DocPDF Sharing Community - File Manager - PDF Files

image

29 Intermittent exercise in the heat

29 intermittent exercise in the heat jeponline journal of exercise physiologyonline official journal of the americ
14 Jan, 2023
Date
372.61 KB
Size
2459
Views
1469
Downloads
A
Pic
Pic
Pic
S
Pic
P
Pic
+42

Start relevant disscusion about this document:

Preview PDF

Showing preview pdf file

Drop related files here or click to upload.

Upload up to 10 files

Related Files

Showing 7 files
Icon
29 INTERMITTENT EXERCISE IN THE HEAT JEPONLINE JOURNAL OF
29 intermittent exercise in the heat jeponline journal of exercise physiologyonline offi
Icon
胸腔內科標準病歷範本 CASE 1 1主述:NON PRODUCTIVE COUGH AND INTERMITTENT FEVER
胸腔內科標準病歷範本 case 1 1.主述:non productive cough and intermittent fever for 3 weeks. 2. present illness this 32 years old man of no syst
Icon
INTERMITTENT ALTERNATE CARE PROVIDER INSTRUCTIONS FORM 2085RC PAGE 3
intermittent alternate care provider instructions form 2085rc page 3 july 2006 child’s name: (include any nicknames)   age:
Icon
0 INTERMITTENT POSITIVEPRESSURE BREATHING EFFECTS IN PATIENTS WITH HIGH
0 intermittent positivepressure breathing effects in patients with high spinal cord injury isabelle laffont md phd, djamel bensmail m
Icon
FORM 2085R INSTRUCTIONS PLACEMENT AUTHORIZATION INTERMITTENT ALTERNATE CARE PURPOSE
form 2085r instructions placement authorization intermittent alternate care purpose to authorize an intermittent alternate care c
Icon
KEY + INDEPENDENT INTERMITTENT HELP 0 TOTALFULL HELP ROUTINES
key + independent intermittent help 0 total/full help routines monitoring form name: routine: arri
Sharing community where you can transfers and download files. At present more than 1.000.000 documents are submitted to our system. Do you need us to host your document? You can upload documents for a free. Invite DocPDF Collaboratorsto create great outstanding read to read community.
- Followers
- @DocPDF
- #DocPDF
SPREAD KNOWLEDGE - SHARE IT! Copy and paste the link wherever you want and start sharing!
Link:

Transcript

29
Intermittent exercise in the heat
JEPonline
Journal of Exercise Physiologyonline

Official Journal of The American
Society of Exercise Physiologists (ASEP)
ISSN 10979751
An International Electronic Journal
Volume 4 Number 3 August 2001

E nvironmental Exercise Physiology
EVALUATION OF A PHYSIOLOGICAL STRAIN INDEX FOR USE DURING INTERMITTENT
EXERCISE IN THE HEAT
R.W. GOTSHALL, D.J. DAHL AND N.J. MARCUS.
Health and Exercise Science, Colorado State University, Fort Collins
CO 80523.

ABSTRACT
R.W. GOTSHALL, D.J. DAHL AND N.J. MARCUS. Evaluation Of A
Physiological Strain Index For Use During Intermittent Exercise In The
Heat. JEPonline. 2001;4(3):2229. A physiological heat strain index
that includes a combination of heart rate and core temperature has
been proposed as an index of heat strain for use to monitor heat
strain during continuous, steadystate exercise. The current study
evaluates this physiological heat strain index during workrest,
intermittent, exercise in the heat. Ten subjects each participated in
either a 60minute steadystate or 60minute intermittent (15 min
exercise, 5 min rest; repeated 3 times) exercise protocol in normal
(20oC, 50% RH), hotdry (40oC, 35% RH), and hothumid (35oC, 70% RH)
conditions. Exercise was walking on the treadmill at 1.34 m/sec (3
mph), 5% grade. Heart rate was determined with a heart rate monitor
and core temperature was determined by rectal temperature probe. The
physiological heat strain index was calculated from heart rate and
core temperature. The physiological heat strain index distinguished
between normal and heat conditions for both protocols. However, only
the steadstate exercise protocol resulted in physiological heat
strain differences between hotdry and hothumid conditions. Heat
strain was less for the intermittent protocol. The results confirm
previous investigations using the physiological heat strain index
during steadystate exercise in the heat, and extend the usefulness of
this index to intermittent, workrest, exercise in the heat.
Keywords: Stress, Work, Environment, Humidity, Thermoregulation, Core
Temperature, Heart Rate

INTRODUCTION
While indices of heat stress have become widely used in occupational
settings (1), attempts at developing adequate indices of heat strain
have been less successful (57). The onset of heatrelated
injury is insidious. Athletes, military personnel, firefighters, and
other industrial workers often continue to perform unaware that they
are, or are rapidly becoming, victims of hyperthermia (3). From 1979
through 1996, the Centers for Disease Control reported 6864 deaths
attributed to excessive heat exposure, though not all of these
occurred in those at work or exercising (3). The increased need for
workers to wear heavy, impermeable clothing while working in hot
environments has the potential to increase heatrelated injuries. In
1994, the US Air Force reported 19 individuals hospitalized due to
excessive heat exposure (4). That same year, the US Army reported
196 individuals hospitalized for heat illness (4).
To ameliorate risk for workers and athletes who perform in the heat,
both environmental heat stress and physiological heat strain are
important to consider. In order to effectively monitor the
physiological heat strain, physiological variables must be included.
However, these variables should be combined to produce an effective
heat strain index for use across environments. Therefore, a simple,
easily calculated physiological strain index for use in hot
environments that would provide rapid and accurate assessment of heat
strain potentially could reduce the risk of heat exposure.
Moran et al. (11) have developed a physiological heat strain index
(PSI) that places the heat strain on a scale of 0 through 10. This
potentially standardizes the interpretation of the heat strain across
individuals and environments. Moran and colleagues (811) have
evaluated the PSI under a variety of hot environmental conditions,
primarily using database information on subjects who had exercised
continuously in the heat. Their data are convincing in that the PSI
discriminated among the various hot, hothumid, and normal conditions.
In one prospective study whose primary purpose was to investigate the
potential influence of gender on the PSI, the PSI again was able to
discriminate among the environmental conditions (10).
Most work environments and protocols do not involve continuous,
steadystate exercise, but rather, workrest cycles. Monitoring of
heat strain during intermittent exercise is especially important for
those individuals wearing protective clothing while working in the
heat, in which rest cycles are mandatory. The PSI is an index of the
physiological strain and should track the changes in heat strain
occurring as rest cycles are employed. The concern lies in the use of
Tr in the setting of workrest cycling. Tr is usually greater and
responds more slowly than the Tesophogeal (1214) to changes in
work intensity. Tr responds to changes in blood temperature with a
time constant of ~12 min, while Tesophogeal, for comparison, responds
with a time constant of about ~1 min (14). Thus, there is the
concern that the PSI might not reflect the heat strain associated with
workrest cycles during an intermittent exercise protocol due to a
failure of Tr to change. However, because the PSI includes HR as well
as Tr, it was hypothesized in this study that the changes in HR
associated with workrest cycles might obviate this concern. It was
reasoned that HR would respond to workrest cycles reflecting the
changes in metabolic heat production, and more appropriately
correspond to heat strain. Therefore, the purpose of this study was to
evaluate the PSI under varying hothumid conditions in subjects
performing continuous, steadystate exercise or performing workrest
cycles. We hypothesized that the PSI would effectively discriminate
among the environmental conditions during both continuous and
intermittent exercise.
METHODS
Prior to the onset of this study, approval was obtained from the
Colorado State University Human Research Committee and all procedures
were in accordance with the ethical standards of the Helsinki
Declaration of 1975. Twelve men and eight women volunteered for this
study. All subjects were apparently healthy as ascertained by health
questionnaire. Subjects were regularly exercising a minimum of 3 days
per week, 1 hour per day, for at least the last 6 months. Subjects
with a history of heatrelated illness were not eligible for the
study. Subjects refrained from exercise, alcohol, and overthecounter
medication for 24 hours and from caffeine for 12 hours prior to each
test period.
Prior to the environmental exposures, each subject performed a maximal
exercise stress test using a modified Balke protocol on a Quinton Q65
treadmill (Quinton, Seattle, WA). Exercise ECG was recorded for heart
rate and rhythm determination. Expired gases were collected and
analyzed using a TrueMax 2400 metabolic cart (ParvoMedics, Sandy, UT).
Subjects were divided into two groups of 6 men and 4 women for the two
different exercise protocols, continuous, steadystate exercise (SS)
and intermittent exercise (INT). Each subject was exposed in an
environmental chamber to each of three environmental conditions in
random order, normal (N: 20oC, 50% RH), hotdry (HD: 40oC, 35% RH),
and hothumid (HH: 35oC, 70% RH). Following 10 min of seated rest data
collection, the SS subjects walked on the treadmill at 1.34 m/s (3
mph), 5% grade for 60 min. The INT group walked on the treadmill under
the same conditions, but walked for a 15min interval followed by
5min interval of seated rest repeated up to the 60 min of total time.
Prior to entering the environmental chamber, each subject was weighed
in the nude; dressed in tshirt, shorts, running shoes and socks; and
instrumented for physiological measurements. A rectal temperature
probe (YSI, Yellow Springs, OH) was selfinserted 10 cm passed the
anal sphincter. A Polar heart rate monitor (Polar, USA) was placed
around the chest. Core (rectal) temperature (Tr) and heart rate (HR)
were recorded continuously via AcqKnowledge v3.5.3 acquisition
software (Biopac, Santa Barbara, CA) and stored on computer. Core
temperature of 39oC or HR in excess of 180 b/min would have terminated
the heat exposure trial. No trial had to be terminated. Tr and HR were
averaged for the last 90 sec of rest, and for 60 sec at 5, 30 and 60
min of exercise for the SS protocol. Tr and HR were averaged for the
last 90 sec of rest, and for the last 60 sec of each of the exercise
and subsequent rest periods for the INT protocol.
Each subject was permitted water ad libitum. A weighed filled water
bottle was provided that was again weighed after the exposure to
determine amount consumed. Subjects immediately exited the chamber
upon completion of the protocol, stripped, toweldried, and obtained a
nude body weight. Sweat loss and rate were calculated by subtraction
of the postbodyweight from the prebody weight corrected for water
consumption.
The physiological strain index (PSI) was calculated according to Moran
et al. (11). The equation used was:
PSI (5 * (Tri Tr0)/ ((39.5 Tr0)) + (5 * (HRi HRo) * (180HR0))
Where Tri and HRi are simultaneous measurements taken at any time
during the heat exposure; and Tr0 and HR0 are the seated resting
values in the chamber prior to beginning the exercise protocol. The
PSI yields values between 1 and 10 when values for HR and Tr fall
between 60180 bpm and 36.5o39.5oC, respectively.
A twoway (time, climate), repeated measures ANOVA was used for each
of the two groups to analyze variables for the three climatic
exposures. Where differences were found, post hoc analysis was
performed with Fisher's LSD Multiple Comparison Test. For comparisons
between the two groups, a twoway (time, group) ANOVA was used for
each climatic exposure, with the Fisher's LSD Multiple Comparison Test
used for post hoc analysis. All statistics were accomplished with
NCSS2000 software (NCSS Kaysville, UT). Significance was set at
p<0.05.
RESULTS
Table 1 presents the subject's characteristics. There were no
significant differences between the two groups. Table 2 shows the
volume of sweat lost for each climatic condition for each group. While
there were significant increases in sweat loss for both HD and HH
compared to N for both groups, there were no differences between HD
and HH for either group. Sweat loss was the same for both SS and INT
groups for each climatic condition.
Table 1. Subject Characteristics.
SS, n10
INT, n10
Age (years)
251.0
241.0
Height (cm)
1773.2
17.6
Weight (kg)
69.34.4
74.55.4
VO2max (mL/kg/min)
50.72.2
49.22.4
Values are mean SEM. SS, continuous, steadystate exercise
protocol; INT, intermittent exercise protocol.
Table 2. Sweat loss in each of the climatic conditions (mL).
SS
INT
N
19463
312114
HD
86953*
1125330*
HH
871112*
1075340*
Values are mean SEM. SS, continuous, steadystate exercise protocol;
INT, intermittent exercise protocol; N, normal climate; HD, hotdry
climate;
HH, hothumid climate. *p<0.05, compared to N.
Figure 1 presents the HR, Tr, and PSI data for SS exercise. HR was
higher while resting in HD and HH conditions. HR was elevated with the
SS exercise, being more elevated during HD and HH, and becoming
highest in HH by 60 min. Core temperature, Tr, was the same at rest
for N and HD, but slightly lower for HH. All Tr values increased with
exercise, reaching higher levels with HD and HH than for N. No
differences in exercise Tr values were detected between HD and HH. The
PSI rose with exercise, but increased more with HD and HH. PSI for HH
was greater than HD by 60 min of SS exercise.
For intermittent exercise (Figure 2), HR was again slightly higher
than N at rest in HD and HH. With exercisesit cycles, HR increased
and declined with exercise and sit, respectively, for all conditions.
During the exercisesit cycles, HR was highest for HD and HH, but not
different between them. Tr was the same for all conditions and did not
change significantly over the 60 min for any condition. PSI increased
with exercise and declined with sitting rest throughout the 60 min.
PSI remained higher during HD and HH, but not different between these
two conditions.
Table 3. Comparison of continuous (SS) and intermittent (INT)
protocols for heart rate, core temperature and physiological strain
index.
Condition
SS
INT
N
HD
HH
N
HD
HH
Heart Rate (b/min):
Rest
663
795
755
685
755
756
Peak
984
1197
1238
968
1149
12010
Core Temperature (C):
Rest
37.10.1
37.20.1
36.90.1
37.10.1
37.30.1
37.00.2
Peak
37.40.1
37.80.1
37.70.1
37.40.1
37.70.1
37.40.3
Physiological Strain Index:
Rest
0
0
0
0
0
0
Peak
2.00.2
3.40.3
3.80.4
1.90.2
2.80.2*
2.90.4*
Values are mean SEM. *p<0.05, compared to corresponding SS climatic
condition.

Figure 1. Responses of heart rate, rectal temperature and
physiological strain index to continuous, steadystate exercise in
three climatic conditions. Values are means SEM. Significance among
climatic conditions is indicated for each time period by letter,
dissimilar letters are significantly different at p<0.05. Same letters
are not different from one another.
Table 3 shows the comparison of resting and peak values for HR, Tr,
and PSI between the two exercise protocols, SS and INT. Resting and
peak HR were similar between the two protocols, as were Tr values. PSI
was less for INT during HD and HH than for SS under the same
conditions.
DISCUSSION
Heat stress is the combination of environmental and physical work
factors that constitute the heat load on an individual while working.
Heat strain is the physiological response to the heat stress that
includes the direct effect of the heat load on the body, as well as
the compensatory thermoregulatory responses to the heat stress. Heat
stress increases the risk of increased frequency of accidents and
therefore the safety of workers. Additionally, the risk of
heatinduced disorders such as heat cramps, heat exhaustion, and heat
stroke increases with additional heat stress. Finally, worker
productivity is lowered by heat stress and the workrest cycles
employed to reduce heat strain (1,2). The goal of any program
developed for working in the heat, especially for those requiring
protective clothing, is to optimize productivity while maximizing
safety and minimizing health risks of individuals. Thus, effective
monitoring of physiological heat strain would permit the determination
of the level of heat strain relative to threshold limit values (TLV)
(1), thereby optimizing the worker's work/rest cycles and minimizing
risk.

Figure 2. Responses of heart rate, rectal temperature and
physiological strain index to intermittent exercise in three climatic
conditions. Values are means SEM. Significance among climatic
conditions is indicated for each time period by letter, dissimilar
letters are significantly different at p different from one another.
It was hypothesized that the combining of HR and Tr within the PSI
would make the PSI applicable to the setting of workrest cycles in
the heat. The results of this study indicate that the PSI was
effective in distinguishing between the normal condition and both
conditions in the heat. Furthermore, the PSI increased and decreased
accordingly with work and rest, respectively. Tr did not reflect these
cycles, but HR did. Therefore, the PSI appropriately indicated heat
strain during both SS and INT protocols.
In the present study, the PSI discriminated between HD and HH
conditions by 60 minutes of SS exercise, confirming previous studies
(9). In contrast, the PSI did not discriminate between these two
conditions during the intermittent exercise protocol. The question is
whether this an accurate depiction of the differences in heat strain
between the two protocols involving these environmental conditions, or
whether the INT protocol reduced the ability of the PSI to distinguish
between these two heat conditions. In evaluating the individual
indicators of heat strain, HR and Tr, there were no differences
indicated between INT and SS protocols with regard to peak values
obtained (Table 3). While, HR was different for these two climatic
conditions during SS, and not during INT. As seen in table 2, the
overall heat strain was greater for the steadystate exercise than for
the intermittent protocol. Therefore, it is likely that the PSI is
appropriately documenting the lesser heat strain of the INT protocol.
Additionally, the difference in heat strain between HD and HH during
INT exercise is small and likely not detected by any of the measures
of heat strain. It is not surprising that INT exercise generates less
heat strain than SS exercise, as heat is permitted to dissipate from
the individual during the rest cycle and there is less heat produced
metabolically.
In conclusion, this study has confirmed the use of the PSI in
representing heat strain during continuous exercise in the heat. The
results also indicate that the PSI appropriately documents heat strain
during intermittent exercise. The ease of calculation and scaling of
the PSI make it attractive as a monitor of heat strain under a variety
of exercise and work conditions.

Address for Correspondence: Robert Gotshall, Ph.D., Professor, Health
and Exercise Science, Colorado State University, Fort Collins, CO
805231582; Phone: (970) 4916374 ; FAX: (970) 4910445 ; email:
[email protected]

REFERENCES
1.
American Conference of Governmental Industrial Hygienists. TLVs
threshold limit values and biological exposure indices for
198586. 9198. 1991. Cincinnati OH, ACGIH.
2.
Belard JL, Stanevich RL. Overview of heat stress among waste
abatement workers. Applied Occup Environ Hygiene
1995;10(11):903907.
3.
Centers for Disease Control and Prevention. Heat related illness
and deaths Missouri, 1998 and United States, 19791986. Morbid
Mortal Weekly Rep 1999;48:469473.
4.
Gardner JW, Amoroso PJ, Grayson JK, Helmkamp J, Jones BH.
Hopitalizations due to injury: Inpatient medical records data.
Milit Med 164,565143. 1999.
5.
Gonzalez RR, McLellan TM, Withey WR, Chang SK, Pandolf KB. Heat
strain models applicable for protective clothing systems:
comparison of core temperature response. J Appl Physiol
1997;83(3):10171032.
6.
Hubac M, Strelka F, Borsky I, Hubacova L. Application of the
relative summary climatic indices during work in heat for
ergonomic purposes. Ergonomics 1989;32(7):733750.
7.
McArdle B, Dunham W, Holling HE, Ladell WSS, Scott JW, Thompson ML
et al. The Prediction of the Physiological Effects of Warm and Hot
Environments: The P4SR Index. R.N.P. 47/391. 1947. London, Medical
Research Council.
8.
Moran DS, Horowitz M, Meiri U, Laor A, Pandolf KB. The
physiological strain index applied to heatstressed rats. J Appl
Physiol 1999;86(3):895901.
9.
Moran DS, Montain SJ, Pandolf KB. Evaluation of different levels
of hydration using a new physiological strain index. Am J Physiol
1998;275:R854R860.
10.
Moran DS, Shapiro Y, Laor A, Izraeli S, Pandolf KB. Can gender
differences during exerciseheat stress be assessed by the
physiological strain index? Am J Physiol 1999;276:R1798R1804.
11.
Moran DS, Shitzer A, Pandolf KB. A physiological strain index to
evaluate heat stress. Am J Physiol 1998;44:R129R134.
12.
Nielsen B, Nielsen M. Body temperature during work. Acta Physiol
Scand 1962;56:120129.
13.
Saltin B, Hermansen L. Esophageal, rectal, and muscle temperature
during exercise. J Appl Physiol 1966;21:17571762.
14.
Sawka MN, Wenger BC, Pandolf KB. Thermoregulatory responses to
acute exercise, heat stress and heat acclimation. In: Handbook of
Physiology, Environmental Physiology. Bethesda MD: Am Physiol Soc,
1995:157185.

More Files

Showing 20 files
Icon
DOCUMENT CONTROL NUMBER APPROVED BY NUMBER OF PAGES CONP0001
document control number approved by number of pages conp0001 5 ems clause 4.3.1 effective date/revision 08/15/201
Icon
EVIDENTIARY MATTERS (OPEN SESSION) PAGE 46039 1 TUESDAY 28
evidentiary matters (open session) page 46039 1 tuesday, 28 january 2014 2 [open session] 3 [the accused entered court] 4 [the
Icon
CHAPTER 1 INTRODUCTION TO CRISIS DISASTER AND RISK MANAGEMENT
chapter 1 introduction to crisis, disaster, and risk management concepts introduction emergency management is most simply defin
Icon
W EEKLY STUDY TIMETABLE YOU DO NOT NEED TO
w eekly study timetable you do not need to study from 8am10pm; decide which hours of the day you can concentrate best and remember to take
Icon
FOFA7 ALIEN IDENTIFICAITON NUMBER (UDLNR)PERSONAL ID FOR OFFICIAL USE
fo/fa7 alien identificaiton number (udl.nr.)/personal id for official use only date received received by (name) a
Icon
5 ASSUMPTION AND AMENDMENT AGREEMENT BETWEEN Ø
5 assumption and amendment agreement between ø (the “mortgagor”) and ø (the “guarantor”) and royal trust c
Icon
SUBJECTGRADE LEVEL OR COURSE UNIT LESSON LESSON
subject/grade level or course unit: # lesson: # lesson synopsis: students investigate the reasons for exploring texas, including the
Icon
RC52 INCREASING THE NUMBER OF NOTIFICATIONS OF FINAL REGULATORY
rc5/2: increasing the number of notifications of final regulatory actions and communication between parties the conference of the parties,
Icon
NATIONAL PHARMACEUTICAL CONTROL BUREAU MINISTRY OF HEALTH MALAYSIA GUIDANCE
national pharmaceutical control bureau ministry of health malaysia guidance document and guidelines for registration of cel
Icon
ADVICE FOR SCHOOLS FOLLOWING THE VIOLENT INCIDENT IN WOOLWICH
advice for schools following the violent incident in woolwich on wednesday 22nd. may 2013 talking about difficult things in re
Icon
MINORITY WOMEN ANDOR EMERGING SMALL BUSINESS (MWESB) ENGAGEMENT
minority, women and/or emerging small business (mwesb) engagement descri
Icon
BỘ CÔNG THƯƠNG CỤC PHÒNG VỆ THƯƠNG MẠI 
bộ công thương cục phòng vệ thương mại  bản lưu hành hạn chế  bản lưu hành công khai (điền vào ô thích hợp) bản câu hỏi
Icon
C ONSULTANT PROVIDER ENROLLMENT PACKET COMPLETE PACKETS
c onsultant provider enrollment packet complete packets must be submitted to odds b
Icon
CAPÍTULO 15 APARTADO 1537 PÁGINA 550551 TEMPLATE CLASS T
capítulo 15, apartado 15.3.7 página 550551 template class t min (t a, t b) { if (a b) return a; else return b; }
Icon
FOOD SERVICE ORDER FORM PO BOX 3000 THE PAS
food service order form po box 3000, the pas, mb r9a 1m7 cafeteria – tel: 2046278643 fax: 20462
Icon
LAST EDITED SEPT 12 2012 SOMALIA CAP 2012 –CLUSTER
last edited sept 12, 2012 somalia cap 2012 –cluster response plan template somalia cap 2012: cluster response plan template ►guidance
Icon
LAW OF THE REPUBLIC OF UZBEKISTAN ON PROTECTED NATURAL
law of the republic of uzbekistan on protected natural territories 2004 section ii. general provisions (articles 110) section i
Icon
PAGE | 295 CHAPTER 41 THE ROLE OF SIMULATED
page | 295 chapter 41: the role of simulated immersion in exhibitions stephen bitgood technical report no. 9020. (1990) jackson
Icon
R ESERVATION FORM FROM WORLDWIDE SYMPOSIUM ON GEOGRAPHICAL INDICATIONS
r eservation form from: worldwide symposium on geographical indications 1012 june, 2009, sofia, bulgaria room rate: standard r
Icon
NEWSLETTER ISSUE 5 CONTENTS WHAT LIES BENEATH? MORE FOOD
newsletter issue 5 contents what lies beneath? more food for the journey the story so far… autumn 2010 | edinburg