oSIST prEN ISO 8996:2021

Ergonomics of the thermal environment - Determination of metabolic rate (ISO/DIS 8996:2020)

Ergonomie der thermischen Umgebung - Bestimmung des körpereigenen Energieumsatzes (ISO/DIS 8996:2020)

Der (körpereigene) Energieumsatz bzw. die körpereigene Energieerzeugung, als Umwandlung von chemischer in mechanische und thermische Energie, ist ein Maß für den Energieaufwand der Muskelarbeit und ermöglicht es, die Tätigkeiten quantitativ abzuschätzen. Der Energieumsatz ist eine wichtige Größe bei der Bestimmung des Wohlbefindens oder der Belastung, die sich durch ein warmes Umgebungsklima ergeben können. Besonders in einem sehr warmen Umgebungsklima wird die Wärmebelastung durch das bei der Muskelarbeit auftretende hohe Maß an körpereigener Wärmeerzeugung erhöht, da große Mengen an Wärme hauptsächlich durch das Verdunsten von Schweiß abgegeben werden müssen. Im Gegensatz dazu unterstützt ein hohes Maß an körpereigener Wärmeerzeugung in einem kaltem Umgebungsklima den Ausgleich übermäßiger Wärmeverluste über die Haut und verringert so die Kältebelastung.
Diese Internationale Norm legt unterschiedliche Verfahren für die Bestimmung des Energieumsatzes im Bereich der Ergonomie der thermischen Arbeitsumgebung fest. Die Internationale Norm kann auch für andere Anwendungsgebiete, zum Beispiel für die Bewertung von Arbeitsverfahren, des Energieaufwands für spezielle Aufgaben oder Sportaktivitäten sowie des Gesamtenergieaufwands einer Tätigkeit usw., angewendet werden.
Die in dieser Internationalen Norm enthaltenen Abschätzungen, Tabellen und anderen Daten beziehen sich auf die allgemeine Arbeitsbevölkerung. Die Anwender sollten in Bezug auf besondere Gruppen, Kinder, ältere Personen, Personen mit Körperbehinderungen usw. entsprechende Korrekturen vornehmen. Persönliche Merkmale, z. B. Körpermasse, können verwendet werden, wenn der Körper durch Laufen oder Steigen bewegt wird (Anhang A und Anhang B). Geschlecht, Alter und Körpermasse sind in Anhang C für die Bestimmung des Energieumsatzes auf Grundlage der Herzfrequenz berücksichtigt.

Ergonomie de l'environnement thermique - Détermination du métabolisme énergétique (ISO/DIS 8996:2020)

Ergonomija toplotnega okolja - Ugotavljanje presnovne toplote (ISO/DIS 8996:2020)

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN ISO 8996:2021
01-januar-2021
Ergonomija toplotnega okolja - Ugotavljanje presnovne toplote (ISO/DIS
8996:2020)
Ergonomics of the thermal environment - Determination of metabolic rate (ISO/DIS
8996:2020)
Ergonomie der thermischen Umgebung - Bestimmung des körpereigenen
Energieumsatzes (ISO/DIS 8996:2020)

Ergonomie de l'environnement thermique - Détermination du métabolisme énergétique

(ISO/DIS 8996:2020)
Ta slovenski standard je istoveten z: prEN ISO 8996
ICS:
13.180 Ergonomija Ergonomics
oSIST prEN ISO 8996:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 8996:2021
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oSIST prEN ISO 8996:2021
DRAFT INTERNATIONAL STANDARD
ISO/DIS 8996
ISO/TC 159/SC 5 Secretariat: BSI
Voting begins on: Voting terminates on:
2020-10-26 2021-01-18
Ergonomics of the thermal environment — Determination
of metabolic rate

Ergonomie de l'environnement thermique — Détermination du métabolisme énergétique

ICS: 13.180
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
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STANDARDS MAY ON OCCASION HAVE TO
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WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 8996:2020(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
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PROVIDE SUPPORTING DOCUMENTATION. ISO 2020
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oSIST prEN ISO 8996:2021
ISO/DIS 8996:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

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ii © ISO 2020 – All rights reserved
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Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 The units ....................................................................................................................................................................................................................... 1

5 The 4 levels of methods for estimating the metabolic rate ...................................................................................... 2

6 The accuracy of the estimation of the metabolic rate .................................................................................................... 3

7 Level 1, Screening: Classification of metabolic rate by categories....................................................................4

8 Level 2, Observation .......................................................................................................................................................................................... 4

8.1 E valuation of metabolic rate for a given activity ......... ............................................................................................... 4

8.2 E valuation of the mean metabolic rate over a given period of time ......................................................... 5

9 Level 3, Analysis .................................................................................................................................................................................................... 5

9.1 E valuation of metabolic rate using heart rate .............................................................................................................. 5

9.1.1 Principle of the method ............................................................................................................................................. 5

9.1.2 Accuracy of the (HR − M) relationship .......................................................................................................... 6

9.1.3 Validity of the (HR − M) relationship ............................................................................................................. 6

9.1.4 HR components not linked to the dynamic muscular load ......................................................... 7

9.2 E valuation of metabolic rate by accelerometry .......................................................................................................... 7

10 Level 4, Expertise ................................................................................................................................................................................................. 8

10.1 E valuation of metabolic rate by measurement of oxygen consumption rate .................................... 8

10.1.1 Partial and integral method.................................................................................................................................... 8

10.1.2 Evaluation of metabolic rate from oxygen consumption rate ................................................11

10.1.3 Evaluation of oxygen uptake ...............................................................................................................................11

10.1.4 Calculation of metabolic rate..............................................................................................................................13

10.2 E valuation of metabolic rate by the doubly labelled water method for long term

measurements ......................................................................................................................................................................................13

10.3 E valuation of metabolic rate by direct calorimetry — Principle ..............................................................14

Annex A (informative) Evaluation of the metabolic rate at level 1, Screening........................................................15

Annex B (informative) Evaluation of the metabolic rate at level 2, Observation .................................................17

Annex C (informative) Evaluation of the metabolic rate at level 3, Analysis ............................................................21

Annex D (informative) Evaluation of the metabolic rate at level 4, Expertise .........................................................23

Annex E (normative) Correction of the heart rate measurements for thermal effects .................................25

Annex F (informative) Uncertainties of the integral method ...................................................................................................27

Bibliography .............................................................................................................................................................................................................................29

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Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: www .iso .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 5,

Ergonomics of the physical environment, Work Group WG 1, Ergonomics of the thermal environment.

This third edition cancels and replaces the second edition (ISO 8996:2004), which has been technically

revised.
The main changes compared to the previous edition are as follows:

— The metabolic rate associated with a given task and estimated using the methods described in this

document is expressed in watts.

— At Level 1, Screening, the method classifying metabolic rate according to occupation was removed,

and revised procedures are provided for the evaluation of metabolic rate for given activities (Level

2, Observation), and when using heart rate (Level 3, Analysis).

— The accuracy of the methods for estimating the metabolic rate was re-evaluated in light of the recent

literature, and consequently the integral method is no longer recommended at Level 4, Expertise.

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oSIST prEN ISO 8996:2021
DRAFT INTERNATIONAL STANDARD ISO/DIS 8996:2020(E)
Ergonomics of the thermal environment — Determination
of metabolic rate
1 Scope

The metabolic rate, as a conversion of chemical into mechanical and thermal energy, measures the

energetic cost of muscular load and gives a quantitative estimate of the activity. Metabolic rate is an

important determinant of the comfort or the strain resulting from exposure to a thermal environment.

In particular, in hot climates, the high levels of metabolic heat production associated with muscular

work aggravate heat stress, as large amounts of heat need to be dissipated, mostly by sweat evaporation.

On the contrary, in cold environments, high levels of metabolic heat production help to compensate for

excessive heat losses through the skin and therefore reduce the cold strain.

This International Standard specifies different methods for the evaluation of metabolic rate in the

context of ergonomics of the thermal working environment. It can also be used for other applications —

for example, the assessment of working practices, energetic cost of specific jobs or sport activities, the

total energy cost of an activity, etc.

The estimations, tables and other data included in this International Standard concern the general

working population. Users should make appropriate corrections when they are dealing with special

populations including children, aged persons, people with physical disabilities, etc. Personal

characteristics, e.g. body mass, may be used if the body is moved due to walking or climbing (Annex A

and B). Gender, age and body mass are considered in Annex C for the evaluation of the metabolic rate

from heart rate.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 9886, Ergonomics — Evaluation of thermal strain by physiological measurements

ISO 13731, Ergonomics of the thermal environment — Vocabulary and symbols

ISO 15265, Ergonomics of the thermal environment — Risk assessment strategy for the prevention of stress

or discomfort in thermal working conditions
3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
4 The units

The metabolic rate associated with a given task and estimated using the methods described in this

document shall be expressed in watts.
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If the task does not involve displacements, the metabolic rate will not vary as a function of the size and

the weight of the subject. If it involves displacements, then the weight of the person must be taken into

account (see Annex B).

As the heat associated to this metabolic rate and produced inside the body must leave it essentially

through the skin, thermophysiologists usually express the metabolic rate per unit of body surface

area (in W⋅m ) and the estimations of thermal comfort and thermal constraints described in other

standards of this series are always done using metabolic rates in W⋅m .
5 The 4 levels of methods for estimating the metabolic rate

The mechanical efficiency of muscular work — called the ‘useful work’ — is low. In most types of

industrial work, it is so small (a few percent) that it is assumed to be nil. This means that the energy

spent while working is assumed to be completely transformed into heat. For the purposes of this

International Standard, the metabolic rate is assumed to be equal to the rate of heat production.

Table 1 lists the different approaches presented in this International Standard for determining the

metabolic rate.

These approaches are structured following the philosophy exposed in ISO 15265 regarding the

assessment of exposure. Four levels are considered:

— Level 1, Screening: a method simple and easy to use is presented to quickly classify as light,

moderate, high or very high the mean workload according to the kind of activity.

— Level 2, Observation: a time and motion study is presented for people with full knowledge of the

working conditions but without necessarily a training in ergonomics, to characterize, on average, a

working situation at a specific time:

A procedure is described to successively record the activities with time, estimate the metabolic rate of

each activity using formulas and data presented in Annex B and compute the time weighted average

metabolic rate.

— Level 3, Analysis: one method is addressed to people trained in occupational health and ergonomics

of the thermal environment. The metabolic rate is evaluated from heart rate recordings over a

representative period. This method for the indirect evaluation of metabolic rate is based on the

relationship between oxygen uptake and heart rate under defined conditions. Another method at

this level is based on the use of accelerometry to record body movement.

— Level 4, Expertise: 3 methods are presented. They require very specific measurements made by

experts:

— Method 4A: the oxygen consumption measured over short periods (10 min to 20 min);

— Method 4B: the so-called doubly labelled water method aiming at characterizing the average

metabolic rate over much longer periods (1 to 2 weeks);
— Method 4C: a direct calorimetry method.
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Table 1 — Levels for the evaluation of the metabolic rate
Level Method Accuracy Inspection of the work place
Classification according to Rough information Very great
Not required
activity risk of error
Screening
2 High error risk
Time and motion study Required
Observation Accuracy: ± 20 %
Medium error risk
3A: Heart rate measurement
Study required to determine a rep-
under defined conditions
Accuracy: ± 10 %
resentative period
Analysis
3B: Accelerometry High risk of error
4A: Measurement of oxygen Errors within the limits of
Time and motion study necessary
consumption the accuracy of the measure-
ment or of the time and motion
study, if assumptions (10.1.1, Inspection of work place not re-
4B: Doubly labelled water
10.1.4) are met quired, but leisure activities must
4 method
be evaluated.
Accuracy: ± 5 %
Expertise
Errors within the limits of the
accuracy of the measurement
4C: Direct calorimetry Inspection of work place not required.
or of the time and motion study
Accuracy: ± 5 %
6 The accuracy of the estimation of the metabolic rate

The accuracy of the results are provided in Table 1 as coefficient of variation (CV), i.e. the percentage

ratio of the standard deviation to the mean, and should be understood as indicative values, which might

increase due to non-controlled influences discussed below. The accuracy increases from level 1 to

level 4 and, as far as possible, the most accurate method should be used.

— At level 1, Screening, the method provides only a rough estimate and there is considerable scope

for error. This limits its accuracy considerably. At this level, an inspection of the work place is not

necessary.

— At level 2, Observation, the accuracy of the time and motion study depends upon the accuracy of

the formulas used (see Annex B), but mostly upon the level of training of the observer and his/her

knowledge of the working conditions: the possibility for errors is high.
— At level 3, Analysis,

— the accuracy of the estimated metabolic rate is influenced by the accuracy of the (HR − M ) relationship

used, as other stress factors can influence the heart rate;

— the accuracy level of 10 %–15 % (Malchaire et al. 2017) will only be achieved in field situations

(Rodahl et al. 1974; Dubé et al. 2016), if the (HR − M) relationship is individually calibrated for each

subject during a cardiac stress test with activities that are representative for the type of work under

consideration (cf. 9.1.3), and if the estimates are corrected for the thermal HR component (Annex E)

(Vogt et al. 1973; Kampmann et al. 2001). Otherwise, the error when using (HR − M) relationships

defined for groups (Annex C) will rise dramatically and the accuracy level will fall behind level 2

methods (Bröde and Kampmann 2019);

— the accuracy of the evaluation using accelerometers is highly dependent upon the instruments used

as well as on the type of work, and the method appears to be more appropriate for long term than

short term evaluation.
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— At level 4, Expertise, the accuracy is determined as well by the measurement system (gas volume

and oxygen fraction) as by the dynamics of oxygen uptake.
It can be assumed that:

— For a person trained in the activity, the variation is about 5 % under laboratory conditions;

— Under field conditions, i.e. when the activity to be measured is not exactly the same from test to test,

a variation of up to 20 % can be expected;

— In hot conditions, an increase of metabolic rate by 7 % per degree rise in core temperature related

to the Q -effect with typical Q = 2 may be expected. This increase may vary largely between

10 10

different persons with Q values between 1 and 8 (Kampmann and Bröde 2015) and may occur

well below an oxygen uptake of 1 l O ⋅min .

— In cold conditions, an increase of up to 400 W may be observed when shivering occurs.

— Heavy clothing might also increase the metabolic rate by 20 % or more, by increasing the weight

carried by the subject and decreasing the subject’s ease of movement.
Attention must be drawn to the fact that the accuracy depends also upon:
— the representativeness of the time period observed;

— the possible disturbance of the normal activity by the observer and/or the procedure. In this regard,

the method based on heart rate recordings appears to be one that interferes the least with the

activity;

— the number of measurements: repetition is one method to reduce random measurement error.

Based on the CV of an unbiased estimate, the formula (actual CV/requested CV) approximates the

required number of repetitions (Vogt et al. 1976). This implies that in order to achieve the 10 %

accuracy level, two measurements would be necessary with a method actually providing 14 %,

while four repetitions would be needed with 20 % accuracy, and even 9 with 30 %. Of course, this

improvement only will work if no systematic errors are inherent.
7 Level 1, Screening: Classification of metabolic rate by categories

The metabolic rate can be estimated approximately using the classification given in Annex A. Table A.1

defines five classes of metabolic rate: resting, low, moderate, high, very high. For each class, a range of

metabolic rate values is given as well as a number of examples. These activities are supposed to include

short rest pauses. The examples given in Table A.1 illustrate the classification.

As the accuracy of this method is low, it should only be used for classification purposes without

interpolation between the 4 levels.
8 Level 2, Observation
8.1 E valuation of metabolic rate for a given activity

Annex B gives mean values or formulas for estimating the metabolic rate in watts in the following cases:

— At rest;
— When walking with/without load at < 6 km⋅h ;
— When running with/without load at ≥ 6 km⋅h ;
— When going up or down stairs and ladders;
— When lifting or lowering loads without displacement;
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— For activities without displacement, from the observation of the body segment involved in the work:

both hands, one arm, two arms, the entire body;

— Taking into account the body posture: sitting, kneeling, crouching, standing, standing stooped;

8.2 E valuation of the mean metabolic rate over a given period of time

To evaluate the average metabolic rate over a given period of time, it is necessary to carry out a detailed

study of the work. This involves:
— Determining the list of activities performed during this period of time;

— Estimating the metabolic rate for each of these activities taking account of their characteristics and

using the data in Annex B: speed of displacement, heights climbed, weights manipulated, number of

actions carried out, etc.;

— Determining the time spent at each activity over the whole period of time considered.

The time weighted average metabolic rate for the time period can then be evaluated using the equation:

M= Mt (1)
∑ ii
i=1
where
M is the average metabolic rate for the work cycle, W;
M is the metabolic rate for activity i, W;
t is the duration of activity i, min;

T is the total duration, min, of the period of time considered, and is equal to the sum of the partial

durations t .

The procedure of this time and activity evaluation is further described in Annex B.

9 Level 3, Analysis
9.1 E valuation of metabolic rate using heart rate
9.1.1 Principle of the method

In the case of dynamic work using major muscle groups, with only a small amount of static muscular

and mental loads, the metabolic rate may be estimated by measuring the heart rate while working.

Under such conditions, a linear relationship exists between the metabolic rate and the heart rate. If the

above mentioned restrictions are taken into account, this method can be more accurate than the level 1

and level 2 methods of evaluation (see Table 1 and Clause 6) and is considerably less complex than the

methods listed at level 4.
The relationship between heart rate and metabolic rate can be written as:
M = a + b HR (2)
where
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M is the metabolic rate, W;
HR is the heart rate measured, beats⋅min ;
a and b are coefficients

The heart rate may be recorded continuously, for example by the use of telemetric equipment, or, with a

reduction in accuracy, measured manually by counting the arterial pulse rate.

The mean heart rate may be computed over fixed time intervals, for example 1 min, over a given period

of time or over the whole shift time.
The accuracy of this estimation of the metabolic rate depends upon:
— The accuracy and validity of the relation (2)
— The magnitude of the HR components not linked to the dynamic muscular load
9.1.2 Accuracy of the (HR − M) relationship

The relationship between heart rate and metabolic rate can be determined by different methods of

decreasing accuracy:

— The most accurate method consists of recording the heart rate and corresponding oxygen

consumption at different effort levels during a cardiac stress test, e.g. on an ergometer or a treadmill.

The (HR − M) relation can be used provided the durations of the efforts at each level are such that

stable HR and oxygen consumption values are reached. Such a procedure is very strenuous and is

usually performed in a medical environment.

— A simpler procedure consists of recording the stable heart rate during a few dynamic efforts

whose metabolic rates are known. The accuracy is then reduced as the oxygen consumption is not

measured.
— Expression (3) can be derived from evaluations of:
— the heart rate at rest under neutral thermal conditions, HR , beats⋅min ;
— the metabolic rate at rest, M , W;
— the maximum working capacity, MWC, W;
— the maximum heart rate HR , beats⋅min ;
max

— the increase in heart rate per unit of metabolic rate: RM = (HR − HR )/(MWC − M )

max 0 0
The (HR − M) relation is then given by:
M = M + (HR − HR)/RM (3)
0 0

The accuracy of this relation is a function of the validity of the measurements or estimations of HR , M ,

0 0
HR and MWC. Annex C proposes formulas for estimating these 4 parameters
max

Table C.1 provides direct evaluations of the (HR − M) relationship for women and men with ages ranging

from 20 years to 65 years and body masses ranging from 50 kg to 110 kg. The precision is then further

reduced.
9.1.3 Validity of the (HR − M) relationship

The question relates to the relevance of the (HR − M) relation directly or indirectly derived from a

cardiac stress test using the great muscular group of the legs, in the event of a work carried out with the

upper limbs. Studies showed that the V during manual crank efforts was 23 % to 30 % lower than

O2max
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that measured for the same HR value during a cardiac stress test on bicycle or treadmill. Using that

(HR − M) relation results therefore in an overestimation of the real energy expenditure.

9.1.4 HR components not linked to the dynamic muscular load
The heart rate at a given time may be regarded as the sum of several components:
HR = HR + ∆HR + ∆HR + ∆HR + ∆HR + ∆HR (4)
0 M S th N ε
where

HR is the heart rate, in beats per minute, at rest under neutral thermal conditions;

∆HR is the increase in heart rate, in beats per minute, due to dynamic muscular load, under neutral

thermal conditions;

∆HR is the increase in heart rate, in beats per minute, due to static muscular work (this component

depends on the relationship between the force used and the maximum voluntary force of the

working muscle group);

∆HR is the increase in heart rate, in beats per minute, due to heat stress (the thermal component

is discussed in ISO 9886);
∆HR is the increase in heart rate, in beats per minute, due to mental load;

∆HR is the change in heart rate, in beats per minute, due to other factors, for example respiratory

effects, circadian rhythms, dehydration.

In the presence of static muscular work, dynamic work with small muscle groups and/or mental loads,

the slope of th
...