What Declining EF and PWHR Really Mean
In endurance training, progress isn’t always about smashing intervals or watching your FTP soar. Sometimes, it’s about listening to the subtle whispers your data sends, and two of the most insightful whispers come from Efficiency Factor (EF) and Power-to-Heart Rate Ratio (PWHR).
Over the past few months, I’ve been seeing a trend in a few athletes’ data: a downward slope in both EF and PWHR. On the surface, it might not look dramatic, a small tilt in the trend, but in the world of aerobic performance, these are the canaries in the coal mine.
So let’s unpack what these numbers are telling us.
What is Efficiency Factor?
In plain English, EF is a measure of how much power (watts) you’re producing relative to your heart rate. It’s calculated as:
EF = Normalized Power ÷ Average HR
If your EF is going up, you’re becoming more aerobically efficient, more bang for your heartbeat. If it’s trending down, something’s up.
PWHR – The Cousin Who Speaks Truth
Power-to-Heart Rate Ratio (PWHR) is another clever metric. It reflects how much power you’re sustaining for each beat of your heart. Drop in this number? You might still be riding hard, but your body’s working harder for less output.
A falling PWHR and EF is a double signal that we should pause and reflect.
So Why Might These Metrics Drop?
Here’s what we’re usually looking at:
- Cumulative fatigue (you’ve been training hard, maybe too hard)
- Under-recovery (sleep, nutrition, life stress)
- Poor fuelling (low-carb rides when your body needed support)
- Environmental factors (training in heat or at altitude)
- Health niggles (minor illness, inflammation, poor gut health)
The key is this: Your heart is still working hard (HR stable), but your output is slipping. You’re not lazy, you’re likely just carrying some hidden fatigue.
What Should You Do?
1. Take a Recovery Week. Ease off the gas. Drop the volume, dial down the intensity. Your body needs to reset, not grind harder.
2. Sleep Like It’s Your Job. I don’t mean “getting into bed.” I mean quality sleep: cold, dark room, consistent bedtime, no doomscrolling.
3. Fuel Like a Pro. Eat your carbs. Under-fueling is one of the most common reasons for suppressed performance. This isn’t the week for fasted rides.
4. Hydrate and Chill: Electrolytes, downtime, maybe even yoga if that’s your thing. Recovery isn’t just about doing less, it’s about actively supporting adaptation.
5. Test Again After recovery, revisit your aerobic efficiency:
- A steady Zone 2 ride
- 60–90 minutes with minimal HR drift
- Watch how EF and PWHR respond
If they rebound? Brilliant. That confirms it was fatigue, not a fitness slide.
Final Word
Your fitness isn’t defined by one week, or even one month. But if your data is quietly telling you that you’re sliding off your peak, don’t ignore it.
Training isn’t about chasing numbers, it’s about adapting smartly. And sometimes the smartest thing to do is to rest with purpose.
Add a comment or use the contacts page if you'd like to chat more about how to measure your efficiency factor and power to heart rate ratio, the impacts of cardiovascular drift, and how we reverse these potentially negative trend .
Safe Cycling !