Resting heart rate
 

Reading about different heart rates, I'm wondering if mine is too low. I've measured it at 38 average over 5 different "normal" mornings and averaged. It's generally about 8-10 beats more if I had too much to drink (7 or 8 beers) and didn't sleep well, at 47-49. That's right after I wake up, not moving. Have slept wearing my Polar to get it accurately.

I'm nearly 26 yo, 180lbs, 5'7" (heavy build - not overweight, maybe 14% BF). I'm quite fit aerobically and eat very healthy food wise, but I smoke a little, and drink a fair bit (this IS Ireland...). So is RHR of 38 a sign of good fitness, or a tell tale of dodgy blood pressure?

It sounds good to me! I used to see mine in the low 40s by wearing the HRM to bed. I'd set an alarm at 42 bpm and lie there very still until the alarm went off. I never tried sleeping with the HRM on.

It is amazing how overtraining, over drinking, over eating, and lack of sleep do drive the heartrate up. It's no wonder that many heart attacks happen right after a large meal.

Also, I don't think blood pressure would come into play here. A doctor would probably tell you that as long as you have good energy, no dizzy spells, etc., then enjoy the good resting HR while it lasts.

Around 44 today after 25 miles cycle, 2 hour (low-intensity) sailing and 3 beers last night. Yeah, I hope the 38 is just being relatively in shape.

The polar strap is fine to wear sleeping so long as it's not too tight, though sometimes it's too loose to make contact both sides and doesn't detect.

Next time I see a doctor I'll have a chat about some of the HR and training stuff, it's interesting.

Alrocket, below is some info from UpToDate, a medical info source for physicians, that might be helpful to you (the numbers in square brackets are references--you can ignore them):

"Sinus bradycardia is a rhythm in which fewer than the normal number of impulses arise from the sinoatrial (SA) node. The normal heart rate has been considered historically to range from 60 to 100 beats/min, with sinus bradycardia being defined as a sinus rhythm with a rate below 55 to 60 beats/min. However, a study in 500 normal subjects using an electrocardiographically recorded heart rate found the mean afternoon heart rate for men and women to be about 70 beats/min with two standard deviation limits of 46 and 93 beats/min in men and 51 and 95 beats/min for women; there was no significant age-related effect...

"Sinus bradycardia occurs in normal children [3] and adults [4,5], particularly during sleep when rates of 30 beats/min and pauses of up to 2 seconds are not uncommon [4,6]. It may also be seen in the absence of heart disease in the following settings:

At rest, in 25 to 35 percent of asymptomatic individuals under 25 years of age [7].

In well-conditioned athletes [8,9].

In some elderly patients [10].


There is no prognostic significance to sinus bradycardia in otherwise healthy subjects. In subjects over the age of 40, for example, there is no adverse effect on longevity.

PATHOPHYSIOLOGIC SINUS BRADYCARDIA — Sinus bradycardia can be seen in a variety of pathophysiologic settings (show table 1):

Exaggerated vagal activity — Vasovagal responses may be associated with a profound bradycardia due to heightened parasympathetic activity and sympathetic withdrawal on the SA node. The combination of the slow heart rate and an associated decline in peripheral vascular resistance is often sufficient to produce presyncope or syncope. (See "Neurocardiogenic (vasovagal) syncope and carotid sinus hypersensitivity").

There are a variety of stimuli for vagal activation:

Pressure on the carotid sinus, as may occur with a tight collar or with the impact of the stream of water in a shower

Vomiting or coughing

Valsalva maneuver when straining at stool

Sudden exposure of the face to cold water

Prolonged standing via a Bezold-Jarisch reflex


Hypervagotonia can also result in chronic (ie, nonepisodic) resting sinus bradycardia. This is the primary mechanism of resting bradycardia in well-trained athletes (see "Athletes" below). Junctional bradycardia and Mobitz type I AV block can also be seen in this setting.

Increased intracranial pressure — Increased intracranial pressure should be excluded when sinus bradycardia occurs in a patient with neurologic dysfunction. (See "Evaluation and management of elevated intracranial pressure in adults", section on Clinical manifestations).

Sinus node dysfunction — Sinus bradycardia may be the first manifestation of SA node dysfunction and the sick sinus syndrome [12,13]. This problem can be induced by virtually any disorder affecting the SA node. (See "Manifestations and causes of the sick sinus syndrome").

Acute myocardial infarction — Sinus bradycardia occurs in 15 to 25 percent of patients with acute myocardial infarction, particularly those affecting the inferior wall since the right coronary artery supplies the SA node in approximately 60 percent of people. Increased vagal activity is primarily responsible, and the bradycardia is typically transient. If treatment is necessary because of hemodynamic compromise or ischemia, sinus bradycardia usually responds well to intravenous atropine (0.6 to 1.0 mg in the majority of cases) (show table 2A-2B). (See "Supraventricular arrhythmias after myocardial infarction", section on Sinus bradycardia).

Athletes — The majority of well-trained endurance athletes have a sinus bradycardia at rest [8,9]. This has traditionally been attributed to increased vagal tone induced by exercise conditioning. However, studies in which atropine and propranolol are given to block the parasympathetic and sympathetic pathways suggest that the intrinsic physiology of the sinoatrial node may be altered [14]. (See "Arrhythmia in athletes").

Obstructive sleep apnea — Individuals with obstructive sleep apnea frequently have sinus bradycardia that may be severe (<30 beats per minute) during apneic episodes [15-17]. Therapies to improve the apnea frequently alleviate the bradycardia [15]. On the other hand, pacing for sinus node dysfunction may improve indices of apnea [18]. (See "Cardiovascular and cerebrovascular effects of sleep apnea").

Drugs — A number of drugs can depress the SA node and slow the heart rate. These include parasympathomimetic agents, sympatholytic drugs (beta blockers, reserpine, guanethidine, methyldopa, clonidine), cimetidine, digitalis, calcium channel blockers, amiodarone and other antiarrhythmic drugs, and lithium.

Other — Other causes of sinus bradycardia include hypothyroidism, hypothermia, hypoxia, and some infections.
...
TREATMENT — Treatment is not indicated in asymptomatic patients with sinus bradycardia...."

Thanks Crimson, much appreciated. I did a google to find more info:

"Commonly, sinus bradycardia is an incidental finding in otherwise healthy individuals, particularly in young or sleeping patients. Other causes of sinus bradycardia are related to increased vagal tone.

Physiologic causes of increased vagal tone include the bradycardia seen in athletes. "

Sounds good to me (cos I really don't like the "prognosis" section on some of those pages).