The most economical cadence increases with increasing workload

Several studies have suggested that the most economical cadence in cycling increases with increasing workload. However, none of these studies have been able to demonstrate this relationship with experimental data. The purpose of this study was to test the hypothesis that the most economical cadence in elite cyclists increases with increasing workload and to explore the effect of cadence on performance. Six elite road cyclists performed submaximal and maximal tests at four different cadences (60, 80, 100 and 120 rpm) on separate days. Respiratory data was measured at 0, 50, 125, 200, 275 and 350 W during the submaximal test and at the end of the maximal test. The maximal test was carried out as an incremental test, conducted to reveal differences in maximal oxygen uptake and time to exhaustion (short-term performance) between cadences. The results showed that the lowest oxygen uptake, i.e. the best work economy, shifted from 60 rpm at 0 W to 80 rpm at 350 W (P<0.05). No difference was found in maximal oxygen uptake among cadences (P>0.05), while the best performance was attained at the same cadence that elicited the best work economy (80 rpm) at 350 W (P<0.05). This study demonstrated that the most economical cadence increases with increasing workload in elite cyclists. It was further shown that work economy and performance are related during short efforts (~5 min) over a wide range of cadences.     

Efficiency in cycling: a review

We focus on the effect of cadence and work rate on energy expenditure and efficiency in cycling, and present arguments to support the contention that gross efficiency can be considered to be the most relevant expression of efficiency. A linear relationship between work rate and energy expenditure appears to be a rather consistent outcome among the various studies considered in this review, irrespective of subject performance level. This relationship is an example of the Fenn effect, described more than 80 years ago for muscle contraction. About 91% of all variance in energy expenditure can be explained by work rate, with only about 10% being explained by cadence. Gross efficiency is strongly dependent on work rate, mainly because of the diminishing effect of the (zero work-rate) base-line energy expenditure with increasing work rate. The finding that elite athletes have a higher gross efficiency than lower-level performers may largely be explained by this phenomenon. However, no firm conclusions can be drawn about the energetically optimal cadence for cycling because of the multiple factors associated with cadence that affect energy expenditure.     

Linear increase in optimal pedal rate with increased power output in cycle ergometry

Summary This experiment was designed to estimate the optimum pedal rates at various power outputs on the cycle ergometer. Five trained bicycle racers performed five progressive maximal tests on the ergometer. Each rode at pedal rates of 40, 60, 80, 100, and 120 rev·min^–1. Oxygen uptake and heart rate were determined from each test and plotted against pedal rate for power outputs of 100, 150, 200, 250, and 300 W. Both and heart rate differed significantly among pedal rates at equivalent power outputs, the variation following a parabolic curve. The low point in the curve was taken as the optimal pedal rate; i.e., the pedal rate which elicited the lowest heart rate or for a given power output. When the optimum was plotted against power output the variation was linear. These results indicate that an optimum pedal rate exists in this group of cyclists. This optimum pedal rate increases with power output, and when our study is compared to studies in which elite racers, or non-racers were used, the optimum seems to increase with the skill of the rider.     

Changes in heart rate recovery after high-intensity training in well-trained cyclists

Heart rate recovery (HRR) after submaximal exercise improves after training. However, it is unknown if this also occurs in already well-trained cyclists. Therefore, 14 well-trained cyclists (VO_2max 60.3 ± 7.2 ml kg⁻¹ min⁻¹; relative peak power output 5.2 ± 0.6 W kg⁻¹) participated in a high-intensity training programme (eight sessions in 4 weeks). Before and after high-intensity training, performance was assessed with a peak power output test including respiratory gas analysis (VO_2max) and a 40-km time trial. HRR was measured after every high-intensity training session and 40-km time trial. After the training period peak power output, expressed as W kg⁻¹, improved by 4.7% (P = 0.000010) and 40-km time trial improved by 2.2% (P = 0.000007), whereas there was no change in VO_2max (P = 0.066571). Both HRR after the high intensity training sessions (7 ± 6 beats; P = 0.001302) and HRR after the 40-km time trials (6 ± 3 beats; P = 0.023101) improved significantly after the training period. Good relationships were found between improvements in HRR_40-km and improvements in peak power output (r = 0.73; P < 0.0001) and 40-km time trial time (r = 0.96; P < 0.0001). In conclusion, HRR is a sensitive marker which tracks changes in training status in already well-trained cyclists and has the potential to have an important role in monitoring and prescribing training.     

Freely chosen pedal rate during free cycling on a roller and ergometer cycling

The purpose of this study was to examine the effect of regulation of work rate, computer controlled versus controlled by the subject, on the relationship between work rate, freely chosen pedal rate (FCC) and gross efficiency. Eighteen male cyclists participated in the study. One group, freely cycling (FC) on a competition bike mounted on an electromagnetic roller, could use gearing and cadence to achieve each work rate. The other group (EC) was cycling on an ergometer which enables a constant work rate, independent of cadence. Subjects performed an increasing work rate protocol from 100 W up to exhaustion. We found a strong interaction between group and work rate on cadence (P < 0.001). In the FC group, work rate affected cadence (P < 0.001), increasing from 72 rpm at 100 W to 106 rpm at 350 W. For the EC group, no work rate effect was present (average FCC 92 rpm). Gross efficiency increased with work rate for both groups. The efficiency–cadence relationship was strongly affected by the protocol. At a given work rate, very similar efficiency values were obtained at highly different cadences. The discrepancy in the FCC-work rate relationship between the EC group and the FC group may be related to the manner in which one can regulate work rate. FCC depends not only on work rate but is also affected considerably by the manner in which the work rate can be controlled by cadence. This finding may have important implications for the interpretation of the preferred pedaling rate, especially how this is related to optimizing metabolic cost.     

The effect of salbutamol on performance in endurance cyclists

The effect of salbutamol (S) on cycling performance was examined in 15 highly trained non-asthmatic male cyclists. A double-blind, randomized cross-over design was used with S or placebo (P) administered using a metered-dose inhaler and a spacer device 20 min before each testing session. The S dose was 400 μg (four puffs), which is twice the normal therapeutic level. Subjects were habituated to all the laboratory procedures in the week prior to actual data collection. The subjects performed four tests under S and P conditions on separate days over 2 weeks. These included measurement of maximal O₂ uptake (cycle ergometry) with assessment of pulmonary function before and after, a submaximal (90% of ventilatory threshold) square-wave work transition from a base of unloaded cycling, a 60-s modified Wingate test, and a simulated 20 km time trial. No significant differences were observed in any of the dependent variables related to aerobic endurance or cycling performance between the S and P conditions. These results support other findings that an acute dose (400 μg) of S has no performance-enhancing properties.     

Changes in performance,maximal oxygen uptake and maximal accumulated oxygen deficit after 5, 10 and 15 days of live high:train low altitude exposure

Nineteen well-trained cyclists (14 males and 5 females, mean initial V˙O_2max 62.3 ml kg^–1 min^–1) completed a multistage cycle ergometer test to determine maximal mean power output in 4 min (MMPO_4min), maximal oxygen uptake (V˙O_2max) and maximal accumulated oxygen deficit (MAOD). The athletes were divided into three groups, each of which completed 5, 10 or 15 days of both a control condition (C) and live high:train low altitude exposure (LHTL). The C groups lived and trained at the ambient altitude of 610 m. The LHTL groups spent 8–10 h night^–1 in normobaric hypoxia at a simulated altitude of 2,650 m, and trained at the ambient altitude of 610 m. The changes to MMPO_4min, V˙O_2max and MAOD in response to LHTL altitude exposure were not significantly different for the 5-, 10- and 15-day treatment periods. For the pooled data from all three treatment periods, there were significant increases in MMPO_4min [mean (SD) 5.15 (0.83) W kg^–1 vs 5.34 (0.78) W kg^–1] and MAOD [50.1 (14.2) ml kg^–1 vs 54.9 (13.1) ml kg^–1] in the LHTL athletes between pre- and post-altitude exposure. There were no significant changes in MMPO_4min [5.09 (0.76) W kg^–1 vs 5.16 (0.86) W kg^–1] or MAOD [50.5 (14.1) ml kg^–1 vs 49.1 (13.0) ml kg^–1] in the C athletes over the corresponding period. There were significant increases in V˙O_2max in the athletes during both the LHTL [63.2 (9.0) ml kg^–1 min^–1 vs 64.1 (9.0) ml kg^–1 min^–1] and C [62.0 (8.6) ml kg^–1 min^–1 vs 63.4 (9.2) ml kg^–1 min^–1] conditions. In these athletes, there was no difference in the impact of 5, 10 or 15 days of LHTL on the increases observed in MMPO_4min, V˙O_2max or MAOD; and LHTL increased MMPO_4min and MAOD more than training at low altitude alone. Electronic Publication     

The effects of replacing a portion of endurance training by explosive strength training on performance in trained cyclists

To investigate the effects of replacing a portion of endurance training by strength training on exercise performance, 14 competitive cyclists were divided into an experimental (E; n=6) and a control (C; n=8) group. Both groups received a training program of 9 weeks. The total training volume for both groups was the same [E: 8.8 (1.1) h/week; C: 8.9 (1.7) h/week], but 37% of training for E consisted of explosive-type strength training, whilst C received endurance training only. Simulated time trial performance (TT), short-term performance (STP), maximal workload ( ) and gross (GE) and delta efficiency (DE) were measured before, after 4 weeks and at the end of the training program (9 weeks). No significant group-by-training effects for the markers of endurance performance (TT and ) were found after 9 weeks, although after 4 weeks, these markers had only increased (P<0.05) in E. STP decreased (P<0.05) in C, whereas no changes were observed in E. For DE, a significant group-by-training interaction (P<0.05) was found, and for GE the group-by-training interaction was not significant. It is concluded that replacing a portion of endurance training by explosive strength training prevents a decrease in STP without compromising gains in endurance performance of trained cyclists. Electronic Publication     

Peak power output predicts maximal oxygen uptake and performance time in trained cyclists

Summary The purposes of this study were firstly to determine the relationship between the peak power output (W _peak) and maximal oxygen uptake (VO_2max) attained during a laboratory cycling test to exhaustion, and secondly to assess the relationship betweenW _peak and times in a 20-km cycling trial. One hundred trained cyclists (54 men, 46 women) participated in the first part of this investigation. Each cyclist performed a minimum of one maximal test during whichW _max andVO_2max were determined. For the second part of the study 19 cyclists completed a maximal test for the determination ofW _peak, and also a 20-km cycling time trial. Highly significant relationships were obtained betweenW _peak andVO_2max (r=0.97,P<0.0001) and betweenW _peak and 20-km cycle time (r= –0.91,P<0.001). Thus,W _peak explained 94% of the variance in measuredVO_2max and 82% of the variability in cycle time over 20 km. We concluded that for trained cyclists, theVO_2max can be accurately predicted fromW _peak, and thatW _peak is a valid predictor of 20-km cycle time.     

Physiological characteristics of elite short- and long-distance triathletes

The purpose of this study was to compare the physiological responses in cycling and running of elite short-distance (ShD) and long-distance (LD) triathletes. Fifteen elite male triathletes participating in the World Championships were divided into two groups (ShD and LD) and performed a laboratory trial that comprised submaximal treadmill running, maximal then submaximal ergometry cycling and then an additional submaximal run. 'In situ' best ShD triathlon performances were also analysed for each athlete. ShD demonstrated a significantly faster swim time than LD whereas V˙O_2max (ml kg^–1 min^–1), cycling economy (W l^–1 min^–1), peak power output ( , W) and ventilatory threshold (%V˙O_2max) were all similar between ShD and LD. Moreover, there were no differences between the two groups in the change (%) in running economy from the first to the second running bout. Swimming time was correlated to (r=–0.76; P<0.05) and economy (r=–0.89; P<0.01) in the ShD athletes. Also, cycling time in the triathlon was correlated to (r=–0.83; P<0.05) in LD. In conclusion, ShD triathletes had a faster swimming time but did not exhibit different maximal or submaximal physiological characteristics measured in cycling and running than LD triathletes. Electronic Publication     

Relationship between the increase of effectiveness indexes and the increase of muscular efficiency with cycling power

We determined the index of effectiveness (IE), as defined by the ratio of the tangential (effective force) to the total force applied on the pedals, using a new method proposed by Mornieux et al. (J Biomech, 2005), while simultaneously measuring the muscular efficiency during sub-maximal cycling tests of different intensities. This allowed us to verify whether part of the changes in muscular efficiency could be explained by a better orientation of the force applied on the pedals. Ten subjects were asked to perform an incremental test to exhaustion, starting at 100 W and with 30 W increments every 5 min, at 80 rpm. Gross (GE) and net (NE) efficiencies were calculated from the oxygen uptake and W _Ext measurements. From the three-dimensional force’s measurements, it was possible to measure the total force (F _Tot), including the effective (F _Tang) and ineffective force (F _Rad+Lat). IE has been determined as the ratio between F _Tang and F _Tot, applied on the pedals for three different time intervals, i.e., during the full revolution (IE_360°), the downstroke phase (IE_180°Desc) and the upstroke phase (IE_180°Asc). IE_360° and IE_180°Asc were significantly correlated with GE (r=0.79 and 0.66, respectively) and NE (r=0.66 and 0.99, respectively). In contrast, IE_180°Desc was not correlated to GE or to NE. From a mechanical point of view, during the upstroke, the subject was able to reduce the non-propulsive forces applied by an active muscle contraction, contrary to the downstroke phase. As a consequence, the term ‘passive phase’, which is currently used to characterize the upstroke phase, seems to be obsolete. The IE_180°Asc could also explain small variations of GE and NE for a recreational group.     

Revisiting the effect of posture on high-intensity constant-load cycling performance in men and women

It was recently observed that inclining the body from a supine to upright position improved the performance of high-intensity, constant-load cycling to a larger extent in men than women (Egaña et al. in Eur J Appl Physiol 96:1–9, 2006), although this gender-related effect was based on a small number of men (n  =  5) and women (n  =  5). To explore this effect further, we studied the effect of body tilt on cycling performance in a larger and different group of men (n  =  8) and women (n  =  18). Peak power, peak \({{\dot{V}}\hbox{O}_{2}}\) and the ventilatory threshold (VT) were determined during an upright maximal graded cycle test, and a high-intensity test (80% peak power) was performed to failure in both the upright and supine positions. Performance was significantly longer in the upright compared with supine position in men (17.4 ± 7.7 vs. 7.6 ± 3.4 min) and women (14.1 ± 6.0 vs. 6.0 ± 3.7 min). The magnitude of this postural effect was not significantly different between men and women; whereas it was significantly correlated with the relative intensity of exercise expressed as a function of VT (r  =  ?0.39). These data demonstrate that the postural effect on high-intensity cycling performance is not influenced by gender; but that it is related to the intensity of exercise relative to the ventilatory threshold.     

Occurrence of electromyographic and ventilatory thresholds in professional road cyclists

The temporal relationship between the electromyographic (EMG) and ventilatory thresholds was investigated during incremental exercise performed by eight professional road cyclists. The exercise, performed on a cycloergometer, started at 100 W with successive increments of 26 W·min^–1 until exhaustion. Gas exchange and the root mean square value of EMG (RMS) from eight lower limb muscles were examined throughout the exercise period. Professional cyclists achieved a maximal oxygen consumption, i.e. O_2max, of 5.4 (0.5) l·min^–1 [74.6 (2.5) ml·min^–1·kg^–1, range: 67.8–82.4 ml·min^–1·kg^–1] and a maximum power (W_max) of 475 (30) W (range: 438–516 W). Our results showed at least the occurrence of a first EMG threshold (EMG_Th1) in 50% (gastrocnemius lateralis) of the subjects and a second EMG threshold (EMG_Th2) in 63% (gastrocnemius medialis). EMG_Th1 occurred significantly before the first ventilatory threshold (VT₁), i.e. at 52 (2)% and 62 (9)% of W_max, respectively. Inversely, no significant difference was observed between the occurrence of EMG_Th2 and the second ventilatory threshold (VT₂), i.e. at 86 (1)% and 89 (7)% of W_max, respectively. These results suggest that the use of EMG may be a useful non-invasive method for detecting the second ventilatory threshold in most of the muscles involved in cycling exercise.     

The anthropometrical and physiological characteristics of elite water polo players

In order to examine the physical and physiological demands of water polo, we assessed the profile of elite water polo players. Nineteen male professional water polo players (age: 25.5±5.0 years, height: 184.5±4.3 cm body mass: 90.7±6.4 kg) underwent body composition assessment by dual-energy X-ray absorptiometry. We also evaluated peak oxygen consumption O_2peak, lactate threshold (LT), energy cost of swimming (C_s), anaerobic capacity and isokinetic shoulder strength. Body fat (%) was 16.8±4.4, lean mass (LM) 75.1±4.9 kg and bone mineral density (BMD) 1.37±0.07 g·cm^–2 . O_2peak was 57.9±7 ml·kg^–1· min^–1 . LT was identified at 3.9±0.7 mmol·l^–1 at a swimming velocity (v) of 1.33±0.05 m·s^–1 with a heart rate of 154±7 bpm, corresponding to an intensity of 83±9 of O_2peak. The average C_s of swimming at the LT was 1.08±0.04 kJ·m^–1 . C_s at LT was correlated to body mass index (BMI) (r=0.22, P=0.04) and to swimming performance at 400 m (r=0.86, P=0.01) and 4×50 m (r=0.84, P<0.01). Internal rotator muscles were stronger compared to the external rotators by a 2:1 ratio. This study provides a quantitative representation of both physical and physiological demands of water polo and proposes a comprehensive battery of tests that can be used for assessing the status of a team.     

Salivary IgA response to prolonged exercise in a hot environment in trained cyclists

The aim of this study was to determine the effects of prolonged exercise in hot conditions on saliva IgA (s-IgA) responses in trained cyclists. On two occasions, in random order and separated by 1 week, 12 male cyclists cycled for 2 h on a stationary ergometer at 62 (3)% O_{2 max} [194 (4) W; mean (SEM)], on one occasion (HOT: 30.3°C, 76% RH) and on another occasion (CONTROL: 20.4°C, 60% RH). Water was available ad-libitum. Venous blood samples and 2-min whole unstimulated saliva samples were collected at pre, post and 2 h post-exercise. The s-IgA concentration was determined using a sandwich-type ELISA. Exercising heart rate, rating of perceived exertion, rectal temperature, corrected body mass loss (P<0.01) and plasma cortisol (P<0.05) were greater during HOT. The decrease in plasma volume post-exercise was similar on both trials [HOT: –6.7 (1.1) and CONTROL: –6.6 (1.3)%; P<0.01]. Saliva flow rate decreased post-exercise by 43% returning to pre-exercise levels by 2 h post-exercise (P<0.05) with no difference between trials. Saliva IgA concentration increased post-exercise (P<0.05) with no difference between trials. Saliva IgA secretion rate decreased post-exercise by 34% returning to pre-exercise levels by 2 h post-exercise (P<0.05) with no difference between trials. These data show that a prolonged bout of exercise results in a reduction in s-IgA secretion rate. Additionally, these data demonstrate that performing prolonged exercise in the heat, with ad libitum water intake, does not influence s-IgA responses to prolonged exercise.     

A physiological counterpoint to mechanistic estimates of “internal power” during cycling at different pedal rates

Reported values of internal power (IP) during cycling, generated by the muscles to overcome energy changes of moving body segments, are considerably different for various biomechanical models, reflecting the different criteria for estimation of IP. The present aim was to calculate IP from metabolic variables and to perform a physiological evaluation of five different kinematic models for calculating IP in cycling. Results showed that IP was statistically different between the kinematic models applied. IP based on metabolic variables (IP_met) was 15, 41, and 91 W at 61, 88, and 115 rpm, respectively, being remarkably close to the kinematic estimate of one model (IP_Willems-COM: 14, 43, and 95 W) and reasonably close to another kinematic estimate (IP_Winter: 8, 29, and 81 W). For all kinematic models there was no significant effect of performing 3-D versus 2-D analyses. IP increased significantly with pedal rate – leg movements accounting for the largest fraction. Further, external power (EP) affected IP significantly such that IP was larger at moderate than at low EP at the majority of the pedal rates applied but on average this difference was only 8%.     

The effect of cycling followed by running on respiratory muscle performance in elite and competition triathletes

This study investigated the possibility of there being differences in respiratory muscle strength and endurance in elite and competition triathletes who have similar maximal oxygen uptakes (VO_2max) and ventilatory thresholds (Th_vent). Five internationally-ranked elite, [mean (SD) age 23.8 (1.4) years] and six nationally- and regionally-ranked competition [age 21.1 (1.1) years] male triathletes performed two successive trials: first an incremental cycle test to assess VO_2max and Th_vent and second 20 min of cycling followed by 20 min of running (C-R) at intensities higher than 85% VO_2max. Cardioventilatory data were collected every minute during the two trials, using an automated breath-by-breath system. Maximal expiratory and inspiratory (P _Imax) strength were assessed before and 10 min after C-R from the functional residual capacity. Respiratory muscle endurance was assessed 1 day before and 30 min after C-R by measuring the time limit (t _lim). The results showed firstly that during C-R, the competition triathletes had significantly (P<0.05) higher minute ventilation [mean (SEM) 107.4 (3.1) compared to 99.8 (3.7) l·min^–1], breathing frequency [44.4 (2.0) compared to 40.2 (3.4) ·min^–1] and heart rate [166 (3) compared to 159 (4) beats·min^–1] and secondly that after C-R, they had significantly lower P _Imax [127.1 (4.2) compared to 130.7 (3.0) cmH₂O] and t_lim [2:35 (0:29) compared to 4:12 (0:20) min] than the elite triathletes. We conclude that, despite similar VO_2max and Th_vent, the competition triathletes showed less extensive adaptive mechanisms, including those in the respiratory muscles, than did the elite triathletes. This led to higher ventilation, which appeared to be the cause of the faster development of fatigue in the inspiratory muscles in this group. Electronic Publication     

Validity of a velodrome test for competitive road cyclists

The aim of this study was to evaluate the validity of a velodrome field test consisting of repeated rides of 2,280 m, with an initial speed of 28 km·h^–1 and increments of 1.5 km·h^–1 interspersed with 1-min recovery periods until exhaustion. A group of 12 male competitive road cyclists performed maximal cycling tests under velodrome and laboratory conditions. Velodrome oxygen uptake ( O₂) and power output were estimated using equations previously published. Physiological responses to the two tests were compared. Relationships between performance in the velodrome and physiological parameters measured in the laboratory were studied. Maximal power output, heart rate and O₂ were similar in the velodrome and the laboratory [372 (SD 50) vs 365 (SD 36) W, 195 (SD 8) vs 196 (SD 9) beats·min^–1 and 4.49 (SD 0.56) vs 4.49 (SD 0.46) l·min^–1, respectively], while maximal velodrome blood lactate concentration was significantly higher [13.5 (SD 2.1) vs 11.8 (SD 3.1) mmol·l^–1]. Velodrome heart rate was higher at submaximal exercise intensities representing 40%, 50% and 60% of maximal aerobic power, and velodrome blood lactate concentration was also higher at 60%, 70% and 80% of maximal aerobic power. The laboratory parameter that showed the highest correlation with the maximal cycling speed in the velodrome was maximal oxygen uptake ( O_2max) expressed per unit of body mass (r = 0.93). In addition, the accuracy of different methods of estimation of the metabolic cost of cycling, rolling resistance, air resistance coefficients and O_2max were compared. Significant differences were found. In conclusion, the present results indicated the validity of a velodrome test used to estimate maximal aerobic parameters of competitive road cyclists, as long as the estimation is made using established equations. When road cyclists are tested in the laboratory, physiological values should be expressed per unit of body surface area or body mass, to predict more accurately the cyclist's performance level under specific field conditions.     

The role of muscle pump in the development of cardiovascular drift

This study examined the role of muscle pump in the development of cardiovascular drift (CV_drift) during cycling. Twelve healthy males (23.4 ± 0.5 years, mean ± SE) exercised for 90 min with 40 and 80 pedal revolutions per minute (rpm) at the same oxygen consumption, in two separate days. CV_drift was developed in both conditions as indicated by the drop in stroke volume (SV) and the rise in heart rate (HR) from the 20th min onwards (ΔSV = −16.2 ± 2.0 and −17.1 ± 1.0 ml beat⁻¹; ΔHR = 18.3 ± 2.0 and 17.5 ± 3.0 beats min⁻¹ for 40 and 80 rpm, respectively, P < 0.05) but without difference between conditions. Mean cardiac output (CO₂ rebreathing) was 14.7 ± 0.3 l min⁻¹ and 15.0 ± 0.3 l min⁻¹, and mean arterial pressure was 100.0 ± 1.0 mmHg and 96.7 ± 0.8 mmHg for 40 and 80 rpm, respectively, without significant changes over time, and without difference between conditions. Electromyographic activity (iEMG) was lower throughout exercise with 80 rpm (35.6 ± 1.2% and 11.0 ± 1.0% for 40 and 80 rpm, respectively). Similarly, total hemoglobin, determined with near-infrared spectroscopy (NIRS) was 58.0 ± 0.8 (AU) for 40 rpm and 53.0 ± 1.4 (arbitrary units) for 80 rpm, from 30th min onwards (P < 0.05), an indication of lower leg blood volume during the faster pedal rate condition. Thermal status (rectal and mean skin temperature), blood and plasma volume changes, blood lactate concentration, muscle oxygenation (NIRS signal) and the rate of perceived exertion were similar in the two trials. It seems that muscle pump is not an important factor for the development of CV_drift during cycling, at least under the present experimental conditions.     

Reliability of a cycling time trial in a glycogen-depleted state

The aim of this study was to investigate the reliability of a protocol designed to simulate endurance performance in events of long duration (∼5 h) where endogenous carbohydrate stores are low. Seven male subjects were recruited (age 27 ± 7 years, VO_2max 66 ± 5 ml/kg/min, W _max 367 ± 42 W). The subjects underwent three trials to determine the reliability of the protocol. For each trial subjects entered the laboratory in the evening to undergo a glycogen-depleting exercise trial lasting approximately 2.5 h. The subjects returned the following morning in a fasted state to undertake a 1-h steady-state ride at 50% W _max followed by a time trial of approximately 40-min duration. Each trial was separated by 7–14 days. The trials were analysed for reliability of time to completion of the time trial using a coefficient of variation (CV), with 95% confidence intervals (data are mean ± SD). The times to complete the three trials were 2,546 ± 529, 2,585 ± 490 and 2,568 ± 555 s for trials 1, 2 and 3, respectively. The CV between trials 1 and 2 was 4.5% (95% CI 2.9–10.4%) and between trials 2 and 3, 3.8% (95% CI 2.4–9.9%). There was no difference in oxygen uptake, respiratory exchange ratio, carbohydrate oxidation, fat oxidation, plasma glucose concentration and plasma lactate concentration between the three trials. Therefore we can conclude that prior glycogen depletion does produce a reliable measure of performance with metabolic characteristics similar to ultraendurance exercise.