Superior performance of African runners in warm humid but not in cool environmental conditions

2004 ◽  
Vol 96 (1) ◽  
pp. 124-130 ◽  
Author(s):  
Frank E. Marino ◽  
Mike I. Lambert ◽  
Timothy D. Noakes
Keyword(s):  
Relative Humidity ◽  
Heat Production ◽  
Environmental Conditions ◽  
Heat Storage ◽  
Treadmill Running ◽  
Superior Performance ◽  
Running Speed ◽  
Cool Condition ◽  
Thermoregulatory Responses ◽  
Cool Conditions

The purpose of this study was to examine the running performances and associated thermoregulatory responses of African and Caucasian runners in cool and warm conditions. On two separate occasions, 12 ( n = 6 African, n = 6 Caucasian) well-trained men ran on a motorized treadmill at 70% of peak treadmill running velocity for 30 min followed by an 8-km self-paced performance run (PR) in cool (15°C) or warm (35°C) humid (60% relative humidity) conditions. Time to complete the PR in the cool condition was not different between groups (∼27 min) but was significantly longer in warm conditions for Caucasian (33.0 ± 1.6 min) vs. African (29.7 ± 2.3 min, P < 0.01) runners. Rectal temperatures were not different between groups but were higher during warm compared with cool conditions. During the 8-km PR, sweat rates for Africans (25.3 ± 2.3 ml/min) were lower compared with Caucasians (32.2 ± 4.1 ml/min; P < 0.01). Relative rates of heat production were less for Africans than Caucasians in the heat. The finding that African runners ran faster only in the heat despite similar thermoregulatory responses as Caucasian runners suggests that the larger Caucasians reduce their running speed to ensure an optimal rate of heat storage without developing dangerous hyperthermia. According to this model, the superior running performance in the heat of these African runners can be partly attributed to their smaller size and hence their capacity to run faster in the heat while storing heat at the same rate as heavier Caucasian runners.

Exercise and Heat Stress: Inflammation and the Iron Regulatory Response

2021 ◽  
pp. 1-6
Author(s):  
Alannah K.A. McKay ◽  
Rachel McCormick ◽  
Nicolin Tee ◽  
Peter Peeling
Keyword(s):  
Heart Rate ◽  
Heat Stress ◽  
Venous Blood ◽  
Treadmill Running ◽  
Maximum Heart Rate ◽  
Physiological Strain ◽  
Running Speed ◽  
Hot Environments ◽  
The Impact ◽  
Cool Conditions

This study determined the impact of heat stress on postexercise inflammation and hepcidin levels. Twelve moderately trained males completed three, 60-min treadmill running sessions under different conditions: (a) COOL, 18 °C with speed maintained at 80% maximum heart rate; (b) HOTHR, 35 °C with speed maintained at 80% maximum heart rate; and (c) HOTPACE, 35 °C completed at the average running speed from the COOL trial. Venous blood samples were collected pre-, post-, and 3-hr postexercise and analyzed for serum ferritin, interleukin-6 (IL-6), and hepcidin concentrations. Average HR was highest during HOTPACE compared with HOTHR and COOL (p < .001). Running speed was slowest in HOTHR compared with COOL and HOTPACE (p < .001). The postexercise increase in IL-6 was greatest during HOTPACE (295%; p = .003). No differences in the IL-6 response immediately postexercise between COOL (115%) and HOTHR (116%) were evident (p = .992). No differences in hepcidin concentrations between the three trials were evident at 3 hr postexercise (p = .407). Findings from this study suggest the IL-6 response to exercise is greatest in hot compared with cool conditions when the absolute running speed was matched. No differences in IL-6 between hot and cool conditions were evident when HR was matched, suggesting the increased physiological strain induced from training at higher intensities in hot environments, rather than the heat per se, is likely responsible for this elevated response. Environmental temperature had no impact on hepcidin levels, indicating that exercising in hot conditions is unlikely to further impact transient alterations in iron regulation, beyond that expected in temperate conditions.

scholarly journals Running economy, not aerobic fitness, independently alters thermoregulatory responses during treadmill running

2014 ◽  
Vol 117 (12) ◽  
pp. 1451-1459 ◽  
Author(s):  
Jovana Smoljanić ◽  
Nathan B. Morris ◽  
Sheila Dervis ◽  
Ollie Jay
Keyword(s):  
Aerobic Fitness ◽  
Heat Balance ◽  
Physical Characteristics ◽  
Running Economy ◽  
Treadmill Running ◽  
Whole Body ◽  
Maximum Oxygen Consumption ◽  
Running Speed ◽  
Metabolic Heat ◽  
Thermoregulatory Responses

We sought to determine the independent influence of running economy (RE) and aerobic fitness [maximum oxygen consumption (V̇o2max)] on thermoregulatory responses during treadmill running by conducting two studies. In study 1, seven high (HI-FIT: 61 ± 5 ml O2·kg−1·min−1) and seven low (LO-FIT: 45 ± 4 ml O2·kg−1·min−1) V̇o2max males matched for physical characteristics and RE (HI-FIT: 200 ± 21; LO-FIT: 200 ± 18 ml O2·kg−1·km−1) ran for 60 min at 1) 60%V̇o2max and 2) a fixed metabolic heat production (Hprod) of 640 W. In study 2, seven high (HI-ECO: 189 ± 15.3 ml O2·kg−1·km−1) and seven low (LO-ECO: 222 ± 10 ml O2·kg−1·km−1) RE males matched for physical characteristics and V̇o2max (HI-ECO: 60 ± 3; LO-ECO: 61 ± 7 ml O2·kg−1·min−1) ran for 60 min at a fixed 1) speed of 10.5 km/h and 2) Hprod of 640 W. Environmental conditions were 25.4 ± 0.8°C, 37 ± 12% RH. In study 1, at Hprod of 640 W, similar changes in esophageal temperature (ΔTes; HI-FIT: 0.63 ± 0.20; LO-FIT: 0.63 ± 0.22°C; P = 0.986) and whole body sweat losses (WBSL; HI-FIT: 498 ± 66; LO-FIT: 497 ± 149 g; P = 0.984) occurred despite different relative intensities (HI-FIT: 55 ± 6; LO-FIT: 39 ± 2% V̇o2max; P < 0.001). At 60% V̇o2max, ΔTes ( P = 0.029) and WBSL ( P = 0.003) were greater in HI-FIT (1.14 ± 0.32°C; 858 ± 130 g) compared with LO-FIT (0.73 ± 0.34°C; 609 ± 123 g), as was Hprod (HI-FIT: 12.6 ± 0.9; LO-FIT: 9.4 ± 1.0 W/kg; P < 0.001) and the evaporative heat balance requirement (Ereq; HI-FIT: 691 ± 74; LO-FIT: 523 ± 65 W; P < 0.001). Similar sweating onset ΔTes and thermosensitivities occurred between V̇o2max groups. In study 2, at 10.5 km/h, ΔTes (1.16 ± 0.31 vs. 0.78 ± 0.28°C; P = 0.017) and WBSL (835 ± 73 vs. 667 ± 139 g; P = 0.015) were greater in LO-ECO, as was Hprod (13.5 ± 0.6 vs. 11.3 ± 0.8 W/kg; P < 0.001) and Ereq (741 ± 89 vs. 532 ± 130 W; P = 0.007). At Hprod of 640 W, ΔTes ( P = 0.910) and WBSL ( P = 0.710) were similar between HI-ECO (0.55 ± 0.31°C; 501 ± 88 g) and LO-ECO (0.57 ± 0.16°C; 483 ± 88 g), but running speed was different (HI-ECO: 8.2 ± 0.6; LO-ECO: 7.2 ± 0.4 km/h; P = 0.025). In conclusion, thermoregulatory responses during treadmill running are not altered by V̇o2max, but by RE because of differences in Hprod and Ereq.

Inorganic salt hydrates and zeolites composites studies for thermochemical heat storage

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ata Ur Rehman ◽  
Muhammad Zahir Shah ◽  
Shehla Rasheed ◽  
Wasim Afzal ◽  
Muhammad Arsalan ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Water Sorption ◽  
Inorganic Salt ◽  
Heat Storage ◽  
Water Molecules ◽  
Thermochemical Heat Storage ◽  
Dehydration Enthalpy ◽  
Salt Hydrates ◽  
Heat Storage Materials ◽  
Pure Salt

Abstract Salt hydrates (MgSO4 and ZnSO4) impregnated in zeolites, offer a variety of improvements, mostly providing a large surface area for salt hydrates and water molecules. A composite of 5 and 10% of salt contents were prepared as heat storage materials. The study’s finding showed that dehydration enthalpy of MgSO4 (1817 J g−1) and ZnSO4 (1586 J g−1) were 10 and 15% improved than pure salt hydrates by making composites. During the hydration process of composites, the water sorption is 30–37% improved and further the increasing of salt contents in composites enhances more 10% increase in the water resorption. The cyclicability of MgSO4/zeolite and ZnSO4/zeolite were 45 and 51% improved than their corresponding pure salt hydrates. The effect of humidity on the water sorption result reveals that composites of MgSO4/zeolite and ZnSO4/zeolite at 75% relative humidity (RH), the mass of water are 51 and 40% increase than 55% RH.

Thermoregulatory responses during competitive marathon running

1977 ◽  
Vol 42 (6) ◽  
pp. 909-914 ◽  
Author(s):  
M. B. Maron ◽  
J. A. Wagner ◽  
S. M. Horvath
Keyword(s):  
Skin Temperature ◽  
Marathon Running ◽  
Heat Illness ◽  
Mean Skin Temperature ◽  
Total Water ◽  
Water Losses ◽  
Thermoregulatory Responses ◽  
Marked Disparity ◽  
Skin Temperatures ◽  
Cool Conditions

To assess thermoregulatory responses occuring under actual marathon racing conditions, rectal (Tre) and five skin temperatures were measured in two runners approximately every 9 min of a competitive 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. Tre plateaued after 35--45 min (runner 1 = 40.0--40.1, runner 2 = 38.9--39.2 degrees C). While runner 2 maintained a relatively constant level for the remainder of the race, runner 1 exhibited a secondary increase in Tre. Between 113 and 119 min there was a precipitous rise in Tre from 40.9 to 41.9 degrees C. Partitional calorimetric calculations suggested that a decrease in sweating was responsible for this increment. However, runner 1's ability to maintain his high Tre and running pace for the remaining 44 min of the race and exhibit no signs of heat illness indicated thermoregulation was intact.

An Experimental Investigation of the Effects of the Environmental Conditions and the Channel Depth for an Air-Breathing Polymer Electrolyte Membrane Fuel Cell

2008 ◽  
Vol 5 (4) ◽  
Author(s):  
Yong Hun Park ◽  
Jerald A. Caton
Keyword(s):  
Fuel Cell ◽  
Relative Humidity ◽  
Flow Field ◽  
Current Density ◽  
Environmental Conditions ◽  
Polymer Electrolyte Membrane ◽  
Channel Depth ◽  
Air Breathing ◽  
Fuel Cell Performance ◽  
Electrolyte Membrane

The effects of the environmental conditions and the channel depth for an air-breathing polymer electrolyte membrane fuel cell were investigated experimentally. The fuel cell used in this work included a membrane and electrode assembly, which possessed an active area of 25 cm2 with Nafion® 117 membrane. Triple serpentine designs for the flow fields with two different flow depths were used in this research. The experimental results indicated that the relative humidity and temperature play an important role with respect to fuel cell performance. The fuel cell needs to be operated at least 20 min to obtain stable performance. When the shallow flow field was used, the performance increased dramatically for low humidity and slightly for high humidity. The current density was obtained around only 120 mA/cm2 at 30°C with an 80% relative humidity, which was nearly double the performance for the deep flow field. The minimum operating temperature for an air-breathing fuel cell would be 20°C. When it was 10°C at 60% relative humidity, the open circuit voltage dropped to around 0.65 V. The fuel cell performance improved with increasing relative humidity from 80% to 100% at high current density.

EFFECT OF PRE-FREEZING HAMS ON QUALITY ATTRIBUTES OF DRY-CURED PRODUCT

1972 ◽  
Vol 35 (2) ◽  
pp. 98-101 ◽  
Author(s):  
P. P. Graham ◽  
T. N. Blumer
Keyword(s):  
Weight Loss ◽  
Relative Humidity ◽  
Environmental Conditions ◽  
Water Loss ◽  
Moisture Loss ◽  
Internal Tissue ◽  
Surface Ph ◽  
Aging Period ◽  
Acceptable Quality ◽  
Fresh State

Hams were frozen, stored, and thawed before dry-curing to study the profiles of quality as related to environmental conditions. Quality appraisals and sampling were done after thawing, after curing, and after 30 days aging in an atmosphere where temperature and relative humidity were controlled at about 34.5 C and 62.5%, respectively. The pH, water, NaCl, and fat contents were determined. Surface pH of hams increased from the thawed fresh state to the unstored cured state, but decreased generally after the aging period (stored cured ham). The pH was higher on the surface than that of corresponding internal areas. The pH of the internal tissue was lower for thawed product than cured or aged product. The average percent water decreased during curing and aging periods. Water loss after curing and after aging in the prefrozen hams was greater than that reported for unfrozen hams. The quantity of water, NaCl, and fat varied among the several muscle areas and reasons for variation are discussed. All hams were of acceptable quality at each appraisal period. Decreasing moisture levels of hams were reflected by decreases in conformation scores throughout the processing periods. Increased firmness was accompanied by weight loss, moisture loss, and increased NaCl percentage.

scholarly journals Isolated individuals and groups show opposite preferences toward humidity

2018 ◽  
Author(s):  
Mariano Calvo Martín ◽  
Stamatios C. Nicolis ◽  
Isaac Planas-Sitjà ◽  
Jean-Christophe de Biseau ◽  
Jean-Louis Deneubourg
Keyword(s):  
Relative Humidity ◽  
Environmental Conditions ◽  
Group Level ◽  
Individual Level ◽  
Negative Effect ◽  
Multi Level ◽  
The Individual ◽  
Shed Light ◽  
Selection Of

AbstractCockroaches, like most social arthropods, are led to choose collectively among different alternative resting places. These decisions are modulated by different factors, such as environmental conditions (temperature, relative humidity) and sociality (groups size, nature of communications). The aim of this study is to establish the interplay between environmental conditions and the modulation of the interactions between individuals within a group leading to an inversion of preferences. We show that the preferences of isolated cockroaches and groups of 16 individuals, on the selection of the relative humidity of a shelter are inversed and shed light on the mechanisms involved. We suggest that the relative humidity has a multi-level influence on cockroaches, manifested as an attractant effect at the individual level and as a negative effect at the group level, modulating the interactions.

scholarly journals Development of gypsy moth (Lymantria dispar L) on the foliage of Quercus cerris L., Q. Petraea (matt) Liebl. and Q. Robur L. in the controlled conditions

2007 ◽  
pp. 55-67 ◽  
Author(s):  
Slobodan Milanovic
Keyword(s):  
Relative Humidity ◽  
Host Plant ◽  
Gypsy Moth ◽  
Lymantria Dispar ◽  
Environmental Conditions ◽  
Quercus Robur ◽  
Quercus Petraea ◽  
The Other ◽  
Study Results ◽  
Quercus Cerris

The development of Gypsy moth (Lymantria dispar L) was monitored in laboratory conditions, on the foliage of the species Quercus cerris L. Quercus petraea (Matt) Liebl. and Quercus robur L. The experiment was established in the controlled environmental conditions, at the temperature of 25?C, photoperiod 14:10 (day: night) and relative humidity 70%. The objective of the research was to determine the suitability of the study host plant species for gypsy moth development. The study results show that Gypsy moth caterpillars cultivated on Q. petraea foliage had a lower survival, higher number of moultings, longer preadult development and lower fecundity, which makes this species less suitable compared to the other two. Gypsy moth caterpillars cultivated on Q. cerris foliage had the highest survival degree the lowest number of moultings, the shortest preadult development and the highest fecundity, which makes this species the most favourable for gypsy moth development. Q. robur was between the former two species in this respect.

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