Heart rate and cadence advice

Hi, I'm looking for some guidance on trail running as it relates to cadence and heart rate.

I'm coming off of a bout of runners knee and I upped my cadence as an attempt to prevent further injury. This has gone pretty successfully, and for the most part, I'm able to keep cadence up on road runs without a significant increase in effort (as measured by heart rate).

However, on trails, I've found that to keep my cadence above 170 means to virtually guarantee my HR is above 170bpm. 170bpm average over a 4-8 mile run (what I usually do on trails) seems a little high, and it's got me questioning my fitness. However, I know that if I were to lower my cadence, it would lower my effort level and I'd be able to bring the HR back down to more appropriate training levels.

On most of these runs, I feel fine. By the end of 5-8 miles, of course I feel sufficiently exerted, but I wouldn't say I'm "exhaused", or "destroyed", or any other term for being completely spent. I'm rarely sore after these runs, so I feel like my conditioning isn't as bad as that elevated HR indicates.

So my question: Is cadence so important that I should continue to shoot for 170+ on my trail runs, even though it means my heart rate is consistently high (170+), or should I prioritize keeping my HR in a more reasonable range (sub-165) and let cadence be what it may?

Thanks in advance for any advice.

I have had issues with runner's knee as well, so I can relate (doctor called it patalla chondromalacia - basically, pain under the kneecap). I do think shorter steps helps. The thing that has helped the most, however, are core and hip muscle exercises. Particularly glutes, hip adductor and hip abductor muscles. If you sit a lot (like I used to) those muscles are weak and likely causing downstream issues, eg, the knee.

Anyway... I don't think higher cadence translates to higher effort. In fact it probably should lower effort.

The increase in heart rate on trails is likely due to the harder terrain. Most trails even if they don't seem hilly require a more effort than a perfectly flat surface like a road.

I wouldn't worry about holding to any specific cadence on trails. It's not reasonable on uneven surfaces and variable terrain, inclines. Practicing higher cadence on roads is good for, well... practice. But on trails you have to go more "by feel" when it comes to stride length and cadence, and even speed. (Adjust stride by feel, watching your heart rate monitor to assess overall effort)

The idea is to take shorter steps both up and downhill; the key thing is keep your feet "under you" and your center of gravity directly over your feet. Do that and your effort level goes down. If it doesn't, then you simply need to slow down.

I appreciate your thoughts regarding cadence on trails. I'll try allowing myself to dip into the 160's on trails, and see how I feel.

I, also, got the "chondromalacia" diagnosis, along with inflamed plica. I did PT 3 days/week for 3 months, strengthening hips/glutes. However, I never got out of the patella stabilizing brace, and still have to ice every day. Only recently (go figure) did the PT discover I have insanely low ROM in dorsiflexion (ankle flexibility when toes move toward leg, the opposite of "pointing your toes). At this point, we are thinking this is the cause of the continued inflammation in the knee from running. Unfortunately, this lack of ROM may not be fixable since it may just be my bone structure. I'm getting x-rays to find out, and also looking into orthotics.

It's an ongoing saga, but I thought you'd be interested since you've had similar issues.

Thanks for your thoughts.