Top 10 questions about training data and technology

Data can sharpen your training if you know what to look for and how to act. Here are the most common questions riders ask about power, TSS, wearables, and readiness—plus practical steps you can use this week.

Power and performance metrics

1) How do I read my power-duration curve?

Your power-duration curve (also called a power curve or PDC) shows your best sustainable watts across durations. It maps your strengths and gaps and helps target training.

• What the shapes mean:
  • 5–30 seconds: neuromuscular power/sprint
  • 1–5 minutes: anaerobic capacity and VO2max
  • 20–60 minutes: threshold/FTP
  • 2–6 hours: aerobic endurance
• Timeframes: compare last 42–90 days vs all-time. A drop in the near-term curve vs all-time often signals fatigue, fewer maximal efforts, or a different focus.
• Action: choose 2–3 target durations that match your goals and schedule a standard test set (e.g., 2 x 5 min, 1 x 20 min) every 4–6 weeks to update zones and track progress.

Tip: if your curve is flat in the 3–8 minute range, VO2max work will likely move both your VO2 and FTP. If it dips at 20–40 minutes, threshold and tempo work are your levers.

2) FTP, CP, or both—what should I use?

FTP (functional threshold power) is a practical estimate of your maximal steady-state power for ~40–70 minutes. CP (critical power) comes from a mathematical model using short maximal efforts (typically 2–20 minutes) and provides both CP and W’ (anaerobic work capacity).

• Use FTP if your platform and plan are built around it and you can test with steady efforts.
• Use CP if your software supports it and you regularly do a spread of maximal efforts (e.g., 3, 5, 12, 20 min). CP often tracks changes faster and gives you W’.
• Be consistent: pick one primary anchor for zones so your TSS and intensity factor (IF) are stable over time.

Good practice: maintain both when possible—use CP/W’ for interval design and FTP for communication and historic comparability.

3) What intervals actually raise FTP?

Raising FTP comes from more quality time near threshold and improving oxygen delivery (VO2max). Proven structures:

• Threshold (90–100% FTP):
  • 3 x 16 min, 2 x 20 min, 4 x 10 min (progress time-in-zone from 30–60+ minutes per session)
• VO2max (106–120% FTP):
  • 4–6 x 3–5 min with equal or slightly shorter recovery; alternate weeks with threshold blocks
• Tempo and sweet spot (76–90% FTP):
  • 45–120 min continuous or broken into blocks; build durability and raise your ceiling for future threshold work

Weekly template example: two quality days (VO2max + threshold), one long endurance ride, and low-intensity rides between. Progress by adding minutes in zone, not by chasing maximal days every week.

4) Why are my indoor and outdoor watts different?

Many riders see 3–8% lower indoor power for the same effort. Common reasons:

• Cooling and heat stress: inadequate fans raise heart rate and lower sustainable watts.
• Ergonomics: fixed position and fewer micro-breaks indoors increase local muscle fatigue.
• Device differences: drivetrain losses, different power meters, or uncalibrated trainers.

Fixes:

• Use at least one high-velocity fan pointed at torso and head.
• Calibrate/zero your trainer and power meter, warm up 5–10 minutes first.
• Consider separate indoor and outdoor FTP/CP settings if the gap persists.

Load, fatigue, and readiness

5) What is TSS and how much should I do per week?

TSS (training stress score) blends duration and intensity to estimate load. It’s built from normalized power (NP) and intensity factor (IF).

TSS ≈ (seconds × NP × IF) / (FTP × 3600) × 100

Guidelines (assumes sensible progression and recovery):

Two key rules:

• Progress 5–8% per week on average, with a deload every 3–5 weeks.
• Quality beats quantity: protect your key interval days even if total TSS looks smaller.

6) What are CTL, ATL, and TSB—and how should I use them?

These are rolling summaries of TSS:

• CTL (chronic training load): ~42-day average—your fitness trend.
• ATL (acute training load): ~7-day average—your recent fatigue.
• TSB (training stress balance): yesterday’s freshness (CTL minus ATL, often lagged).

Practical use:

• Build: raise CTL gradually; avoid big spikes in ATL.
• Taper: aim for TSB trending toward +10 to +25 for A-events, while keeping a touch of intensity.
• Context matters: a CTL of 80 from mostly endurance rides feels different than 80 built with a lot of high IF work.

Remember: these are guides, not targets. Pair them with RPE, sleep, and life stress.

7) Is heart rate still useful if I have power?

Yes. Power is external load; heart rate shows internal response. Use both:

• Decoupling (Pw:Hr): on steady endurance rides, if heart rate drifts upward >5–7% at constant power, it may indicate heat, dehydration, or low aerobic durability.
• Day-to-day readiness: unusually high HR at easy watts can flag fatigue or heat stress; unusually low HR with low power can signal accumulated fatigue.
• Zone checks: verify your aerobic rides with HR sitting in zone 2 while power stays easy.

Use a chest strap for accuracy, especially for intervals.

8) How should I use HRV in training?

Heart rate variability (HRV) can help quantify recovery, but only when measured consistently.

• Measure at the same time each morning, seated or supine, before caffeine.
• Track trends (7–14 day rolling) rather than reacting to single low days.
• Decision rule: normal HRV and normal resting HR—execute the plan; suppressed HRV and elevated resting HR for 2+ days—reduce intensity 20–40% or swap for endurance; persistently suppressed—take true recovery.
• Confounders: alcohol, late meals, heat, travel, illness, and poor sleep can all suppress HRV.

HRV is a useful nudge, not a veto. Cross-check with how you feel and how you perform.

Devices, calibration, and data hygiene

9) How accurate are wearables and which data should I trust?

• Power meters: quality strain-gauge meters and smart trainers are typically ±1–2% when calibrated and warmed up.
• Wrist optical HR: can be off by 3–10 bpm, especially during hard efforts or in the cold. A chest strap is more reliable for intervals.
• GPS speed: fine for rides, not for intervals. Use power for pacing and speed only for context.
• Elevation: barometric sensors beat GPS on rolling terrain but can drift with weather; relative elevation change is usually more reliable than absolute altitude.
• Sleep and SpO2: consumer sleep stages are estimates. Treat them as trends, not diagnostics.

For critical sessions and testing, prioritize: power meter (calibrated), chest strap HR, and consistent recording setup.

10) What are best practices for calibration and setup?

• Zero-offset your power meter after a short warm-up; repeat if temperature changes significantly.
• Perform a trainer spindown/calibration after warming the unit; set correct bike weight and wheel circumference where applicable.
• Set crank length and power source consistently across head units and apps.
• Use the same bike/drivetrain for testing blocks; clean chain and consistent tire pressure if using wheel-on trainers.
• Disable excessive power smoothing for intervals; you want real-time feedback, not averaged illusions.
• Check that FTP/CP and training zones are updated after tests; mis-set FTP skews IF and TSS.
• Time-sync devices and auto-pause behavior; mark intervals with the lap button.
• Do an occasional dual-record (trainer + crank/pedal meter) to spot-check accuracy.

Quick checklist: turn data into better training

• Week 1: audit your setup (calibrate devices, confirm crank length, update FTP/CP).
• Pick two benchmark efforts from your power-duration curve (e.g., 5 min and 20 min) and schedule them in fresh conditions.
• Set a realistic TSS target based on hours available; plan a 5–8% ramp for 2–3 weeks.
• Anchor one VO2max and one threshold session weekly; grow total time-in-zone.
• Log RPE and morning HR/HRV; adjust intensity if HRV is suppressed 2+ days.
• Use heart rate to police endurance days; avoid turning Z2 into tempo.
• Every 4–6 weeks: re-test, update zones, and compare 42–90 day curves to confirm progress.

Use your data to answer simple questions: What is my goal? Which duration matters? Am I fresher or fitter this month? Then shape the next week accordingly.