The submaximal IsoForge modes (Hold Steady, Make Waves) train at a target force below the patient's maximum. The target is set as a percentage of the patient's recent MVIC on the same joint and action. The platform can auto-populate that target from the patient's most recent assessment, but the percentage itself is a clinical decision driven by what you're trying to train and where the patient is in their rehab.
This article walks the percent-MVIC framing, the target ranges that match common training goals, and how the platform helps you keep the target anchored to the patient's current capacity rather than a stale number from months ago.
Why percent-MVIC matters more than absolute force
Force steadiness is not a single number that means the same thing at every target. It's force-dependent. At low target forces (5 to 10% MVIC), the coefficient of variation is high, the motor unit pool is sparse, and small fluctuations in synaptic input cause large relative fluctuations in force output. As the target percentage rises, CV declines toward a relatively constant value at moderate-to-high force, reflecting fuller motor unit recruitment and tighter common drive (Enoka & Farina 2021). The same patient holding 5% MVIC and 50% MVIC produces meaningfully different motor-control challenges; both are training, but they are training different things.
The practical consequence is that "hold at 10% MVIC" for one patient and "hold at 10% MVIC" for another patient are roughly comparable training stimuli even if the absolute force values are very different. Conversely, "hold at 100 N" for two patients is two different training stimuli if their MVICs are 200 N and 600 N respectively. Percent-MVIC keeps the target anchored to the patient's own capacity.
The auto-populate option
IsoForge can pre-fill the target as a percentage of the patient's most recent assessment on the matching joint and action. The auto-populate uses the average peak force across the patient's last bilateral or unilateral MVIC session. You can accept the suggestion or override it.
When the auto-populate is wrong:
- The patient's last MVIC was a long time ago and they have changed capacity since. Re-assess before setting the target. A target based on a four-month-old MVIC is going to be either too easy (patient has improved) or too hard (patient has regressed). Either way, the training stimulus is off.
- The last MVIC had data-quality issues. If the assessment was excluded or the trials were noisy, the auto-populate inherits the bad number. Look at the most recent assessment before accepting.
- You're working a different joint or action than the most recent assessment. Auto-populate matches on joint plus action. If you tested knee extension last week and you want to train hip abduction today, the auto-populate has nothing to draw on.
Target ranges by training goal
Common targets, with the caveat that these are starting frames rather than prescriptions. The right target for a specific patient depends on their pathology, their stage of rehab, and how they look on the assessment.
Low-target steadiness training (5 to 15% MVIC). Trains fine motor control at low force where steadiness deficits often present clinically. Useful for patients with neurological involvement, persistent quadriceps inhibition post-ACLR, or older patients with motor-unit changes. The CV at this target range is higher in absolute terms but more sensitive to training adaptations.
Moderate-target sustained holds (20 to 40% MVIC). The most common Hold Steady setting. Trains sustained-output capacity at a force the patient can hold for the full set duration without fatigue. Good general-purpose training, especially in mid-phase rehab when the patient has capacity but lacks endurance at moderate intensity.
Higher-target hold work (50 to 70% MVIC). Pushes into the range where fatigue starts to dominate the within-set trajectory. Set durations need to be shorter (15 to 30 seconds rather than 30 to 60). Useful for late-phase rehab and athletes who need to develop strength endurance at near-functional intensities.
Above 70% MVIC. Not typical IsoForge territory. The line between submaximal training and maximum-effort assessment blurs above 70%. If you need to train near-maximum, an MVIC set during the assessment workflow is usually the right tool, not a submaximal IsoForge mode.
How the target interacts with steadiness metrics
If the IsoForge session is going to be reviewed against steadiness criteria (the patient's CV or nRMSE compared to a previous session, for instance), the target the comparison sits on matters. A patient who improved their CV at 30% MVIC across two sessions improved on the same task. A patient whose CV at 30% looks better than their CV at 60% from the previous session has not necessarily improved; they're holding a different target.
This is one of the reasons the training summary versus clinical metrics distinction matters. The platform deliberately keeps IsoForge session summaries separate from assessment metrics: the assessment metrics are at the patient's true peak and are comparable across visits; the training summary is at whatever target the clinician picked, and is comparable only when the target is held constant.
What to do next
- Re-assess before starting an IsoForge block, not after. A fresh MVIC gives the auto-populate something current to work with, and it gives you a baseline to compare the post-block re-assessment against.
- Hold target percentage constant within a training block. Changing the percentage every session makes the within-block trajectory uninterpretable.
- Change percentage when you progress to the next phase, not in the middle. Phase progressions are deliberate; mid-block changes blur the signal.
See choosing an IsoForge game mode for picking between Hold Steady and Make Waves at any given target, and dosing IsoForge sessions across a rehab block for set count, frequency, and progression timing.
References
- Enoka RM, Farina D. Force steadiness, from motor units to voluntary actions. Physiology (Bethesda). 2021;36(2):114-130. doi:10.1152/physiol.00027.2020