Fourteen specifically trained subjects were solicited for this study. They had at least 5 years of competitive cycling experience and trained 8 hours per week in sprint track cycling and/or BMX. All were successful at national-level events and none had any history of pathology of the lower-limb muscles or joints.
Three subjects were not retained in data processing because of signal loss in the collection of ventilatory data or non observance of the given pedalling rate. Then, eleven trained men (age 24.9 ± 6.5 y, height 1.79 ± 0.05 m and body mass 75.3 ± 8.2 kg) volunteered for this study. They were informed of the nature of the study, and the possible risks and discomforts associated with the experimental procedures, before giving their written consent to participate. The experimental design of the study was approved by the local Ethics Committee of Saint-Germain-en-Laye (France; acceptance n°2009-A01004-53), and was carried out in accordance with the Declaration of Helsinki.
The protocol, carried out during the pre-competition period, included two sessions separated by two days: (1) a first session consisting of anthropometric measurements, resting spirometric monitoring (volume and flow), a torque-velocity cycling test, and an incremental test performed until exhaustion on a calibrated cycle ergometer, (2) a second session consisting of a constant-load, supra-maximal cycle test performed until exhaustion; in a pilot study, we observed that the body temperature was not increased by more than 1°C during this test.
During the first visit, anthropometric data were recorded, subjects were familiarized with the spirometric tests to be performed in this study, and three resting spirometric tests were recorded in order to test the reliability of the measures (Figure 3). Subjects began with a warm-up of 15 min of cycling at 100–150 W, 1 min of recovery and a 5-s sprint. After a 5-min recovery, participants were asked to perform three maximal cycling sprints (5 s separated by 3 min of recovery) according to a previous protocol (Dorel et al. 2010). Three different resistive torques of 0, 0.4-0.7, 1–1.5 Nm/kg body mass were applied to obtain maximal force and power values over a large range of pedaling rates among the three bouts. After computation, the data from the three sprints were used to draw force- and power-velocity relationships and hence to determine maximum power (Pmax) and the corresponding specific optimal pedaling rate (f
opt) at which Pmax occurred (for details, see (Dorel et al. 2010)).
After 20 min of rest, they performed an incremental cycle test (IT) to determine their and power output at (, i.e. the power that elicited ). The progressive protocol consisted of 6 min of pedaling at 100 W followed by a stepped ramp increase in power output of 20 W.min-1 until volitional exhaustion. Participants were instructed to maintain their chosen preferred cadence for as long as possible, and the test was completed when the cadence fell more than 10 rpm below this value for more than 5 s despite strong verbal encouragement. All respiratory and cardiac variables were recorded continuously.
During the second session, subjects were asked to perform a standard warm-up: 8 min at 150 W, 2 min at 260 W, a recovery period (i.e., 2 min), a 10-s sprint of progressively increasing intensity with the last 3 s performed at a maximal all-out intensity, 90 s of recovery and finally two brief all-out sprints (5 s in duration) interspersed with 90 s of recovery. After a further 10 minutes of passive recovery, subjects performed the cycling exercise (Tlimsupra) at a constant power output (PsupraΔ30%) for as long as possible until exhaustion. PsupraΔ30% was defined as the supra-maximal intensity above MAP corresponding to an increment of 30% of the difference between Pmax (estimated from torque-velocity test) and . Subjects were required to keep a constant pedalling rate (i.e., corresponding to f
opt minus 10%). No information relative to test duration was given to the subjects. The test continued until complete exhaustion: either until the cyclists voluntarily chose to stop the exercise or until they were no longer able to maintain their initial test cadence (± 3 rpm), which was considered as a failure to maintain the required task (i.e., the target power output at a constant cadence). Respiratory and cardiac responses were recorded continuously during the entire experimental session. Arterialised capillary blood samples (85 μL) were taken from a hyperemized ear-lobe just before the start of Tlimsupra (7 min after the end of the warm-up), at exhaustion, and 5 and 8 min during the passive recovery.
Material and data collection/processing
All testing sessions took place in a well-ventilated laboratory at a temperature of 20–22°C and were conducted using an electronically-braked cycle ergometer (Excalibur Sport, Lode, Groningen, The Netherlands). Vertical and horizontal positions of the saddle, handlebar height, crank and stem lengths were set to match the most comfortable and usual position of the participants.
Spirometric variables, [i.e. forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), Tiffeneau index (FEV/FVC), forced inspiratory volume (FIVC) forced inspiratory volume in 1 s (FIV1), forced expiratory flow at that point that is 25, 50 or 75% from FVC (FEV25, 50 or 75)] (Figure 2A) were measured with an ergospirometric device (Spirobank II, MIR, Roma, Italy) before and 3 min after the end of Tlimsupra. The precision and reproducibility of the data (FEV1 and FVC) have been reported (Liistro et al. 2006). Before Tlimsupra, a minimum of three satisfactory inspiratory and expiratory efforts were conducted with the highest measurement being defined as maximal. At the end of the Tlimsupra, and due to time-constraints (recovery influence), only one satisfactory measurement was asked to the subjects in order to measure the exercise-induced changes in the respiratory function.
During both IT and Tlimsupra, , , CO2 production , respiratory frequency (RF), VT and end-tidal oxygen tension (PETO2) were recorded breath by breath with a fixed gas exchange system (Quark CPET, Cosmed, Roma, Italy). Calibration of the gas analyser was performed according to the manufacturer’s instructions before each test for each subject. To avoid artefacts in recording signals, the finger was warmed with a vasodilator ointment 10–15 min before starting the measurement. The apparatus was automatically calibrated before each test. During the IT, breath-by-breath gas exchange values were smoothed (i.e., 3-s central moving average). In order to characterize the subjects, the highest value in a 30-s period was considered as the . The criteria used for the determination of were threefold: a plateau in despite an increase in power output, a respiratory exchange ratio (RER) above 1.1, and a heart rate (HR) above 90% of the predicted maximal HR. For the purpose of comparing, over the same period of sampling, with the peak value of measured during Tlimsupra, the highest 5-s average was also determined. To determine during Tlimsupra (and as previously reported (Hanon et al. 2010)), values were smoothed (i.e. 3-s central moving average) and then a 5-s average was applied in order to compare and other ventilatory responses (VT, RF, ), with those of cardiac output (CO), stroke volume (SV) and changes in SaO2 at the same time.
For Tlimsupra, the end value was defined as the average during the last 5-s period and the decrease was considered as . The decline was considered as a decrease, when the magnitude of the phenomenon was larger than 5% of the peak value while the power of exercise continued to be above (Billat et al. 2009). The same criterion was applied to the other cardio-respiratory variables.
The of the respiratory muscles (VRMO2, expressed in mL.min-1), was calculated from the work of breathing (WB, kg.min-1) using the equation proposed by Coast et al. (Coast et al. 1993):
The ventilatory reserve (VR) was defined as expressed as a percent of the estimated resting MVV (maximal voluntary ventilation):
(Johnson et al. 1996).
A bio-impedance method was used to determine SV, HR and CO (Physioflow, Manatec Type PF05L1, Strasbourg, France). The basis for this technique and its application, validity and reliability for exhaustive exercise testing have been described (Lepretre et al. 2004), and it has been demonstrated that thoracic hyperinflation does not alter CO (Charloux et al. 2000). For this experiment, SV, HR and CO values were averaged every five seconds.
Blood metabolic responses
Prior to, 0 and 3 min post-IT, blood samples were collected and analysed for lactate concentration using a Lactate Pro analyser (Arkray, Japan). Prior to and post-Tlimsupra session, arterialised capillary blood samples (85 μL) were analysed to measure blood pH, [La], SaO2, PaO2 and CO2 (PaCO2) and bicarbonate concentration ([HCO3
-]) with an i-STAT dry chemistry analyser (Abbott, Les Ulis, France).
Data are reported as mean ± SD. Because subjects did not perform exactly the same exercise duration, data were expressed relative to the % of total duration (every 5% of Tlimsupra duration) for Figure 1 and for ANOVA. Changes in gas-exchange variables during Tlimsupra were evaluated by a one-way analysis of variance (ANOVA), with repeated-measures across each 5% interval, followed by multiple comparisons (Student-Newman-Keuls) to test the effect of time on the variables. The intra-class correlation (ICC) was calculated for pre-test spirometric data. Relationships between variables (ventilatory, cardio-dynamic, arterial oxygen saturation, metabolic parameters and ) at different times of the test and final Tlimsupra performance were analyzed by a Pearson’s correlation coefficient. In order to measure the strength of the relationship between the decrease and a given variable, while controlling the effect of the other variables, Pearson partial correlations were also calculated. The level of significance was set at P < 0.05. Finally, aiming to compare the difference in main variables, between the subject who exhibited a > 5% decrease in and the others, effect sizes (ES) were calculated using Cohen’s d. Effect sizes of 0.8 or greater, around 0.5 and 0.2 or less were considered as large, moderate, and small, respectively. The level of significance was set at P < 0.05.