Now in beta on TestFlight

You train at the edge. Know exactly where it is.

TeraThreshold reads every run your Garmin records and answers four questions: how well you moved, how much training stress you are carrying, what your body is telling you, and where your fitness stands. Every answer is built from your own data, and your form is judged against your own normal at each pace, not against population averages. Built for elite and sub-elite runners.

Join the TestFlight How it works

For iPhone with iOS 17 or later and a Garmin watch. United States only.

The Risk tab with an Injury Risk Increased notification over an Injury Risk score of 77, High. The Form tab: a Form score of 71 with a two-month trend, a Focus card on stride length with an A-Skips drill, and two insights. The Profile tab: a Race Fitness of 58, Sub-elite, with 5K and 10K predictions, heart-rate zones, body composition and weekly training volume in miles.
FormHow well did I move?

A 0–100 score for every run, built from stretches of one to four minutes, each compared with how you normally run at that pace.

Form scoring RiskHow much am I carrying?

A 0–100 Injury Risk estimate from five stress pathways, read as Low, Moderate, Elevated or High.

Injury Risk BodyWhat is my body saying?

Tight, sore or painful, marked on nine areas of a body map and counted in your Injury Risk.

Body check-in ProfileWhere is my fitness?

A Race Fitness number from the fastest pace you hold with a steady heart rate, with race predictions, seven paces and five zones.

Profile

Connect once. Then train.

Nothing to log and nothing to sync by hand. Your Garmin account is your sign-in, and every run reaches TeraThreshold on its own after your watch syncs with Garmin Connect.

  1. Connect Garmin

    Tap Continue with Garmin and approve access on Garmin's own page. That sign-in is your account: no email and no password to create, and TeraThreshold never sees your Garmin password.

  2. Past runs import

    With Garmin's historical-data permission on, earlier activities, sleep and HRV import in the background, and the app shows the import's progress while it runs.

  3. Every run is read

    New runs arrive on their own. Each one is named, scored for form, added to your baseline, and folded into your Injury Risk and your profile.

  4. Tell it how you feel

    Mark anything tight, sore or painful on the body map. It counts toward your Injury Risk until you clear it.

What it reads from Garmin

  • Activity files, including running dynamics
  • Heart rate, pace, GPS and elevation
  • Sleep and overnight HRV
  • Body composition, if you share health data
  • Stryd power and form data, when your watch records it
Form

Running form, scored against your own baseline

Your watch measures ground contact, stride length, vertical oscillation, cadence and balance on every run. TeraThreshold compares each stretch of one to four minutes, after a three-minute warm-up, with how you normally move at that same pace, makes allowances for heat, cold, steep grades and altitude, and rolls the result into one score from 0 to 100. Every comparison is you against you.

  • Pace-matched, never self-flattering. Your baseline is kept per pace band, and each run is scored before it joins the baseline, so a run is never compared with itself.
  • A Focus for today. The metric furthest below your normal. On an off day it comes with a drill, such as A-Skips for stride length or Metronome Strides for cadence, and for stride length or cadence, what it costs you: “Costs ~10 sec/mi at the same effort.”
  • Breakdown by effort. Easy, moderate and hard runs are tracked separately, each metric against its previous-period average, with a trend of Improving, Declining or Holding Steady.
  • Insights over weeks. “Form has plateaued.” “Form is rock-solid.” “Easy-pace form improving, hard-pace declining.” Each is read from your last six to eight weeks of scores.
The Form tab scrolled to the metric breakdown: cadence, ground contact time, vertical oscillation, stride length, vertical ratio and stance time, each against the runner's own average, with a Holding Steady trend.

What the score is made of

Shown on every run's detail screen

71 · this run
Poor Form0–33
Fair Form34–66
Great Form67–100
Quality 45%
Your mechanics against your baseline at the same pace. Matching your normal scores in the mid-60s; better than normal scores higher.
Stability 15%
How steady each metric stays within a stretch, stride after stride.
Resilience 30%
Whether your mechanics hold as the run goes on, including the last quarter against the first.
Efficiency 10%
Cardiac drift and pace per heartbeat: how hard your heart works for the same speed. Without heart-rate data, its share goes to Quality and Resilience.

How your form held up

Each run's four quarters, compared on the Form tab

  • Resilient

    The last quarter lands within three points of the first. Form held steady.

  • Gradual Fade

    Form drifts more than three points from where you started, without the final quarter being the low point.

  • Late Fade

    Your last quarter is your weakest, below both the first and the third.

  • Early Struggle

    The opening quarter scores below the second. You took a while to settle in.

The run's detail screen describes the pattern in plain words, such as “Form dropped late”, and adds when the drop started, how many points it cost and the cardiac drift, for example “starting at 31:40 · 6 pts drop · 4.1% cardiac drift”.

Risk

Injury risk from your load, mechanics and recovery

Injury Risk is a 0 to 100 estimate of the stress your recent training has left you carrying. It is recalculated each time a run syncs: the run is scored across five stress pathways, and the headline adjusts for how your load, sleep and HRV are trending. Anything you mark on the body map is added on top.

  • Findings in plain words. Each names what happened, usually the number behind it, and the next step. The most severe from the last seven days come first.
  • A Focus. The one thing flagging most right now, or “Nothing flagging today”.
  • Training load. Your acute-to-chronic workload ratio with its band, Detraining, Optimal, Building or Danger, and Fitness, Fatigue and Form (CTL, ATL and TSB).
  • Alerts when the level matters. A push when a newly synced run moves your level into or out of Elevated or High. Moving between Low and Moderate stays quiet.

Four levels

The level decides when you get an alert

77 · High
Low0–14
Moderate15–34
Elevated35–59
High60–100

Five stress pathways

Each shows its worst of your last three runs and a trend over ten

Overload
Load against what you are used to: workload ratio, weekly volume, heavy three-day blocks, streaks and spikes over your 30-day maximum.
Fatigue
How far your mechanics and heart rate drift within a run against your baseline, plus pacing, stops and trends across runs.
Impact
Estimated impact load, downhill running, terrain, and weekly climb and descent against your usual.
Asymmetry
Left/right ground-contact balance against your own normal.
Recovery
Hours of sleep, overnight HRV against your baseline, and time since your last run against how long it takes to recover.

What a finding looks like

Three of nearly 100 finding types

  • OverloadHardest session in 30 days

    Load was 118% of your 30-day max — a top-tier overuse risk factor

    Follow with 1-2 easy/short runs to allow adaptation
  • FatigueEasy-run efficiency is declining

    Speed/HR ratio dropped 1.8σ below baseline over last 3 easy runs — possible accumulated fatigue

    Consider extra recovery days — your body is working harder for the same output
  • AsymmetryGait changed — possible side protection

    Balance drifted +2.1z while cadence dropped — may be protecting one side

    Check for pain/tightness on the favored side, consider gait analysis
Body

Your body is an input, not an afterthought

Niggles are data. Open the body map from the Risk tab, tap an area to mark it Tight, tap again for Sore, again for Pain. There are nine areas, each left and right, front and back, from the lower back to the feet. Marks are weighted and added to your Injury Risk, up to a cap.

  • Weighted by severity and place. Pain counts six times as much as tightness. A calf, hamstring or soleus counts more than the lower back, a shin or a foot, and the same area on both sides counts more again.
  • Pain sets a floor. A painful calf on its own keeps your Injury Risk at Elevated or above, however light your training has been.
  • It fades only as it should. A check-in fades by its most severe mark: tightness over about three days, soreness over about a week, each to a floor. Pain does not fade, and it weighs more if it lasts beyond two days. Saving the map restarts the clock, and every mark counts until you clear it.
  • A history. Check-In History lists every check-in from the last 30 days, area by area, so you can see what keeps coming back.

Areas

  • Back
  • Hip
  • Glute
  • Quad
  • Hamstring
  • Calf
  • Soleus
  • Shin
  • Foot

Severity

  • Tight
  • Sore
  • Pain
Profile

Threshold, Race Fitness and zones that move with your training

No lab visit and no time trial. TeraThreshold looks at your outdoor runs from the last 90 days for the fastest pace you hold for half an hour or more while your heart rate stays steady, turns it into a Race Fitness number using the pace relationships Jack Daniels published, and nudges it as new runs come in. Your level, race predictions and paces follow from that number; your heart-rate zones follow from your threshold heart rate.

  • Race predictions for 5K, 10K, 21K and 42K from your current Race Fitness. The demo runner's card shows 58 (58.3 before rounding) with 5K 17:28 and 10K 36:15.
  • Seven named paces. Recovery, Easy, Marathon, Tempo, Threshold, Interval and Repetition. Easy, Tempo and Threshold are measured from your own runs once there is enough data, with the heart rate you hold there. The rest are projected from your Race Fitness and marked Predicted.
  • Five heart-rate zones from your lactate threshold: Recovery below 85%, Aerobic 85–90%, Tempo 90–95%, Threshold 95–100% and VO2max above. Threshold and max heart rate start from your watch settings, or your age, and refine from your runs.
  • Running economy and volume. Cadence, ground contact, stride length and vertical oscillation at tempo pace against target ranges; week, month and year totals; and a label for your intensity mix, such as Well polarized, Mostly aerobic or Threshold heavy.

Five levels

Shown next to your Race Fitness. With 50 or more logged activities, Beginner and Recreational move up one level.

58 · Sub-elite
Beginner<35
Recreational35–41
Competitive42–49
Sub-elite50–59
Elite60+

Every session, named and broken down

Runs are named from their structure: how long you spent at each effort, and whether there were repeats, a fast finish or a steady build. Races are recognised by standard distance, with an effort check up to 15K, then matched by start location, distance and month against a catalogue of races and named after the event.

One run, top to bottom

  1. Name
    Steady Run · 6.04 mi · 42 min · 7:04/mi

    Named from pace: at least 70% at easy or steady effort, under 5% at threshold or harder, and no repeats.

  2. Form
    71 · Great Form

    Quality 72, Stability 81, Resilience 61, Efficiency 78, and a note: “Your form dropped off toward the end of the run.”

  3. Mechanics
    Cadence 184 spm against your 180 · Ground contact 225 ms against your 229

    Every metric your watch recorded, against your own average, rated Good, Neutral or Concern.

  4. Load
    Training load 106 · ACWR 0.85, Optimal

    Heart-rate load adjusted for hills, form and drift, with your acute load of 62 against a chronic 72.

  5. Best efforts
    1 mi 6:59 · 5K 21:56

    The fastest stretches inside the run, from 400 m up to the marathon, flagged when they are personal records.

  6. Heart rate
    67% in zone 4, 156–164 bpm

    Time in each zone, set from your threshold of 164 and your max of 183.

Also on the run's screen: splits by kilometer, mile or lap, the workout's phases, and separate form scores for flat, uphill and downhill.

How runs are named

Each name comes from a rule about effort, repeats and pace. Treadmill and track runs get “· Treadmill” or “· Track” added.

Race
A standard race distance, with an effort check up to 15K, named for the event and year, or e.g. “Half Marathon Race”.
Easy Run
Mostly easy effort, under 75 minutes.
Recovery Run
Under 75 minutes with no steady or harder effort.
Steady Run
At least 70% easy or steady, under 5% at threshold or harder.
Long Run
75 minutes or more, mostly easy or steady, e.g. “14mi Long Run”.
Tempo
One sustained block of 10 minutes or more at tempo effort, e.g. “4mi Tempo”.
Intervals
Repeats, named for their intensity, e.g. “4x8min Tempo Intervals”, Threshold, VO2max or Mixed.
Fartlek
Four or more unstructured surges.
Ladder
Efforts that rise, fall or pyramid in distance.
Progressive Run
Each quarter at least 3% faster than the last.
Fast Finish
The last 12–30% at least 7% faster.
Negative Split Run
The second half at least 5% faster.
Time Trial
One hard block covering most of the run, e.g. “3mi Time Trial”.
Heatmap

Your own averages on a grid of pace against how long you held it, from one minute to an hour. Heart rate by default; switch to grade-adjusted pace or any running-dynamics metric your watch records. A banner says what improved or declined after your latest run, and tapping a cell shows its average, spread and consistency.

Method

The analysis, in the open

Every number in TeraThreshold is computed by our own code from your data. The scores come from established sports-science methods and statistics, so each one can be explained. Machine learning is used where it helps: to pick each run's headline and the drills to suggest. Nothing you record is sent to an outside AI service.

  1. PELT · hidden semi-Markov model

    Splitting a run

    Change-point detection cuts each run where pace, heart rate, grade or power shifts. A hidden semi-Markov model built from your own zones labels each stretch warm-up, easy, steady, threshold, VO2max, recovery or cool-down.

  2. Grade-adjusted pace · Minetti 2002

    Flattening the hills

    Uphill and downhill pace is converted to its flat-ground equivalent from the measured energy cost of running on slopes, so a climb is not mistaken for a bad day.

  3. Exponentially weighted baselines

    Learning your normal

    Your heart rate and every running-dynamics metric are kept per pace band and duration. Each cell updates as an exponentially weighted average that favours recent runs, and readings more than four standard deviations out are rejected.

  4. Z-scores · condition allowances

    Scoring form

    Each stretch is measured in standard deviations from your own normal at that pace, eased for heat, cold, steep grades and altitude, then combined into Quality, Stability, Resilience and Efficiency.

  5. Friel threshold · Daniels equations

    Finding your threshold

    Threshold heart rate comes from your best steady 30-minute efforts, cross-checked against a piecewise-linear fit of heart rate on pace. Your Race Fitness, race predictions and paces follow from the running equations Jack Daniels published.

  6. Banister TRIMP · EWMA

    Measuring load

    Training load is Banister's heart-rate impulse, adjusted for hills, form breakdown and cardiac drift. Fitness and fatigue are 42-day and 7-day exponentially weighted averages.

  7. Transparent rules

    Estimating injury risk

    About 90 signal checks score the five pathways, with caps and diminishing returns so no single sign dominates, then recovery, load trend and your check-ins adjust the total. It is a stress estimate, not a probability, and the findings show which signals fired.

  8. Random forests

    Machine learning

    Random-forest classifiers read around 90 features of each run's form analysis to pick its headline and severity, and choose which drills to suggest for your weakest metric. The sentences you read are written templates, not generated text.

Read-only. Revocable. Deletable.

Your training data is used for your analysis. We do not sell it and we do not show ads.

Read-only Garmin access

TeraThreshold reads what you allow on Garmin's consent screen: your activities, and if you choose, health data (sleep, HRV and body composition) and past activities. It never writes to your Garmin account.

No Garmin password

Sign-in happens on Garmin's own page, so TeraThreshold receives an access token, never your password. Disconnect in Settings deletes that token and stops syncing, and you can also remove TeraThreshold under Connected Apps in Garmin Connect.

Delete everything

Delete your account from Settings. After a 30-day window in which you can change your mind, your data and your login are removed.

Free and Pro

Every new account starts with 30 days of Pro, no card needed. After that, keep the free tier or subscribe for $12.99 a month.

Free

$0Always free, no card needed.
  • Form score and its trend
  • Injury Risk score, level and trend line
  • Body check-in and its history
  • Profile: Race Fitness, race predictions, paces, zones and economy
  • Heatmap and your named activity list
Join the TestFlight

Pro

30-day trial
$12.99/monthAnnual plan in the app. Cancel anytime.
  • Everything in Free
  • Run detail: sub-scores, biomechanics, fatigue, load, best efforts, zones and splits
  • Form analysis: Focus and drills, breakdown by effort, insights and durability
  • Risk analysis: five stress pathways, findings, Focus and training load
Start 30 days of Pro

Prices in US dollars. When the trial ends, Pro features lock and nothing is charged unless you subscribe. Subscriptions are billed through Apple, renew automatically and can be canceled anytime from your Apple ID settings.

Questions

Which watches work?

Any Garmin watch that syncs to Garmin Connect. The Form score uses whichever running dynamics your run records: ground contact time, vertical oscillation, stride length and left/right balance need a watch that records them, or an HRM-Pro strap or Running Dynamics Pod. A Stryd pod adds leg spring stiffness and form power. Race Fitness, paces, zones and training load need only heart rate and pace.

How is this different from the numbers in Garmin Connect?

Your watch records the raw numbers. TeraThreshold compares each one with your own history at the same pace, scores how it holds up through a run, and connects it to your training load, your sleep and HRV, and anything you mark on the body map.

Does TeraThreshold use AI?

Yes, in a specific place: random-forest models pick each run's headline and the drills to suggest. Every score, level, zone, pace and alert comes from sports-science methods and statistics applied to your own data, so each one can be explained. Nothing you record is sent to an outside AI service such as ChatGPT or Claude.

Is it on the App Store?

Not yet. TeraThreshold is in beta on TestFlight for iPhone. Leave your email below and Apple will send you a TestFlight invite.

Where is it available?

In the United States, on iPhone with iOS 17 or later. Distances and paces show in miles by default; you can switch to kilometers in Settings.

Does it work with Apple Watch, Apple Health or Strava?

Not yet. TeraThreshold connects to Garmin today.

How soon will I see scores?

New runs appear shortly after your watch syncs. A Form score compares a run with your baseline, so it needs a few earlier runs at similar paces, and your Race Fitness needs enough steady running to find your threshold. Until then the Form score is marked low confidence and your Race Fitness shows as not yet measured.

Does it work on a treadmill or a track?

Yes. Treadmill and track runs are scored and named, with “· Treadmill” or “· Track” added to the name. Race Fitness is estimated from outdoor runs only.

What does TeraThreshold read from my Garmin account?

What you allow on Garmin's consent screen: activity data, and optionally health data (sleep, HRV and body composition) and historical data. Access is read-only, and you can disconnect Garmin from Settings at any time.

Is TeraThreshold medical advice?

No. Its scores and suggestions are estimates computed from your training data to help you make training decisions. An Injury Risk score is not a prediction that you will or will not get hurt. For pain, illness or injury, see a qualified professional.

Can I delete my data?

Yes. Delete your account from Settings. You have 30 days to cancel the deletion; after that your data and your login are removed.

What does Pro cost?

$12.99 a month after 30 days of Pro free. An annual plan is also available in the app, and you can cancel anytime. When the trial ends, Pro features lock and nothing is charged unless you subscribe.

TeraThreshold is in TestFlight

The iPhone app is in beta. Leave your email and Apple will send you a TestFlight invite. Install it, sign in with your Garmin account, and your first session is analyzed minutes after it syncs.

We share this address with Apple only to send the invite. Privacy Policy