Isometric Testing & Benchmarking

How to use Isometric Mode for strength assessment, bilateral comparisons, and return-to-sport benchmarking.

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What Isometric Mode measures

Isometric Mode locks the cable at a fixed point and records force output against an immovable resistance. The device captures peak force, average force, time-to-peak, and force-time curve data — all exportable as CSV via the Beyond+ app.

This gives you a portable, repeatable strength assessment tool without the cost or footprint of a dedicated isokinetic dynamometer or force plate. It won't replace gold-standard lab equipment, but for field testing, clinic-based screening, and longitudinal tracking, it provides clinically useful data.

Setting up an isometric test

Mount VOLTRA I at the appropriate height for the test. Consistency matters — document mount height, patient position, and joint angle for each test so you can reproduce it.
Select Isometric Mode from the home screen.
Set the cable length by pulling to the desired test position. The device locks at this point.
Instruct the patient to push or pull against the locked cable with maximal effort for the test duration (typically 3–5 seconds).
Review the force output on-screen or in the Beyond+ app. Export data for documentation.

For bilateral comparisons, repeat the test on the contralateral side using identical positioning. The Limb Symmetry Index (LSI) can be calculated from peak force values: (involved / uninvolved) × 100.

Common testing protocols

Quadriceps isometric strength

Mount at knee height. Patient seated with knee at 60–90° of flexion (document the angle). Ankle strap or handle attached below the knee. Patient extends against the locked cable for 3–5 seconds of maximal voluntary contraction.

This is particularly relevant for ACL rehabilitation, patellofemoral conditions, and post-total knee replacement. Serial testing at consistent intervals (e.g., 4-week blocks) provides objective progression data.

Hamstring isometric strength

Mount at floor level or use the Travel Platform. Patient prone or seated. Ankle strap attached. Patient flexes knee against locked resistance. Compare bilateral values for hamstring-related injury screening.

Shoulder / upper limb

Mount at appropriate height for the test position. Common applications include shoulder external rotation strength (relevant for throwing athletes, rotator cuff rehab) and grip-related assessment with adapted handle setups.

Mid-thigh pull

Use the Travel Platform as a floor anchor. Patient stands on the platform and pulls upward against the locked cable in a standardized position. Provides a general lower-body strength metric comparable to a force plate mid-thigh pull, with the caveat that absolute force values will differ due to the cable angle.

Interpreting and using the data

The primary outputs from isometric testing are:

Peak force — Maximum force produced during the contraction. The most commonly used metric for bilateral comparison and longitudinal tracking.

Time-to-peak — How quickly the patient reaches maximum force. May be relevant for explosive readiness or rate-of-force-development screening.

Force-time curve — Available in the CSV export. Shows the force profile across the entire contraction, which can reveal compensatory patterns or fatigue characteristics.

For return-to-sport decisions, a commonly referenced threshold is LSI ≥ 90%, though this should be interpreted alongside other clinical criteria rather than used as a standalone gate. VOLTRA I's data provides one data point in a broader decision framework — it doesn't replace clinical judgement.

Practical tips

Standardize everything: mount height, joint angle, patient position, verbal cuing, test duration. Small setup variations will introduce noise into your data.
Allow 2–3 practice trials before recording. Patients who haven't done isometric testing before often produce higher values on subsequent attempts as they learn to recruit effectively.
Use the Beyond+ app to export and timestamp tests. This makes it easier to track progression across sessions and share data with referrers.
The Travel Platform is useful for field-based testing where a rack isn't available — it provides a consistent floor anchor point.