THE STRONG­EST SCI­EN­TIST

Go with your heart.

Men's Health (South Africa) - - CONTENTS - By Dr. Mike Posthu­mus PhD in ex­er­cise science; head of the high-per­for­mance divi­sion at SSISA; co-owner of Science to Sport; elite MTB rider and cy­cling coach

It’s the last day of the ABSA Cape Epic, which starts in Welling­ton and fin­ishes at Val de Vie. It’s most def­i­nitely not all down­hill from here, as the day starts with a bru­tally long climb right to the top of Du Toit­skloof Pass.

I give it ab­so­lutely all I have on the uphill, sweat pour­ing down my face, pant­ing with the ef­fort. I’m on the prover­bial limit.

Not a new ex­pe­ri­ence, this week; how­ever, a quick look at my heart-rate mon­i­tor, and the read­ings are very dif­fer­ent from what they were in the first few days of the race. Alarm­ingly, my heart rate is only 135 bpm – at this level of in­ten­sity, my heart rate would nor­mally be closer to 165 bpm.

Thank­fully, ex­pe­ri­ence has taught me that this is one hun­dred per­cent nor­mal.

Heart-rate mon­i­tors have be­come ex­tremely pop­u­lar with gym-go­ers. But – be­sides the fact that most modern op­ti­cal heart-rate mon­i­tors are of­ten woe­fully in­ac­cu­rate – your ac­tual heart rate, even if ac­cu­rately mea­sured, is rather in­signif­i­cant.

Let me ex­plain. Your heart rate is an in­di­ca­tion of train­ing in­ten­sity. The higher your train­ing in­ten­sity, the higher your heart rate. As your fit­ness level in­creases, you would ex­pect your heart rate to be­come lower at a spe­cific rel­a­tive in­ten­sity.

How­ever, track­ing this is not as easy as it may seem. The caveat here is that on any given day, your heart rate may be up to 10 beats higher or lower, sim­ply due to com­mon day-to-day changes. Qual­ity and quan­tity of sleep, stress, to­bacco, caf­feine, re­cent or cur­rent ill­ness, tem­per­a­ture and cur­rent fit­ness level are only some of the fac­tors that may skew your re­sults.

At any given ex­er­cise in­ten­sity, there­fore, you can ex­pect a range of heart rates, depend­ing on these fac­tors. Be­cause of this vari­abil­ity, in­ter­pret­ing your heart rate be­comes more com­pli­cated than you might imag­ine.

For ex­am­ple: acute fa­tigue, stress or lack of sleep of­ten re­sult in higher heart rate, whereas a more chronic re­sponse from a high train­ing load would re­sult in a de­crease in sym­pa­thetic ac­tiv­ity (“fight or flight” re­sponses), and an in­crease in parasym­pa­thetic ac­tiv­ity (“rest and di­gest” re­sponses), which would lower your rest­ing and sub-max­i­mal heart rate.

What is com­monly ex­pe­ri­enced dur­ing stage races – as I did, climb­ing to the top of the Pass on the last day of the Epic – was a de­creased sym­pa­thetic re­sponse, thanks to seven hard days of rac­ing. It was cer­tainly not an in­di­ca­tion of in­creased fit­ness lev­els.

Changes in heart rate due to im­prove­ments in fit­ness may not be as large as in this ex­am­ple, how­ever. So how do we ac­cu­rately mon­i­tor whether or not we’re mov­ing in the right di­rec­tion?

A re­cent sys­tem­atic re­view by Saw and col­leagues pub­lished in the Bri­tish Jour­nal of Sports Medicine com­pared the use­ful­ness of ob­jec­tive mea­sures (such as heart rate, and other in­trin­sic phys­i­o­log­i­cal val­ues), and sub­jec­tive mea­sures (such as ath­lete self-re­port­ing of well­ness, fa­tigue and ef­fort). The re­view found that sub­jec­tive re­port­ing of well-be­ing was in fact more sen­si­tive than from ob­jec­tive mea­sures.

What does this mean for you? Well, if you per­form a sub-max­i­mal ef­fort, then sim­ply ask­ing your­self how it felt, or rat­ing your per­ceived ef­fort, might give you a bet­ter idea of your over­all progress than look­ing at your heart rate or any other ob­jec­tive phys­i­o­log­i­cal marker.

So again, my mes­sage is: go back to the ba­sics, and learn to ap­pre­ci­ate how you’re feel­ing while you’re train­ing.

Gaug­ing your­self us­ing your own per­cep­tion may be one of the best in­di­ca­tors of over­all pro­gres­sion in fit­ness.

“Sim­ply ask­ing your­self how it felt might give you a bet­ter idea of your over­all progress.”

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