SIST EN ISO 8996:2022

Ergonomics of the thermal environment - Determination of metabolic rate (ISO 8996:2021)

This document specifies different methods for the determination of metabolic rate in the context of
ergonomics of the thermal working environment. It can also be used for other applications, e.g. the
assessment of working practices, the energetic cost of specific jobs or sport activities and the total
energy cost of an activity. The methods are classified in four levels of increasing accuracy: level 1,
Screening, with a table giving examples of activities with low, moderate and high metabolic rates; level
2, Observation, where the metabolic rate is estimated by a time and motion study; level 3, Analysis,
where the metabolic rate is estimated from heart rate recordings or accelerometers measurements;
and level 4, Expertise, where more sophisticated techniques are described. The procedure to put into
practice these methods is presented and the uncertainties are discussed.

Ergonomie der thermischen Umgebung - Bestimmung des körpereigenen Energieumsatzes (ISO 8996:2021)

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 8996:2021)

Le présent document spécifie différentes méthodes visant à déterminer le métabolisme énergétique dans le domaine de l’ergonomie de l’environnement de travail thermique. Il peut cependant être également utilisé en vue d’autres applications, par exemple l’évaluation des pratiques de travail, le coût énergétique de travaux ou d’activités sportives spécifiques et le coût énergétique global d’une activité. Les méthodes sont classées en quatre niveaux de précision croissante: niveau 1, Typologies, avec un tableau donnant des exemples d’activités avec métabolismes énergétiques faibles, modérés et élevés; niveau 2, Observation, où le métabolisme énergétique est estimé par une étude des temps et des mouvements; niveau 3, Analyse, où le métabolisme énergétique est estimé à partir d’enregistrements de la fréquence cardiaque ou de mesures d’accéléromètres; et niveau 4, Expertise, où des techniques plus sophistiquées sont décrites. Le mode opératoire pour mettre en pratique ces méthodes est indiqué et les incertitudes sont examinées.

Ergonomija toplotnega okolja - Ugotavljanje presnovne toplote (ISO 8996:2021)

Ta dokument določa različne metode za ugotavljanje presnovne toplote v kontekstu ergonomije toplotnega delovnega okolja. Primeren je tudi za druge vrste uporabe, npr. ocenjevanje delovnih praks, energetskih stroškov za posamezno delovno mesto ali športno dejavnost in skupnih energetskih stroškov posamezne dejavnosti. Metode so razvrščene v štiri stopnje povečanja natančnosti: stopnja 1 – presejanje, s preglednico primerov dejavnosti z nizko, zmerno in visoko prenosno toploto; stopnja 2 – opazovanje, pri čemer se presnovna toplota oceni na podlagi študije časa in gibanja; stopnja 3 – analiza, pri čemer se presnovna toplota oceni na podlagi zapisov srčnega utripa ali meritev merilnikov pospeška; ter stopnja 4 – strokovno znanje, pri čemer so opisane kompleksnejše tehnike. Predstavljen je postopek uporabe teh metod v praksi in obravnavane so negotovosti v zvezi s tem.

General Information

• Status: Published
• Public Enquiry End Date: 10-Jan-2021
• Publication Date: 28-Mar-2022
• ICS: 13.180 - Ergonomics
• Technical Committee: VSN - Safety of machinery
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 03-Jan-2022
• Due Date: 10-Mar-2022
• Completion Date: 29-Mar-2022
• Ref Project: EN ISO 8996:2021 - Ergonomics of the thermal environment - Determination of metabolic rate (ISO 8996:2021)

Relations

• Revised: SIST EN ISO 8996:2005 - Ergonomics of the thermal environment - Determination of metabolic rate (ISO 8996:2004)
• Effective Date: 06-Sep-2017
• Replaces: SIST EN ISO 8996:2005 - Ergonomics of the thermal environment - Determination of metabolic rate (ISO 8996:2004)
• Effective Date: 29-Dec-2021
• Replaces: SIST EN ISO 8996:2005 - Ergonomics of the thermal environment - Determination of metabolic rate (ISO 8996:2004)
• Effective Date: 08-Jun-2022

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 8996:2022
01-maj-2022
Nadomešča:
SIST EN ISO 8996:2005
Ergonomija toplotnega okolja - Ugotavljanje presnovne toplote (ISO 8996:2021)
Ergonomics of the thermal environment - Determination of metabolic rate (ISO
8996:2021)
Ergonomie der thermischen Umgebung - Bestimmung des körpereigenen
Energieumsatzes (ISO 8996:2021)

Ergonomie de l'environnement thermique - Détermination du métabolisme énergétique

(ISO 8996:2021)
Ta slovenski standard je istoveten z: EN ISO 8996:2021
ICS:
13.180 Ergonomija Ergonomics
SIST EN ISO 8996:2022 en,fr,de

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

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SIST EN ISO 8996:2022
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SIST EN ISO 8996:2022
EN ISO 8996
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2021
EUROPÄISCHE NORM
ICS 13.180 Supersedes EN ISO 8996:2004
English Version
Ergonomics of the thermal environment - Determination
of metabolic rate (ISO 8996:2021)

Ergonomie de l'environnement thermique - Ergonomie der thermischen Umgebung - Bestimmung

Détermination du métabolisme énergétique (ISO des körpereigenen Energieumsatzes (ISO 8996:2021)

8996:2021)
This European Standard was approved by CEN on 3 December 2021.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8996:2021 E

worldwide for CEN national Members.
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SIST EN ISO 8996:2022
EN ISO 8996:2021 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 8996:2022
EN ISO 8996:2021 (E)
European foreword

This document (EN ISO 8996:2021) has been prepared by Technical Committee ISO/TC 159

"Ergonomics" in collaboration with Technical Committee CEN/TC 122 “Ergonomics” the secretariat of

which is held by DIN.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by June 2022, and conflicting national standards shall be

withdrawn at the latest by June 2022.

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

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 8996:2004.

Any feedback and questions on this document should be directed to the users’ national standards

body/national committee. A complete listing of these bodies can be found on the CEN website.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 8996:2021 has been approved by CEN as EN ISO 8996:2021 without any modification.

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SIST EN ISO 8996:2022
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SIST EN ISO 8996:2022
INTERNATIONAL ISO
STANDARD 8996
Third edition
2021-12
Ergonomics of the thermal
environment — Determination of
metabolic rate
Ergonomie de l'environnement thermique — Détermination du
métabolisme énergétique
Reference number
ISO 8996:2021(E)
© ISO 2021
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SIST EN ISO 8996:2022
ISO 8996:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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 on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
© ISO 2021 – All rights reserved
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SIST EN ISO 8996:2022
ISO 8996:2021(E)
Contents Page

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

Introduction .................................................................................................................................................................................................................................v

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

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

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

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

5 The four levels of methods for estimating the metabolic rate ............................................................................ 1

6 Level 1, Screening: classification of metabolic rate by categories ..................................................................3

7 Level 2, Observation .........................................................................................................................................................................................3

7.1 E valuation of metabolic rate for a given activity ..................................................................................................... 3

7.2 E valuation of the mean metabolic rate over a given period of time ....................................................... 4

7.3 Accuracy ....................................................................................................................................................................................................... 4

8 Level 3, Analysis.................................................................................................................................................................................................... 4

8.1 E valuation of metabolic rate using heart rate ............................................................................................................ 4

8.1.1 Principle of the method ................................................................................................................................................ 4

8.1.2 Determination of the (HR–M) relationship for purely dynamic muscular

work ............................................................................................................................................................................................... 5

8.1.3 E valuation of the metabolic rate as a function of HR in real situations ............................ 6

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

9 Level 4, Expertise ................................................................................................................................................................................................ 8

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

9.1.1 Partial and integral method ..................................................................................................................................... 8

9.1.2 Evaluation of metabolic rate from oxygen consumption rate................................................. 10

9.1.3 E valuation of oxygen uptake ................................................................................................................................ 11

9.1.4 Calculation of metabolic rate .................. .............................................................................................................. 13

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

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

9.3 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

Bibliography .............................................................................................................................................................................................................................27

iii
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SIST EN ISO 8996:2022
ISO 8996:2021(E)
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 of 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

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, in collaboration with the European Committee for

Standardization (CEN) Technical Committee CEN/TC 122, Ergonomics, in accordance with the

Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

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

revised.
The main changes 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 has been

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 has been reevaluated in light of

the recent literature and consequently the integral method is no longer recommended at level 4,

Expertise.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2021 – All rights reserved
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SIST EN ISO 8996:2022
ISO 8996:2021(E)
Introduction

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.

The estimations, tables and other data included in this document concern the general working

population. Corrections can be needed when dealing with special populations, including children, aged

persons or people with physical disabilities. Personal characteristics, such as body mass, may be used if

the body is moved due to walking or climbing (Annex B). Gender, age and body mass are considered in

Annex C for the evaluation of the metabolic rate from heart rate.
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SIST EN ISO 8996:2022
INTERNATIONAL STANDARD ISO 8996:2021(E)
Ergonomics of the thermal environment — Determination
of metabolic rate
1 Scope

This document specifies different methods for the determination of metabolic rate in the context of

ergonomics of the thermal working environment. It can also be used for other applications, e.g. the

assessment of working practices, the energetic cost of specific jobs or sport activities and the total

energy cost of an activity. The methods are classified in four levels of increasing accuracy: level 1,

Screening, with a table giving examples of activities with low, moderate and high metabolic rates; level

2, Observation, where the metabolic rate is estimated by a time and motion study; level 3, Analysis,

where the metabolic rate is estimated from heart rate recordings or accelerometers measurements;

and level 4, Expertise, where more sophisticated techniques are described. The procedure to put into

practice these methods is presented and the uncertainties are discussed.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.

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

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

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 shall be taken into

account (see Annex B).

As the heat associated to this metabolic rate and produced inside the body leaves 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 ISO 7243, ISO 7730,

ISO 7933 and ISO 11079 are done using metabolic rates in W⋅m .
5 The four 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 per cent) 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 document, the

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

Table 1 lists the different approaches presented in this document for determining the metabolic rate.

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SIST EN ISO 8996:2022
ISO 8996:2021(E)

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 formulae 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 its

relationship with heart rate under defined conditions. Another method at this level is based on the

use of accelerometery to record body movement.

— Level 4, Expertise: three 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 week to 2 weeks);
— Method 4C: a direct calorimetry method.
Table 1 — Levels for the evaluation of the metabolic rate
Level Method Uncertainty Inspection of the work place
1 Rough information
Classification according to
Not required
activity
Screening Very great risk of error
2 High error risk
Time and motion study Required
Observation Uncertainty: ± 20 %
3A: Heart rate measure-
Medium error risk
ment under defined condi-
Study required to determine a rep-
Uncertainty: ± 10 to 15 %
tions
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 meas-
urement or of the time and
motion study, if assumptions Inspection of work place not re-
4B: Doubly labelled water
(9.1.1, 9.1.4) are met quired, but leisure activities shall
method
4 be evaluated.
Uncertainty: ± 5 %
Expertise
Errors within the limits of
the accuracy of the meas-
Inspection of work place not
urement or of the time and
4C: Direct calorimetry
required.
motion study
Uncertainty: ± 5 %

The uncertainty of each method is 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 can

increase due to non-controlled influences discussed as follows. The accuracy at each level is discussed

in describing the methods in Clauses 6 to 9. It increases from level 1 to level 4 and, as far as possible, the

most accurate method should be used.
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SIST EN ISO 8996:2022
ISO 8996:2021(E)
Attention should be drawn to various sources of variations:

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

— Heavy clothing can 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.
The accuracy depends also upon the following:
— 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 a 10 %

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

while four repetitions would be needed with 20 % uncertainty, and nine with 30 %. Of course,

this improvement will only work if no systematic errors are inherent. It is recommended that the

metabolic rate from all the samples is evaluated and the mean value adopted as the metabolic rate

of the condition studied.
6 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 and 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.
An inspection of the work place is not necessary.
The examples given in Table A.1 illustrate the classification.

As the method provides only a rough estimate of the metabolic rate with considerable possibilities

for error, it should only be used for classification purposes without interpolation between the four

categories.
7 Level 2, Observation
7.1 Evaluation of metabolic rate for a given activity

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

— at rest;
— for activities with displacements:
— when walking with or without load at < 6 km⋅h ;
— when running with or without load at ≥ 6 km⋅h ;
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SIST EN ISO 8996:2022
ISO 8996:2021(E)
— when going up or down stairs and ladders;
— for activities without displacement
— when lifting or lowering loads 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;
7.2 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, e.g. speed of displacement, heights climbed, weights manipulated,

number of actions carried out;

— 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 Formula (1):

M= Mt (1)
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.

The time and duration of the study shall be representative of the activity in all its possible variations:

the duration may be rather short if the work cycle is short and repetitive, and very long when the

activities change permanently.
7.3 Accuracy

The accuracy of the time and activity procedure depends upon the accuracy of the formulas used (see

Annex B), but mostly upon the level of training of the observers and their knowledge of the working

conditions: the possibility for errors is high.
8 Level 3, Analysis
8.1 E valuation of metabolic rate using heart rate
8.1.1 Principle of the method

In the case of pure dynamic work using major muscle groups, with no static muscular, thermal and

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

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ISO 8996:2021(E)

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 is considerably less complex than the methods listed in

level 4. In that case, the relationship between heart rate and metabolic rate is shown in Formula (2):

M = a + b HR (2)
where
M is the metabolic rate, W;
HR is the heart rate measured, beats⋅per 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 in Formula (2);
— the magnitude of the HR components not linked to the dynamic muscular load.
8.1.2 Determination of the (HR–M) relationship for purely dynamic muscular work

The (HR–M) relation can be determined by different methods of decreasing accuracy:

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

consumption at different effort levels during a cardiac stress test, for example on an ergometer or

a treadmill in a thermically neutral environment. 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.

Studies showed that when the cardiac test consists of manual crank efforts, instead of cycling on

a bicycle or walking on a treadmill the metabolic rate for the same HR value is 23 % to 30 % lower

and the validity of (HR−M) will be limited to activities involving only the upper body and limbs.

Conversely, the (HR–M) relation derived from tests on an ergometer or treadmill will mainly be

valid for activities involving the lower limbs and the entire body.

This method of determination of the (HR–M) relationship is very strenuous and may only be

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