Cycling Terms Explained: FTP, TSS, HRV, CTL & Zones

What Is FTP in Cycling?

FTP stands for Functional Threshold Power. It's the highest average power you can sustain for approximately one hour, measured in watts.

FTP is the baseline metric for most training plans. Once established, your Coach customizes every session to your exact capability, preventing workouts from being too easy or overly fatigue-inducing.

Your FTP scales as your aerobic capacity improves. Most riders test or re-estimate their FTP every 6 to 8 weeks.

Ask your Coach:

• "How has my FTP changed this year?"
• "Am I due for an FTP test?"

ASK YOUR COACH

FTP Quick FAQ

• How do I test my FTP? A standard method is a 20-minute all-out test effort, using 95% of that average power output. Alternatively, your Coach can automatically estimate it from your regular structured workouts.
• Does FTP change over time? Yes. It increases with training consistency and declines during prolonged rest or off-season breaks.

CHECK MY FTP

What Are CTL, ATL, and TSB?

These three core metrics track your training volume, cumulative stress, and immediate race readiness:

• CTL (Chronic Training Load / Fitness): Your rolling average training load over the past 6 weeks. Higher values indicate higher baseline fitness.
• ATL (Acute Training Load / Fatigue): Your rolling average training load over the past 7 days. It spikes rapidly after intense efforts.
• TSB (Training Stress Balance / Form): The mathematical difference between CTL and ATL (TSB = CTL - ATL). A positive number indicates freshness; a deeply negative number signals heavy accumulated fatigue.

Isolated numbers offer limited value. Monitoring trends prior to key target workouts or race day is essential.

Ask your Coach:

• "How is my form right now?"
• "This week versus last week, what changed?"

CHECK MY FORM

What Is HRV and Why It Matters

HRV stands for Heart Rate Variability. It measures the variation in time intervals between consecutive heartbeats.

A higher baseline HRV typically indicates proper recovery and autonomic balance. A sustained dip in HRV over several days can signal underlying fatigue, high stress, or impending illness.

Most modern smartwatches track nocturnal HRV. Your Coach evaluates nocturnal HRV alongside sleep metrics and resting heart rate to contextualize your daily readiness.

Ask your Coach:

• "How has my HRV been trending this month?"
• "Am I overreaching?"

CHECK MY HRV TREND

What Are Cycling Training Zones?

Training zones segment your effort levels into distinct intensity bands based on percentages of your FTP or Max Heart Rate. Each zone targets specific metabolic adaptations:

Executing workouts within target zones optimizes training efficiency. A common beginner error is riding every session at a generic "medium-hard" effort.

Ask your Coach:

• "How much time did I spend in zone 4 yesterday?"
• "Did my power fade across the intervals on Tuesday?"

SEE MY ZONES

What Is TSS (Training Stress Score)?

TSS (Training Stress Score) quantifies the overall workload of a single workout by factoring in both total duration and relative intensity.

A short high-intensity interval session and a long low-intensity endurance ride can yield an identical TSS value. Daily TSS totals continuously feed into your cumulative CTL (Fitness) and ATL (Fatigue) values.

Ask your Coach:

• "Show me only the hard days from April."
• "How has my weekly training load trended since January?"

CHECK MY TRAINING LOAD

What Is Best 20-Minute Power?

Your Best 20-Minute Power is the highest average wattage sustained continuously for 20 minutes.

Because athletes can typically hold roughly 95% of their peak 20-minute power for a full hour effort, this metric serves as the industry standard benchmark for estimating FTP.

Ask your Coach:

• "What's my best 20-minute power?"
• "Best 20-minute power this season?"
• "What was my peak 20-minute power on yesterday's ride?"

Note: The Coach tracks historical peak efforts for power and heart rate data. Historical rankings for cadence or speed metrics are not currently evaluated.

CHECK MY BEST POWER

TSS®, Training Stress Score®, NP®, Normalized Power®, and IF® are registered trademarks of Peaksware, LLC.