Measuring Force
What each force metric measures
A force-time curve holds more than a peak. The rise contains rate of force development, split into an early window driven mostly by neural drive and a late one dominated by contractile properties. The plateau contains steadiness, which is a motor-control measure rather than a strength one. Between sides sits symmetry. These articles define each metric, say what moves it, and give the reference ranges where the literature supports one.
Build-up (RTD Late), sustained force development from 100 to 200 ms
Build-up is RTD Late, the rate of force development across the 100 to 200 ms window from onset. Unlike Explosiveness (RTD Early), which is dominated by neural drive, the late window is dominated by the muscle's own contractile machinery. Read it alongside RTD Early; the relationship between the two windows is more informative than either alone.
Control, reading drift from peak, steadiness, and smoothness together
Control is the three plateau-window metrics on every session, Drift from peak (nRMSE), Steadiness (CV), and Smoothness (Yank). They are not redundant. They answer different questions about the same hold, how far the patient sagged from peak, how much their output wavered around the mean, and how jerky that wavering was. Reading them as a set is what the literature argues for, and it's what the platform surfaces.
Custom metrics, the outcome measures the force curve can't capture
Force and torque describe one slice of recovery. Hop tests, range of motion, and patient-reported outcomes describe the rest, and return-to-sport decisions hold up better when all of them sit on one timeline. How to use the Clinical Outcomes panel, which hop tests carry the most information, and where the evidence says outcome measures help and where it says they don't.
Explosiveness, what RTD Early actually means
Explosiveness is the rate of torque development (RTD Early) in the first 75 ms, and it reflects explosive, neurally driven force production. The ACL return-to-sport literature has been pointing at it for years. This is how ForceIQ computes it, what the number means clinically, and when to weight it heavily in your read.
Limb Symmetry Index, the weighted average and what the headline hides
How LSI is computed across the metric set, why per-metric components are capped at 100% before averaging, and what the "lowest metric" surface beside the headline is for. A green overall LSI does not mean every component is recovered, and the radar usually tells the more useful story.
Strength, reading peak force, peak torque, and mass-normalized values
Strength is the headline number, the peak force or peak torque a trial reached. What it means, what it doesn't capture on its own, when to read it in force vs torque vs mass-normalized form, and how it relates to the other metrics on the same trial.