Marginal Effects of a Large Caffeine Dose on Heat Balance During Exercise-Heat Stress

2011 ◽  
Vol 21 (1) ◽  
pp. 65-70 ◽  
Author(s):  
Brett R. Ely ◽  
Matthew R. Ely ◽  
Samuel N. Cheuvront
Keyword(s):  
Body Temperature ◽  
Heat Balance ◽  
Endurance Performance ◽  
Cycle Ergometer ◽  
Heat Illness ◽  
Caffeine Consumption ◽  
Physiological Strain ◽  
Mean Body Temperature ◽  
Hot Environment ◽  
Ergometer Exercise

The use of caffeine supplements in athletic and military populations has increased in recent years. Excessive caffeine consumption in conjunction with exercise in a hot environment may predispose individuals to heat illness.Purpose:To examine heat balance induced by a large dose of caffeine during exercise in a hot environment.Methods:Ten men, not heat acclimated and not habitual caffeine users, consumed either caffeine (CAF; 9 mg/kg) or placebo (PLA) before performing cycle-ergometer exercise for 30 min at 50% VO2peak in a 40 °C, 25% relative humidity environment while body temperature (core and skin) and ratings of thermal comfort (TC) were monitored. Heat-exchange variables were calculated using partitional calorimetry and thermometry.Results:Mean body temperature (Tb) was higher (p < .05) with CAF (37.18 ± 0.15 °C) than with PLA (36.93 ± 0.15 °C) at the start of exercise. Heat production was slightly higher (~8 W, p < .05) with CAF. There were no differences in heat storage, dry heat gains, TC, or Tb during exercise.Conclusions:A caffeine dose of 9 mg/kg does not appreciably alter heat balance during work in a hot environment. The small increase in Tb observed with CAF was undetected by the participants and is unlikely to increase physiological strain sufficiently to affect endurance performance or risk of heat illness.

Effects of the Menstrual Cycle on Serum Carnitine and Endurance Performance of Women

2020 ◽  
Vol 41 (07) ◽  
pp. 443-449
Author(s):  
Tomoka Matsuda ◽  
Tamaki Furuhata ◽  
Hazuki Ogata ◽  
Kayoko Kamemoto ◽  
Mizuki Yamada ◽  
...  
Keyword(s):  
Menstrual Cycle ◽  
Endurance Performance ◽  
Cycle Ergometer ◽  
Free Carnitine ◽  
Blood Levels ◽  
Serum Free ◽  
Ergometer Exercise ◽  
Early Follicular Phase ◽  
Total Carnitine ◽  
Midluteal Phase

AbstractThis study aimed to investigate the effect of the menstrual cycle on serum carnitine and the endurance performance of healthy women. Fifteen eumenorrheic women underwent cycle ergometer exercise at 60% maximal oxygen uptake (V̇ O2max) for 45 min, followed by exercise at an intensity that was increased to 80% V̇ O 2max until exhaustion, during two menstrual cycle phases, including the early follicular phase (FP) and the midluteal phase (LP). The blood levels of estradiol, progesterone, total carnitine, free carnitine, and acylcarnitine were assessed. Compared with the FP, the LP had significantly lower serum total carnitine (p<0.05) and free carnitine (p<0.01). Moreover, the group with decreased endurance performance in the LP than in the FP showed a significantly higher change in serum free carnitine compared with the group that showed improved endurance performance in the LP than in the FP (p<0.05). The results of this study suggested that the changes in serum free carnitine during the menstrual cycle might influence endurance performance.

Thermal influence of sunshine and clothing on men walking in humid heat

1962 ◽  
Vol 17 (2) ◽  
pp. 311-316 ◽  
Author(s):  
F. N. Craig ◽  
E. G. Cummings
Keyword(s):  
Body Temperature ◽  
Temperature Gradient ◽  
Air Temperature ◽  
Indoor Air ◽  
Physiological Strain ◽  
Mean Body Temperature ◽  
Clothing Insulation ◽  
Air Temperatures ◽  
Rate Of Increase ◽  
Thermal Influence

For two men walking on a treadmill and wearing two layers of permeable clothing, the same physiological strain measured by the rate of increase in mean body temperature could be produced a) next to a building outdoors in the sunshine with an average air temperature of 85 F and humidity of 20 mm Hg and b) indoors with the same humidity and an air temperature 10 F higher. Under these conditions, the underwear was mainly wet with sweat and the outer layer was mainly dry. In comparable indoor tests on a third subject, the temperature of the underwear approached equilibrium 1 or 2 F lower than the temperature of the skin at air temperatures of 85 and 115 F. The error in calculating clothing insulation introduced by assuming the clothing to be dry is determined by the size and direction of the temperature gradient between skin and air. Adding 10 F to the indoor air temperature does not duplicate all the effects of sunshine. Submitted on September 15, 1961

The Na+-K+-ATPase α2 gene and trainability of cardiorespiratory endurance: the HERITAGE Family Study

2000 ◽  
Vol 88 (1) ◽  
pp. 346-351 ◽  
Author(s):  
Tuomo Rankinen ◽  
Louis Pérusse ◽  
Ingrid Borecki ◽  
Yvon C. Chagnon ◽  
Jacques Gagnon ◽  
...  
Keyword(s):  
Maximal Oxygen Consumption ◽  
Endurance Performance ◽  
Cycle Ergometer ◽  
Electrolyte Balance ◽  
Exercise Tests ◽  
Maximal Power Output ◽  
Length Polymorphisms ◽  
Ergometer Exercise ◽  
Exon 1 ◽  
N 93

The Na+-K+-ATPase plays an important role in the maintenance of electrolyte balance in the working muscle and thus may contribute to endurance performance. This study aimed to investigate the associations between genetic variants at the Na+-K+-ATPase α2 locus and the response (Δ) of maximal oxygen consumption (V˙o 2 max) and maximal power output (W˙max) to 20 wk of endurance training in 472 sedentary Caucasian subjects from 99 families. V˙o 2 max andW˙max were measured during two maximal cycle ergometer exercise tests before and again after the training program, and restriction fragment length polymorphisms at the Na+-K+-ATPase α2 (exons 1 and 21–22 with Bgl II) gene were typed. Sibling-pair linkage analysis revealed marginal evidence for linkage between the α2 haplotype and ΔV˙o 2 max ( P= 0.054) and stronger linkages between the α2 exon 21–22 marker ( P = 0.005) and α2 haplotype ( P = 0.003) and ΔW˙max. In the whole cohort, ΔV˙o 2 max in the 3.3-kb homozygotes of the exon 1 marker ( n = 5) was 41% lower than in the 8.0/3.3-kb heterozygotes ( n = 87) and 48% lower than in the 8.0-kb homozygotes ( n = 380; P = 0.018, adjusted for age, gender, baselineV˙o 2 max, and body weight). Among offspring, 10.5/10.5-kb homozygotes ( n = 14) of the exon 21–22 marker showed a 571 ± 56 (SE) ml O2/min increase inV˙o 2 max, whereas the increases in the 10.5/4.3-kb ( n = 93) and 4.3/4.3-kb ( n= 187) genotypes were 442 ± 22 and 410 ± 15 ml O2/min, respectively ( P = 0.017). These data suggest that genetic variation at the Na+-K+-ATPase α2 locus influences the trainability ofV˙o 2 max in sedentary Caucasian subjects.

Metabolic, body temperature and hormonal responses to repeated periods of prolonged cycle-ergometer exercise in men

1992 ◽  
Vol 64 (1) ◽  
pp. 26-31 ◽  
Author(s):  
H. Kaciuba-Uscilko ◽  
B. Kruk ◽  
M. Szczypaczewska ◽  
B. Opaszowski ◽  
E. Stupnicka ◽  
...  
Keyword(s):  
Body Temperature ◽  
Cycle Ergometer ◽  
Hormonal Responses ◽  
Cycle Ergometer Exercise ◽  
Ergometer Exercise

Persistence of supercompensated muscle glycogen in trained subjects after carbohydrate loading

1997 ◽  
Vol 82 (1) ◽  
pp. 342-347 ◽  
Author(s):  
Harold W. Goforth ◽  
Jr., David A. Arnall ◽  
Brad L. Bennett ◽  
Patricia G. Law
Keyword(s):  
Muscle Glycogen ◽  
Vastus Lateralis ◽  
Endurance Performance ◽  
Peak Oxygen Uptake ◽  
Cycle Ergometer ◽  
Male Athletes ◽  
Trained Subjects ◽  
Carbohydrate Loading ◽  
Low Protein ◽  
Ergometer Exercise

Goforth, Jr., Harold W., David A. Arnall, Brad L. Bennett, and Patricia G. Law. Persistence of supercompensated muscle glycogen in trained subjects after carbohydrate loading. J. Appl. Physiol. 82(1): 342–347, 1997.—Several carbohydrate (CHO)-loading protocols have been used to achieve muscle glycogen supercompensation and prolong endurance performance. This study assessed the persistence of muscle glycogen supercompensation over the 3 days after the supercompensation protocol. Trained male athletes completed a 6-day CHO-loading protocol that included cycle ergometer exercise and dietary manipulations. The 3-day depletion phase began with 115 min of cycling at 75% peak oxygen uptake followed by 3 × 60-s sprints and included the subjects consuming a low-CHO/high-protein/high-fat (10:41:49%) diet. Subjects cycled 40 min at the same intensity for the next 2 days. During the 3-day repletion phase, subjects rested and consumed a high-CHO/low-protein/low-fat (85:08:07%) diet, including a glucose-polymer beverage. A 3-day postloading phase followed, which involved a moderately high CHO diet (60%) and no exercise. Glycogen values for vastus lateralis biopsies at baseline and postloading days 1–3 were 408 ± 168 (SD), 729 ± 222, 648 ± 186, and 714 ± 196 mmol/kg dry wt, respectively. The CHO-loading protocol increased muscle glycogen by 1.79 times baseline, and muscle glycogen remained near this level during the 3-day postloading period. Results indicate that supercompensated muscle glycogen levels can be maintained for at least 3 days in a resting athlete when a moderate-CHO diet is consumed.

Influence of the timing of fluid ingestion on temperature regulation during exercise

1993 ◽  
Vol 75 (2) ◽  
pp. 688-695 ◽  
Author(s):  
S. J. Montain ◽  
E. F. Coyle
Keyword(s):  
Body Weight ◽  
Heat Stress ◽  
Fluid Intake ◽  
Body Weight Loss ◽  
Sodium Concentration ◽  
Cycle Ergometer ◽  
Fluid Ingestion ◽  
Hot Environment ◽  
Time Period ◽  
Ergometer Exercise

The purpose of this investigation was to determine whether the timing of fluid ingestion affects thermoregulation during exercise-heat stress. On four occasions, seven endurance-trained cyclists [age 25 +/- 2 (SE) yr, body weight 70.5 +/- 3.3 kg, maximal O2 uptake (VO2max) 4.69 +/- 0.11 l/min] performed 140 min of cycle ergometer exercise at 62–66% of VO2max in a hot environment (33 degrees C dry bulb, 51% relative humidity, wind speed 2.5 m/s). The subjects drank 1,173 +/- 44 ml of a carbohydrate-electrolyte beverage after 0 min (D0), 40 min (D40), or 80 min (D80) of exercise or consumed the same total volume in small aliquots throughout exercise (DT). The exercise-heat stress resulted in calculated sweating rates of approximately 1,200 ml/h and a body weight loss of 2.9 +/- 0.1% after 140 min of exercise. After fluid intake in the D0, D40, and D80 trials, there was a time period (approximately 40 min) in which the increases in serum osmolality and sodium concentration and the reduction in blood volume were attenuated. During that same time period, there was an attenuated rise in esophageal temperature (Tes; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Testosterone Attenuates Age-Related Fall in Aerobic Function in Mobility Limited Older Men With Low Testosterone

2016 ◽  
Vol 101 (6) ◽  
pp. 2562-2569 ◽  
Author(s):  
Thomas W. Storer ◽  
Shalender Bhasin ◽  
Thomas G. Travison ◽  
Karol Pencina ◽  
Renee Miciek ◽  
...  
Keyword(s):  
Medical Center ◽  
Exercise Physiology ◽  
Academic Medical Center ◽  
Older Men ◽  
Peak Oxygen Uptake ◽  
Cycle Ergometer ◽  
Aerobic Performance ◽  
Mobility Limitations ◽  
Age Related ◽  
Ergometer Exercise

Abstract Context: Testosterone increases skeletal muscle mass and strength, but the effects of testosterone on aerobic performance in mobility-limited older men have not been evaluated. Objective: To determine the effects of testosterone supplementation on aerobic performance, assessed as peak oxygen uptake (V̇O2peak) and gas exchange lactate threshold (V̇O2θ), during symptom-limited incremental cycle ergometer exercise. Design: Subgroup analysis of the Testosterone in Older Men with Mobility Limitations Trial. Setting: Exercise physiology laboratory in an academic medical center. Participants: Sixty-four mobility-limited men 65 years or older with low total (100–350 ng/dL) or free (&lt;50 pg/dL) testosterone. Interventions: Participants were randomized to receive 100-mg testosterone gel or placebo gel daily for 6 months. Main Outcome Measures: V̇O2peak and V̇O2θ from a symptom-limited cycle exercise test. Results: Mean (SD) baseline V̇O2peak was 20.5 (4.3) and 19.9 (4.7) mL/kg/min for testosterone and placebo, respectively. V̇O2peak increased by 0.83 (2.4) mL/kg/min in testosterone but decreased by −0.89 (2.5) mL/kg/min in placebo (P = .035); between group difference in change in V̇O2peak was significant (P = .006). This 6-month reduction in placebo was greater than the expected −0.4-mL/kg/min/y rate of decline in the general population. V̇O2θ did not change significantly in testosterone but decreased by 1.1 (1.8) mL/kg/min in placebo, P = .011 for between-group comparisons. Hemoglobin increased by 1.0 ± 3.5 and 0.1 ± 0.8 g/dL in testosterone and placebo groups, respectively. Conclusion: Testosterone supplementation in mobility-limited older men increased hemoglobin and attenuated the age-related declines in V̇O2peak and V̇O2θ. Long-term intervention studies are needed to determine the durability of this effect.

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