Choosing an IsoForge Arcade game

The Arcade is the primary IsoForge surface. It has six games, and they are not six skins over one training. Each asks the patient to produce a different shape of force over time, and the evidence on force-tracking tasks is clear that distinct shapes engage distinct motor-control strategies (Amematsro et al. 2025). Picking a game is a clinical decision about which subskill you want to load.

Two things are true of all six. The target is set from the patient's own recent maximum, so the same game is a different physical task for every patient. And the difficulty adapts during play, which changes how you read the results. That second point is the part most worth understanding before you prescribe, so it has its own section below.

The original four modes are still available at any time. They are covered in choosing a classic IsoForge game mode, and the mapping between the two sets is at the end of this article.

The games

The hub groups them by what they train. Force control: Force Tracking (Ember Drift), Isometric Repeaters (Cinder Updraft), Force Targeting (Slag Break) and Force Modulation (Bellows Battery). Impulse and rate: Explosive Force (Forge Runner) and Contract and Relax (Spark Pulse).

Each game has two names. Its clinical name says what it trains and stays the same whatever art the patient plays it in, and every record (the dashboard, session detail, Progress, the File Library) leads with it. Its game name belongs to the art and is what the patient sees on screen: Ember Drift in the original forge art.

Force Tracking (Ember Drift)

Force steers an ember down a corridor. Pushing harder lifts it, easing lowers it, and the corridor wanders, so there is no setting where holding still is correct. As difficulty rises the corridor narrows.

What it trains. Continuously corrected submaximal force. The patient has to notice an error and close it while still producing force, which is a different task from settling onto a fixed target and staying there. Because the corridor moves slowly enough to react to, this is largely closed-loop control: the patient watches, corrects, watches again.

What it reports. Drift from target (tracking nRMSE): the tracking error as a percentage of target, computed after the session from the recorded force against the target the patient actually saw. Lower is better.

Best for. Patients whose assessment shows a Control deficit and who have enough capacity to modulate force rather than just hold it. It is the first suggestion when Drift from peak (nRMSE) is the lowest of the three Control measures, because tracking a moving target trains noticing a gap from the intended level and closing it, which is what a hold that sags from peak is failing to do. Also a good first Arcade game for a patient who found a static hold tedious, because the task is the same skill with something to do.

Explosive Force (Forge Runner)

Gaps scroll toward the player and each is cleared with a fast, explosive push. Jump height comes from how hard and how quickly force rises, not from how long it is held.

What it trains. Rapid force production. A patient clears dozens of gaps in a set, which means dozens of small ballistic efforts, a different stimulus from the one or two maximal efforts a formal assessment collects. Rate of force development declines faster than peak strength during disuse and recovers on its own timeline (Ruggiero and Gruber 2024), so it is worth training as its own target rather than assuming it follows strength back.

What it reports. Impulse: the average force-time integral behind each jump, in newton-seconds. Higher is better.

Best for. Patients whose Speed readings, Explosiveness and Build-up (the RTD windows), lag the uninvolved side while Strength has largely recovered. Also athletes whose sport demands repeated rapid efforts rather than one maximal one. For the assessment-side reading, see what Explosiveness (RTD Early) actually means.

Contract and Relax (Spark Pulse)

A rhythm game. The patient produces repeated pulses on a beat, and the interval between pulses matters as much as the pulses themselves. Failing to release fully between efforts costs the run.

What it trains. Repeatable pulses and clean relaxation between them. Relaxation is the half of the cycle a clinician usually cannot see and therefore cannot coach. A patient who cannot let go between efforts will produce a rising baseline across a set, and the game surfaces that immediately rather than at the end.

What it reports. Rhythm steadiness (pulse-timing CV): the variability of the interval between pulses, as a percentage. Lower means steadier timing. Relaxation time is reported alongside it.

Best for. Patients who produce a good single pulse but degrade across repeated efforts, and late-phase work where the goal is repeatability rather than magnitude. Explosive sustained and ballistic pulse-like contractions do not yield the same rate of force development values (Kozinc et al. 2022), so a patient who looks fine on a sustained assessment can still be poor at repeated pulses.

Isometric Repeaters (Cinder Updraft)

An isometric hold protocol in game form. The run works through a ramp, a series of holds at the prescribed force, a staircase of step increases, and gusts that push the target around. Each wave is a set.

What it trains. Sustained graded holds across a full working set, including holding through a disturbance. This is the closest Arcade game to a conventional trapezoid force-tracing protocol, which is the form most of the force-steadiness literature uses (Enoka and Farina 2021).

What it reports. Smoothness (yank), in percent per second: the rate at which force wavered during the steady part of each hold. Lower means a smoother hold. Alongside it come Steadiness (hold CV), how much force wavered around its mean, and hold drift, the sag from the start of a hold to the end, which behaves as a within-session fatigue signal and is not something a single peak value will show you. On yank as a smoothness measure and its limits, see the Control metrics.

Best for. Tendon loading protocols, where the prescription is already a sustained submaximal isometric hold and the practical problem is that unsupervised holds drift off target without anyone noticing. Also early-phase work after a period of unloading, and any patient whose Control metrics are the limiting factor on their symmetry index. It is also an option when strength is the gap: run at a higher share of the patient's maximum, with short sets, the same holds load capacity as well as control.

Force Targeting (Slag Break)

Force sets the height of a plate at the side of the court. Cyan cores fly toward it, and the patient raises or lowers the plate to meet each one where it will arrive. Grey slag comes in among them and should be let through. Holding the plate steady while nothing is coming fills a heat meter, and a full meter splits the next return into three cores.

What it trains. Grading force to a level the patient has to predict, then arriving at it before the ball does, plus withholding on the slag. The plate covers 80 to 120 percent of the prescribed force, so every return is made close to the prescription. Below that the plate rests out of play, so a relaxed patient cannot return anything by accident. The heat meter rewards a quiet hold between returns, which keeps the patient under load rather than dropping to rest after each one.

What it reports. Miss size (intercept error): at each crossing, the gap between the force the patient held and the force the core needed, as a percentage of target. The median is reported, misses included. Lower is better. Release errors (slag returned when it should have been let through) and Waiting steadiness, how still force stayed while nothing was coming, are reported alongside it.

Best for. A patient who already holds steadily at one level and now needs to move between levels on demand. No single assessment metric maps to it, so it is a progression choice rather than a deficit-driven one.

Force Modulation (Bellows Battery)

Force slides a turret along a rail beneath a formation of cinders, and the turret fires on its own. Each column of the formation sits at its own force level, seven of them between 80 and 120 percent of the prescribed force, so aiming at a column means holding that level. Green coolant tanks are mixed into the formation, and destroying one is the error the game counts. The way to avoid it is to move off that column.

What it trains. Precise force at several discrete levels, held long enough to clear a column, and the decision to move off a no-go target. Everything below 80 percent of target is out of play, so the whole set is spent close to the prescribed force.

What it reports. Aim error: while the turret is parked, how far force sat from the nearest column's level, as a percentage of target. Lower is better. Overshoot on moves between levels is reported once there are enough moves to read it, along with the number of coolant tanks destroyed.

Best for. Later-phase work where the patient can sustain moderate force and the goal is precision at more than one level. Like Force Targeting it is a progression choice, not something an assessment deficit points to directly.

Adaptive difficulty, and what it costs

Each game carries one difficulty setting that moves during play. After each rep or segment the game looks at how often the patient succeeded and adjusts, aiming to hold them in a 70 to 85 percent success band. It hardens slowly and eases quickly, on the reasoning that frustration costs a patient more than boredom does.

This is a direct implementation of the challenge point idea: practice is most productive when task difficulty sits near the edge of the learner's current ability rather than at either extreme, and the useful difficulty is relative to the individual, not to the task (Guadagnoli and Lee 2004). A fixed difficulty is right for exactly one patient on exactly one day.

Four practical consequences:

• Difficulty is tracked per patient, per game, and per joint, action, and limb. A patient's right knee setting does not leak onto their left knee or their shoulder. This matters because the whole point of bilateral training is that the two sides are not equivalent.
• It carries between sessions, but each session starts slightly easier than the last one ended. The patient gets a warm-up rather than being dropped straight back into their hardest setting.
• You can turn it off. Fixed easy, normal, and hard settings are available if you want a constant task, for instance when you are deliberately repeating a session to compare it.
• The score stops being a trend. This is the real cost and it is worth being explicit about. If the task gets harder every time the patient improves, a flat score across four sessions may mean no change or it may mean steady improvement against steadily rising difficulty. The reported outcome for each game is computed after the session from the recorded force signal, not from the game score, precisely so there is something comparable to look at. Read the outcome, not the score, when you want a trend. The score is for the patient in the room.

Why the games are not interchangeable

What looks like the same muscle action on the surface can engage substantially different control machinery underneath. High-density recordings from primary motor cortex during continuous force tracking show that distinct force-profile families (static holds, slow ramps, slow sines, fast sines, chirps) occupy distinct neural state-space regions, and that closed-loop reactive strategies suffice for slow-changing profiles while faster profiles require pre-planned, template-based control (Amematsro et al. 2025).

The practical translation is that you cannot substitute a slow tracking task for a fast pulsed one and expect the same adaptation. Force Tracking and Isometric Repeaters load reactive correction and sustained grading. Explosive Force and Contract and Relax load pre-planned production, because at the speeds they demand there is no time to react and correct within a single effort. Force Targeting and Force Modulation sit between the two: the patient can see the level coming and plans the move to it, then corrects while holding it there.

A useful heuristic: if the patient has time to see the error and fix it during the effort, you are training correction. If they do not, you are training the plan.

Mapping from the classic modes

If you know the original four, this is roughly where they land. The Arcade games are not reskins and the tasks differ in real ways, so treat this as orientation rather than equivalence.

Where you want a clean, fixed, repeatable task with no adaptive layer, the classic mode is the better instrument. Where engagement across a full set is the limiting factor, the Arcade game is.

A starting framework

Five patterns that cover most rehab progressions. None is exclusive, and a single block can rotate through several.

1. Control deficit (Drift from peak, Steadiness, or Smoothness lagging on the involved side; nRMSE, CV, or yank in technical terms). Start with Isometric Repeaters to load the hold directly, then move to Force Tracking once the patient can hold cleanly and needs to grade force rather than just sustain it. When Drift from peak has the lowest LSI of the three, reverse the order: start with Force Tracking, and move to Isometric Repeaters once force tracks the path cleanly.
2. Speed deficit (Explosiveness or Build-up lagging on the involved side by more than strength explains). Start with Explosive Force. Move to Contract and Relax once single pulses are clean, because that is where repeatability rather than magnitude becomes the limit.
3. Small Control deficit (the lowest of Drift from peak, Steadiness and Smoothness between 90 and 100%). Holding is no longer the limit, so the work moves to grading force to set levels: Force Targeting, then Force Modulation. These games mix prediction with force accuracy, which is why they are a refinement once control is close to symmetric rather than the answer to a large deficit.
4. Strength deficit (Strength LSI under 90%). Before training it, it is worth knowing what kind of gap it is: a Focal Joint Cooling Test on the same test shows whether force rises once the joint is cooled, which points to inhibition (limited access to capacity) rather than weakness. For training, one option is Isometric Repeaters at a higher share of the patient's maximum. The suggestion opens the prescription at 55% of MVIC with 20-second sets; Isometric Repeaters steps the hold up by its tolerance, so at the default the top demand is about 66%, inside the 50 to 70% band setting submaximal targets gives for higher-target hold work. Whether a higher-intensity hold suits this patient at this stage, and at what dose, is your call. The game's own Smoothness and Steadiness readings come with it. If a Control deficit is suggested for the same test, that card starts with Force Tracking instead, so the two do not both open Isometric Repeaters.
5. Repeatability deficit (good single efforts, degrading across a set). Contract and Relax directly. Watch relaxation time rather than the score.

The first four are read from the assessment for you. The IsoForge hub suggests games from the patient's latest visit, and the Training focus card on the patient's dashboard does the same for whichever visit is on screen. A Control deficit is a Drift from peak, Steadiness, or Smoothness LSI under 90%; from 90 to 100% it is the small Control deficit. A Speed deficit is an Explosiveness or Build-up LSI under 90% that also sits at least 10 points below Strength LSI, because a weaker limb is also a slower one and that is a strength problem, not an explosive one. A Strength deficit is a Strength LSI under 90%, and one test can show more than one deficit. Both surfaces cite the number behind each suggestion and open the game with the test and side filled in, plus the 55% starting target and 20-second sets for a strength suggestion. The fifth pattern has no assessment measure, so it stays your call.

What to do next

• Pick the game from the assessment deficit. Engagement is a tiebreaker between two clinically defensible choices, not the primary criterion.
• Read the reported outcome, not the score, when tracking progress. The score moves with difficulty by design.
• Let the adaptation run for at least two or three sessions before judging it. It starts a new patient in the middle of the range and needs a few segments of evidence to settle.

See setting submaximal targets from a recent MVIC for picking the target force, dosing IsoForge sessions across a rehab block for set count and frequency, and reading IsoForge training summaries for how training data sits alongside assessment data.

References

• Amematsro EA, Trautmann EM, Marshall NJ, et al. Motor cortex flexibly deploys a high-dimensional repertoire of subskills. bioRxiv. 2025. doi:10.1101/2025.09.07.674717
• 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
• Guadagnoli MA, Lee TD. Challenge point: a framework for conceptualizing the effects of various practice conditions in motor learning. Journal of Motor Behavior. 2004;36(2):212-224. doi:10.3200/JMBR.36.2.212-224
• Kozinc Ž, Pleša J, Djurić D, Šarabon N. Comparison of rate of force development between explosive sustained contractions and ballistic pulse-like contractions during isometric ankle and knee extension tasks. Applied Sciences. 2022;12(20):10255. doi:10.3390/app122010255
• Ruggiero L, Gruber M. Neuromuscular mechanisms for the fast decline in rate of force development with muscle disuse, a narrative review. J Physiol. 2024. doi:10.1113/JP285667