Gender difference in the metabolic response to prolonged exercise with [13C]glucose ingestion

The metabolic response to a 120-min cycling exercise with ingestion of [¹³C]glucose (3 g kg^–1) was compared in women in the follicular phase of the cycle [n=6; maximum rate of oxygen uptake (O_2max) 44.7 (2.6) ml kg^–1 min^–1] and in men [n=6; O_2max 54.2 (4.3) ml kg^–1 min^–1] working at the same relative workload (~65% O_2max: 107 and 179 W in women and men, respectively). We hypothesized that the contribution of endogenous substrate oxidations (indirect respiratory calorimetry corrected for protein oxidation) to the energy yield will be similar in men and women, but that women will rely more than men on exogenous glucose oxidation. Over the exercise period, the respective contributions of protein, lipid and carbohydrate oxidation to the energy yield, were similar in men [3.7 (0.9), 21.7 (2.9) and 74.6 (3.5)%] and women [3.4 (0.8), 21.5 (2.2), 75.1 (2.5)%]. The rate of exogenous glucose oxidation was ~45% lower in women than men (0.5 and 0.6 g min^–1 vs 0.7 and 0.9 g min^–1, between min 40 and 80, and min 80 and 120, respectively). However, when the ~39% difference in absolute workload and energy expenditure was taken into account, the contribution of exogenous glucose oxidation to the energy yield was similar in men and women: 22.5 vs 24.2% between min 40 and 80, and 25.7 and 28.5% between min 80 and 120, respectively. These data indicate that when fed glucose, the respective contributions of the oxidation of the various substrates to the energy yield during prolonged exercise at the same %O_2max are similar in men and in women in the follicular phase of the cycle.     

Metabolic fate of a large amount of 13C-glycerol ingested during prolonged exercise

We have shown that the oxidation rate of exogenous glycerol and glucose during prolonged exercise were similar when ingested in small amounts (0.36 g/kg) (J Appl Physiol 90:1685,2001). The oxidation rate of exogenous carbohydrate increases with the amount ingested. We, thus, hypothesized that the oxidation rate of exogenous glycerol would also be larger when ingested in large amount. The study was conducted on six male subjects exercising for 120 min at 64 (2)%VO₂max while ingesting 1 g/kg of ¹³C-glycerol. Substrate oxidation was measured using indirect respiratory calorimetry corrected for protein oxidation, and from V ¹³CO₂ at the mouth. The ¹³C enrichment of plasma glucose was also measured in order to follow the possible conversion of ¹³C-glycerol into glucose. In spite of the large amount of glycerol ingested and absorbed (plasma glycerol concentration = 8.0 (0.3) mmol/l at min 100), exogenous glycerol oxidation over the last 80 min of exercise [8.8 (1.6) g providing 4.1 (0.7)% of the energy yield] was similar to that observed when 0.36 g/kg was ingested. The comparison between the ¹³C enrichment of plasma glucose and the oxidation rate of ¹³C-glycerol showed that a portion of exogenous glycerol was converted into glucose before being oxidized, but also suggested that another portion could have been directly oxidized in peripheral tissues.     

White blood cell response to uphill walking and downhill jogging at similar metabolic loads

Summary The object of this study was to determine whether leukocytosis would occur in response to eccentric exercise, to concentric exercise, and/or to possible increases in serum corticol levels. Eight men performed 2 bouts of exercise at 46% for 40 min. Subjects initially walked up a 10% grade (UW); 2 weeks later they jogged down a 10% grade (DJ), a form of eccentric exercise known to induce delayed onset muscle soreness (DOMS). Venous blood samples were drawn before and after each exercise bout (0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, and 5 h). Total and differential WBCc and serum cortisol levels were assessed. Results were analyzed using repeated measures ANOVA (2 × 11). Subjects experienced severe DOMS after DJ. There was a significant difference in TWBCc (p<0.0001) between UW and DJ. Post-hoc testing revealed no significant increase over baseline values for UW; after DJ there was a 46% increase over baseline values (p<0.05) initially seen at 1.0 h. These increases in TWBCc were predominantly a reflection of increases in neutrophils which were significant (p<0.0001) when compared to baseline values at 1.0, 1.5 and 2.0 h (∼60%). No significant neutrophil increases were seen after UW. Cortisol levels were similar for both groups pre-exercise (UW=367.1±38.6, DJ=320.2±44.16 mnol · L⁻¹ x±SE) and decreased similarly for both groups after exercise, and thus were not related to the post-exercise neutrophilia. In conclusion, the neutrophilia seen after the DJ appeared to be a response to differences in the exercise, not plasma cortisol levels. Thus a bout of eccentric exercise appears to induce a significant post-exercise increase in neutrophils seen between 1.0 and 2.0 h after the termination of exercise.     

Effect of a 20-day ski trek on fuel selection during prolonged exercise at low workload with ingestion of <Superscript>13</Superscript>C-glucose

Fuel selection was measured in five subjects (36.0 ± 10.5 years old; 87.3 ± 12.5 kg; mean ± SD) during a 120-min tethered walking with ski poles (1.12 l O₂ min⁻¹) with ingestion of ¹³C-glucose (1.5 g kg⁻¹), before and after a 20-day 415-km ski trek [physical activity level (PAL) ~3], using respiratory calorimetry, urea excretion, and ¹³C/¹²C in expired CO₂ and in plasma glucose. Before the ski trek, protein oxidation contributed 9.7 ± 1.6% to the energy yield (%En) while fat and carbohydrate (CHO) oxidation provided 73.5 ± 5.5 and 16.7 ± 6.5%En. Plasma glucose was the main source of CHO (52.9 ± 9.5%En) with similar contributions from exogenous glucose (27.2 ± 3.1%En), glucose from the liver (25.6 ± 8.3%En) and muscle glycogen (20.9 ± 4.0%En). Endogenous CHO contributed 46.6 ± 3.9%En. Following the ski trek %En from protein, fat, CHO, exogenous glucose and endogenous CHO were not significantly modified (10.1 ± 1.3, 15.8 ± 6.7, 74.1 ± 6.5, 28.7 ± 3.0 and 45.5 ± 7.5%En, respectively) but the %En from plasma glucose and glucose from the liver (41.1 ± 3.6 and 12.4 ± 4.0%En) were reduced, while that from muscle glycogen increased (33.0 ± 4.5%En). These results show that in subjects in the fed state with glucose ingestion during exercise, CHO is the main substrate oxidized, with major contributions from both exogenous and endogenous CHO. Following a ~3-week period of prolonged low intensity exercise, the %En from protein, fat, CHO, exogenous glucose and endogenous CHO were not modified. However, the %En from glucose released from the liver was reduced (possibly due to an increased insulin sensitivity of the liver) while that from muscle glycogen was increased. Ethical standards: the experiments reported in this study comply with the current laws of Canada.