Biomechanical parameters measurement.
For all experimental conditions, a pressure sensor fixed on the runner’s right shoe was used to determine the period between two ground contacts for the same foot. From this signal, the stride duration was continuously recorded and stride pattern characteristics (i.e., stride rate: SR and stride variability: SV) were calculated during the first 5 min (0–5 min) and the last 5 min (10–15 min) of each running bout.
All data were expressed as mean ± standard deviation (SD). The locomotor pattern variability during running was described using the coefficient of variation (SD/mean × 100) for each athlete (3). A two-way variance analysis plan (2 × 3) for repeated measures was performed to analyze the effect of the period time and the cycling cadence by using V̇O2, V̇E, RER, SR, and SV values as dependant variables. For this analysis, the stride variability (in %) was analyzed after an arcsine transformation. Newman-Keuls post hoc test was used to determine differences among all pedaling cadences and periods during exercise. A paired t-test was used to analyze a) differences in V̇O2max, V̇Emax, and V̇O2 at VT values between the two incremental tests and b) variations between the energetically optimal cadence and the freely chosen cadence during CTeoc. The 0.05 level of significance was used for all statistical procedures.
The mean data for the maximal parameters recorded during the two incremental tests are presented in Table 1. No significant differences (P > 0.05) were found concerning V̇O2max, V̇Emax, and V̇O2at VT values recorded during the incremental cycling and running tests. These results indicate the homogeneity of aerobic aptitude of our triathletes whatever the locomotion mode.
The energetically optimal cadence determination.
The quadratic trend for the description of the V̇O2-cadence relationship was found in all subjects, and the mean value of regression coefficient was r = 0.80 ± 0.2. The mathematical determination of the mean EOC (lower point) was identified at 72.3 ± 5.0 rpm (range 63.5–78.1 rpm). A significant difference was identified between EOC and FCC during CTeoc (72.3 ± 5.0 vs 81.9 ± 11.7 rpm, P < 0.05).
Cycling Bouts of C-R
The mean values in pedaling cadences recorded during the 30-min exercise were for MOC, FCC, and EOC bouts: 90.2 ± 0.8, 81.2 ± 7.2, and 72.5 ± 4.6 rpm, respectively. The statistical analysis indicated a significant difference between the mean values in the three cycling cadences (P < 0.05). No significant variation in FCC was found during the 30-min cycling (respectively for the 3- to 5-min and 28- to 30-min intervals: 81.1 ± 7.5 vs 81.3 ± 7 rpm, P > 0.05). Lastly, no significant differences in FCC and EOC were observed between the third session (CTeoc) and C-R sessions (P > 0.05).
Table 2 shows the changes in physiological parameters during the experimental protocol. A significant effect of the exercise duration was observed on ΔV̇O2 during the first 30-min (V̇O2(28–30)-V̇O2(3–5), P < 0.05) only during MOC and FCC bouts (+12.0% and +10.4%, respectively), whereas no significant difference in ΔV̇O2 was found at EOC (P > 0.05). During the 30-min cycling, V̇O2 values recorded during EOC were significantly lower than those reported in the other conditions (P < 0.05). Furthermore, a significant increase in ΔV̇E during the 30 min (V̇E(28–30)-V̇E(3–5) was identified only during MOC (+26.1%;P < 0.05). Within this framework, the cost of ventilation (VRMO2, in mLO2·min−1) significantly increased between the 3- to 5-min and 28- to 30-min intervals (+48.7%) and represented 26.8% of V̇O2 rise.
Cycle-Run Succession Sessions
The results are presented in Table 3. Whatever the prior cycling cadence, the stride rate (SR) recorded during the subsequent run was significantly higher than during the isolated run (+7.2%). No significant difference in stride variability (SV) was found whatever the condition (P > 0.05).
In agreement with previous results (12), no significant variation in mean V̇O2 and V̇E was observed during the IR session. Conversely, a significant effect of a prior cycling exercise was observed on V̇O2 values during the subsequent run (P < 0.05, Table 2). In comparison with the isolated run, oxygen uptake and ventilation values were significantly higher whatever the prior pedaling cadence (V̇O2: +11.7% and V̇E: +15.7%, P < 0.05). The cost of ventilation (VRMO2, in mLO2·min−1) significantly increased during the run of C-R sessions when compared with the IR session (+39.6%) and represented 26.3% of V̇O2 rise. Furthermore, a significant increase in ΔV̇O2 during the 15-min subsequent run (V̇O2(43–45)-V̇O2(33–35) was identified during the MOC-run and FCC-run sessions (+4.1% and +3.6% respectively, P < 0.05). In contrast, no rise in ΔV̇O2 was observed during the EOC-run session, and the V̇O2 values recorded during this condition were significantly lower than those obtained in the other conditions (P < 0.05).
The main findings of this study indicate a significant effect of pedaling cadence choice on oxygen uptake variability with exercise duration during cycling bouts and during the subsequent run of cycle-run succession sessions. Furthermore, our results confirm the significant alteration in energy cost of running (Cr) after a prior cycling bout when compared with an isolated run session.
Cycling economy and exercise duration.
The present results show a decrease in cycling economy (CE, i.e., V̇O2 during submaximal cycling at a given work rate) after a 30-min exercise performed at the theoretical mechanical optimal cadence (MOC, 90 rpm; (21) and at the freely chosen cadence (FCC, 81.2 ± 7.2 rpm). In contrast, no significant variation in CE was observed at the energetically optimal cadence (EOC, 72.5 ± 4.6 rpm) with exercise duration. To the best of our knowledge, little information is available concerning the effect of pedaling cadence choice on CE during prolonged exercise (3,5). In a first study, Coast et al. (5) have not reported any cadence choice effect (40–120 rpm) on CE during a 20-min exercise at 85% V̇O2max (approximately 300 W) in five cyclists. However, Brisswalter et al. (3) reported an effect of cycling cadence (50–110 rpm) on CE during a 30-min cycling exercise conducted at 80% of the maximal power output (291.0 ± 25 W) in 10 triathletes. Our values recorded for a power output corresponding to 272.1 ± 17.9 W are in agreement with this previous study and indicate a significant effect of pedal cadence choice on V̇O2 variability during a 30-min cycling bout.
During moderate- to high-intensity exercise, one of the factors often used to explain changes in V̇O2 with exercise duration and pedal cadence manipulation is a modification in muscle fiber recruitment (3,24). Within this framework, Woledge (30) has suggested that the supplementation of Type I by Type II fibers during prolonged exercise would be linked to a decrease in thermodynamic muscle efficiency leading to an increase in energy cost. Thus, in our study, one first hypothesis could relate the increase in ΔV̇O2 at high pedal cadences (>80 rpm) during the first 30-min of cycling to an additional recruitment of Type II muscle fibers, which have a lower muscle efficiency (i.e., higher energy phosphate produced per oxygen molecule consumed) than Type I fibers (30). On the contrary, no variation in cycling economy was observed after a 30-min exercise at EOC, providing support for the hypothesis that the adoption of this cadence in subjects could be related to the greater participation of Type I fibers. Nevertheless, the relationship between pedaling cadence, muscle fibers recruitment (based on iEMG), and cycling economy is not clearly identified. Therefore, it could be interesting in such studies to analyze simultaneously the cycling economy variability and the activity of the larger working muscle mass involved in cycling at different cadences (range 50–110 rpm) during prolonged exercise.
In this study, our triathletes spontaneously choose a pedaling cadence (81 rpm) significantly higher than the most economical cadence (73 rpm). The choice of high pedaling cadence leads to an increase in oxygen uptake classically related to an increase in internal work for repetitive limb movements (8,26) and/or to an increase in the ventilation cost (6). On the one hand, Francescato et al. (8) have indicated that the fraction of overall V̇O2 consumption due to internal work for a subject pedaling at 100 W and 60 rpm was about 0.2 while this fraction was about 0.6 at 100 rpm. On the other hand, for mean group values, our results show a significant increase of V̇E only at the end of MOC bout. Based on the equations proposed by Coast et al. (6), the cost of ventilation estimated from the increase in the work of breathing (WB) could explain approximately only 26.8% of the V̇O2 increase with exercise duration.
Our data confirm previous results indicating that minimization of aerobic demand is not a key determinant of preferred cadence choice in trained subjects (3,19,26,27). For cycling exercises of short duration, an apparent conflict is systematically observed between the energetically optimal cadence and the self-selected cadence in experienced cyclists, trained runners (19,27), or triathletes (3). Several hypotheses are advanced to explain the adoption of high pedaling cadences. On the one hand, it has been reported that the peak pedal force in cyclists reached a minimum value for cadences between 90 and 100 rpm (23), suggesting a pedaling skill to reduce pedal force at the highest pedaling cadences (26). Within this framework, Takaishi et al. (27) hypothesized that the reason that cyclists adopt a higher cadence is closely related to the reduction of neuromuscular fatigue in working muscles (i.e., minimum value of muscles iEMG) rather than the economy (i.e., less energy expenditure) for pedaling-exercise. On the other hand, Marsh and Martin (19) have suggested that aerobic fitness level may become important in preferred cadence selection because trained runners with no cycling experience but a history of endurance training selected high pedaling cadences comparable to those reported in experienced cyclists. However, for long-duration cycling exercise (>30 min), this discrepancy between the energetically optimal cadence and the self-selected cadence is not systematically observed in triathletes (17,28). Recent studies have indicated a reduction in FCC toward the most economical cadence after 1-h and 2-h cycling exercise at a constant power output (17,28). Further multidisciplinary studies seem therefore necessary to study factors that decide preferred cadence especially during prolonged exercise.
Cycling exercise and energy cost of the subsequent run.
According to previous results (11–13), the energy cost of running (Cr, i.e., V̇O2 during submaximal running at a given intensity) was significantly higher after cycling bouts when compared with an isolated run session (+11.7%). The mean relative values of V̇O2 for IR and C-R sessions ranged from 74.5 to 83% V̇O2max, respectively. These results recorded after 45 min of exercise could be related to those reported by several authors, comparing either an overground triathlon race or a simulated cycle-run succession in laboratory with an isolated run (respectively for IR vs C-R: 73 and 77 vs 78 and 83% V̇O2max) (11–13).
Within this framework, the change in stride rate-stride length combination is often suggested to account for a substantial portion in the Cr variability (4). In our study, the 7.2% increase in stride rate during C-R sessions may be linked to an increase in mechanical work and therefore to the increase of energy cost of running. This result is in agreement with previous studies that have showed, with the appearance of fatigue, a significant increase in stride rate and a decrease in stride length to maintain constant the running speed (7). This could suggest in our study that when subjects realized a cycle exercise just before running, the fatigue process in the lower limb musculature is important and could explain, in part, the difference in energy cost between the isolated run and the cycle-run succession session.
Cycling cadence choice and energy cost variability in running.
One of the most interesting findings of this study is the observation of a continual increase in V̇O2 during the 15-min run after the highest pedal cadences (MOC, FCC). For exercise lasting less than 15 min, the continual increase in V̇O2 beyond the 3rd min of exercise (i.e., delayed steady state) has been termed the slow component of oxygen uptake kinetics (V̇O2SC) (1,2,14,24). According to previous studies, the work rate of exercise associated with the appearance of a V̇O2SC is above lactate or ventilatory thresholds (i.e., heavy exercise) (2,14,24). Postulated mechanisms responsible for this V̇O2SC include rising muscle temperature (i.e., Q10 effect), cardiac and ventilatory muscle work, lactate kinetic, catecholamines, and recruitment of less-efficient Type II muscle fibers (24).
In our study, one possible explanation for the appearance of a V̇O2SC during the subsequent run (MOC-run and FCC-run) could be the difference in metabolic level of exercise recorded at the end of MOC and FCC bouts. This first hypothesis could be linked to previous studies (1,25,27) which suggest that a relationship exists between the appearance of a V̇O2SC and the progressive greater use of fast-twitch motor units during a 15-min bout of cycling performed at a high intensity.
Classically, it has been reported that a progressive increase in exercise intensity would be expected to recruit a larger population of Type II fibers (24,25,27). In our study, the work intensity at the end of cycling bout ranges from 78% V̇O2max for the EOC-run session to 84–85% V̇O2max for MOC-run and FCC-run sessions. Thus, we suggest that more Type II fibers are recruited at the start of the running session after the FCC and MOC bouts. Conversely, our results show a lower energy cost during the 30-min cycling exercise and during the 15-min subsequent run session when subjects adopt the energetically optimal cadence at the same power output. Because of the lower metabolic intensity (i.e., 78% V̇O2max after cycling exercise), we hypothesized that the adoption of EOC induce a lower proportion of Type II fibers during the 30-min exercise. These hypothesis could explain, for a part, a reduction in V̇O2SC during the subsequent run and appear to be in agreement with results of Barstow et al. (1), who have reported a correlation between the reduction of V̇O2SC and the percentage of Type I fibers in the vastus lateralis. Nevertheless, this relationship between the V̇O2SC and the nature of fiber recruitment has not been systematically validated.
Recently, Lucia et al. (18) have reported the appearance of a V̇O2SC without any changes in EMG data (rms-EMG and mean power frequency) recorded during a 20-min exercise at a high power output in professional cyclists. Furthermore, most of the previous studies have investigated the mechanisms underlying the V̇O2SC during an isolated running (2) or a cycling exercise (1), indicating a larger V̇O2SC in cycling when compared with running (14). Within this framework, to the best of our knowledge, no information is available concerning the V̇O2SC during a run session after a cycling exercise. During the last decade, some authors have analyzed the effects of prior high-or low-intensity cycling on V̇O2SC of subsequent high-intensity cycling exercise (9,16). These authors have showed a significant reduction in V̇O2SC (between the 3rd min and the 6th min) after a prior high-intensity exercise. Gerbino et al. (9) have suggested that this reduction in V̇O2SC during the second cycling exercise could be explained by hemodynamic modifications leading to an improvement of muscle perfusion.
According to this hypothesis, one explanation of our results could be the difference in muscle perfusion between a run realized after cycling and an isolated run. For instance, Matsui et al. (20) have measured muscular blood flow immediately after treadmill and bicycle exercise and reported that the blood flow in the thigh after a cycling exercise test was significantly higher than that in the calf. In addition, these authors reported no significant difference in blood flow between thigh and calf after treadmill running exercise. Moreover, during cycling Gotshall et al. (10) have suggested a muscle overperfusion with increasing pedaling cadences (from 50 to 110 rpm) during a 5-min cycling exercise. This improved perfusion of the working musculature consequent to the higher cycling cadence was explained by an increase in muscle blood flow and a decrease in systemic vascular resistance. Therefore, based on these previous results we hypothesize that during cycling, activated muscles (i.e., vastus lateralis and medialis) (26,27) become overperfused with increasing pedaling cadence (10). In contrast, the muscles used in running (i.e., muscles of the calf) become relatively less perfused during the cycling task. Later, during running, these previously less active calf muscles become active, accounting for the greater V̇O2SC during the subsequent run. Future research is necessary to validate this previous hypothesis because of the inconsistency of results in this area.
In conclusion, results of this study indicate that prior high cycling cadences (MOC, FCC) contribute to the appearance of a V̇O2 slow component during subsequent running. However, the choice of the energetically optimal cadence leads to a reduction in energy cost of locomotion during cycling and the subsequent run. Thus, we suggest that cycling near the energetically optimal cadence is beneficial in term of V̇O2 after 30 min and could become a strategy in anticipation of the running performance. In the context of multisport activities such as triathlon or duathlon, further investigations are necessary to identify metabolic and neuromuscular mechanisms underlying relationships between prior cycling cadences and energy cost of running variability during subsequent running. Also missing is the need for future performance-based evaluations of different cycling to run strategies.
The authors gratefully acknowledge all the triathletes who took part of the experiment for their high cooperation and motivation.
Address for correspondence: F. Vercruyssen, Unité Ergonomie Sportive et Performance, Université de Toulon-Var, Avenue de L’université, BP 132, F-83957 La Garde cedex, France; E-mail: email@example.com.
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Keywords:©2002The American College of Sports Medicine
LOCOMOTION; TRIATHLETES; ENERGY COST; CYCLE-RUN SUCCESSION; CYCLING CADENCE, V̇O2 SLOW COMPONENT; STRIDE RATE