Heart rate & lactic acid buildup?

I crosstrain (weights, running, biking, stepping, etc...). I use a heart rate monitor and here is something I%26#039;ve observed which I have no explanation for. During a 5k running race, from training and experience, into the beginning of my second mile I set a pace that keeps me just under my lactate threshold which I know to be 186 bpm. Now I%26#039;ve never cycled for real or gotten on one of those mountain bikes, but I do ride the bikes at the gym. Here is what is peculiar. Most bikes at the gym have level of intensity 1-20. After warmup I gradually ascend the intensity, at around level 16 my heart rate only reaches the 160s but I start to feel the lactic acid burn in my legs. I suspect part of this phenomenom is because different leg muscles are targeted in running vs. cycling, but my legs are significantly strong (can squat 315 and deadlift 405). Anyone aware why my LT is lower for cycling than for running?

Heart rate %26amp; lactic acid buildup?

Don%26#039;t confuse lactate threshold with lactic acid buildup.

Just because you have a specific muscle group going anaerobic doesnt mean your cardiovascular system has reached LT. It is entirely possible for a muscle group to be working anaerobically but your CV system still has the ability to supply oxygen to the rest of your muscles, so your HR will remain below LT. Sort of like doing crunches, you can easily drive your abdominal muscles anaerobic and induce lactic acid buildup, but your HR will remain below LT.

If you were to drop your squat weight to below %26#039;warm-up%26#039;, then try to bang out one squat per second until %26#039;failure%26#039;, I suspect you might find the same result in your HR, depending on just how much weight you use.

Heart rate %26amp; lactic acid buildup?

You%26#039;re right about using different muscles being the cause. Specifically, you use fewer muscles in cycling, so the individual muscles are doing more work. Leg strength (as far as squatting and dead lifting) doesn%26#039;t have anything to do with your lactate threshold unless you are squatting until you reach 160 bpm.

Heart rate %26amp; lactic acid buildup?

Awesome question - I can rarely work up a sweat on a spin bike - it totally pisses my wife off %26#039;cause she%26#039;s next to me with her shirt soaked!!!

Seriously though - I have the same problem - 5 or 10K at 185 all day long, shoes willing, no problems. Then, I go kill the spin bike!!!

Thanks for the question - I just put an answer in so I wouldn%26#039;t loose it!