Mastering Your Training Zones: A Guide to Field Tests
As a multisport athlete, one of the most powerful tools in your arsenal is understanding and utilizing personalized training zones. These zones help you train smarter, avoid burnout, and optimize performance across swimming, cycling, and running. Drawing from Joe Friel's seminal work, The Triathlete's Training Bible (now in its fourth edition as of my last update), we'll dive into how to establish your key thresholds through simple field tests. These thresholds—Threshold Heart Rate (LTHR), Functional Threshold Power (FTP) for cycling, and Critical Swim Speed (CSS) or Threshold Pace for swimming—serve as the foundation for setting your zones.
Once you have these metrics, you can plug them into our calculators or apps (like those from Training Peaks) to generate precise heart rate, power, or pace zones. This ensures your workouts are tailored to your current fitness level, making every session count. Remember, thresholds can shift with training, so retest every 4-8 weeks when you're well-rested.
Let's break it down by discipline, focusing on Friel's field-tested methods.
Why Thresholds Matter
Before we get into the tests, a quick primer: Your threshold is essentially the tipping point where your body shifts from primarily aerobic (fat-burning, sustainable) effort to anaerobic (lactate-accumulating, high-intensity) work. Training at or near threshold builds endurance and efficiency. Friel emphasizes field tests over lab assessments because they're accessible, free, and reflect real-world conditions. No fancy equipment needed—just a heart rate monitor, power meter (for cycling), or stopwatch.
Establishing Threshold Heart Rate (LTHR) for Running
LTHR is your average heart rate during a hard, sustained effort—typically what you could hold for about an hour in a race. It's used to set heart rate zones for running (and sometimes cycling if you lack a power meter).
The Field Test
Friel's recommended protocol is a 30-minute solo time trial on a flat, traffic-free course:
- Warm-up: 15-20 minutes easy running, followed by 3-4 short accelerations (20-30 seconds each) to get your heart pumping.
- The Test: Run as hard as you can for 30 minutes, aiming for even pacing. Imagine it's a race where you want to finish strong without fading.
- Data Collection: At the 10-minute mark, hit the lap button on your heart rate monitor. Your LTHR is the average heart rate from minutes 10-30 (this accounts for the initial ramp-up).
- Tips: Do this alone to avoid external motivation skewing results. If you're new to intense efforts, build up gradually and consult a doctor.
Establishing Threshold Pace (FTPa) for Running
In Joe Friel's system — as detailed in publications like The Triathlete’s Training Bible, Total Heart Rate Training, and his TrainingPeaks guides — threshold pace for running is called Functional Threshold Pace (FTPa). This is the fastest average pace you can sustain for approximately one hour in a well-paced effort. It's the key benchmark for setting running pace zones, providing an objective measure of intensity that's more reliable than heart rate alone in variable conditions.
FTPa approximates your lactate threshold pace (often sustainable for ~45–60 minutes in trained athletes) and is determined through a straightforward field test.
The Field Test
Joe Friel recommends a solo 30-minute time trial (not a race) to estimate FTPa accurately and avoid race-day adrenaline or external factors that could skew results.
- Warm-up Thoroughly: Start with 15–20 minutes of easy running, including 3–4 short strides or accelerations (20–30 seconds each) to prime your legs and prepare for hard effort.
- The Test: Run as hard as you can sustain for the full 30 minutes — all by yourself, on a flat course (track, road, or treadmill) for consistent pacing. Go hard from the start but pace evenly; many athletes start too aggressively and fade, so aim to finish strong. This should feel like a "redline" effort you could theoretically hold a bit longer if pushed (closer to a 45–60 minute race feel).
- Data Collection: Use a GPS watch or accelerometer for accurate pace tracking. Your Functional Threshold Pace (FTPa) is the average pace for the entire 30 minutes (not just the last portion, unlike the heart rate version of the test).
- Tips for Success:
- Test solo to eliminate drafting or group motivation.
- Repeat the test every 4–8 weeks (especially early in base/build periods) — pacing improves with practice, leading to more accurate results as you learn to negative-split or hold steady.
- Alternative: If you have a recent solo 60-minute race effort (or very hard effort), use the average pace from that as FTPa directly.
This method keeps things simple and field-based, aligning with Friel's practical, athlete-centered approach. Once established, your threshold pace becomes the foundation for precise, progressive training — helping you hit the right intensities for tempo runs, intervals, and long efforts without over- or underdoing it.
Retest regularly as fitness improves; even small shifts in FTPa signal big gains! As always, listen to your body and combine with perceived effort for the best results.
Functional Threshold Power (FTP) for Cycling
For cyclists, power is king—it's objective and unaffected by external factors like wind or hills. FTP is the highest power output you can sustain for about an hour, and it's the benchmark for power-based zones.
The Field Test
Friel advocates a 20-minute time trial (a variation of the classic Hunter Allen/Andrew Coggan method) on a steady course or trainer:
- Warm-up: 15-20 minutes easy spinning, including 3-5 one-minute high-cadence efforts and a 5-minute all-out push to clear the pipes.
- The Test: Ride all-out for 20 minutes. Pace yourself—start conservatively to avoid blowing up.
- Calculation: Take your average power for the full 20 minutes and multiply by 0.95 (to estimate your 60-minute capability). That's your FTP in watts.
- Tips: Use a power meter (crank, pedal, or hub-based). Indoor trainers work great for consistency. Hydrate well and ensure you're recovered from prior workouts.
Note: If you prefer heart rate for cycling, you can derive cycling LTHR from the same test (average HR over the 20 minutes, minus 5-10 bpm adjustment from running LTHR).
Critical Swim Speed (CSS) or Threshold Pace for Swimming
Swimming thresholds are pace-based, as heart rate monitors aren't reliable in water. CSS (also called Threshold Pace or T-Pace) is the fastest pace you can hold for about 1500-2000 yards/meters without fading—your "threshold" for swim workouts.
The Field Test
Friel outlines a straightforward test using two time trials in a pool (preferably 25 or 50 yards/meters):
- Warm-up: 10-15 minutes easy swimming, plus drills and a few build-ups.
- Test 1: Swim 400 yards/meters all-out, recording your time.
- Recovery: Rest 5-10 minutes (easy swim or full rest).
- Test 2: Swim 200 yards/meters all-out, recording your time.
- Calculation: CSS pace per 100 = (400 time - 200 time) / (400 - 200) yards/meters, adjusted to per-100 pace. More precisely: CSS = (Distance2 - Distance1) / (Time2 - Time1), but convert to pace.
- Tips: Focus on technique; poor form inflates times. Test in your typical pool length. For yards vs. meters, convert if needed (1 yard ≈ 0.914 meters).
Your CSS pace sets swim zones, like endurance (CSS + 5-10 seconds/100) or speed work (faster than CSS).
Putting It All Together: Using Calculators for Zones
With your LTHR, FTP, and CSS in hand, head over to our calculators page. Input your thresholds, and they'll spit out 5-7 zones based on Friel's system— from recovery (Zone 1) to anaerobic capacity (Zone 5c). For multisport athletes, remember zones are sport-specific; don't mix running LTHR with cycling LTHR.
Pro Tip: Track your tests in a training log. Improvements in thresholds signal progress—celebrate those gains!
Training zones aren't set in stone; they're a guide. Listen to your body, and if something feels off, adjust. As Friel says in The Triathlete's Training Bible, consistency and periodization are key to peaking on race day. Happy training—your next PR awaits!
Disclaimer: Always consult a healthcare professional before starting intense training, especially if you have health concerns.
