Peak force or peak torque is the maximum force value the patient produced during the active window of a trial. It is the most commonly cited isometric strength variable and the one clinicians have been recording for the longest, but the way ForceIQ reports it (and the way the literature increasingly recommends reading it) is alongside the time-locked rate-of-force-development windows, not in isolation.
The definition
Peak is the maximum value in the force signal from onset to end of contraction, in Newtons. If patient height is entered and the joint and action have an anthropometric moment-arm model, that peak force is also converted to peak torque (Nm) using the estimated moment arm. If bodyweight is entered as well, both values are also reported in mass-normalized form (N/kg for force, Nm/kg for torque). The platform stores all three in SI units and converts to display preferences (lbs, ft-lbs, kgm) at render time without ever mutating the stored values.
The display defaults:
- Torque (Nm) is the default when height is set. It's the value the clinical literature reports.
- Force (N) is the fallback when height is not set. Still useful for within-patient longitudinal tracking; comparison to literature requires the moment-arm conversion.
- Mass-normalized (Nm/kg or N/kg) is what you toggle to when comparing across patients or against return-to-sport literature targets. Common knee-extension targets sit around 3.0 to 3.1 Nm/kg post-ACLR, with healthy normative means around 3.4 Nm/kg in males and 2.8 Nm/kg in females on the same protocol (Norris et al. 2024).
What peak is good for
The case for peak as the headline strength variable is strong and uncomplicated. It is the most reliable measurement on a trial (ICCs above 0.95 are routinely achievable with a clean protocol), it correlates well with self-reported function in patients post-ACLR, and it has the most published normative data behind it of any metric the platform reports. When you need a single number to characterize a patient's strength capacity on a joint, peak is that number.
It also anchors mass normalization. Nm/kg is the form most return-to-sport thresholds and meta-analytic effect sizes are reported in, which makes it the right comparison point for any literature-grounded clinical decision.
What peak misses
Peak captures how much force the patient produced. It does not capture how fast they produced it, whether they sustained it, or how smoothly they sustained it. Those are the questions the other metric tiles answer.
The pattern that shows up over and over in the rate-of-force-development literature is patients who recover their peak strength on the involved side but remain noticeably slower to develop force in the first 75 ms. Peak symmetry can read at 95% while RTD Early symmetry sits at 70%, and that is a meaningfully different clinical picture than the peak number alone suggests.
There's also a subtler point about peak rate of force development specifically. The maximum value of RFD across a contraction is dominated by maximum voluntary force itself: peak RFD typically occurs around 60 ms after onset and is largely a function of MVF (Del Vecchio 2022; D'Emanuele et al. 2023). Peak RFD may not add much information beyond peak force itself, which is one of the reasons the platform reports time-locked RTD windows (0 to 75 ms, 100 to 200 ms) rather than peak RFD. The time-locked windows decompose the rise into neural and contractile phases that peak alone collapses.
The practical translation: peak tells you the patient's ceiling. The other tiles tell you what shape their effort takes getting there and holding it.
When to read peak in force versus torque
If the patient has height entered and the joint and action have a moment-arm model, default to torque. The number is what the literature reports, the comparisons to return-to-sport thresholds work, and the longitudinal trend renders in Nm.
If the patient has no height, fall back to force. Within-patient progress is still measurable in N because the moment arm is constant for the patient between visits (assuming the dynamometer setup hasn't changed). Cross-patient and cross-literature comparisons require the moment-arm conversion to be in place, which is one of the reasons height is flagged as a load-bearing patient field on adding patients.
If you're trying to compare a patient against published normative data or return-to-sport thresholds, switch to mass-normalized (Nm/kg) unless the literature you're working against reports in something else. Most knee-extension thresholds in the ACL literature are in Nm/kg.
Reliability and minimal detectable change
Peak is the most reliable metric on the platform, but reliable does not mean exact. Even with a clean protocol on a clean device, the published minimal detectable change for normalized peak knee-extension torque post-ACLR is around 0.36 Nm/kg (95% CI 0.28 to 0.47), with a standard error of measurement near 0.13 Nm/kg (Norris et al. 2024). Changes smaller than the MDC between two of the same patient's visits are inside measurement noise and should not be over-interpreted as clinical progress or regression.
This number is protocol-specific. It assumes a 60-degree knee-extension protocol with the positioning conventions described in setting up a reliable isometric knee extension assessment. Different protocols, different joints, and different patient populations have different MDCs.
What to do next
- Default to torque (Nm) display when height is set. Comparison to literature and to other clinicians becomes trivial.
- Toggle to mass-normalized (Nm/kg) when making a return-to-sport-style call. That's the unit the thresholds are published in.
- Read peak alongside the RTD windows and the steadiness metrics, not in isolation. Recovered peak with persistent RTD or steadiness asymmetry is a real pattern the dashboard is designed to surface.
References
- Norris R, Morrison S, Price A, et al. Inline dynamometry provides reliable measurements of quadriceps strength in healthy and ACL-reconstructed individuals and is a valid substitute for isometric electromechanical dynamometry following ACL reconstruction. The Knee. 2024;46:136-147. doi:10.1016/j.knee.2023.12.006
- Del Vecchio A. Neuromechanics of the rate of force development. Exerc Sport Sci Rev. 2022. doi:10.1249/JES.0000000000000306
- D'Emanuele S, Tarperi C, Rainoldi A, et al. Neural and contractile determinants of burst-like explosive isometric contractions of the knee extensors. Scand J Med Sci Sports. 2023;33(2):127-135. doi:10.1111/sms.14244