The Physiological Strain Index Modified for Trained Heat-Acclimatized Individuals in Outdoor Heat

in International Journal of Sports Physiology and Performance
Restricted access

Purchase article

USD  $24.95

Student 1 year subscription

USD  $107.00

1 year subscription

USD  $142.00

Student 2 year subscription

USD  $203.00

2 year subscription

USD  $265.00

Purpose: To determine if the Physiological Strain Index (PSI), in original or modified form, can evaluate heat strain on a 0–10 scale, in trained and heat-acclimatized men undertaking a competitive half-marathon run in outdoor heat. Methods: Core (intestinal) temperature (TC) and heart rate (HR) were recorded continuously in 24 men (mean [SD] age = 26 [3] y, VO2peak = 59 [5] mL·kg·min−1). A total of 4 versions of the PSI were computed: original PSI with upper constraints of TC 39.5°C and HR 180 beats·min−1 (PSI39.5/180) and 3 modified versions of PSI with each having an age-predicted maximal HR constraint and graded TC constraints of 40.0°C (PSI40.0/PHRmax), 40.5°C (PSI40.5/PHRmax), and 41.0°C (PSI41.0/PHRmax). Results: In a warm (26.1–27.3°C) and humid (79–82%) environment, all runners finished the race asymptomatic in 107 (10) (91–137) min. Peak TC and HR were 39.7°C (0.5°C) (38.5–40.7°C) and 186 (6) (175–196) beats·min−1, respectively. In total, 63% exceeded TC 39.5°C, 71% exceeded HR 180 beats·min−1, and 50% exceeded both of the original PSI upper TC and HR constraints. The computed heat strain was significantly greater with PSI39.5/180 than all other methods (P < .003). PSI >10 was observed in 63% of runners with PSI39.5/180, 25% for PSI40.0/PHRmax, 8% for PSI40.5/PHRmax, and 0% for PSI41.0/PHRmax. Conclusions: The PSI was able to quantify heat strain on a 0–10 scale in trained and heat-acclimatized men undertaking a half-marathon race in outdoor heat, but only when the upper TC and HR constraints were modified to 41.0°C and age-predicted maximal HR, respectively.

Byrne is with the Faculty of Health and Human Sciences, Peninsula Allied Health Centre, School of Health Professions, University of Plymouth, Plymouth, United Kingdom. Lee is with Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Republic of Singapore.

Byrne (chris.byrne@plymouth.ac.uk) is corresponding author.
  • 1.

    Sawka MN, Leon LR, Montain SJ, Sonna LA. Integrated physiological mechanisms of exercise performance, adaptation, and maladaptation to heat stress. Compr Physiol. 2011;1(4):1883–1928. PubMed ID: 23733692

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2.

    Moran DS, Shitzer A, Pandolf KB. A physiological strain index to evaluate heat stress. Am J Physiol. 1998;275(1, pt 2):129–134. PubMed ID: 9688970

    • Search Google Scholar
    • Export Citation
  • 3.

    Moran DS. Stress evaluation by the physiological strain index (PSI). J Basic Clin Physiol Pharmacol. 2000;11(4):403–423. PubMed ID: 11248950 doi:10.1515/JBCPP.2000.11.4.403

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4.

    Moran DS, Kenney WL, Pierzga JM, Pandolf KB. Aging and assessment of physiological strain during exercise-heat stress. Am J Physiol Regul Integr Comp Physiol. 2002;282(4):R1063–R1069. PubMed ID: 11893610 doi:10.1152/ajpregu.00364.2001

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5.

    Moran DS, Montain SJ, Pandolf KB. Evaluation of different levels of hydration using a new physiological strain index. Am J Physiol. 1998;275(3, pt 2):R854–R860. PubMed ID: 9728084

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6.

    Byrne C, Lee JK, Chew SA, Lim CL, Tan EY. Continuous thermoregulatory responses to mass-participation distance running in heat. Med Sci Sports Exerc. 2006;38(5):803–810. PubMed ID: 16672830 doi:10.1249/01.mss.0000218134.74238.6a

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7.

    Ely BR, Ely MR, Cheuvront SN, Kenefick RW, Degroot DW, Montain SJ. Evidence against a 40 degrees C core temperature threshold for fatigue in humans. J Appl Physiol. 2009;107(5):1519–1525. doi:10.1152/japplphysiol.00577.2009

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8.

    Mohr M, Nybo L, Grantham J, Racinais S. Physiological responses and physical performance during football in the heat. PLoS ONE. 2012;7(6):e39202. PubMed ID: 22723963 doi:10.1371/journal.pone.0039202

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9.

    Racinais S, Periard JD, Karlsen A, Nybo L. Effect of heat and heat acclimatization on cycling time trial performance and pacing. Med Sci Sports Exerc. 2015;47(3):601–606. PubMed ID: 24977692 doi:10.1249/MSS.0000000000000428

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 10.

    Lucia A, Hoyos J, Santalla A, Earnest C, Chicharro JL. Tour de France versus Vuelta a Espana: which is harder? Med Sci Sports Exerc. 2003;35(5):872–878. PubMed ID: 12750600

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11.

    Veltmeijer MT, Eijsvogels TM, Thijssen DH, Hopman MT. Incidence and predictors of exertional hyperthermia after a 15-km road race in cool environmental conditions. J Sci Med Sport. 2015;18(3):333–337. PubMed ID: 24930073 doi:10.1016/j.jsams.2014.04.007

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12.

    DeMartini JK, Martschinske JL, Casa DJ, et al. Physical demands of National Collegiate Athletic Association Division I football players during preseason training in the heat. J Strength Cond Res. 2011;25(11):2935–2943. PubMed ID: 21904245 doi:10.1519/JSC.0b013e318231a643

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13.

    Aughey RJ, Goodman CA, McKenna MJ. Greater chance of high core temperatures with modified pacing strategy during team sport in the heat. J Sci Med Sport. 2014;17(1):113–118. PubMed ID: 23689104 doi:10.1016/j.jsams.2013.02.013

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14.

    Periard JD, Racinais S, Knez WL, Herrera CP, Christian RJ, Girard O. Thermal, physiological and perceptual strain mediate alterations in match-play tennis under heat stress. Br J Sports Med. 2014;48(suppl 1):i32–i38.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 15.

    Jay O, Bain AR, Deren TM, Sacheli M, Cramer MN. Large differences in peak oxygen uptake do not independently alter changes in core temperature and sweating during exercise. Am J Physiol Regul Integr Comp Physiol. 2011;301(3):R832–R841. PubMed ID: 21697517 doi:10.1152/ajpregu.00257.2011

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16.

    Cramer MN, Jay O. Explained variance in the thermoregulatory responses to exercise: the independent roles of biophysical and fitness/fatness-related factors. J Appl Physiol.2015;119(9):982–989. doi:10.1152/japplphysiol.00281.2015

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17.

    Selkirk GA, McLellan TM. Influence of aerobic fitness and body fatness on tolerance to uncompensable heat stress. J Appl Physiol. 2001;91(5):2055–2063. doi:10.1152/jappl.2001.91.5.2055

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18.

    Selkirk GA, McLellan TM, Wright HE, Rhind SG. Mild endotoxemia, NF-kappaB translocation, and cytokine increase during exertional heat stress in trained and untrained individuals. Am J Physiol Regul Integr Comp Physiol. 2008;295(2):R611–R623. PubMed ID: 18565834 doi:10.1152/ajpregu.00917.2007

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 19.

    Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. J Am Coll Cardiol. 2001;37(1):153–156. PubMed ID: 11153730 doi:10.1016/S0735-1097(00)01054-8

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20.

    Nes BM, Janszky I, Wisloff U, Stoylen A, Karlsen T. Age-predicted maximal heart rate in healthy subjects: the HUNT fitness study. Scand J Med Sci Sports. 2013;23(6):697–704. PubMed ID: 22376273 doi:10.1111/j.1600-0838.2012.01445.x

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 21.

    Esteve-Lanao J, Lucia A, deKoning JJ, Foster C. How do humans control physiological strain during strenuous endurance exercise? PLoS ONE. 2008;3(8):e2943. PubMed ID: 18698405 doi:10.1371/journal.pone.0002943

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 22.

    Hornery DJ, Farrow D, Mujika I, Young W. An integrated physiological and performance profile of professional tennis. Br J Sports Med. 2007;41(8):531–536; discussion 536. PubMed ID: 17472999 doi:10.1136/bjsm.2006.031351

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 23.

    Wingo JE, Ganio MS, Cureton KJ. Cardiovascular drift during heat stress: implications for exercise prescription. Exerc Sport Sci Rev. 2012;40(2):88–94. PubMed ID: 22410803 doi:10.1097/JES.0b013e31824c43af

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 24.

    Tikuisis P, McLellan TM, Selkirk G. Perceptual versus physiological heat strain during exercise-heat stress. Med Sci Sports Exerc. 2002;34(9):1454–1461. PubMed ID: 12218738 doi:10.1097/00005768-200209000-00009

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 25.

    Lee JK, Nio AQ, Lim CL, Teo EY, Byrne C. Thermoregulation, pacing and fluid balance during mass participation distance running in a warm and humid environment. Eur J Appl Physiol. 2010;109(5):887–898. PubMed ID: 20237797 doi:10.1007/s00421-010-1405-y

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 26.

    Byrne C, Lim CL. The ingestible telemetric body core temperature sensor: a review of validity and exercise applications. Br J Sports Med. 2007;41(3):126–133. PubMed ID: 17178778 doi:10.1136/bjsm.2006.026344

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 27.

    Brotherhood JR. Heat stress—a challenge for sports science in Australia. J Sci Med Sport. 2008;11(1):1–2. PubMed ID: 18078785 doi:10.1016/j.jsams.2007.10.014

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 28.

    Achten J, Jeukendrup AE. Heart rate monitoring: applications and limitations. Sports Med. 2003;33(7):517–538. PubMed ID: 12762827 doi:10.2165/00007256-200333070-00004

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 29.

    Schlader ZJ, Raman A, Morton RH, Stannard SR, Mundel T. Exercise modality modulates body temperature regulation during exercise in uncompensable heat stress. Eur J Appl Physiol. 2011;111(5):757–766. PubMed ID: 20978782 doi:10.1007/s00421-010-1692-3

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 30.

    Selley EA, Kolbe T, Van Zyl CG, Noakes TD, Lambert MI. Running intensity as determined by heart rate is the same in fast and slow runners in both the 10- and 21-km races. J Sports Sci. 1995;13(5):405–410. PubMed ID: 8558627 doi:10.1080/02640419508732256

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 31.

    Robinson S. Temperature regulation in exercise. Pediatrics. 1963;32(suppl):691–702.

  • 32.

    Pugh LG, Corbett JL, Johnson RH. Rectal temperatures, weight losses, and sweat rates in marathon running. J Appl Physiol. 1967;23(3):347–352. PubMed ID: 6047956 doi:10.1152/jappl.1967.23.3.347

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 33.

    Wyndham CH, Strydom NB. The danger of an inadequate water intake during marathon running. S Afr Med J. 1969;43(29):893–896. PubMed ID: 5821601

  • 34.

    Maron MB, Wagner JA, Horvath SM. Thermoregulatory responses during competitive marathon running. J Appl Physiol. 1977;42(6):909–914. PubMed ID: 881391 doi:10.1152/jappl.1977.42.6.909

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 35.

    Maughan RJ, Leiper JB, Thompson J. Rectal temperature after marathon running. Br J Sports Med. 1985;19(4):192–195. PubMed ID: 4092138 doi:10.1136/bjsm.19.4.192

  • 36.

    Noakes TD, Myburgh KH, du Plessis J, et al. Metabolic rate, not percent dehydration, predicts rectal temperature in marathon runners. Med Sci Sports Exerc. 1991;23(4):443–449. PubMed ID: 2056902 doi:10.1249/00005768-199104000-00009

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 37.

    Armstrong LE, Pumerantz AC, Fiala KA, et al. Human hydration indices: acute and longitudinal reference values. Int J Sport Nutr Exerc Metab. 2010;20(2):145–153. PubMed ID: 20479488 doi:10.1123/ijsnem.20.2.145

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 38.

    Cheuvront SN, Kenefick RW, Montain SJ, Sawka MN. Mechanisms of aerobic performance impairment with heat stress and dehydration. J Appl Physiol. 2010;109(6):1989–1995. doi:10.1152/japplphysiol.00367.2010

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 242 242 16
Full Text Views 35 35 2
PDF Downloads 10 10 2