, before dropping below baseline concentrations following the 10-minute steady-state cycling. Blood glucose concentrations then increased above baseline following completion of the TT. This increase following the TT also occurred in the WAT and PLA trials. In the CHO trial, blood glucose concentrations
Stephen A. Mears, Kathryn Dickinson, Kurt Bergin-Taylor, Reagan Dee, Jack Kay and Lewis J. James
Oliver Faude, Tim Meyer and Wilfried Kindermann
The work rate (WR) corresponding to ventilatory threshold (VT) is an appropriate intensity for regenerative and low-intensity training sessions. During incremental ramp exercise, VO2 increase lags behind WR increase. Traditionally, a VO2 time delay (t d) of 45 seconds is used to calculate the WR at VT from such tests. Considerable inaccuracies were observed when using this constant t d. Therefore, this study aimed at reinvestigating the temporal relationship between VO2 and WR at VT.
20 subjects (VO2peak 49.9 to 72.6 mL · min–1 · kg–1) performed a ramp test in order to determine VT and a subsequent steady-state test during which WR was adjusted to elicit the VO2 corresponding to VT. The difference in WR and heart rate at VT was calculated between the ramp and the steady-state test (WRdiff, HRdiff) as well as the time delay corresponding to WRdiff during ramp exercise.
Mean values were t d = 85 ± 26 seconds (range 38 to 144), WRdiff = 45 ± 12 W (range 23 to 67), HRdiff = 1 ± 9 beats/min (range –21 to +15). The limits of agreement for the difference between WR at VT during ramp and steady-state exercise were ± 24 W. No signifi cant influence on t d, WRdiff, or HRdiff from differences in endurance capacity (VO2peak and VT; P > .10 for all correlations) or ramp increment (P = .26, .49, and .85, respectively) were observed.
The wide ranges of t d, WRdiff, and HRdiff prevent the derivation of exact training guidelines from single-ramp tests. It is advisable to perform a steady-state test to exactly determine the WR corresponding to VT.
Matthew Zimmermann, Grant Landers, Karen E. Wallman and Jacinta Saldaris
This study examined the physiological effects of crushed ice ingestion before steady state exercise in the heat. Ten healthy males with age (23 ± 3 y), height (176.9 ± 8.7 cm), body-mass (73.5 ± 8.0 kg), VO2peak (48.5 ± 3.6 mL∙kg∙min-1) participated in the study. Participants completed 60 min of cycling at 55% of their VO2peak preceded by 30 min of precooling whereby 7 g∙kg-1 of thermoneutral water (CON) or crushed ice (ICE) was ingested. The reduction in Tc at the conclusion of precooling was greater in ICE (-0.9 ± 0.3 °C) compared with CON (-0.2 ± 0.2 °C) (p ≤ .05). Heat storage capacity was greater in ICE compared with CON after precooling (ICE -29.3 ± 4.8 W∙m-2; CON -11.1 ± 7.3 W∙m-2, p < .05). Total heat storage was greater in ICE compared with CON at the end of the steady state cycle (ICE 62.0 ± 12.5 W∙m-2; CON 49.9 ± 13.4 W∙m-2, p < .05). Gross efficiency was higher in ICE compared with CON throughout the steady state cycle (ICE 21.4 ± 1.8%; CON 20.4 ± 1.9%, p < .05). Ice ingestion resulted in a lower thermal sensation at the end of precooling and a lower sweat rate during the initial stages of cycling (p < .05). Sweat loss, respiratory exchange ratio, heart rate and ratings of perceived exertion and thirst were similar between conditions (p > .05). Precooling with crushed ice led to improved gross efficiency while cycling due to an increased heat storage capacity, which was the result of a lower core temperature.
Hélène Perrault, Maria Tzovanis, Dominique Johnson, André Davignon, Claude Chartrand, Abdelkader Mokrane and Réginald A. Nadeau
This study compares the autonomic responses of 9 adolescents (mean ± SEM: 17±1 years) successfully operated for tetralogy of Fallot (TOF) in early childhood and 8 age-matched healthy controls (CTRL) using R-R and blood pressure variability. Continuous ECG and BP recordings were obtained during spontaneous and controlled respiration (CR) at 0.20 Hz as well as after an 85° head-up tilt (HUT) and during steady-state cycling at heart rates of 100 and 120 bpm, selected to reflect partial and complete cardiac vagal withdrawal. TOF exhibited total R-R variance and HF power (ms2) lower than CTRL under both spontaneous (938 ± 322 vs. 1,714 ± 296) and CR (1,541 ± 527 vs. 4,725 ± 1,207; p < .05), which may be indicative of a lower cardiac vagal activity. HUT decreased the R-R HF component, which remained lower in TOF than CTRL and increased the diastolic BP LF component in TOF but not in CTRL. Exercise decreased the R-R HF power more in TOF than CTRL. The exaggerated diastolic BP and limited heart rate responses to tilting and the more marked vagal withdrawal at Ex120 in TOF may be suggestive of a disturbance in the cardiac sympathetic response. Further studies are needed to confirm these observations on larger groups of young adults successfully operated for TOF.
Tali Bar-Or, Oded Bar-Or, Heather Waters, Arif Hirji and Storm Russell
Although portable heart rate (HR) monitors are commonly used to assess energy expenditure, little is known about their suitability for preschoolers. To validate the Polar Vantage XL monitor (XL), the HRs of twenty-seven 3- to 5-year-old girls and boys were measured using the XL and ECG simultaneously. During rest, values for both methods were virtually identical (ECG = 97.3 ± 7.5, XL = 97.9 ±7.2, r = .99 for lying, and ECG = 111.1 ± 16.5, XL = 110.4± 16.3 for sitting). XL nonsignificantly underestimated HR during 1–2 min of non-steady-state cycling (ECG = 142.7 ± 11.0, XL = 140.2 ± 11.5, r = .93) and significantly overestimated it during recovery (ECG = 112.4 ± 12.8, XL = 118.0 ± 12.3, r = .92). To assess social acceptability of wearing the XL, twenty-three 3- to 5-year-old girls and boys were observed twice for 60–90 min. Approximately 90% of the time, their responses were rated as enthusiastic/positive or agreed. Only 3–5% of children refused to wear the XL. In conclusion, the XL is highly valid and socially acceptable, when used with 3- to 5-year-old children.
Elizabeth M. Broad, Ronald J. Maughan and Stuart D.R. Galloway
In a randomized, placebo-controlled, double-blind crossover design, 15 trained males undertook exercise trials during two 4 wk supplementation periods, with either 3 g L-Carnitine L-tartrate (LCLT) or 3 g placebo (P) daily. Total carbohydrate and fat oxidation during 90 min steady state cycling were not different between 0 or 4 wk within LCLT or P trials (mean ± standard deviation: carbohydrate oxidation P0 99 ± 36, P4W 111 ± 27, LCLT0 107 ± 33, LCLT4W 112 ± 32 g, respectively; fat oxidation P0 99 ± 28, P4W 92 ± 21, LCLT0 94 ± 18, LCLT4W 90 ± 22 g, respectively). Subsequent 20 km time trial duration was shorter after P (P0 31:29 ± 3:50, P4W 29:55 ± 2:58 min:s, P < 0.01), with no significant change over LCLT (LCLT0 31:46 ± 4:06, LCLT4W 31.19 ± 4.08 min:s). Four weeks LCLT supplementation had no effect on substrate utilization or endurance performance.
Carl J. Hulston and Asker E. Jeukendrup
The purpose of this study was to investigate the possibility of a placebo effect from carbohydrate (CHO) intake during prolonged exercise. Ten endurance-trained male cyclists performed 3 experimental trials consisting of 120 min of steady-state cycling at 61% VO2max followed by a time trial (TT) lasting approximately 60 min. During exercise participants ingested either plain water (WAT), artificially colored and flavored water (PLA), or a 6% carbohydrate-electrolyte solution (CES). PLA and CES were produced with identical color and taste. To investigate the possibility of a placebo effect from CHO intake, participants were told that both flavored solutions contained CHO and that the purpose of the study was to compare CHO drinks with water. Mean power output during TT was 218 ± 22 W in WAT, 219 ± 17 W in PLA, and 242 ± 27 W in CES. Performance times were 66.35 ± 6.15, 65.94 ± 5.56, and 59.69 ± 2.87 min for WAT, PLA, and CES, respectively. Therefore, CES ingestion enhanced TT performance by 11.3% compared with WAT (p < .05) and 10.6% compared with PLA (p < .05), with no difference between PLA and WAT. In conclusion, during a prolonged test of cycling performance, in which participants were not fully informed of the test conditions, there was no placebo effect when participants believed they had ingested CHO. In contrast, the real effect of CHO intake was a 10.6% improvement in TT cycling performance.
L. Christopher Eschbach, Michael J. Webster, Joseph C. Boyd, Patrick D. McArthur and Tammy K. Evetovich
It has been suggested that Eleutherococcus senticosus (ES). also known as Siberian ginseng or ciwuija. increases fat utilization in humans. The purpose of this study was to examine the physiological responses to supplementation with ES in endurance cyclists. Using arandomized. double-blind crossover design. 9 highly-trained men (28 ± 2 years. V̇O2max 57.3±2.0 ml · kg−1 · min−1) cycled for 120 min at 60% V̇O2max followed by a simulated 10-km lime trial. Diet was controlled, and ES (1,200 mg · day−1) or a placebo (P) were administered for 7 days prior to each of the two trials. Oxygen consumption, respiratory exchange ratio, and heart rate were recorded every 30 min, and rating of perceived exertion. plasma [lactate], and plasma [glucose j were recorded every 20 min during the 120 min of steady state cycling. There were no significant differences (p > .05) between the ES and P groups at any steady-state time interval or during the cycling time trial (ES = 18.10 ± 0.42, P = 17.83 ± 0.47 min). In contrast with previous reports, the results of this study suggest that ES supplementation does not alter steady-state substrate utilization or 10-km cycling performance time.
Jeffrey B. Wheeler, Robert J. Gregor and Jeffrey P. Broker
Pedal kinetics, including the applied moment (Mz) about an axis orthogonal to the pedal surface and passing through the center of pressure, were measured across three shoe/pedal interface systems (toe-clip and strap, clipless fixed, clipless float) and three workrates (150, 250, 350 W) during steady-state cycling using specially developed multicompatible force pedals. The applied moment (Mz) at the pedal is an important contributor to the corresponding axial moment realized at the knee and has implications for studying overuse injury mechanics and prevention of cycling-related knee pain. Data were collected from 27 knee pain free (KPF) cyclists and 7 cyclists with cycling-related knee pain. The largest applied moments (Mz) were observed when clipless fixed pedals were employed, while clipless float pedals significantly attenuated the applied moment. Cyclists with chronic knee pain exhibited Mz patterns markedly different from the KPF group, supporting the theory that relatively high moments, particularly internally applied moments during the power phase, may be related to knee loads and subsequent overuse injury. Our general conclusion is that clipless pedal float designs quantifiably reduce applied moments at the shoe/pedal interface without compromising power transmitted to the bike.
M.J. Anderson, J.D. Cotter, A.P. Garnham, D.J. Casley and M.A. Febbraio
This study examined the effect of glycerol ingestion on fluid homeostasis, thermoregulation, and metabolism during rest and exercise. Six endurance-trained men ingested either 1 g glycerol in 20 ml H2O · kg−1 body weight (bw) (GLY) or 20 ml H2O · kg−1 bw (CON) in a randomized double-blind fashion, 120 min prior to undertaking 90 min of steady state cycle exercise (SS) at 98% of lactate threshold in dry heat (35 °C, 30% RH), with ingestion of CHO-electrolyte beverage (6% CHO) at 15-min intervals. A 15-min cycle, where performance was quantified in kJ, followed (PC). Pre-exercise urine volume was lower in GLY than CON (1119 ± 97 vs. 1503 ± 146 ml · 120 min−1; p < .05). Heart rate was lower (p < .05) throughout SS in GLY, while forearm blood flow was higher (17.1 ± 1.5 vs. 13.7 ± 3.0 ml · 100 g tissue · min−1; < .05) and rectal temperature lower (38.7 ± 0.1 vs. 39.1 ± 0.1 °C; p < .05) in GLY late in SS. Despite these changes, skin and muscle temperatures and circulating catecholamines were not different between trials. Accordingly, no differences were observed in muscle glycogenolysis, lactate accumulation, adenine nucleotide, and phosphocreatine degradation or inosine 5′-monophosphate accumulation when comparing GLY with CON. Of note, the work performed during PC was 5% greater in GLY (252 ± 10 vs. 240 ± 9 kJ;p < .05). These results demonstrate that glycerol, when ingested with a bolus of water 2 hours prior to exercise, results in fluid retention, which is capable of reducing cardiovascular strain and enhancing thermoregulation. Furthermore, this practice increases exercise performance in the heat by mechanisms other than alterations in muscle metabolism.