Nicolas J.A. Berger

Influence of hyperoxia on pulmonary O2 uptake kinetics following the onset of exercise in humans

The purpose of this study was to examine the influence of hyperoxic gas (50% O2 in N2) inspiration on pulmonary oxygen uptake (V(O2)) kinetics during step transitions to moderate, severe and supra-maximal intensity cycle exercise. Seven healthy male subjects completed repeat transitions to moderate (90% of the gas exchange threshold, GET), severe (70% of the difference between the GET and V(O2) peak) and supra-maximal (105% V(O2) peak) intensity work rates while breathing either normoxic (N) or hyperoxic (H) gas before and during exercise. Hyperoxia had no significant effect on the Phase II V(O2) time constant during moderate (N: 28+/-3s versus H: 31+/-7s), severe (N: 32+/-9s versus H: 33+/-6s) or supra-maximal (N: 37+/-9s versus H: 37+/-9s) exercise. Hyperoxia resulted in a 45% reduction in the amplitude of the V(O2) slow component during severe exercise (N: 0.60+/-0.21 L min(-1) versus H: 0.33+/-0.17 L min(-1); P < 0.05) and a 15% extension of time to exhaustion during supra-maximal exercise (N: 173+/-28 s versus H: 198+/-41 s; P < 0.05). These results indicate that the Phase II V(O2) kinetics are not normally constrained by (diffusional) O2 transport limitations during moderate, severe or supra-maximal intensity exercise in young healthy subjects performing upright cycle exercise.

Influence of recombinant human erythropoietin treatment on pulmonary O2 uptake kinetics during exercise in humans

We hypothesized that 4 weeks of recombinant human erythropoietin (RhEPO) treatment would result in a significant increase in haemoglobin concentration ([Hb]) and arterial blood O2‐carrying capacity and that this would (1) increase peak pulmonary oxygen uptake during ramp incremental exercise, and (2) speed kinetics during ‘severe’‐, but not ‘moderate’‐ or ‘heavy’‐intensity, step exercise. Fifteen subjects (mean ±s.d. age 25 ± 4 years) were randomly assigned to either an experimental group which received a weekly subcutaneous injection of RhEPO (150 IU kg−1; n= 8), or a control group (CON) which received a weekly subcutaneous injection of sterile saline (10 ml; n= 7) as a placebo, for four weeks. The subjects and the principal researchers were both blind with respect to the group assignment. Before and after the intervention period, all subjects completed a ramp test for determination of the gas exchange threshold (GET) and , and a number of identical ‘step’ transitions from ‘unloaded’ cycling to work rates requiring 80% GET (moderate), 70% of the difference between the GET and (heavy), and 105% (severe) as determined from the initial ramp test. Pulmonary gas exchange was measured breath‐by‐breath. There were no significant differences between the RhEPO and CON groups for any of the measurements of interest ([Hb], kinetics) before the intervention. Four weeks of RhEPO treatment resulted in a 7% increase both in [Hb] (from 15.8 ± 1.0 to 16.9 ± 0.7 g dl−1; P < 0.01) and (from 47.5 ± 4.2 to 50.8 ± 10.7 ml kg−1·min−1; P < 0.05), with no significant change in CON. RhEPO had no significant effect on kinetics for moderate (Phase II time constant, from 28 ± 8 to 28 ± 7 s), heavy (from 37 ± 12 to 35 ± 11 s), or severe (from 33 ± 15 to 35 ± 15 s) step exercise. Our results indicate that enhancing blood O2‐carrying capacity and thus the potential for muscle O2 delivery with RhEPO treatment enhanced the peak but did not influence kinetics, suggesting that the latter is principally regulated by intracellular (metabolic) factors, even during exercise where the requirement is greater than the , at least in young subjects performing upright cycle exercise.

Influence of exercise intensity on skeletal muscle blood flow, O2 extraction and O2 uptake on‐kinetics

Following the start of low‐intensity exercise in healthy humans, it has been established that the kinetics of muscle O2 delivery is faster than, and does not limit, the kinetics of muscle O2 uptake. Direct data are lacking, however, on the question of whether O2 delivery might limit O2 uptake kinetics during high‐intensity exercise. In this study, we made frequent measurements of muscle blood flow, arterial‐to‐venous O2 difference (a–difference) and O2 uptake following the onset of multiple transitions of both low‐intensity and high‐intensity knee‐extension exercise in the same subjects. We show that although blood flow kinetics is slower for high‐intensity compared with low‐intensity exercise, this does not result in slower O2 uptake kinetics. These results indicate that muscle O2 delivery does not limit O2 uptake during knee‐extension exercise in healthy humans.

Influence of dichloroacetate on pulmonary gas exchange and ventilation during incremental exercise in healthy humans

We hypothesised that dichloroacetate (DCA) would reduce blood lactate accumulation, pulmonary carbon dioxide output (.V(CO2)) and ventilation (.V(E)) at sub-maximal work rates, and improve exercise tolerance during incremental exercise in healthy humans. Nine males (mean+/-SD, age 27+/-4 years) completed, in random order, two ramp incremental cycle ergometer tests to the limit of tolerance following the intravenous infusion of DCA (75 mg/kg body mass in 80 ml saline) or an equivalent volume of saline (as placebo). Relative to control, blood [lactate] was significantly reduced by DCA immediately before exercise (CON: 0.7+/-0.2 vs. DCA: 0.5+/-0.2mM; P<0.05) and throughout exercise until 630s (P<0.05). Blood [HCO(3)(-)] was significantly higher in the DCA condition from 360s until 720s of exercise (P<0.05). .V(CO2) and .V(E) were both lower throughout exercise in the DCA condition, with the differences reaching significance at 90 and 180s for .V(CO2) (P<0.05) and at 90, 180, 450, 540, 630, and 810s for .V(E) (P<0.05). Exercise tolerance was not significantly altered (CON: 1029+/-109 vs. DCA: 1045+/-101s). Infusion of DCA resulted in reductions in blood [lactate], .V(CO2) and .V(E) during sub-maximal incremental exercise, consistent with the existence of a link between the bicarbonate buffering of metabolic acidosis and increased CO(2) output. However, the reduced blood lactate accumulation during sub-maximal exercise with DCA did not enhance exercise tolerance.

Topical and Ingested Cooling Methodologies for Endurance Exercise Performance in the Heat

This systematic review and meta-analysis aimed to assess studies which have investigated cooling methodologies, their timing and effects, on endurance exercise performance in trained athletes (Category 3; VO2max ≥ 55 mL·kg·min−1) in hot environmental conditions (≥28 °C). Meta-analyses were performed to quantify the effects of timings and methods of application, with a narrative review of the evidence also provided. A computer-assisted database search was performed for articles investigating the effects of cooling on endurance performance and accompanying physiological and perceptual responses. A total of 4129 results were screened by title, abstract, and full text, resulting in 10 articles being included for subsequent analyses. A total of 101 participants and 310 observations from 10 studies measuring the effects of differing cooling strategies on endurance exercise performance and accompanying physiological and perceptual responses were included. With respect to time trial performance, cooling was shown to result in small beneficial effects when applied before and throughout the exercise bout (Effect Size: −0.44; −0.69 to −0.18), especially when ingested (−0.39; −0.60 to −0.18). Current evidence suggests that whilst other strategies ameliorate physiological or perceptual responses throughout endurance exercise in hot conditions, ingesting cooling aids before and during exercise provides a small benefit, which is of practical significance to athletes’ time trial performance.

Changes in Pain and Nutritional Intake Modulate Ultra-Running Performance: A Case Report

Ultra-endurance running provides numerous physiological, psychological, and nutritional challenges to the athlete and supporting practitioners. We describe the changes in physiological status, psychological condition, and nutritional intake over the course of two 100-mile running races, with differing outcomes: non-completion and completion. Athlete perception of pain, freshness, and motivation differed between events, independent of rating of perceived exertion. Our data suggest that the integration of multiple sensations (freshness, motivation, hunger, pain, and thirst) produce performance. Increases in carbohydrate feeding (+5 g·h−1) and protein intake (+0.3 g·kg−1) also likely contributed to successful completion of a 100-mile race, by reducing the fractional utilization of maximal oxygen uptake and satiating hunger, respectively. Nutritional data support the notion that the gut is a trainable, and critical organ with respect to ultra-endurance performance. Finally, we propose future research to investigate the rate at which peak feeding occurs throughout ultra-endurance events, as this may further serve to personalize sports nutrition strategies.