Sports medicine · Patient guide
Isokinetic testing, objective muscle-strength assessment for ACL rehab, return-to-sport and injury prevention.
Isokinetic dynamometry measures peak torque, work and power of a muscle group at constant angular velocity. Objective benchmark for ACL / meniscal rehab, hamstring : quadriceps ratios, symmetry indices and safe return-to-sport clearance.
Key facts
- 01
Definition
Isokinetic dynamometry — measurement of peak torque at a constant angular velocity.
- 02
Objective and reproducible
Removes examiner bias — the machine controls velocity, you produce force.
- 03
Peak torque, work and power
Three complementary strength metrics captured across the full range of motion.
- 04
Limb symmetry index (LSI)
Injured-limb strength expressed as a percentage of the uninjured side.
- 05
Hamstring : quadriceps ratio
Balance between agonist and antagonist — a key ACL and hamstring-strain marker.
- 06
Foundation of return-to-sport
Guideline benchmark within the return-to-sport clearance battery.
Preparation and the test
From consultation to report — what happens, in order.
A clean, seven-step pathway — from your sports-medicine consultation to the written report your rehab team can act on.
Phase 1 · Before
Consultation and warm-up
Phase 2 · On the day
~45 minutes on the dynamometer
Phase 3 · After
Same-day report
- 01
Before
Sports-medicine or physio consultation
A short assessment of your injury, surgery date, current rehab stage and sport-specific demands.
- 02
Before
Warm up on the cycle
Five to ten minutes on a stationary bike to raise muscle temperature and prime the joint.
- 03
On the day
Position on the dynamometer
You are seated on a Biodex, HUMAC or Cybex system with the joint axis carefully aligned to the machine.
- 04
On the day
Test at 60°/s and 180°/s
Slow-speed testing captures peak strength; faster testing reflects the demands of sport.
- 05
On the day
Peak torque and endurance measured
Concentric and — where appropriate — eccentric torque, work and fatigue index are recorded.
- 06
On the day
Both limbs compared
Uninjured side first, then injured, so the machine can calculate limb-symmetry and H:Q ratios.
- 07
After
Written report with LSI
A full report — peak torque, work, power, LSI and H:Q ratio — goes to you and your rehab team the same day.
Typical appointment: 45–60 minutes. Written report: same day.
What it shows
The numbers isokinetic testing gives you.
Peak torque, work, power, symmetry and agonist : antagonist balance — the objective foundation of a modern return-to-sport decision.
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Quadriceps peak torque
Maximum knee-extensor force — the anchor metric after ACL and knee surgery.
-
Hamstring peak torque
Maximum knee-flexor force — critical for sprinters, footballers and dancers.
-
Hamstring : quadriceps ratio
Balance between the two — a low ratio raises ACL and hamstring-strain risk.
-
Limb symmetry index
Injured limb as a percentage of uninjured — the single most-quoted RTS metric.
-
Endurance / fatigue index
How torque decays across repeated repetitions — a marker of muscular endurance.
-
Baseline for post-op rehab
An early post-op reading you and your team can track against over the coming months.
-
Return-to-sport benchmark (LSI ≥ 90%)
The widely cited threshold within the return-to-sport clearance battery.
-
Red flag: severe strength deficit + persistent pain — orthopaedic re-evaluation
A large deficit alongside ongoing pain warrants orthopaedic review, not more loading.
Next steps
What we do with the results.
The report is the starting point — the deficits it shows drive a targeted programme, staged progressions and a proper return-to-play battery.
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Structured strength programme
A progressive, individualised resistance plan built around your deficits.
-
Sports rehabilitation
Physiotherapy-led rehab that translates strength gains into function.
-
Sports-specific reconditioning
Drills and loading patterns matched to the demands of your sport.
-
Return-to-run and return-to-jump progression
Staged progressions with objective criteria at each step.
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Return-to-play testing battery
The full clearance battery — isokinetic, hop tests, movement screen, sport-specific work.
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Injury-prevention programme
Nordic hamstrings, Copenhagen adduction and eccentric work to reduce recurrence risk.
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Repeat testing at 3 months
Re-test to confirm progress and re-target the programme.
-
Multi-disciplinary team review
Surgeon, sports physician, physio and S&C together — the safest way through the last mile.
Red flags
When isokinetic testing is not the whole answer.
A dynamometer is a tool, not a decision-maker. These are the situations where the number alone doesn’t clear you to load — and the right next step is a clinician, not another rep.
-
Severe strength deficit
A large LSI shortfall — reload and reassess rather than push to return-to-sport.
-
Failed post-op rehab
Plateaued progress after surgery — trigger a full multi-disciplinary review.
-
Recurrent hamstring strain
Repeated hamstring injury needs eccentric-strength testing and a targeted programme.
-
ACL graft failure
Suspected graft failure warrants surgical review before any further loading.
-
Patellofemoral pain syndrome
Anterior knee pain that limits testing — modify the protocol and address the driver.
-
Neurological weakness pattern
A pattern that does not fit the injury — refer for neurological assessment.
-
Post-op stiffness
Loss of range that blocks a full arc of motion — treat before re-testing.
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Chronic tendinopathy
Long-standing tendon pain benefits from isokinetic-guided heavy slow-resistance work.
-
Compartment-syndrome risk
Exertional leg pain with paraesthesia — stop testing and refer for compartment pressures.
Frequently asked
Everything we get asked about isokinetic testing.
Quick answers on LSI, H:Q ratio, dynamometer choice and how isokinetic testing sits inside the return-to-sport decision.
-
What is isokinetic testing?
Isokinetic testing — also called isokinetic dynamometry — measures the peak torque, work and power of a muscle group while a machine holds the movement at a constant angular velocity. It is the most objective, reproducible way to quantify muscle strength in a rehab or return-to-sport setting.
-
What is a limb symmetry index (LSI)?
The LSI expresses the strength of your injured limb as a percentage of your uninjured limb. An LSI of 100% means the two sides are equal. Return-to-sport batteries commonly use an LSI ≥ 90% for both quadriceps and hamstrings as one of several clearance criteria.
-
What is the hamstring : quadriceps ratio and why does it matter?
The H:Q ratio compares hamstring strength to quadriceps strength on the same limb. A ratio that is too low is linked to higher rates of ACL injury and hamstring strain, particularly in sprinting and change-of-direction sports.
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When is isokinetic testing appropriate?
It is most often used after ACL reconstruction and meniscal surgery, for recurrent hamstring strain, in chronic tendinopathy management, and as part of the return-to-sport clearance battery for pivoting sports.
-
Which dynamometer will I be tested on?
The three most common systems are Biodex, HUMAC (formerly Cybex NORM) and Cybex. The metrics — peak torque, work, power, LSI, H:Q ratio — are comparable across systems when the same speeds and protocols are used.
-
How is isokinetic testing used to clear return to sport?
It sits inside a wider battery that also includes hop tests, movement-quality screens, sport-specific drills and psychological readiness. An LSI ≥ 90% and an appropriate H:Q ratio are two of the objective criteria in that battery — not the whole decision.
Sources
The guidance behind this page.
- British Association for Sport and Exercise Medicine.
- Chartered Society of Physiotherapy.
- American Academy of Orthopaedic Surgeons.
- International Society of Biomechanics.
Published 2026-07-30 · Reviewed 2026-07-30 · Next review 2027-07-30 · 5-minute read
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In practice, in London
Booking isokinetic testing privately in London — what actually happens
With isokinetic testing, the London question is usually about report turnaround and the radiologist reading it — not whether the scan is available. Waiting lists on the NHS for isokinetic testing vary widely by borough and by how the GP letter reads. Privately in London, we can normally offer a slot inside the same week, sometimes within 48 hours if there’s a cancellation. The difference isn’t clinical quality — the consultants are frequently the same faces you’d see on the NHS — it’s the calendar.
A typical private booking for isokinetic testing in London starts with a consultant conversation — sometimes in person on Harley Street or Marylebone, sometimes on video if that suits better. Any imaging or diagnostics happen at a nearby CQC-registered facility, and reports usually land within 24 to 72 hours. The whole loop, from first call to written report, is often done inside a fortnight. For isokinetic testing specifically, the difference between a routine report and a sub-speciality read is where private care earns its keep.
Fit matters more than people expect. For isokinetic testing, the right consultant depends on what you actually need — a second opinion, a definitive diagnosis, a bridge into treatment, or reassurance that nothing’s being missed. We match on that, not on who has the biggest brochure. If a test isn’t the right next step, we’ll say so before you book anything.