Maximum HR when doing Z4 intervals

  • Creator
  • #41226
    Cosmic Hillbilly

    Hi, I scanned the past posts to see if I could find any questions similar to mine. I apologize if my question has already been answered.

    I live in central Idaho and my goal is to be able to hike up steep mountains easier and faster than my hiking buddies. I am 58-years old and not an athlete in training, I am a backcountry skier, hiker, and hunter. I spent the past 2+years “training” (hiking) in Zones 1 and 2 to cure ADS. My AeT is now 8 to 10% of my AnT. Lately, I started to slowly introduce Z3 intervals and now I am at a point where I started to do occasional Z4 intervals (once a week to once every two weeks).

    For the Z4 intervals, I hike ambitiously up a 30% hill. The summit is only about 4700’ feet in elevation. I noticed that I cannot get to my VO2 max HR of 172, no matter how hard I try. The highest I can get to is around 166. Even though I cannot sustain the 166 HR for very long it still feels like l like I am not at the maximum “fatigue” in my breath and muscles. I should add that getting to 172 was not an issue before I started concentrating on Z1 and Z2 hikes a few years ago.

    My question is, is there a possibility that my maximum HR is limited by weakness in my fast-twitch fibers in my legs…kind of like not all my FT fibers are kicking in? If so, I assume that over time, hiking in Z4 will eventually build up my limited FT fibers? I have not been doing any weighted ME hikes. Maybe doing weighted ME once a week is recommended for my situation? Thank you!

  • Participant
    Dada on #41267

    I may quote from TftuA, p. 96:

    Especially for the less well trained, the duration of Zones 4 will be limited by lack of localized muscular endurance. […] your legs are screaming, your heart rate tops out in zone 3 levels. So you don’t get the intended benefit of zone 4. You need to improve ME before.

    Best regards

    Cosmic Hillbilly on #41273

    Thank you Dada! I forgot I read that in the past.

    Anonymous on #41356

    Also… Remember that maximum heart rate:

    1. …is the top of Zone 5;
    2. …doesn’t accurately measure an intensity because heart rate stops increasing well before the load does; and
    3. …is of limited use other than in a cocktail party conversation.

    The bottom of Z4 is defined by your anaerobic threshold heart rate. If you hit that number, then you can assume that the load was Z4 or greater (probably greater).

    Cosmic Hillbilly on #41358

    Thank you Scott! That is good information. I forgot to add to my original post that it is possible for me to hit my VO2 HR (172) when doing faster hikes on less gradient (10%) but not on steeper grades. I was thinking that weaker FT fibers are limiting my speed and therefore my high-end HR on steeper gradients.
    Thank you!

    Anonymous on #41560

    …it is possible for me to hit my VO2 HR (172)…

    Why do you think 172 is your VO2 HR? Was it tested in a lab?

    …when doing faster hikes on less gradient (10%) but not on steeper grades.

    This is likely due to a difference in relative strength between your legs and your cardiovascular system.

    In a high-cadence activity (flat running, cycling, etc), training loads become more cardiovascular than peripheral, so heart rate and respiration will climb faster and to greater degrees. The load per step is lower, so we can spin our legs faster, putting more stress on our cardiovascular system.

    In a low-cadence activity (hiking, mountaineering, “big ring” cycling), training loads become more peripheral than cardiovascular, so heart rate and respiration will be slower to climb and are less likely to get very high. The load per step is higher, cadence is lower, putting less stress on our cardiovascular system.

    As your legs get stronger, you’ll be able to put more stress on your heart and lungs, and heart rate will climb.

    Cosmic Hillbilly on #41570

    Hi Scott, yes before I did a separate lab test for my Aet and Ant, I did a gas exchange test at Boise State and it was determined that my VO2 max was around 172.

    Your answer makes a lot of sense. I was kind of thinking that my leg strength is lagging a bit behind. I appreciate you answering my question!

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