Parson

After cycling for a month or so, I got a Garmin 500 and heart rate monitor. I was eager to figure out my LT and after doing the 20 minute test on the first ride with the HR monitor, I figured out roughly 169bpm seemed to be my LT.

I've been riding around 3 days a week since then, for a month. I haven't done a LT test since the first one, but when my heart rate gets to above 165 now, it seems unsustainable for long periods of time. I don't think I could sustain 169 for 20 minutes anymore.

I'm wondering if my cardio system has improved more quickly than my legs have. Is this possible? I'm thinking maybe my heart and lungs are working better so that when I'm doing the same amount of work or more work with my legs that I did a month ago, my heart is able to beat slower. If true, in order to sustain a HR of 169, my legs would have to be able to work a lot harder than they did a month ago and they don't have the strength/endurance for that yet.

I'll do another LT 20 min test eventually, but in the mean time, I'm just curious about this. Am I just imagining things and I need to HTFU and keep going at 169bpm for 20 mins or is this something that happens frequently with beginners?

Thanks for any info.

gregf83 

The HR you can sustain for a 20 min interval will vary based on a number of factors: your fitness, hydration level, core temperature and a few others. I find the HR I have while riding at or near threshold power varies a fair amount during the season.

The bottom line is you don't need to be a slave to your HR while riding. Continue to monitor it during longer intervals but ride the intervals based on perceived exertion rather than rigidly sticking to a number.

achoo

And yes, it's possible your LTHR could be dropping as your heart becomes stronger, say by pumping more blood with each beat.

FWIW, when I'm fatigued my LTHR is lower.

Athens80

Yes, this could be the case in at least two scenarios.

First, your cardiovascular system could have improved faster than your muscular system, just as you suggest, so that your legs' best work over 20 minutes is not enough to tax your heart to its limit.

Second, even with riding three days a week, your legs could be fatigued to the point that they are temporarily weakened and need a bit more rest and recovery before they can go at full power again. This can happen with sudden increases in intensity or volume of training, such as the first couple of months of beginning to ride with any regularity.

Carbonfiberboy 

This always happens to me during the season. Since you just started riding regularly, it will be even more noticeable for you. There's a good chance it will continue to drop. Max HR also drops. Since you can ride at LT by perceived exertion, as Greg points out, the larger thing is that it's best to figure zones off LT. If your LT drops, so do all your zones.

After a while, say a year or two, this will stabilize. You'll go up a little in the off season, and down a little during the season, and you'll just note those changes naturally.

It is true that your LT will go back up if you stop training. However that's probably not your best choice.

The other possibility is that you're overcooked. Over-reached, they call it. If you can punch on by your old LT, you're not overcooked. If your MHR is now your old LT, or even below, you are overcooked and need to take 3 days off or easy rides only, then try a tough hill again and see if you've recovered,.

Parson

Thanks for all the solid input everyone. I'm glad to hear that it's a real phenomenon and not just my imagination or anything like that. I tried to take it a bit easy on today's ride, but I find myself wanting to push harder. It will be raining the next two days so I'll use that to rest and see how things go. I appreciate the info.. thanks.