TrainingPeaks Workout File Formats Explained: CSV vs ZWO vs FIT vs ERG vs MRC

Athletes regularly mix up workout file formats because they sound interchangeable. They are not. CSV, ZWO, FIT, ERG, and MRC each solve a different problem, and using the wrong one creates unnecessary friction.

If your goal is simply “get this plan onto my TrainingPeaks calendar,” file-format confusion is often the exact thing slowing you down.

The Short Version

• CSV: best for bulk plan import and calendar creation
• ZWO: best for structured trainer workouts, especially Zwift-style session files
• FIT: best for completed workout data and device files
• ERG / MRC: legacy or platform-specific structured workout formats

TrainingDojo is most useful when the problem is plan structure and calendar upload. If you are juggling a whole season plan, CSV is usually the cleanest path.

CSV: The Best Format for Whole Plans

CSV is simple tabular data. It is not sexy, but it is extremely good at representing a block of workouts: day number, sport, title, duration, description, phase, and so on.

That makes CSV ideal when:

• You generated a plan with ChatGPT or another AI
• Your plan lives in Excel or Google Sheets
• You want to import dozens of workouts at once
• You care more about calendar structure than trainer-file fidelity

This is the format TrainingDojo is designed around, because it maps naturally to “entire plan to TrainingPeaks.”

ZWO: Great for Individual Structured Trainer Workouts

ZWO files are structured workout files commonly associated with indoor cycling workflows. They are useful when you want a specific interval session encoded with steps, durations, and targets.

They are less useful when your real problem is seasonal planning. A folder of ZWO files is still not a full calendar. You still have to organize where those workouts belong, how they map into your block, and how the surrounding endurance, recovery, and race days fit together.

That is why many athletes need both:

• ZWO for certain trainer sessions
• CSV-style plan structure for the overall calendar

If that is your situation, read our ZWO import guide.

FIT: Best for Recorded Activity Data

FIT files are usually about completed activity data and device recording, not bulk calendar planning. They matter after the workout or during device sync workflows. They are not the format you want for “here is my 14-week plan, please load it.”

ERG and MRC: Useful, but Not Your Main Bottleneck

ERG and MRC have long histories in indoor training ecosystems. They can still matter if you use specific trainer software or older libraries of structured sessions. But for most modern athletes, they are edge formats, not the main operational problem.

The main operational problem is usually this:

I have workouts in one format,
my plan in another format,
and nothing is actually scheduled where I train.

Choose the Format Based on the Job

Ask one question first: what are you trying to move?

• A whole training block: use CSV
• A single structured bike workout: use ZWO
• A completed activity file: use FIT
• Older trainer-session libraries: ERG or MRC may still matter

How This Connects to TrainingDojo

TrainingDojo is most valuable when you need to remove planning friction, not when you are trying to become a file-format expert. If the hard part is getting a complete training plan from AI, spreadsheet, or mixed sources into TrainingPeaks, the answer is usually:

• Normalize the plan into structured CSV
• Preview and adjust the schedule
• Import it into TrainingPeaks

You can keep special-purpose workout files where they make sense. But the plan itself should live in a format that is easy to generate, review, and upload.

The Bottom Line

Most athletes do not have a format problem. They have a workflow problem. CSV is the best bridge when the destination is a full TrainingPeaks calendar. ZWO, FIT, ERG, and MRC still matter, but they are usually supporting formats, not the center of the workflow.

If you need the whole plan imported quickly, start with TrainingDojo's importer. If you still need to generate the plan, start with the AI generator.