Run performance of middle-aged and young adult runners in the heat.

The aging process may impair exercise tolerance in the heat. It is not clear whether this impairment is partly due to a reduction in aerobic capacity. To compare the exercise performance and thermoregulatory responses of middle-aged and young adults with similar aerobic capacities and training statuses, 7 middle-aged (54±2 years; 58±4 ml·kg - 1·min - 1) and 7 young (28±1 years; 61±5 ml·kg - 1·min - 1) male competitive endurance runners underwent 2 10-km self-paced and 2 fixed-workload (90% of race speed) runs until fatigue on a treadmill in hot (40°C) and moderate (20°C) environments on separate days. The runners' total time, average speed, rectal temperature, heat storage rate, physiological strain index, sweat rate, sweat sensitivity, number of heat-activated sweat glands and sweat rate per sweat gland were measured or calculated. Body fat, body surface area, body surface area per body mass, training volume and VO2max were similar between the 2 groups. No differences were observed in total time (59±3; 49±3; 27±2; 54±5 min in the middle-aged and 60±2; 49±3; 27±2; 51±4 min in the young group), average speed, rectal temperature, heat storage rate, physiological strain index, sweat rate (17±7; 15±3; 23±7; 13±2 g.m - 2.min - 1 in the middle-aged and 20±5; 14±4; 22±5; 15±4 g.m - 2.min - 1 in the young group) or sweat sensitivity between age groups (p>0.05) in any trial. The number of heat-activated sweat glands (88±14; 80±18; 90±16; 66±14 cm - 2 in the middle-aged and 43±10; 32±10; 37±11; 31±11 cm - 2 in the young group) was higher, and the sweat rate per sweat gland was smaller, in the middle-aged than the young group (p<0.05) in all of the trials. We conclude that running performance and body thermoregulation are similar between young and middle-aged runners with similar aerobic capacities and training statuses under hot and moderate conditions in self-paced and fixed-intensity runs. The decrease observed in the sweat rate per sweat gland in middle-aged men was compensated for by a higher number of heat-activated sweat glands.

Effects of caffeine and tryptophan on rectal temperature, metabolism, total exercise time, rate of perceived exertion and heart rate

Stimulant properties during exercise have been attributed to cafeine (CAF) and tryptophan (Trp). The purpose of the present study was to investigate the effects of CAF and Trp ingestion on rectal temperature (Tre), total exercise time (TET), oxygen consumption (VO2), carbon dioxide production (VCO2) pulmunary ventilation (VE), heart rate (HR) and rate of perceived exertion (RPE) during exercise on a cycle ergometer at 80 percent of maximal work load, in eight halthy male volunteers. Each subject abstained from caffeine for 48 h and from animal-derived foods for 36 h before each experiment. Aerobic capacity was determined on the first day. In consecutive trials, conducted in a double-blind, randomized, crossed-over manner, each subject recived capsules containing CAF (10mg/Kg), Trp (1.2g), a combination of the two (CAF + TRP), and lactose (PLA), 1 h before exercise. Plasma CAF concentration (PC) was measured by high performance liquid chromatography (HPLC), before (basal concentration) and 1 and 2 h after ingestion of the capsules. At both times after CAF or CAF + Trp ingestion, the PC was elevated compared with the basal concentration (P < 0.05). During exercise, significant increases occured with time in Tre, TET, VO2, VCO2, VE, HR and RPE (P < 0.01) while no significant difference was observed when CAF or CAF+ Trp were compared with control values. Under the conditions of this study, CAF and/or Trp did not affect the physiological parameters measured before, during or after exercise at 80 percent of maximal work load