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Can you explain this?


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I've been wearing my HRM while sleeping the last week as ive been sick and need to check wen im ready to go back... one thing i noticed though is that on a couple nights i get this random HR drop into the 30s for like 5min and then its back up again? Whats up with this? does this mean my resting HR is in the low 30s? And its not like im a superhuman athlete either...


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Sleep physiology

The cycle between sleep and wakefulness involves different stages of

sleep. Currently, scientists divide sleep into two general types: REM (Rapid Eye Movement) and NREM (non-REM). REM sleep is characterized by desynchronization of the electroencephalograph (EEG), loss of skeletal muscle tone, and sympathetic nervous system activity; whereas non-rapid eye movement sleep is characterized by parasympathetic nervous system activity (Legramante & Galante, 2005).

  • Non-REM accounts for 75?80% of total sleep time, and consists of four stages:

    • Stage 1, with near-disappearance of the alpha waves seen in awake states, and appearance for the first time of theta waves. The stage is sometimes referred to as somnolence,

      or "drowsy sleep". It appears at sleep onset (as it is mostly a

      transition state into Stage 2) and is associated with the sudden

      twitches or hypnic jerks many people experience when falling asleep. While these are normal and of no concern, the hypnagogic hallucinations which some people may experience at this stage can be more troublesome. During this period, the subject loses some muscle tone, and conscious awareness of the external environment: Stage 1 can be thought of as a gateway state between wake and sleep.

    • Stage 2, with "sleep spindles" (12?16 Hz) and "K-complexes." The EMG lowers, and conscious awareness of the external environment disappears. This occupies 45?55% of total sleep.
    • Stage 3, with delta waves, also called delta rhythms (.5?4 Hz), is considered part of slow-wave sleep (SWS) and functions primarily as a transition into stage four. Overall it occupies 3?8% of total sleep time.
    • Stage 4 is true delta sleep. It predominates the first third

      of the night and accounts for 10?15% of total sleep time. This is often

      described as the deepest stage of sleep; it is exceedingly difficult to

      wake a subject in this state. This is the stage in which night terrors, bed wetting, sleepwalking, and sleep-talking occur.

  • REM sleep is popularly associated with dreaming, especially bizarre, visual, and seemingly random dreams; however, dreams can also occur during sleep onset (hypnogogia) and during all stages of Non-REM sleep.[4] REM sleep is predominant in the final third of a sleep period; its timing is linked to circadian rhythm and body temperature. The EEG in this period is aroused and looks similar to stage 1, and sometimes includes beta waves. Also known as Stage 5 sleep.
  • Active Sleep is a phase of sleep in neonates that appears similar to Rapid Eye Movement

    (REM) sleep in adults. While it depends on age, neonatal sleep is

    sometimes scored as Active Sleep, Quiet Sleep, and Wake. This is less

    specific than the classification of adult's sleep, and is often based

    on behavioral criteria due to the technical difficulties arising from

    recording EEG from the neonate.

Scientists are divided on the precise relation between Active Sleep

and REM sleep. Some suggest that they are similar, while others say it

is an entirely different state, which represents aspects of the

developing CNS

that are not present in a mature brain, and that certain aspects of REM

are not present in Active Sleep due to the immaturity of the CNS in the


Sleep proceeds in cycles of NREM and REM

phases. In humans, the cycle of REM and NREM is approximately 90

minutes. Each stage may have a distinct physiological function. Drugs

such as alcohol and sleeping pills can suppress certain stages of sleep (see Sleep deprivation). This can result in a sleep that exhibits loss of consciousness but does not fulfill its physiological functions.

Each sleep stage is not necessarily uniform. Within a given stage, a cyclical alternating pattern may be observed.

Both REM sleep and NREM

sleep stages 3 and 4 are homeostatically driven; that is, selective

deprivation of each of these states subsequently causes a rebound in

their appearance once the person is allowed to sleep. This finding

leads to the ubiquitous assumption that both are essential in the sleep

process and its many functions. REM

sleep may also be driven by a circadian oscillator, as studies have

shown that REM is temporally coupled with the circadian rhythm of




....................from Wikipedia


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Can't really explain your case Chris but if I take my own H/R then: I have a resting H/R of 32bpm - sitting / sleeping with all the bells & whistles. I have been off the bike for a few weeks & monitored my h/r closely - the same..When I got back on the bike I could push it up to 160 + very quickly & as the ride progresses it drops nicely --


I got a slight cold recently but nothing erratic on the heart front - so It's all good & I am by no means a super human athlete...


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Guest Michelle

Maybe that's the time of the night when your snoring gets too much & your wife puts her pillow over your face.... and... then she changes her mind 5 minutes later?  Or maybe it's just an error Tongue

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I did something similar (Sleeping while monitoring HR) with my Polar HR monitor, Just check that you didn't move the strap at all. I found a few spikes in my sleep (this could be explained by Pantani's friday eye candyLOL) at about 2am (Rapid eye movement time) my HR dropped considerably but only for about an hour.

This is usually when your house gets broken into

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ek sien jy het 'n oraait droom daar in die middel rond gehad.

Somebody's wide awake...Big%20smile


When your HRM belt is not taut or in the correct position - say, when you roll over - there is the possibility of a spike or dropout.


Chris414, looks like you're using SportTracks (?)

I take it you know that, in SportTracks, HR (and altitude) spikes can be edited out.
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Thanks guys


I thought at first that my HRM strap had slipped so i did it again and out of 6 measurements, 3 of them dropped into the low 30s for the same amount of time at roughly the same time of night.  I think its unlikely that if i was getting messed up readings that it would drop to same values (ie. it didnt go down to like 25bpm...)



And you get 8 hours sleep in....WHAT's UP WITH THAT????  Don't you work? Wink

lol im 17...:D
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Chris414, if I remember right you've got a Garmin 305. For interest, replace the HRM belt battery and see if the readings are still similar.

Several users of the original FR301 belt experienced spikes and dropouts. A fresh battery usually helped. I believe newer models have a better belt, but you never know.



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