manner, strength testing can enhance clinical reasoning.
Equally, clinicians should resist the temptation to interpret every numerical difference as meaningful. A 10% increase in strength may represent excellent progress in one testing protocol but fall entirely within the measurement error of another. Before changing a rehabilitation programme, it’s worth asking a simple question: is this a true physiological change, or is it simply noise? Understanding concepts such as reliability, measurement error and the minimum detectable change allows clinicians to make decisions with greater confidence rather than reacting to every fluctuation in performance. This may sound complicatied, but I simplify this in my courses and in this paper [1].
Using strength testing to guide rehabilitation decisions
A framework for clinical practice
I compiled this flowchart as a quick reference to help your decision-making for when you’re planning your testing schedule and to guide your thoughts and decisions once you’ve collected the data.
Summary
The best clinicians don’t test because the equipment is available or it looks good to the patient, they test because of a specific reason and the outcome may influence what they do next. Sometimes the outcome confirms that rehabilitation is progressing as planned. Sometimes it highlights an unexpected deficit. Sometimes, it may even give you the confidence to progress a patient more quickly than symptoms alone might suggest.
As always, I hope that this was useful. Thanks for reading.
If you want to lean more about dynamometry, strength testing and clinical practice check this out
References
- Minshull C (2025). Mastering the use of hand-held dynamometry in clinical practice. Arch Physiother;15:327–336. [Full Text]
- Lynch et al (2015). Consensus criteria for defining ‘successful outcome’ after ACL injury and reconstruction: a Delaware-Oslo ACL cohort investigation. Br J Sports Med; 49(5):335-342. [Abst]
- Minshull et al (2021). Contralateral strength training attenuates muscle performance loss following anterior cruciate ligament (ACL) reconstruction: a randomized-controlled trial. Eur J Appl Physiol;121(12):3551-3559 [Abst]
