Search Results

The purpose of this study was to clarify the effect of sex on plasma catecholamine responses to sprint exercise in adolescents and adults. Thirty-six untrained participants took part in this study—9 girls and 10 boys (Tanner Stage 4) and 9 women and 8 men. Each participant performed a 6-s sprint test on a cycle ergometer. Plasma adrenaline (A) and noradrenaline (NA) concentrations were determined successively at rest (A₀ and NA₀), immediately after the 6-s sprint test (A_EX and NA_EX), and after 5 min of recovery (A₅ and NA₅). Peak power, expressed in absolute values or relative to body weight and fat-free mass, was significantly higher in boys than in girls and higher in men than in women (p < .001). No sex effect was observed in A_EX in the adolescents, but the NA increase was significantly higher in boys in response to the 6-s sprint (p < .05). In adults, no sex difference was found in NA_EX, but A_EX was significantly higher in men than in women (p < .05). NA_EX was significantly higher in women than in girls (p < .05), and A_EX was significantly higher in men than in boys (p < .01). The results of this study suggest that male and female adolescents and young adults might exhibit different catecholamine responses to sprint exercise.

This study investigated the effects of caffeine on repeated, anaerobic exercise using a double-blind, randomized, crossover design. Seventeen subjects (five female) underwent cognitive (reaction time, number recall) and blood (glucose, potassium, catecholamines, lactate) testing before and after consuming caffeine (6 mg/kg), placebo, or nothing (control). An exercise test (two 60 s maximal cycling bouts) was conducted 90 min after caffeine/placebo consumption. Plasma caffeine concentrations significantly increased after caffeine ingestion, however, there were no positive effects on cognitive or blood parameters except a significant decrease in plasma potassium concentrations at rest. Potentially negative effects of caffeine included significantly higher blood lactate compared to control and significantly slower time to peak power in exercise bout 2 compared to control and placebo. Caffeine had no significant effect on peak power, work output, RPE, or peak heart rate. In conclusion, caffeine had no ergogenic effect on repeated, maximal cycling bouts and may be detrimental to anaerobic performance.

This study assessed the plasma glucose (PG) and hormonal responses to carbohydrate ingestion, prior to exercise in the heat, in a hypohydrated state versus partial rehydration with intravenous solutions. On separate days, 8 subjects (21.0 ± 1.8 years; 57.3 ± 3.7 ml · kg⁻¹ · min⁻¹) exercised at 50% V̇O_2maxin a 33 °C environment until a 4% body weight loss was achieved. Following this, subjects were rehydrated (25 ml · kg⁻¹) with either: 0.45% IV saline (45IV), 0.9% IV saline (9IV), or no fluid (NF). Subjects then ingested 1 g · kg⁻¹ of carbohydrate and underwent an exercise test (treadmill walking, 50% V̇O_2max, 36 °C) for up to 90 min. Compared to pre-exercise level (294 mg · dl⁻¹), PG increased significantly (>124 mg · dl⁻¹) at 15 min of the exercise test in all trials and remained significantly elevated for 75 min in NF, 30 min more than in the 2 rehydration trials. Although serum Insulin increased significantly at 15 min of exercise in the 45IV trial (7.2 ± 1.2 vs. 23.7 ± 4.7 μIU · ml⁻¹) no significant differences between trials were observed. Peak plasma norepinephrine was significantly higher in NF (640 ± 66 pg · ml⁻¹) compared to the 45IV and 9IV trials (472 ± 55 and 474 ± 52 pg · ml⁻¹, respectively). In conclusion, ingestion of a small solid carbohydrate load prior to exercise in the 4% hypohydration level resulted in prolonged high PG concentration compared to partial IV rehydration.

Immune changes in 75 younger (age 37.4 ± 0.9 years) and 23 older (57.0 ± 1.4 years) runners were compared after a competitive marathon, with blood samples collected pre- and immediately and 1.5 hr postrace. Race times were slower for the older group (4.7 ± 0.2 vs. 4.3 ± 0.1 hr, p = .015), but both groups performed at similar intensity (83.4 ± 0.9 vs. 82.9 ± 0.5% HR_max). The pattern of change in plasma cortisol, epinephrine, growth hormone, and blood leukocyte subsets did not differ significantly between the groups postrace. Blood lymphocyte counts were 20–24% lower in the older runners at each time point because of reduced T-cell counts. Postrace, plasma levels of IL-1ra, -10, -6, and -8 rose strongly in all runners, and salivary IgA secretion rate decreased, but no group differences in the pattern of change were noted. In conclusion, younger and older runners experienced similar hormonal and immune changes after running a marathon.

The purpose of this study was to discover whether severe dietary carbohydrate (CHO) restriction modifies the relationship between exercise intensity and hormonal responses to exercise. Changes in the plasma adrenaline (A), noradrenaline (NA), growth hormone (hGH), testosterone (T), and blood lactate (LA) during an incremental exercise performed until volitional exhaustion were determined in 8 physically active volunteers after 3 days on low CHO (<5% of energy content; L-CHO) and isocaloric mixed (M) diets. Following L-CHO diet, the basal plasma A, NA, and hGH concentrations were increased, whilst T and LA levels were decreased. During exercise all the hormones increased exponentially, with thresholds close to that of LA. Neither the magnitude nor the pattern of the hormonal changes were affected by L-CHO diet except the NA threshold, which was lowered. Blood LA response to exercise was diminished and LA threshold was shifted towards higher loads by L-CHO diet. It is concluded that restriction of CHO intake (a) does not affect the pattern of changes in plasma A, hGH, and T concentrations during graded exercise but lowers NA threshold, indicating increased sensitivity of the sympathetic nervous system to exercise stimulus; (b) alters the basal and exercise levels of circulating hormones, which may have an impact on the balance between anabolic and catabolic processes and subsequently influence the effectiveness of training.

This study assessed whether cardiovascular (CV) reactivity patterns indexing challenge and threat states predicted batting performance in elite male county (N = 12) and national (N = 30) academy cricketers. Participants completed a batting test under pressure, before which CV reactivity was recorded in response to ego-threatening audio instructions. Self-reported self-efficacy, control, achievement goals, and emotions were also assessed. Challenge CV reactivity predicted superior performance in the Batting Test, compared with threat CV reactivity. The relationships between self-report measures and CV reactivity, and self-report measures and performance were inconsistent. A small subsample of participants who exhibited threat CV reactivity, but performed well, reported greater self-efficacy than participants who exhibited threat CV reactivity, but performed poorly. Also a small subsample of participants who exhibited challenge reactivity, but performed poorly, had higher avoidance goals than participants with challenge reactivity who performed well. The mechanisms for the observed relationship between CV reactivity and performance are discussed alongside implications for future research and applied practice.