12-Week Indoor Cycling + Easy Running Base Block for intervals.icu

An example 12-week winter base plan for cyclists who want to ride indoors on weekdays, do long rides on weekends, and rebuild an easy running base alongside. The plan is delivered as ready-to-import intervals.icu workouts, plus scripts to load them into your calendar.

• 84 workouts over 12 weeks (48 rides, 36 runs)
• Roughly 5.5 to 9.3 hours of riding and 65 to 150 minutes of running per week
• Bike intensity is prescribed as a percentage of FTP, run intensity as a percentage of max heart rate, so it scales to any athlete
• The first run is 20 minutes; running volume builds gradually, with deload weeks at 4, 8 and 12

Repository contents

File	Purpose
intervals_plan_12wk.json	All 84 workouts (dates, names, workout text, IDs). Source of truth for the scripts.
upload_to_intervals.py	Adds the workouts to your intervals.icu calendar via the API. Skips ones already there.
update_intervals.py	Rewrites descriptions of workouts already in your calendar when the JSON changes.
delete_intervals.py	Bulk deletes training blocks from your calendar by workout ID prefix.
plan_overview.csv	One row per session (date, day, type, name, minutes) for a quick overview.

Weekly structure

Day	Session
Mon	Easy run
Tue	Indoor sweet spot
Wed	Easy run (longest of the week)
Thu	Indoor tempo, then threshold, then short VO2
Fri	Easy run (short, the day before the long ride)
Sat	Long ride: mostly Z2 with sweet spot blocks late
Sun	Long steady Z2 ride

Weeks 4, 8 and 12 are deloads.

Progression

Wk	Tue	Thu	Sat	Sun	Runs Mon/Wed/Fri (min)
1	2x20 SS	3x10 tempo	2:30	2:00	20/25/20
2	2x25 SS	4x10 tempo	2:45	2:00	25/30/25
3	3x20 SS	3x15 tempo	3:00	2:15	30/35/30
4	2x20 SS	easy spin	2:00	1:30	25/30/25
5	2x30 SS	3x10 threshold	3:00	2:15	30/40/30
6	2x35 SS	4x10 threshold	3:15	2:30	35/45/30
7	3x25 SS	5x10 threshold	3:30	2:30	35/50/35
8	2x20 SS	easy spin	2:15	1:30	30/40/30
9	2x40 SS	5x5 VO2	3:15	2:30	40/55/35
10	3x30 SS	5x5 VO2	3:30	2:30	40/60/40
11	1x90 SS	6x5 VO2	3:30	2:30	45/65/40
12	2x20 SS	easy spin	2:15	1:30	35/45/35

SS = sweet spot. Tuesday and Thursday sessions include warmup, rest and cooldown, so some run longer than the headline durations suggest. Peak weeks are about 9.3 hours of riding plus 2 to 2.5 hours of running.

Intensity reference

Work	Target
Z2 / endurance rides	62% FTP, HR roughly at or below 75% of max
Sweet spot	90% FTP
Tempo	82% FTP
Threshold	98% FTP
VO2 intervals	110% FTP
Easy runs	50-73% of max HR, conversational effort; let HR lead, not pace

This block is base only: no strides, tempo or race-pace running. Run/walk is fine in weeks 1-3 if calves or shins complain.

Requirements

• An intervals.icu account
• Python 3 (the scripts use only the standard library, nothing to install)
• Your FTP set under Ride settings, and your max HR set under Run settings, so percentage targets calculate correctly

Usage

Upload to your calendar

1. In intervals.icu, open Settings > Developer Settings and copy your API key and athlete ID (looks like i123456).
2. Set environment variables:

   export INTERVALS_API_KEY="your_api_key"
   export INTERVALS_ATHLETE_ID="i123456"
   

3. Preview, then upload:

   python3 upload_to_intervals.py --dry-run
   python3 upload_to_intervals.py
   

Each workout has an external_id, so re-running the upload skips workouts that are already in your calendar rather than duplicating them.

Treat your API key like a password: don't commit it or put it in a file in the repo.

Changing the start date

Dates are fixed in intervals_plan_12wk.json (week 1 starts Monday, Oct 26, 2026). To start on a different Monday, shift every start_date_local value by the same whole number of weeks before uploading. For example, to move the plan forward by 7 days:

import json, datetime as dt
shift = dt.timedelta(days=7)
events = json.load(open("intervals_plan_12wk.json"))
for e in events:
    d = dt.datetime.fromisoformat(e["start_date_local"]) + shift
    e["start_date_local"] = d.isoformat()
json.dump(events, open("intervals_plan_12wk.json", "w"), indent=1)

Keep the shift a multiple of 7 so the weekly structure stays on the right days.

Editing the plan after upload

upload_to_intervals.py will not change workouts already in your calendar, because it skips matching IDs. To change them:

1. Edit the description text in intervals_plan_12wk.json.
2. Preview and apply only the affected workouts:

   python3 update_intervals.py --match -run --dry-run
   python3 update_intervals.py --match -run
   

--match filters on the workout ID (-run, -ss, -thu, -sat-long, -sun-z2). Omit it to update every workout whose text differs. The update overwrites matched descriptions, including any edits you made by hand in intervals.icu.

Deleting a training block

Preview, then delete every workout whose ID starts with the given prefix:

python3 delete_intervals.py --prefix winter26- --dry-run
python3 delete_intervals.py --prefix winter26-

The script lists the matches and asks you to type delete before removing anything (--yes skips this). Pass several prefixes to remove several blocks at once, use a longer prefix such as winter26-W09 for a single week, or add --from 2026-11-09 to keep everything before a date.

Only workouts with a matching ID are deleted, so workouts you added by hand and completed activities stay in place. Deleting can't be undone, but upload_to_intervals.py can re-add anything still in the plan JSON.

Workout IDs

IDs follow winter26-W{week}-{day}-{type}, for example winter26-W07-tue-ss or winter26-W03-fri-run.

Workout text syntax

Workouts use the intervals.icu text format. Steps start with -, repeats are an Nx header line, and ramps use ramp lo-hi%:

Warmup
- 12m ramp 50-75%

Sweet spot 2x
- 20m 90%
- 5m 55%

Cooldown
- 5m 50%

Run steps use heart rate, e.g. - 25m 50-73% HR. A single value like 73% HR is read as a target rather than a ceiling, so keep a range.

Notes

• This plan is a general template, not personalised coaching. Adjust volume and intensity to your own fitness, schedule and recovery.
• If the total load is too much, shorten the Sunday ride first and leave the runs alone.