Nothing is more frustrating than being sidelined. Whether it’s a stress reaction, shin splints, or tendonitis, the prescription is almost always the same: “Stop running.”
But “stop running” shouldn’t mean “stop training.” The hardest part of cross-training isn’t the effort—it’s the math. If you miss a 45-minute easy run, how long should you sit on the bike to get the same benefit? Is 45 minutes of aqua jogging enough?
The Problem with Guessing If you guess too low, you lose aerobic fitness. If you guess too high, you risk burnout or overtraining before you’ve even healed.
The Solution: The Run Equivalent Calculator This tool takes the guesswork out of your recovery. It uses physiological conversion factors (based on heart rate and metabolic cost) to translate your scheduled run into an exact biking or pool running prescription. It ensures you maintain your cardiovascular engine so that when you are cleared to run, you haven’t lost a step.
🚲 Run Equivalent Calculator
Your Cross-Training Plan
This is known as the 1.5:1 Rule. Running is metabolically “expensive” because you have to support your own body weight and push off the ground against gravity. On a bike, the machine supports your weight. To get the same aerobic stimulus (heart benefit) and burn a similar amount of energy without that gravitational load, you generally need to extend the duration by about 50%.
This is crucial. If you spin with zero resistance, you aren’t doing the work. You should aim for a cadence (RPM) of 90+, but you must add enough resistance that you are sweating and breathing rhythmically—just like you would on a run. If your legs are spinning fast but your lungs aren’t working, turn up the resistance.
Unlike cycling, water provides resistance in every direction. Even though there is no impact on your bones, the hydrostatic pressure of the water pushes blood back to your heart, and the resistance requires significant muscular force to move through. Because of this, 45 minutes in the pool feels just as hard (if not harder!) than 45 minutes on the road.
No, that is normal! Most athletes see a heart rate 10–15 beats per minute lower on the bike for the same perceived effort. This is because your muscles aren’t contracting to absorb the shock of landing. Don’t try to force your heart rate to match your running max, or your legs will give out before your lungs do. Focus on Perceived Exertion (how hard it feels) instead.
The elliptical is a “middle ground” machine. It bears some of your weight, but not as much as a bike. A safe bet is to use a 1.2x conversion. If this calculator prescribes a 60-minute bike ride for a 40-minute run, aim for about 50 minutes on the elliptical.