Thermoregulatory responses during competitive marathon running MICHAEL B. MARON, Institute of Environmental

JEAMES Stress,

A. WAGNER, AND S. M. HORVATH University of California, Santa Barbara,

MARON, MICHAEL B., JEAMES, A. WAGNER, AND S. M. HORVATH. Thermoregulatory responses during competitive marathon running. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 42(6): 909-914. 1977. -To assess thermoregulatory responses occurring under actual marathon racing conditions, rectal (T,,) and five skin temperatures were measured in two runners approximately every 9 min of a competititive marathon run under cool conditions. Race times and total water losses were: runner 1 = 162.7 min, 3.02 kg; runner 2 = 164.6 min, 2.43 kg. Mean skin temperature was similar throughout the race in the two runners, although they exhibited a marked disparity in temperature at individual skin sites. T,, plateaued< after 35-45 min (runner 1 = 40.0-40.1, runner 2 = 38.9-39.2”C). While runner 2 maintained a relatively constant level for the remainder of the race, runner 1 exhibited a secondary increase in T,,. Between 113 and 119 min there was a precipitous rise in Tre from 40.9 to 41.9”C. Partitional calorimetric calculations suggested that a decrease in sweating was responsible for this increment. However, runner l’s ability to maintain his high T,, and running pace for the remaining 44 min of the race and exhibit no signs of heat illness indicated thermoregulation was intact. temperature regulation; long-term work

rectal

temperature;

energy balance;

IN 1903, BLAKE AND LARRABEE (3) published the results of a comprehensive 3-yr study conducted at the Boston Marathon, documenting for the first time the elevation in rectal temperature (T,.,) that occurs during marathon racing. Several temperatures in excess of 40°C in runners finishing in good physical condition were recorded despite the races having been run under relatively cool ambient conditions. Their original observations have since been confirmed many times (4,5,12,13,20,22,24); however, it is not clear whether such high internal temperatures have been maintained throughout the race, as there appear to be no actual interrace measurements. Consequently, in order to provide more information concerning thermoregulation during a marathon race, rectal and skin temperatures, as well as water balance, were monitored in two highly trained runners under competitive conditions.

METHODS

Two highly trained male marathon runners participated in the studyl; selected physical and physiological l The nature and purpose of the ‘study and the risks involved explained verbally and given on a written form to each subject

were prior

California

93106

characteristics are presented in Table 1. During the marathon both runners wore nylon running shorts, a ventilated nylon jersey, and running shoes. Rectal temperature was measured by means of an indwelling vinyl-coated rectal thermistor inserted 9.5 cm into the rectum. Skin temperatures were obtained with a thermistor mounted on a wooden spring-loaded plunger (to ensure adequate skin contact) attached in a ventilated Plexiglas wand. All probes were calibrated several times prior to the race and rechecked after. Prior to the marathon, both runners were given sufficient practice using both probes and executing the following protocol. Approximately every 9 min of the race, the investigators pulled alongside in an automobile and matched speed with the runner. The runner’s rectal probe was connected to a telethermometer unit and a reading was obtained after the runner had checked the position of the probe. Immediately after, he was handed the skin temperature wand and was asked to place the thermistor on the skin in the following order: thigh (upper anterior surface), finger (index finger pad), chest (sternum, level of third rib), forehead, and upper arm (lateral surface). Arm and thigh temperatures were taken at pivot points (slightly below the shoulder and pelvic joints) because the runners’ limb movements during their running precluded adequate thermistor contact with the skin farther down the limb. In the case of the thigh, the runners’ shorts were pinned up to ensure this area was exposed to the environment. During each temperature measurement, dry- and wet-bulb temperatures (Tdb and T,,) were also taken. Additional temperature measurements as well as weights were obtained before and after the race. During the marathon, the runners’ intermediate times were recorded at s-mile intervals and fluid intake was monitored as previously described (13). Water stops were initially placed approximately every 3 miles (corresponding to those placed on the course by the marathon committee) but fluid was made available at more frequent intervals if the runners desired. Both runners consumed a commercially available drink, diluted in half for reasons of taste (8.5 meq/l Na+, 4.0 meqll K+, 8.4 meq/l Cl-, and 2.2 g/100 ml glucose) during the race. In order to provide axdescription of the runners’ ther__~-~__ --to his voluntary consent to participate. The protocol and procedures for this study have been approved by the Committee on Activities Involving Human Subjects, of the University of California, Santa Barbara.

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (130.212.018.096) on August 1, 2018. Copyright © 1977 American Physiological Society. All rights reserved.

MARON,

910 TABLE 1. Selected physical and physiological characteris tics

% max* sg-2 -

Age, yr

Ht,

cm

Wt, kg BSA,

m2

lemin-’

m~~$~’

Best Marathon Time, h:min:s

Distance RudWk, km

WAGNER,

where el and l 2, the emissivities of the subject and environment, were taken as unity; &/A,, the effective radiative area, was considered to be 0.9 body surface area (BSA) (18); and Tdb was used as an approximation of T,,. Storage was calculated from S = (0.1 A Tsk + 0.9 ATre) (0.83) (m&A,) (At), where m was the average of the runner’s pre- and postrace weights; 0.83, the heat capacity of the body in kcal kg-l “C-l; and At, the duration of the observation period in hours. Heat transfer to the ingested fluid was calculated as 1 kcal kg+ OC-l difference between the fluid temperature (assumed to be ambient) and the runner’s Tre at the nearest point of intake. l

ma1 balance during the marathon, the following form of the energy balance equation was utilized M - E, - E,

AND HORVATH

l

l

l

- C, - C,, - R - S - F1 - w = 0

where M is the metabolic free energy production, E, and E,, are evaporative heat losses from the skin and respiratory tract respectively, C, and C,, are convective heat losses from these areas, R is the radiant heat loss, S is the quantity of heat stored, Fl is the heat transferred to the ingested fluid, and W is the external work performed. All values were expressed in kcal -mm2 h-l with calculations being made for both interrace heat transfer rates and the runners’ total race energy balance. In the former case, external work (W) was ignored with the assumption it remained constant throughout the race. For the latter case, W was assigned the value of O.lM (20). M was calculated from 00, measurements obtained on these same two runners during the previous year’s Santa Barbara Marathon (14). An estimate of the metabolic wt loss (calculated from the RQ and the densities of CO, and 02) was then used to calculate total evaporative heat loss (E) by the relation: E = (wt loss + fluid intake - metabolic wt loss) (0.586)/AD, where 0.586 is the heat of vaporization of water in kcal eg-l. E’s during the race were calculated by difference, utilizing the energy balance equation. E,, was estimated by the equation E,, = 0.0023M (44 - P,), (where Pi = partial pressure of water vapor in inspired air) as derived by Fanger (8) and recently validated for workloads of up to 80% x70, rnaxby Mitchell et al. (16). E, was then taken as the difference between E and E,,. C,, was estimated (8) from C,, = 0.0014M (34 - Tdb), while C, was calculated from the formula of Mitchell et al. (15) [C = 6.23 (P,/760)“.5g4 (v)O.“~~(Ts, - T&j. Since it was a calm day, v (the air velocity in m/min) was considered to be equal to the runners’ speed (as calculated from their &mile cumulative times) plus an additional 150 fi/min (0.762 m/min). The latter figure represents the increase in effective wind velocity due to limb movement as observed by Nelson et al. (18) in men walking at 3 mph. This figure was used as an approximation, since there appear to be no comparable data for men running at marathon pace. The five skin temperatures were given the following surface area weightings in calculating Tsk l

0.35 thigh + 0.05 finger + 0.38 chest + 0.05 forehead + 0.17 arm R was calculated from the Stefan-Boltzmann

equation

R = 4.88 x lo+ el e2

Thermoregulatory responses during competitive marathon running.

Thermoregulatory responses during competitive marathon running MICHAEL B. MARON, Institute of Environmental JEAMES Stress, A. WAGNER, AND S. M. HORV...
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