Intervals.icu API

Authentication

Basic auth with username API_KEY and password = your API key. Use athlete id 0 to auto-resolve from the API key.

# Test authentication
curl -s -u "API_KEY:$ICU_API_KEY" "https://intervals.icu/api/v1/athlete/0/profile" | jq '.name, .id'

Environment variable: ICU_API_KEY (set in shell environment).

ICU="https://intervals.icu/api/v1"
AUTH="API_KEY:$ICU_API_KEY"

OpenAPI Spec

Full spec at: https://intervals.icu/api/v1/docs/ (RapiDoc UI) or https://intervals.icu/api/v1/docs/swagger-ui/index.html (Swagger).

Core Endpoints

Activities

# List activities (date range, desc order)
curl -s -u "$AUTH" "$ICU/athlete/0/activities?oldest=2026-01-01&newest=2026-01-31" | jq '.[].name'

# Get single activity (with intervals)
curl -s -u "$AUTH" "$ICU/activity/{id}?intervals=true"

# Get activity streams (power, HR, cadence, GPS, etc.)
curl -s -u "$AUTH" "$ICU/activity/{id}/streams.json?types=watts,heartrate,cadence,altitude"

# Search activities by name or tag
curl -s -u "$AUTH" "$ICU/athlete/0/activities/search?q=tempo&limit=10"

# Download as CSV (all activities)
curl -s -u "$AUTH" "$ICU/athlete/0/activities.csv" -o activities.csv

# Upload activity file (fit/tcx/gpx)
curl -s -u "$AUTH" -F "file=@activity.fit" "$ICU/athlete/0/activities"

Wellness (Daily Metrics)

Fields: weight, restingHR, hrv, hrvSDNN, sleepSecs, sleepScore, sleepQuality, avgSleepingHR, soreness, fatigue, stress, mood, motivation, injury, spO2, vo2max, steps, kcalConsumed, comments, and more.

The wellness endpoint also returns computed fitness fields: ctl (fitness), atl (fatigue), rampRate, ctlLoad, atlLoad, per-sport sportInfo (eftp, wPrime, pMax).

# Get wellness for date range
curl -s -u "$AUTH" "$ICU/athlete/0/wellness.json?oldest=2026-01-01&newest=2026-01-31"

# Get specific fields only
curl -s -u "$AUTH" "$ICU/athlete/0/wellness.json?oldest=2026-03-01&newest=2026-03-22&fields=id,ctl,atl,rampRate,weight,restingHR,hrv,sleepSecs"

# Update wellness (PUT to date id)
curl -s -u "$AUTH" -X PUT "$ICU/athlete/0/wellness/2026-03-22" \
  -H "Content-Type: application/json" \
  -d '{"weight": 84.0, "restingHR": 55, "sleepSecs": 28800, "mood": 4, "comments": "Felt good"}'

# CSV format
curl -s -u "$AUTH" "$ICU/athlete/0/wellness.csv?oldest=2026-01-01&newest=2026-03-22&cols=id,ctl,atl,weight"

Power / Pace / HR Curves

# Power curves: last year, 42 days, all time
curl -s -u "$AUTH" "$ICU/athlete/0/power-curves.json?type=Run&curves=1y,42d,all"

# Pace curves (running)
curl -s -u "$AUTH" "$ICU/athlete/0/pace-curves.json?type=Run&curves=42d,1y"

# HR curves
curl -s -u "$AUTH" "$ICU/athlete/0/hr-curves.json?type=Run&curves=42d"

# Single activity power curve
curl -s -u "$AUTH" "$ICU/activity/{id}/power-curve.json"

Curve specifiers: 1y (past year), 2y, 42d (past 42 days), s0 (current season), s1 (previous), all, r.2026-01-01.2026-03-01 (custom range).

Calendar Events (Planned Workouts)

# List upcoming workouts
curl -s -u "$AUTH" "$ICU/athlete/0/events.json?oldest=2026-03-22&newest=2026-03-29"

# Create a planned workout
curl -s -u "$AUTH" -X POST "$ICU/athlete/0/events" \
  -H "Content-Type: application/json" \
  -d '{
    "category": "WORKOUT",
    "start_date_local": "2026-03-25",
    "name": "Easy Run 45min",
    "type": "Run",
    "moving_time": 2700,
    "description": "45m easy @ Z2 HR"
  }'

# Event categories: WORKOUT, RACE_A, RACE_B, RACE_C, NOTE, HOLIDAY, SICK, INJURED, TARGET

Athlete Profile & Sport Settings

# Get profile (includes weight, timezone, thresholds)
curl -s -u "$AUTH" "$ICU/athlete/0/profile"

# List sport settings (zones, FTP, LTHR, etc.)
curl -s -u "$AUTH" "$ICU/athlete/0/sport-settings"

Gear

# List gear
curl -s -u "$AUTH" "$ICU/athlete/0/gear.json"

Training Load Interpretation

Intervals.icu uses the Banister impulse-response model (PMC — Performance Management Chart):

Form (TSB) Zones

Ramp Rate Guidelines

• <3 CTL/week: Maintenance or slight detraining
• 3-5 CTL/week: Conservative build (recommended for most)
• 5-7 CTL/week: Aggressive build (experienced athletes, monitor closely)
• >7 CTL/week: High injury risk; typically only in training camps

Key Nuances (Expert Knowledge)

1. CTL is not fitness — it’s a proxy for training stress absorbed. Two athletes with CTL=80 may have very different actual fitness.
2. Training load source matters — power-based TSS (cycling) is more reliable than HR-based TRIMP (running/hiking). Intervals.icu estimates load from HR when no power meter is available; these estimates vary in accuracy.
3. EWMA vs rolling averages — Intervals.icu uses EWMA (exponentially weighted moving average), which weights recent sessions more heavily. This is more physiologically realistic than simple rolling averages.
4. Sport-specific loads — The wellness sportInfo array breaks down eFTP, W’, and Pmax per sport. Cross-training loads are combined for overall CTL but interpreted separately.
5. Configurable time constants — Default is 42d (CTL) / 7d (ATL), adjustable per sport via icu_type_settings[].ctlFactor and atlFactor. Non-default constants make cross-athlete comparisons meaningless.
6. The ACWR debate — Acute:Chronic Workload Ratio (ATL/CTL ≈ ACWR) was popularized as injury predictor (“sweet spot” 0.8-1.3). Recent meta-analyses show weak predictive validity for individuals. Use as a rough guide, not a hard rule. EWMA-based ACWR is more sensitive than rolling-average ACWR.
7. Recovery indicators beyond TSB — Combine TSB with wellness data: HRV trend (declining = poor recovery), resting HR (elevated = stress), sleep quality, and subjective scores (mood, soreness, fatigue). A positive TSB with declining HRV still warrants caution.

Practical Decision Framework

When advising on training load:

1. Pull current data: wellness (last 7-14 days), recent activities
2. Check trends, not snapshots: Is CTL rising/stable/falling? Is ramp rate sustainable?
3. Cross-reference wellness: HRV trend, sleep, subjective scores
4. Consider context: Training phase (base/build/peak/recovery), upcoming events, life stress
5. Give specific recommendations: Not just “you’re overreaching” but “reduce volume by ~20% for 3-5 days, prioritize sleep, recheck HRV”

Rate Limits

No published rate limits, but be respectful. Batch date-range queries instead of per-day requests.