Opinion – Tiredness

I’ve been playing with the Vivosmart 4 for a few days now and especially the body battery and Pulse Ox gubbins. Enough to draw some initial conclusions which I think have been bubbling away in my subconscious for a while now.

From my (admitedly naive) perspective, there are a few kinds of tiredness.

  • Sleepy – this is when you’re just tired because you’ve been awake too much.
  • Mental – this is when you’ve worked too hard in the office. This doesn’t affect performance, but may cause you to not do exercise. To overcome this, just do exercise. Maybe a structured plan will help with motivation.
  • Cardio – this kind of tiredness is what most watches measure and is based on heart information.
  • Muscle Oxygen etc. – this is “the wall” and hits during exercise because your muscles don’t have the resources needed to carry on working.
  • Muscle fatigue – fatigue may not be the word, but this encompasses tiredness in muscles as well as muscle damage.

I’ve listed these out to explain my thinking, and my thinking is different for different people. You see, the body can be fit in different ways. An athlete, let’s say runner, who has been running hundreds of miles per week will suffer a little with muscle fatigue, but they are likely to overtrain and suffer with cardio tiredness before that’s an issue. They may also hit muscle O2 issues during training. The otherwise healthy couch potato will have terrible muscles unused to exercise, but may well have the cardio ability to train every day.

And there lies the problem.

We can measure muscle O2 now with specialist devices, but this is only helpful to “elite” athletes really. The rest of us are merely curious. We do measure cardio a lot. Pretty much all of the metrics about fitness on your device are HR based. We can’t measure muscle fatigue. We can’t even reliably guess this one because everyone reacts differently to training, trains differently, starts from a different point, etc. We’d literally have to track all muscle movement and power output to even come close.
Why is that an issue? Because every device I’ve ever owned has consistently said the same thing: ready to train. Body battery pretty much always tells me I’ve still got gas in the tank. I sometimes drop to 80% but an hour of watching TV sends me back to 100%. And I don’t think Body Battery is flawed here, I actually genuinely think it does what it’s supposed to do. And so does the Polar fitness test and the other Garmin ones and all the others.
I’m not good to go though, far from it. This week I decided to just run every day. I have a shiny new treadmill and a bunch of watches to test as well as posts to prepare for my favourite peeps in the world (that’s you, please keep coming and commenting…). My main discovery this week was not really a discovery at all. I’ve known it for a while I just proved it out this week. Because I’m not already a trained athlete my muscles will always stop me from training before my watch tells me anything useful about fatigue. I’ve even been doing recovery runs at low intensity rather than proper runs. No difference. My cardio system is good to go but my muscles are so tired I’m ready to collapse on the treadmill.

So my conclusion, if you hadn’t guessed, is that the Body Battery function of the Vivosmart 4 might well work fine. For all but a small percentage of users though, it makes no difference at all whether it works or not. It will never tell them anything they can action.

Oh, and PulseOx? All this does is test whether my lungs are working. They are. Some comments from medical folk over on DCRainmaker.com confirm this. If you ever EVER get a low reading from PulseOx and you’re not on top of a very, very large rock you’re either dying or the watch has given a spurious reading. The easy way to tell the difference, for those interested:
If you weren’t bored and staring at the massive red glow that keeps you awake at night and wondering why the reading takes so long to produce…seek medical advice. Trust me on this one.


  1. recovery. etc
    1. look at TSB/CTL/ATL/TRIMP calculated from heart rate.
    2. look at elite hrv/ithlete/bioforce etc.

    PulseOx: I see where you are coming from and I think you are over-egging the usefulness of SpO2 for athletes.

    SmO2 – actually would be very useful for beginner athletes looking to do aerobic work and stay in zone eg some people dont understand hr zones (220-age), perhaps their body morphology means that chest straps don’t work and perhaps they use oHR which is likely rubbish. humon hex (for example) just shows you red or green (and blue and amber). Guess what green means dear beginner athlete?

    • Haha I was trying to be kind and assume athletes would see some usefulness there. They are the only group whose muscles wouldn’t be shot before their cardio system.

      SmO2 for begginers? Surely better to get them on a couch to 5k and forget all the tech?

  2. beginners: need to get a good pair of shoes, raise cadence to 90 and train aerobically.

    define aerobically FOR A BEGINNER? it’s got to be easy (like the RPE definition which beginers might not believe as it means they run REALLY slow)

    my partner just came back from a supposedly AEROBIC run with a polar vantage which had my zones. 50% of the time was in z3 ie not aerobic (as it was my z3)…2 years on and we still don’t have proper zones set for my partner who keeps avoiding the issue

    smo2…just go out and run (with a hex) and keep it green. but yes, it wont happen in reality that much

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