Bodyrecomposition Mailbag 4

Having written about what calories are, it’s time to return to the mailbag since this is always an easy way for me to get content.  Today I’ll address questions about heart rate monitors and metabolic rate, agronomist activity levels and calorie levels, NEAT and adaptive thermogenesis,  and then a long answer on the topic of whether to lose fat or gain muscle for a beginner at 20% bodyfat (if I were a different kind of writer I’d that THE ANSWER WILL SHOCK YOU!).

Heart Rate Monitoring and Metabolic Rate

Hey Lyle, Huge fan of your work, it really has changed my life… just wish I’d stumbled upon you a decade ago, I’d be a machine by now! Anyhow, I was just curious about your opinion on heart rate monitors and wether they can be an accurate way of monitoring your metabolism during a cut. I have a Fitbit charge hr which seems to do a pretty solid job. I.e. When I use it to cut I lose weight, bulk I gain weight and my weight is pretty damn stable when I use it to maintain. I’ve noticed that when I cut my resting pulse rate progressively gets lower over the course of the cut and also that I start to burn less and less calories during my workouts.

Answer

In at least a general sense, a drop in heart rate is pretty normal with dieting to lower levels.   For example, in a recent study that attempted to mimick the classic Minnesota Semi-Starvation study, men first overfed for one week before were placed on a 50% calorie reduction for three weeks.  In addition to changes in other metabolic parameters, heart rate went up from 65 to 68 Beats Per Minute (BPM) during overfeeding and dropped to 59 BPM during calorie restriction.    In a yet to be unpublished case study of contest dieting in a male bodybuilder, heart rate dropped by 9 BPM over 16 weeks along with metabolic rate and other hormonal factors.  Given that sympathetic nervous system output declines on a diet, and this is certainly part of the control of resting heart rate, this makes a great deal of sense.

So yes, it is at least qualitatively indicative although I’m don’t think you can use it to quantify how much metabolic rate has dropped specifically.

(more…)