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Medicine & Science in Sports & Exercise:
doi: 10.1249/MSS.0b013e3181e05526
Applied Sciences

Different Effect of Cadence on Cycling Efficiency between Young and Older Cyclists

SACCHETTI, MASSIMO1; LENTI, MAURO1; DI PALUMBO, ALESSANDRO SCOTTO1; DE VITO, GIUSEPPE2

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1Department of Human Movement and Sport Sciences, University of Rome, Rome, ITALY; and 2UCD School of Public Health, Physiotherapy and Population Science, University College Dublin, Dublin, IRELAND

Address for correspondence: Massimo Sacchetti, Ph.D., Department of Human Movement and Sports Sciences, University of Rome "Foro Italico," Piazza Lauro De Bosis 15, 00135 Rome, Italy; E-mail: massimo.sacchetti@uniroma4.it.

Submitted for publication January 2010.

Accepted for publication March 2010.

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Abstract

Purpose: We investigated the difference in the cadence-efficiency relationship between young and older competitive cyclists.

Methods: Eight young (24.3 ± 5.3 yr) and eight older (65.6 ± 2.8 yr) competitive cyclists participated in two laboratory sessions. The first consisted of an incremental maximal cycling test to determine the freely chosen pedal cadence and the maximal power output at V˙O2max and the second for the determination of gross efficiency (GE), calculated as the ratio of external work and energy expenditure (V˙O2). The latter test consisted of 6-min cycling exercise bouts at 40% and 60% of maximal power output and at a cadence of 40, 60, 80, 100, and 120 rpm.

Results: GE was lower in older cyclists than that in young cyclists at all cadences considered and at both levels of power output (P < 0.01). Peak efficiency was reached at 60 rpm in young cyclists (21.2% ± 1.9%), whereas in older cyclists this was observed already at 40 rpm and was not different from that at 60 rpm (18.3% ± 0.6%). The decline in GE with the increase in cadence was more pronounced in older than in young cyclists (P < 0.01) and was mitigated by the increase in power output more in the latter than in the former. These observations were in line with a lower freely chosen cadence recorded during the maximal test in older than that in young (P < 0.01).

Conclusions: The present data indicate that the effect of cadence on cycling efficiency is different between young and older cyclists and that it seems more disadvantageous for the latter to use high cadences. This may help explain why our older cyclists chose to pedal at lower cadences than the younger.

Cycling efficiency has been extensively studied in the last century, either to understand the effect of external workload on physiological stress or to better comprehend the factors influencing exercise performance. Indeed, efficiency is considered one of most important factors affecting endurance performance in competitive cyclists (9,24). Among the several factors that have been considered to characterize cycling efficiency, power output, pedaling rate, and their interaction received particular consideration (14) also to try to explain why young cyclists normally choose to pedal at higher cadences than that characterized by the lowest energy cost in laboratory-based studies.

An additional factor that has been linked to efficiency in cycling is represented by fiber type distribution. In particular, a direct relationship between the proportion of type I muscle fibers and the gross cycling efficiency has been reported (11) and connected to a higher performance during a simulated 1-h time trial (21).

Aging has a profound effect on muscle fiber type distribution and properties (6,12,36) and has therefore the potential to affect efficiency. On the other hand, maintenance of high levels of physical activity can mitigate the effect of the aging process on skeletal muscle (13). Surprisingly, efficiency in the older population has not been thoroughly investigated; most of the studies available on older athletes, which have focused on running economy, have suggested that this does not significantly change with age (23,29).

To date, only few studies have investigated cycling efficiency in older (65-70 yr old) (2-4) or middle-aged (around 50 yr old) (1) individuals, whereas the evidence concerning older cyclists is more scarce (31). Among these studies, one (31) reported a similar cycling economy in a group of 35- to 75-yr-old cyclists but did not consider the effect of cadence. Conversely, Bell and Ferguson (4) measured cycling efficiency at different cadences in young and older physically active but untrained women, but their findings might not directly translate to what is occurring in men who maintained a high level of physical activity throughout their life, as it is often the case in older master athletes.

With this in mind, we compared cycling efficiency in young and older competitive cyclists with a special emphasis on verifying the effect of cadence and power output because these are the two most important factors explaining its acute changes. The freely chosen cadence (FCC) during an incremental cycling test was also investigated to evaluate possible relationships with the effect of cadence on efficiency.

We hypothesized that compared with younger cyclists, older cyclists choose spontaneously a lower pedaling cadence and that this is related to the specificity of the efficiency-cadence relationship.

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METHODS

Subjects

A total of 16 well-trained male competitive cyclists, eight young (Y; 24 ± 5 yr) and eight older (O; 64 ± 4 yr), participated in this study. The characteristics of the two study groups are reported in Table 1. Before entering the study, the older subjects underwent medical screening to exclude cardiovascular, orthopedic, and metabolic diseases. The study was approved by the local ethical committee. After being informed about the purpose of the study and the possible risks connected with the experimental procedures, each participant signed an informed consent.

Table 1
Table 1
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Experimental Protocol

Subjects visited the laboratory in two occasions, separated by at least 3 d. During the first visit, subjects performed a maximal incremental exercise test to exhaustion on an electromagnetically braked cycle ergometer (Lode, Gronigen, The Netherlands) for the determination of maximal oxygen uptake (V˙O2max) and maximal power output (MPO) at which V˙O2max was reached. After a standard warm-up at 50 W in O and 100 W in Y, the workload was increased every 3 min by 25 W, and the test was terminated when the criteria for documentation of V˙O2max were met (plateau in V˙O2 despite increasing work rate; RER ≥ 1.1; reaching of age-predicted HRmax (220 − age)). The ventilatory and gas exchange variables were measured using a breath-by-breath gas analyzer (Quark b2 Cosmed, Rome, Italy). Before each test, the gas analyzers were calibrated with gases of known concentration, whereas the turbine was calibrated using a 3-L syringe.

To investigate possible between-group differences in the freely chosen pedal rate at the different work rates, volunteers did not receive any information about the cadence they were adopting during the incremental tests and were not told that it was one of the parameters of interest.

On the second occasion, the volunteers underwent the experimental trial to evaluate cycling efficiency. Subjects arrived at the laboratory in the morning after consuming a standardized breakfast (30 kJ·kg−1, 60% carbohydrate, 25% fat, 15% protein) 3 h before.

The exercise protocol consisted of 6 min of cycling exercise at a cadence of 40, 60, 80, 100, and 120 rpm performed in a randomized order and at an external power output equivalent to 40% and 60% of MPO. The two intensities were selected with the aim of ensuring aerobic energy turnover in all exercise bouts. The recovery time between each cycling bouts was 5 min, during which the subjects ingested water to maintain fluid balance.

Before each exercise test, the cycle ergometer was adjusted to reproduce the position of the subjects while riding their own bicycles. Throughout the trials, laboratory conditions remained stable in a range of 50%-60% humidity and 19°C-22°C, and subjects were cooled using a fan. Subjects were instructed to refrain from exercise during the last 2 d preceding the experimental trials.

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Determination of efficiency.

During the 6-min cycling bouts, ventilatory and gas exchange variables were measured breath by breath. V˙O2 and RER values recorded during the last 3 min of each exercise bout were averaged for the computation of efficiency. Energy expenditure (kJ·min−1) was calculated using the caloric equivalent of V˙O2 at a given RER. Gross efficiency (GE) was calculated as the ratio between the work accomplished (watt converted into kilojoules per minute) and the energy expended.

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Data Analysis

A repeated-measure ANOVA was used to evaluate the effect of power output and cadence on GE, with between-group measures to determine the effect of age.

Differences in FCC during the incremental test between the two groups were tested using an ANOVA for repeated-measures (power output) with group as between-subjects factor.

If the ANOVA indicated a significant main effect, a post hoc Student t-test with Bonferroni correction was used to locate the differences. Differences in the extreme values of GE (60-120 rpm) between Y and O were evaluated using the Student t-test. Data are presented as mean ± SD. The alpha level was set a priori at 0.05.

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RESULTS

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Incremental cycling test.

V˙O2max and MPO were significantly higher in Y than that in O (Table 2). The analysis of the FCC during the incremental test revealed that the older cyclists were pedaling at lower cadences (P < 0.01) than Y at all levels of exercise intensity (Fig. 1).

Table 2
Table 2
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FIGURE 1-FCC in youn...
FIGURE 1-FCC in youn...
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Efficiency trials.

During the exercise bouts conducted at 60% MPO, the maximal values of RER were 0.93 ± 0.02 in Y and 0.92 ± 0.02 in O, indicating a major contribution of aerobic pathways to energy expenditure.

The effect of cadence and power output on GE in the two study groups is depicted in Figure 2. At all pedal rates and at both levels of power output, GE was higher in Y than that in O (P < 0.01).

FIGURE 2-GE in young...
FIGURE 2-GE in young...
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GE was significantly influenced by pedaling cadence (F = 137, P < 0.0001), and this effect was different in Y versus O (F = 7.772, P < 0.01).

The cadence resulting in the highest value of GE was 60 rpm in Y, whereas in O GE at 40 and 60 rpm was not significantly different. This trend was observed at both levels of power (60% and 40% MPO).

From 60 to 120 rpm and at 40% MPO, GE decreased by 21% ± 5% in Y and by 30% ± 5% in O (P < 0.01). The difference between groups in the reduction of GE when increasing cadence from 60 to 120 rpm was even more pronounced at 60% MPO (11% ± 3% in Y and 23% ± 5% in O) and was meaningful, as indicated by an effect size of 1.8 and 2.6 at 40% and 60% of MPO, respectively.

With the increase in power output, GE increased in both groups and at all pedaling rates. Peak efficiency (at 60 rpm) increased from 21.2% ± 1.9% to 23.7% ± 1.8% in Y and from 18.3% ± 0.6 % to 20.7% ± 1.7 % in O.

A significant interaction between cadence and power output was found (F = 3.225, P = 0.016). This was evident as an attenuation of the reducing effect of high cadences on GE (difference between 60 and 120 rpm), which was, however, more pronounced in Y than that in O (P < 0.05).

Figure 3 shows the mean fractional utilization of V˙O2max as a function of cadence. From 60 to 120 rpm, relative exercise intensity increased by 9% ± 2% in Y and 22% ± 6% in O (P < 0.001) and by 4% ± 4 % in Y and 18% ± 5% in O (P < 0.001) at 40% and 60% MPO, respectively.

FIGURE 3-Fractional ...
FIGURE 3-Fractional ...
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DISCUSSION

In the present study, we investigated cycling GE differences between young and older cyclists, with a special emphasis on verifying the effect of adopting different pedaling rates. The main findings were a) a lower cycling efficiency at the same relative workload in O than that in Y for a wide spectrum of cadences, b) a lower freely chosen pedal rate and most efficient cadence in O than that in Y, and c) a higher reduction in GE with the increase in pedaling rate in O than that in Y. This effect was attenuated by the increase in power output more in Y than that in O.

Among the different factors affecting cycling endurance performance, those resulting in a high mechanical efficiency are considered to play a key role (15). Despite thorough investigation of cycling efficiency in young volunteers, there is a paucity of data concerning older individuals, athletes either trained or untrained. Most of the studies available on efficiency in master athletes have been performed in runners and suggest that running economy may be similar between young and older athletes (29). However, running economy and cycling efficiency are influenced by different factors, such as the capacity of the muscles to store and release elastic energy in the former (35) or the possibility of modulating the force exerted at a given power output using different cadences in the latter (26).

In the present study, we found a lower GE in O than that in Y at the same relative workload for a wide spectrum of cadences. To date, few studies have examined cycling efficiency in older individuals, with a variety of populations investigated. Peiffer et al. (31) reported a similar cycling economy in master cyclists of different ages. However, in that study, cadence was not controlled, subjects were only tested at the same absolute workload, and the caloric equivalent of V˙O2 at a given RER was not considered. These factors make the comparison with the results of the present study very difficult. Conversely, Bell and Ferguson (4) recently measured cycling efficiency at different cadences in older and young women and found, in agreement with the present results, a trend for a lower efficiency at same relative workload in the former. Conversely, Astrand (3) reported a similar cycling efficiency irrespective of age. On the other hand, it should be recognized that the choice of the cadence and the power output used to test cycling efficiency in the different studies represent a critical issue and make the comparison very difficult. Moreover, because of the effect of power output on efficiency and the lower absolute power output used in the older cyclists, we cannot rule out the possibility of a similar efficiency when testing the two groups at the same absolute workload.

To the best of our knowledge and in contrast to the plethora of data available in younger cyclists, no studies have investigated the relation between pedaling rate and GE in older cyclists.

The most efficient cadence recorded in our younger cyclists was within the range (60-80 rpm) previously reported (5,8,14). Moreover, in accordance with previous observations in young individuals (7,32), GE decreased with the increase in cadence, both in Y and in O. However, despite a similar trend, GE in O peaked already at 40 rpm whereas was maximal at 60 rpm in Y. These results are in line with Bell and Ferguson's (4) observations in young and elderly untrained women and suggest a shift of the most efficient cadence toward lower values with aging. Furthermore, the decline in GE at high cadences was steeper in O than that in Y, indicating a lower advantage of the older cyclists in using shorter gears, that is, those resulting in shorter distances covered in each pedal cycle, for a given speed.

With regard to the relationship between efficiency and FCC, several investigations indicated that young cyclists normally choose to pedal on the road at higher cadences (27,34) than those resulting as the most efficient in the laboratory setting (5,7,8,16,18,28,32,37). In contrast, despite the common observation that older cyclists pedal on the road at lower rates than their younger training companions, this has never been translated into scientific evidence. We found that FCC throughout the incremental maximal cycling test was nearly constant in both groups but was significantly lower in O than that in Y. On the basis of a recent report (25), we cannot rule out that using cadence and gears to control the work rate instead of relying on a fixed power output maintained independently of cadence would have resulted in a different trend in FCC during the incremental test; however, the divergence discovered in the absolute FCC values between Y and O remains. The present data, therefore, raise the possibility that the peculiarity of the cadence-efficiency relationship in O may be linked to their lower FCC.

An interesting observation of the present study is the different effect of the increase in cadence on the fractional utilization of V˙O2max in Y versus O. A significant difference in efficiency was found at 40 rpm and both at 40% and 60% MPO when the two groups were exercising at exactly the same relative intensity. At all other cadences (especially at 100 and 120 rpm), O were pedaling at a higher %V˙O2max. The higher increase in relative workload with the increase in pedaling rate in the older cyclists implies that cadence has a different effect on endurance performance potential with respect to the young.

It is possible that young cyclists with a higher V˙O2max do not necessarily have to try to maximize efficiency because a greater metabolic power output at higher cadences may be more relevant to performance than the concomitant, but marginal, decrease in efficiency. The situation is likely to be very different for the master cyclists who respond to an increase in cadence with a higher metabolic cost and possess a more limited maximal aerobic power. Therefore, for the older cyclist, pedaling outside of the most efficient cadence range may be much more demanding and detrimental to performance than for young athletes. This might explain the choice of older cyclists to pedal at lower rates than their younger counterpart. Indeed, the pronounced effect of even small variations in GE on cycling performance has been previously highlighted in relation to time trials (22,30) or to performance changes throughout the same (20) or several competitive seasons (10,33). From this point of view, the differences in GE between groups and with cadence appear relevant for performance.

In accordance with previous reports in young cyclists (7,17,32), in the present study the increase in power output resulted in a higher GE at all cadences in both Y and O. However, whereas the reduction in efficiency from 60 to 120 rpm was attenuated with the increase in power in young cyclists, this was less evident (about half) in older cyclists (7,32).

A proposed explanation for the reduction of the cadence effect at high power outputs is that the cost of moving the legs with a high frequency represents a lower proportion of the total energy expenditure (32). Along this line, it is possible to speculate that the cost of moving the legs could be more influential in O than that in Y because of their lower maximal aerobic power. This was reflected also in the observed higher increase in the fractional utilization of V˙O2max with cadence in O than that in Y at the lower level of power output.

In addition, a difference in the share of noneffective forces with the increase in power output cannot be excluded because it has been reported to lessen with the increase in power output in young (38). Finally, the increase in the cost for stabilizing the upper body at the higher cadences (19) and power outputs might differ between Y and O. Taken together, these data suggest that O cyclists, differently from Y, would not benefit from pedaling at high pedaling rates when riding at higher power outputs. Hence, the choice of using a given cadence to minimize energy expenditure appears more crucial for young than for older cyclists.

In conclusion, the results of the present study indicate that GE is lower in older than that in young cyclists when pedaling at the same relative intensities and for a wide spectrum of cadences. The increase in pedaling rate reduces GE more in older than that in young cyclists, and it is metabolically more demanding in the former than that in the latter. Moreover, the increase in power output mitigates the effect of higher cadences in reducing GE more in young and less in older cyclists. In addition, older cyclists are most efficient at a lower cadence than the young ones.

Taken together, these data suggest that controlling cadence is more crucial for older than for the young cyclists and may help explain why the former choose to pedal at lower rates than the latter.

The study was supported by the Università degli studi di Roma Foro Italico (grant No. N.250-07).

The results of the present study do not constitute endorsement by the American College of Sports Medicine.

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REFERENCES

1. Adams WC. Influence of age, sex, and body weight on the energy expenditure of bicycle riding. J Appl Physiol. 1967;22(3):539-45.

2. Amati F, Dube JJ, Shay C, Goodpaster BH. Separate and combined effects of exercise training and weight loss on exercise efficiency and substrate oxidation. J Appl Physiol. 2008;105(3):825-31.

3. Astrand I. Aerobic work capacity in men and women with special reference to age. Acta Physiol Scand Suppl. 1960;49(169):1-92.

4. Bell MP, Ferguson RA. Interaction between muscle temperature and contraction velocity affects mechanical efficiency during moderate-intensity cycling exercise in young and older women. J Appl Physiol. 2009;107(3):763-9.

5. Belli A, Hintzy F. Influence of pedalling rate on the energy cost of cycling in humans. Eur J Appl Physiol. 2002;88(1-2):158-62.

6. Brunner F, Schmid A, Sheikhzadeh A, Nordin M, Yoon J, Frankel V. Effects of aging on Type II muscle fibers: a systematic review of the literature. J Aging Phys Act. 2007;15(3):336-48.

7. Chavarren J, Calbet JA. Cycling efficiency and pedalling frequency in road cyclists. Eur J Appl Physiol Occup Physiol. 1999;80(6):555-63.

8. Coast JR, Welch HG. Linear increase in optimal pedal rate with increased power output in cycle ergometry. Eur J Appl Physiol Occup Physiol. 1985;53(4):339-42.

9. Coyle EF. Physiological determinants of endurance exercise performance. J Sci Med Sport. 1999;2(3):181-9.

10. Coyle EF. Improved muscular efficiency displayed as Tour de France champion matures. J Appl Physiol. 2005;98(6):2191-6.

11. Coyle EF, Sidossis LS, Horowitz JF, Beltz JD. Cycling efficiency is related to the percentage of type I muscle fibers. Med Sci Sports Exerc. 1992;24(7):782-8.

12. D'Antona G, Pellegrino MA, Adami R, et al. The effect of ageing and immobilization on structure and function of human skeletal muscle fibres. J Physiol. 2003;552(Pt 2):499-511.

13. D'Antona G, Pellegrino MA, Carlizzi CN, Bottinelli R. Deterioration of contractile properties of muscle fibres in elderly subjects is modulated by the level of physical activity. Eur J Appl Physiol. 2007;100(5):603-11.

14. Ettema G, Loras HW. Efficiency in cycling: a review. Eur J Appl Physiol. 2009;106(1):1-14.

15. Faria EW, Parker DL, Faria IE. The science of cycling: factors affecting performance-part 2. Sports Med. 2005;35(4):313-37.

16. Foss O, Hallen J. The most economical cadence increases with increasing workload. Eur J Appl Physiol. 2004;92(4-5):443-51.

17. Gaesser GA, Brooks GA. Muscular efficiency during steady-rate exercise: effects of speed and work rate. J Appl Physiol. 1975;38(6):1132-9.

18. Hansen EA, Andersen JL, Nielsen JS, Sjogaard G. Muscle fibre type, efficiency, and mechanical optima affect freely chosen pedal rate during cycling. Acta Physiol Scand. 2002;176(3):185-94.

19. Hansen EA, Jorgensen LV, Sjogaard G. A physiological counterpoint to mechanistic estimates of "internal power" during cycling at different pedal rates. Eur J Appl Physiol. 2004;91(4):435-42.

20. Hopker J, Coleman D, Passfield L. Changes in cycling efficiency during a competitive season. Med Sci Sports Exerc. 2009;41(4):912-9.

21. Horowitz JF, Sidossis LS, Coyle EF. High efficiency of Type I muscle fibers improves performance. Int J Sports Med. 1994;15(3):152-7.

22. Jeukendrup AE, Craig NP, Hawley JA. The bioenergetics of World Class Cycling. J Sci Med Sport. 2000;3(4):414-33.

23. Joyner MJ. Physiological limiting factors and distance running: influence of gender and age on record performances. Exerc Sport Sci Rev. 1993;21:103-33.

24. Joyner MJ, Coyle EF. Endurance exercise performance: the physiology of champions. J Physiol. 2008;586(1):35-44.

25. Leirdal S, Ettema G. Freely chosen pedal rate during free cycling on a roller and ergometer cycling. Eur J Appl Physiol. 2009;106(6):799-805.

26. Lollgen H, Graham T, Sjogaard G. Muscle metabolites, force, and perceived exertion bicycling at varying pedal rates. Med Sci Sports Exerc. 1980;12(5):345-51.

27. Lucia A, Hoyos J, Chicharro JL. Preferred pedalling cadence in professional cycling. Med Sci Sports Exerc. 2001;33(8):1361-6.

28. Marsh AP, Martin PE, Foley KO. Effect of cadence, cycling experience, and aerobic power on delta efficiency during cycling. Med Sci Sports Exerc. 2000;32(9):1630-4.

29. Morgan DW, Martin PE, Krahenbuhl GS. Factors affecting running economy. Sports Med. 1989;7(5):310-30.

30. Passfield L, Doust JH. Changes in cycling efficiency and performance after endurance exercise. Med Sci Sports Exerc. 2000;32(11):1935-41.

31. Peiffer JJ, Abbiss CR, Chapman D, Laursen PB, Parker DL. Physiological characteristics of masters-level cyclists. J Strength Cond Res. 2008;22(5):1434-40.

32. Samozino P, Horvais N, Hintzy F. Interactions between cadence and power output effects on mechanical efficiency during sub maximal cycling exercises. Eur J Appl Physiol. 2006;97(1):133-9.

33. Santalla A, Naranjo J, Terrados N. Muscle efficiency improves over time in world-class cyclists. Med Sci Sports Exerc. 2009;41(5):1096-101.

34. Sassi A, Rampinini E, Martin DT, Morelli A. Effects of gradient and speed on freely chosen cadence: the key role of crank inertial load. J Biomech. 2009;42(2):171-7.

35. Saunders PU, Pyne DB, Telford RD, Hawley JA. Factors affecting running economy in trained distance runners. Sports Med. 2004;34(7):465-85.

36. Trappe S, Gallagher P, Harber M, Carrithers J, Fluckey J, Trappe T. Single muscle fibre contractile properties in young and old men and women. J Physiol. 2003;552(Pt 1):47-58.

37. Umberger BR, Gerritsen KG, Martin PE. Muscle fiber type effects on energetically optimal cadences in cycling. J Biomech. 2006;39(8):1472-9.

38. Zameziati K, Mornieux G, Rouffet D, Belli A. Relationship between the increase of effectiveness indexes and the increase of muscular efficiency with cycling power. Eur J Appl Physiol. 2006;96(3):274-81.

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The influence of training status, age, and muscle fiber type on cycling efficiency and endurance performance
Hopker, JG; Coleman, DA; Gregson, HC; Jobson, SA; Von der Haar, T; Wiles, J; Passfield, L
Journal of Applied Physiology, 115(5): 723-729.
10.1152/japplphysiol.00361.2013
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Keywords:

MASTER ATHLETE; PEDAL RATE; FREELY CHOSEN PEDAL RATE; CADENCE-EFFICIENCY RELATIONSHIP; AGING

©2010The American College of Sports Medicine

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