Review Article

Sports Medicine 10 (5): 286-302, 1990 0112-1642/90/00 11-0286/$08. 50/0 © Adis International Limited All rights reserved. SPORT2333

Biomechanics of Cycling and Factors Affecting Performance Danny Too Department of Health, Physical Education and Recreation, California State University, Fullerton, California, USA

Contents

Summary ................................................................................................................................... 286 1. Efficiency of Human-Powered Vehicles ............................................................................. 288 2. Cycling Performance in Different Body Positions, Configurations and Orientations .. , 288 2.1 Upright Versus Supine Orientation ............................................................................. 289 2.2 Upright Versus Prone Orientation ............................................................................... 290 2.3 Upright Versus Other Positions ................................................................................... 291 2.3.1 Low Sitting Position ............................................................................................. 29 I 2.3.2 Semirecumbent Position ...................................................................................... 291 2.3.3 Stand-Up Position ................................................................................................ 292 2.4 Effect of Changes in Body Position/Configuration, and Orientation ....................... 293 3. Seat to Pedal Distance ........................................................................................................ 294 3.1 Seat Height ..................................................................................................................... 294 3.2 Crank Arm Length ........................................................................................................ 296 4. Factors Affecting Cycling Energy Expenditure .................................................................. 298 4.1 Workload, Power Output, and Pedalling Rate ........................................................... 298 5. Conclusions .......................................................................................................................... 299

Summary

Cycling performance in human powered vehicles is affected by the interaction of a number of variables, including environment, mechanical and human factors. Engineers have generally focused on the design and development of faster, more efficient humanpowered vehicles based on minimising aerodynamic drag, neglecting the human component. On the other hand, kinesiologists have examined cycling performance from a human perspective, but have been constrained by the structure of a standard bicycle. Therefore, a gap exists between research in the various disciplines. To maximise/optimise cycling performance in human-powered vehicles requires a bridging of this gap through interdisciplinary research. Changes in different variables can affect the energy requirements of cycling. These variables include: (a) changes in body position, configuration, and orientation; (b) changes in seat to pedal distance; and (c) the interaction of workload, power output, and pedalling rate. Changes in these variables alter joint angles, muscle lengths, and muscle moment arm lengths, thus affecting the tension-length, force-velocity-power relationships of multijoint muscles and the effectiveness of force production. This is ultimately manifested as a change in the energetics of cycling. A large number of factors affect cycling performance in human-powered vehicles and

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a gap still exists between cycling research in various disciplines. To bridge this gap, if not completely close it, requires cooperation between disciplines and further interdisciplinary research.

In 1933, Francois Faure defeated the world cycling champion, Lemoire, in a 4km pursuit and broke previously established track records (Whitt & Wilson 1982). What was unique about this feat? Francois Faure was a relatively unknown cyclist, but he had just defeated the world champion and he had accomplished this on a nonconventional bicycle, a recumbent bicycle. Ever since this accomplishment, the Union Cycliste Internationale (the world governing body for bicycle racing) banned the use of aerodynamic devices and recumbent bicycles from racing competition. They, in essence, have defined a bicycle, disqualifying any vehicle that may provide an unfair aerodynamic advantage to the rider. However, this has not deterred the technological development of recumbent bicycles (as evidenced by the formation of the International Human Powered Vehicle Association) nor has it prevented cyclists from seeking ways around the ban (as evidenced by aerodynamic spokes and frames, solid disc wheels, smaller front wheel, aerodynamic suits and helmets, etc). This has created a gap between cycling research in the various disciplines. For instance, designs of human-powered vehicles by engineers have always been based on aerodynamic factors while neglecting the human component. A vehicle would be constructed with a minimal cross-sectional area and as streamline as possible with an aerodynamic fairing to minimise the drag coefficient. With speeds of some humanpowered vehicles, such as the Vector Single, exceeding 60 mph (96.6 km/h) [Gross et al. 1983], it is obvious as to the importance of minimising aerodynamic drag. But, when the drag coefficient and effective frontal area has been reduced to 0.033 and O. 152m2, respectively, as in the Vector Single (compared to 0.335 and 1.83m2, respectively, for a standard upright bicycle) [Gross et al. 1983], it is questionable as to how much lower the aero-

dynamic drag can be reduced, and how significant such changes would be. To further improve performance, it becomes necessary to focus on some aspect other than the aerodynamic properties. The most logical area to explore would be the human engine which powers the vehicle. But, how efficient or effective is a cyclist when pedalling in a supine, semisupine, semiprone. or prone position? What is the most effective body configuration (hip, knee, ankle angles) to maximise force and power production and to optimise tension-length, force-velocity-power interaction of multijoint muscles? To date, there are very few scientific investigations that have systemically examined the body positions, configurations and orientations a cyclist should adopt to maximise performance. Kinesiologists, unlike engineers, have always examined cycling performance based on a human factors perspective. But, these investigations have always been based on the constraints imposed by the structure of a conventional bicycle. These investigations have included the effects on cycling performance with changes in seat height, crank arm length, pedalling frequencies, workloads, total work output, etc. There are a large number of factors affecting cycling performance: environmental factors (e.g. aerodynamic drag, rolling resistance, hills, head and tail winds, altitude); mechanical factors (e.g. wheel size and inertial properties, friction in power transmission, elliptical chainwheels and cams); biomechanical and physiological factors (e.g. muscle length, joint angle, muscle moment arm length, type of lever, speed and type of contraction, fibre type and arrangement, recruitment pattern, etc.) [Burke 1986]. It is beyond the scope of this paper to review all the factors affecting cycling performance. This paper reviews the literature from a biomechanics/energetics perspective and attempts to bridge the gap between cycling research in the various disciplines. Insight is provided regarding the

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body configuration, position, and orientation which maximises cycling performance in human-powered vehicles.

1. Efficiency of Human-Powered Vehicles In a comparison between human-powered vehicles and engines, Whitt and Wilson (1982) indicated that a rider on a bicycle will expend less kilocalories per kilometer-person when compared to a moped with rider, an automobile with 1 or 5 riders, or a diesel commuter train with riders. Even among animals, a human on a bicycle is ranked first in efficiency in terms of energy consumed in moving a certain distance as a function of bodyweight (Wilson 1973). Wilson (1973) states that a walking human consumes about 0.75 cal/g/km, which is not as efficient as a horse, a salmon or a jet transport. With the aid of a bicycle, however, energy consumption for a given distance is reduced to about 0.15 cal/g/km. This 5-fold increase in efficiency appears to be accompanied by a 3- or 4fold increase in travelling velocity (Wilson 1973). This, according to Dill et al. (1954), makes cycling 2.5 times easier than walking. At speeds greater than 8 m/sec (18 mph) air resistance accounts for more than 80% of the total force acting to slow a human-powered vehicle such as a standard bicycle (Gross et al. 1983). Because the force of aerodynamic drag increases as the square of the velocity, and the power necessary to drive an object through this resistance increases as the cube of the velocity (Faria & Cavanagh 1978), it is logical to assume that any change to a vehicle which can alter its aerodynamic properties will enhance the performance of that vehicle given the same energy input. It is well documented that recumbent human-powered land vehicles are more effective aerodynamically than the standard upright seated bicycle (Kyle 1974, 1982; Kyle & Caiozzo 1986; Kyle et al. 1973, 1974; Whitt 1971; Whitt & Wilson 1982). In different investigations, cycling time to exhaustion, power output and oxygen consumption was found to be greater in a standard cycling position than in nonupright positions (Diaz et al. 1978; Metz et al. 1986, 1990).

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The potential use of human-powered vehicles as an efficient mode of transportation is not just limited to usage on land. An underwater bicycle has been shown to reduce human oxygen requirements by almost 40%, yet increase his propulsive effectiveness by as much as 1.6 times compared with underwater swimming with fins (Baz, 1979). The use of a human-powered vehicle as a viable mode of air travel has been demonstrated by the Gossamer Albatross, the first human-powered aircraft to cross the English Channel (Drela & Langford 1985). It required a human power output of 0.25 hp (186.5W) and had a cruising speed of 12 mph (5.4 m/sec) [ME Staff Report 1984J.

2. Cycling Performance in Different Body Positions, Configurations and Orientations The terms body position, body configuration and body orientation are all interrelated, and are often used interchangeably in the literature. In this paper, the body position refers to the location of the cyclist relative to the pedal axle of the bicycle and is determined by the angle of the bicycle seat tube and a vertical line (perpendicular to the ground) passing through the pedal axle. The term body configuration refers to the posture of the cyclist as defined by the angles of the different body segments (hip, knee, ankle) relative to each other. The term body orientation refers to the posture of the cyclist as defined by the angle of the cyclist's trunk relative to the ground (fig. 1). There is a plethora of literature discussing how performance (as determined by maximal velocity) in human-powered vehicles can be improved by altering the cycling body position into a more aerodynamically effective one (Boor 1981; Kirshner 1985; Kyle 1974, 1981, 1982; Kyle et aI. 1973, 1974; Kyle & Edelman 1975; Malewicki 1984; Martin 1979; Nonweiler 1956, 1957). However, most of the literature investigating human performance while cycling in different positions have involved only upright and supine body orientations (Bevegard et al. 1960, 1963; Bishop et al. 1956; Convertino et al. 1984; Cumming 19n; Dickhuth et al.

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Factors Affecting Cycling Performance

1978; Faria et al. 1978; Metz et al. 1986, 1990; Montgomery et al. 1978; Too 1988, 1989a,b, 1990), and only Too (1988, 1989a,b, 1990) has investigated the effect of systematic changes in body position, configuration, and orientation on cycling performance. 2.1 Upright Versus Supine Orientation

Fig. 1. Definition of body position (seat tube angle, top) body configuration (hip angle, centre) and body orientation (trunk or backrest angle, bottom).

1981; Ekelund 1966, 1967a,b; Galbo & Pauley 1974; Granath et al. 1961; Gullbring et al. 1960; Holmgren et al. 1960a,b; Kubicek & Gaul 1977; Reeves et al. 1961; Stenberg et al. 1967; Timmons 1981). Very few studies have investigated these responses in other body positions or orientations (Diaz et al.

Of the studies investigating physiological responses in the upright and supine body orientation, it has been reported that a greater maximal work output and maximal oxygen consumption can be obtained when cycling in a standard upright orientation. Kubicek and Gaul (1977) indicate that the maximal workload obtained was higher in the sitting than in the supine orientation, although the differences were not statistically significant. Astrand and Rodahl (1977) state that 'in maximal work on a bicycle ergometer in the supine position, the oxygen uptake is only about 85% of the value obtained in the sitting position' (p. 305). This would suggest that an upright orientation may allow a greater work output to be accomplished as well as eliciting a larger maximal oxygen consumption. At submaximal workloads there appears to be conflicting evidence whether oxygen consumption values are smaller when pedalling in the supine orientation or are similar in the supine and upright orientations. Bevegard et al. (1960, 1966) reported the oxygen consumptions to be very similar, with statistically nonsignificant differences at submaximal workloads in comparisons between supine and upright cycling orientations. Convertino et al. (J 984) indicated that although the oxygen consumption at steady-state for a submaximal workload was similar for both the supine and upright orientation (1.66 L/min and 1.65 L/min, respectively), the supine oxygen consumption values during the initial 3 minutes of exercise and the total exercise oxygen consumption was significantly smaller (p < 0.05) than the upright orientation. Timmons (1981) found significantly lower oxygen consumption (p < 0.01) values for submaximal workloads (200, 400, 600 and 800 kpm) in the supine orientation when compared to the upright ori-

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entation. These differences were stated to be quite small (mean difference of 5.4% or 76 ml/min between the 2 orientations which amounted to less than 1 ml/kg/min). On the other hand, Granath et al. (1964) reported a submaximal workload corresponding to 84% and 67% of the maximal working intensity for the supine and sitting orientation, respectively. To add to the confusion, Bevegard et al. (1963) reported significantly lower (p < 0.05) oxygen consumption values for a submaximal workload at 800 kpm in the supine orientation, but no significant differences (p > 0.05) at a submaximal workload of 1600 kpm when compared with the upright orientation. Similar difficulties exist when attempting to compare cycling efficiency between supine and upright body orientations. Bevegard et al. (1960) and Convertino et al. (1984) reported no significant differences in efficiency between the supine and upright orientations. However, physiological baselines were not considered by Convertino et al. (1984) in the efficiency calculations. Bevegard et al. (1963) accounting for physiological baselines, found cycling efficiency to be significantly greater in the supine orientation (25.3% vs 23.8% in the

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to be greater (both in L/min and ml/kgfmin) than that attained for the top bar posture (p < 0.05 and p < 0.01, respectively). It should be noted that the term position is used by Faria et al. (1978) instead of posture. But, to avoid confusion, and to be consistent with the terms defined in this paper, posture will be used instead. A top bar posture is described by Faria et al. (1978) as sitting semi-upright on the saddle with the hands resting on the uppermost portion of the handlebars, while a drop bar posture is described as sitting in the saddle while assuming a deep forward lean, with the hands resting on the drop portion of the turned-down handlebars. It should be noted that this deep forward lean in the dropped bar posture can be assumed to place the torso in a prone or semi-prone position. The drop bar posture was also reported to have a significantly greater (1.2 times greater, p < 0.05) maximal work output (in kpm and kpm/kg bodyweight) than the top bar posture, although the maximal heart rate for both postures were not significantly different. It is interesting to note that Faria et al. (1978) indicated that the oxygen uptake at a physical work capacity with a heart rate of 170 beats/min represented 84%

upright) at a submaximal workload of 800 kpm/

of the maximum oxygen uptake (ml/kg/min) for

min, but not significantly greater at 1600 kpm/min (24.6% in the supine to 24.4% in the sitting orientation). Based on the evidence reported in the literature regarding oxygen consumption in the supine and upright orientation, changes in body orientation may affect cycling work output, energy expenditure, and efficiency. However, there was no indication whether the body configuration (hip, knee, ankles) in the supine and upright orientation was standardised or controlled for. Differences in body configuration will alter joint angles, muscle moment arm lengths and their resulting interactions in the tension-length curve, thus possibly confounding the data and results.

both cycling postures, although the absolute values were significantly greater (7% greater with p < 0.01) for the drop bar posture. This would suggest that for the 2 different riding postures, the absolute energy expenditure may be different for submaximal workloads, whereas the relative energy expended may be the same. These differences were believed to be attributed to: (a) the activity of a larger muscle mass (greater use of the arm, shoulder girdle, and lower back muscles) in the drop bar posture; and (b) the greater forward body lean angle in the drop bar posture which appears to relieve the weight of the arms and shoulder girdle from the thorax. This reduced weight plus the suspended chest is believed to ease chest expansion, thereby enhancing pulmonary ventilation potential and possibly decreasing the energy requirement for respiration (Faria et al. 1978). This study would suggest that different body orientations will result in different maximal work

2.2 Upright Versus Prone Orientation Faria et al. (1978), in a comparison between a top bar and drop bar cycling posture, reported the maximal oxygen uptake for the drop bar posture

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Factors Affecting Cycling Performance

output and possibly energy expenditures (depending on how energy expenditure is calculated). However, it is unknown whether the greater lean in the drop bar posture altered the hip angle and placed the working muscles and muscle moment arm length in a more mechanically advantageous position to produce force when compared to the top bar posture. The hip, knee, and ankle angles were not reported and do not appear to have been controlled for. 2.3 Upright Versus Other Positions

2.3.1 Low Sitting Position The physiological responses when comparing cycling in an upright position to other positions would appear to favour the upright position. Diaz et al. (1978) reported significantly greater (p < 0.05) maximal oxygen consumption in an upright position (3.68 L/min or 49.8 ml/kgfmin) than in a low sitting position (3.32 L/min or 44.7 ml/kgfmin). A low sitting position is described by Diaz et al. (1978) to be a cycling position where the torso is upright and the legs horizontally extended. This indicates that greater maximal work output was achieved in an upright position because there is a direct relationship between maximal oxygen consumption and maximal work output. Oxygen consumption at submaximal workloads of 360 and 720 kpm/min was found to be similar in both the low sitting position (14.7 and 24.7 ml/kgfmin) and in the upright position (14.6 and 25.7 ml/kgfmin). However, for each submaximal workload, the relative oxygen consumption (relative to the maximal value of each position) was found to be greater for the low sitting position (33 and 55%, respectively, vs 30 and 52% for the upright position). Despite these differences in relative oxygen consumption, Diaz et al. (1978) found similar efficiencies between the 2 sitting positions for each submaximal workload. It is unknown as to what these differences were attributed to. Diaz et al. (1978) did not report whether physiological baselines were accounted for in the efficiency calculations or what the seat to pedal distances and cycling range of hip, knee, and angles were for the different seating positions.

A similar investigation had been done by HughJones (1947)--on the efficiency of bicycle pedalling in different seating positions. It involved moving a bicycle seat, with an added backrest, into 7 different positions (3, 26, 43, 53, 63, 73 and 83°) around the arc of a circle whose centre was the pedal axle. The seating position was defined by the angle formed between the perpendicular and the line joining the base of the seat backrest to the pedal axle. Submaximal oxygen consumption values plotted with different positions did not reveal any particular trends. However, Hugh-Jones (1947) did indicate that cycling in the normal saddle position (26°) and in' a 63° seat position resulted in lower oxygen consumption values than the other positions, although they were not significantly different from each other. The contribution of the leg weight and use of the backrest were given as explanations for the lower oxygen consumption values found in the normal and 63° saddle positions, respectively. The lack of any trends in oxygen consumption and nonsignificance with different seating positions might have been attributed to the large variances associated with small sample sizes (in this case, n = 2) and/or not having accounted for possible differences in physiological baselines of the different positions. Actual efficiency calculations were not made, comparisons of energy expenditures and seat to pedal distances were not reported, nor was there any indication regarding the body configuration (hip, knee, ankle angles) and orientation in the different cycling positions. The only reference made to body orientation was with the 63° position. Hugh-Jones (1947) described the 63° position as corresponding with the position adopted in the French 'Velocar' (a semirecumbent bicycle).

2.3.2 Semirecumbent Position In a comparison between an upright racing p0sition and a semirecumbent position, Metz et al. (1986, 1990) found cycling performance to be superior in the upright position. Metz et al. (1986, 1990) examining the leg motion during standard and semirecumbent bicycle pedalling, reported that cycling time to exhaustion in a semirecumbent p0.sition was consistently 4 to 5 minutes less than that

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on a standard racing bicycle when tested using a wind load simulator. The test protocol was reported to consist of a riding regimen similar to that used by the US National Team for fitness trials, with a complete test lasting about 16 minutes. In comparing equivalent workloads and power outputs at successive levels, it was determined that the subject tested (an elite cyclist) was unable to maintain the required power output or tolerate the equivalent workload for the same duration on a semirecumbent bicycle when compared to a standard racing bicycle. It was speculated that experienced cyclists might have developed certain coordination patterns or motor programmes which allow them to be more effective and efficient on standard bicycles. This could account for the differences in performance times although Metz et al. (1986, 1990) had indicated that the rider was given ample opportunity to practice on the semirecumbent bicycle. Although the semirecumbent bicycle positioned the cyclists' legs in a dramatically different orientation with respect to the gravity field, no clear differences in joint forces or moments were found by Metz et al. (1986, 1990) when compared with the standard position. Because instrumented pedals were not used and force data was not available, it is unknown whether differences in cycling performance was attributed to varying leg weight contribution in the different cycling positions. Also, because physiological data (oxygen consumption, heart rate, etc.) was not collected, it is difficult to ascertain whether differences in performance between the 2 cycling positions were attributed to differences in efficiency, oxygen consumption, absolute, and/or relative energy expenditure, or some other parameter. It .can be assumed that differences in performance (based on visual observations of the reported cycling positions) were probably attributed to differences in the muscle length and muscle moment arm length interactions by virtue of the 2 different body configurations.

2.3.3 Stand-Up Position There is a question of whether a change in body position and/or orientation altering the leg weight contribution to the force applied on the pedal,

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would affect the physiological response to cycling performance. Montgomery et al. (1978), in comparing the maximal oxygen consumptions between an upright seated position and a stand-up position, reported no significant differences between positions. No evidence was given whether submaximal workloads elicited similar or different oxygen consumption values. Nonsignificant maximal oxygen uptake between the two positions would indicate that the weight of the leg in contributing to cycling work performance may not be important. If the leg weight was a significant factor in affecting the maximal workload attained and the energy expended, one would assume that a stand-up position would enable a cyclist to shift his bodyweight more from side to side. This should allow a greater contribution of the bodyweight to the total force on the pedals, which in tum, should reduce the metabolic demands on the body. In contrast, Kamon et al. (1973), investigating the effects of climbing and cycling with additional weights on the extremities, indicate the oxygen cost per unit when cycling on an ergometer with ankle weights is less than that without ankle weights. This extra weight around the ankles was believed to assist the muscles in moving the pedals against the resistance. However, one would expect the weight contributed by one leg to the pedal on the downstroke would probably be negated by the weight of the other leg resting passively on the pedal during the upstroke. This is supported by data indicating a net downward force on the pedals during the upward (recovery) stroke as well as during the downward (power) stroke (Redfield & Hull I 986a,b; Soden & Adeyefa 1979a,b). Questions related to the possible contribution of forces when pulling up on the toeclips can best be answered by a brief review of the cycling literature involving instrumented pedals. There are many cycling investigations involving the use of force pedals (Bolourchi & Hull 1985; Cornelius & Seireg 1986; Daly & Cavanagh 1976; Davis & Hull 1981, 1982; Ericson & Nisell 1988; Ericson et a1. 1988; Hull & Davis 1981; Hull & Gonzalez 1988; Hull & Jorge 1985; Hull et a1. 1988; Jorge & Hull 1984; Kunstlinger et a1. 1984; McCartney et a1. 1983; Redfield & Hull 1986a,b; Sar-

Factors Affecting Cycling Performance

gent & Davies 1977). The forces recorded on an instrumented pedal, as reported in the literature, vary with the test protocol and phase of the pedal cycle. Mean peak normal forces on the pedal were found to occur in the 90 to 110° range of the pedal cycle (with 0° as top dead centre and 180° as bottom dead centre). These forces varied from 250 to 570N, with pedalling frequency ranges from 60 to 120 rpm, and power outputs from 98 to 778W (Brooke et al. 1981; Gregor & Cavanagh 1976; Gregor et al. 1985; Lafortune & Cavanagh 1980, 1983; Redfield & Hull 1984; Sargent et al. 1978). Soden and Adeyefa (l979a,b) indicate a rider starting on level ground and accelerating at 2.6 m/sec2 was estimated to apply a force of 1448N (more than twice his bodyweight) to the forward pedal and with a pull of 367N (0.56 times bodyweight). With a power output of 770W and a constant pedalling frequency without acceleration, the maximum pull on the rear was reported to be less than lOON; and lower workloads did not result in a pull on the rear pedal. The absence of a pull-up force during the recovery appears to be supported by various investigations when cycling with a large inertial load and with a constant pedalling cadence (Gregor 1976; Hoes et al. 1968; Lafortune et al. 1983). This would be similar to cycling on the level, but would be different when compared to sprinting or hill climbing. The force production pattern in different phases of the pedal cycle and the effect of toeclips and pulling on the pedals in nonconventional cycling position is unknown. 2.4 Effect of Changes in Body Position/ Configuration and Orientation To determine the most effective seating arrangement that would maximise cycling performance regardless of the type of human-powered vehicle, would require a systematic manipulation of body position/configuration while controlling for body orientation and vice-versa. Unfortunately, most human-powered vehicles constructed to establish new speed records are designed to minimise aerodynamic drag, without any other justification

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as to why the performer should be seated in a certain position. Too (1988, 1989a, 1990) in examining the effect of systematic manipulation of 5 body positions (bicycle seat tube angles) and configurations (hip angle) on cycling performance while controlling for body orientation, concluded that an optimal cycling body position/configuration exists that maximised aerobic and anaerobic work. For aerobic work, 16 male subjects were tested in 5 seating positions (0, 25, 50, 75 and 100°) as defined by the angle formed between the bicycle seat tube apparatus and a vertical line (fig. 2). Rotating the seat to maintain a backrest perpendicular to the ground, induced a systematic decrease in hip angle from the 0 to 100° position. The body orientation (trunk perpendicular to the ground) was standardised as was the mean knee and ankle angles, seat-to-pedal distance (100% of greater trochanteric height), and aerobic testing protocol. It was determined that for total work output and maximal aerobic energy expenditure, performance in the 75° seat tube angle position (76.8° mean hip angle configuration) was significantly greater (p < 0.01) than in the other positions, except for the 50° seat tube angle (l00° mean hip angle) [Too 1988, 1990]. Similar results were found with anaerobic power and capacity, using the 30-second Wingate Anaerobic Cycling test with a resistance of 85 g/kg bodyweight (5.0 J/ pedal/rev/kg BW). Cycling performance as measured by anaerobic power and capacity in the 75° body position (seat tube angle) was significantly greater than all the other positions (p < 0.0l), except for the 50° position (Too I 989a). Hull and Gonzalez (1990) also found a seat tube angle of 76° minimised the joint moment cost function of cyling when determined with an optimisation model and that the optimal seat tube angle decreased with increased rider size. Another investigation by Too (l989b) examined the effect of systematic manipulation of body orientation on aerobic cycling performance while controlling for body position/configuration. Using a seat tube angle of 75° with the seat-backrest perpendicular to the ground, 10 male subjects were tested in each of 3 body orientations (60, 90 and

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significant differences in anaerobic power and capacity would be found with changes in body orientation is unknown. The 120° orientation would allow the rider to push against the backrest when cycling whereas the 60° orientation would place the legs in a more advantageous orientation with regards to the line of gravity. Currently, a study is in progress examining this.

3. Seat to Pedal Distance 3.1. Seat Height

Fig. 2. Body positions.

120°) as defined by the angle formed between the seat backrest and a horizontal line parallel to the ground (fig. 3). To obtain the 60 and 120° orientation, the entire cycling apparatus was rotated 60° forward and backwards, respectively. It was determined there were no significant differences in maximal aerobic energy expenditure and total work output with changes in body orientation. Whether

The effectiveness of force production on a bicycle is affected by many factors. One of these factors is the seat height. Alteration of the seat height would not only alter joint angles but also muscle lengths and muscle moment arm lengths, thereby changing the kinematics of cycling. This has been demonstrated using thigh-knee angle diagrams from a simulation output with seat heights at 36.4 and 38 inches (92.5 and 96.5cm), respectively (Nordeen & Cavanagh 1976). This, in turn, would probably change the force output of a muscle. Whether the resulting force will be greater or lower will depend upon the muscle position in the tension-length curve. The change in joint angle mayor may not place the muscle lever moment arm system in a more mechanically advantageous/disadvantageous position to exert force (Titlow et al. 1986). The resultant muscle force and its effectiveness will be based upon the interaction of the position of the muscle in the tension-length curve and the position in the muscle lever moment arm system of the new joint angle. Therefore, with changes in body position and body orientation, there must be corresponding changes in the seat to pedal distance if comparison regarding cycling effectiveness in similar body configurations are to be made. The optimal seat height for a bicycle with an upright seating position was determined by Thomas (I967a,c) to be 109% of the medial aspect of the inside leg from the floor to the symphysis pubis. The seat height was measured from the pedal spindle to the top of the seat along a stright line formed by the crank, seat tube and seat post. This measurement was determined to be accurate with 80%

Factors Affecting Cycling Performance

of all individuals tested (Thomas I 967b) and most efficient for tasks requiring anaerobic work of high intensity for short durations (Hamley & Thomas 1967; Thomas 1967c). Any other position greater or less than this value was less efficient and metabolically more costly. On the other hand, Shennum and deVries (1976) found the most efficient seat height for tasks requiring aerobic work to be 105 to 108% of the inside leg from the floor to the sym-

Fig. 3. Body orientations.

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physis pubis, although they suggest the use of a saddle height of approximately 108 to 109% of symphysis pubis-to-floor distance [based on their oxygen consumption data with the data by Thomas (1967c) and Hamley and Thomas (1967) on power output]. The data by Shennum and deVries (1976) appears to be supported by Nordeen (1976) and Nordeen-Snyder (1977), who indicated the most efficient seat height for aerobic work to be 107.1%

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and by Gregor et al. (1981), who indicated that of the 10 elite male cyclists investigated in his study, the average saddle height was 106% of pubic symphysis height. It should be noted that the data reported by Shennum and deVries (1976), Nordeen (1976) and Nordeen-Snyder (1977), were converted to values which allowed for comparisons with other investigations. The investigation by Shennum and deVries (1976) defined leg length as the measured distance from the ischium to the floor. Using a fully articulated skeleton in the erect position, Shennum and deVries (1976) reported a nearly 5% lower value with their ischium-to-floor method when compared to the Thomas (1967a,b,c) symphysis pubisto-floor technique. There, Shennum and deVries (1976) indicated that to compare their data with those of Thomas (1967c) and Hamley and Thomas (1967), it was necessary to add approximately 5% to their leg length measures. The investigation by Nordeen-Snyder (1977) used seat heights of95, 100, and 105% of trochanteric leg length. Nordeen (1976) indicated the calculated saddle height was divided by the subject's symphysis pubis height to obtain values which could be compared to those of Hamley and Thomas (1967). Therefore, the 95, 100 and 105% of trochanteric leg length (Nordeen-Snyder, 1977) corresponded to 101.7, 107.1, and 112.1% of symphysis pubis height as calculated by Hamley and Thomas (1967). The seat to pedal distance of 100% trochanteric leg length which minimises oxygen consumption, as reported by Nordeen (1976) and Nordeen-Snyder (1977) appear to be different from the trochanteric leg length percentage of the Hodges study (Borysewicz, 1985). Borysewicz (1985) stated that Hodges, in April 1982 at the Olympic Training Center, found that seat height which minimised oxygen consumption was 96% of trochanteric leg length. 11 male cyclists were tested on their own bicycles at 10 different seat heights (ranging from 92% to 100% of trochanteric leg length). Borysewicz (1985) indicated that an ergometer-like device was attached to each cyclists' bicycle and a hydraulic seat post constructed by Hodges allowed manipulation of the resistance and the seat height

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during each test session. The test protocol required each cyclist to complete two 45-minute sessions at 80% of their maximum oxygen consumption. During each session, the cyclists' saddle was randomly raised or lowered 5 to 6 times every 6 to 8 minutes to different trochanteric leg length percentages. Borysewicz (1985) stated the minimal and maximal oxygen consumption values with the same workload was found by Hodges to occur at saddle heights of 96 and 100% of trochanteric leg length, respectively. Because the Hodges study, as reported by Borysewicz (1985) does not appear to be published, it is difficult to determine why there are differences in optimal percentages of trochanteric leg length and what these differences are attributed to, when compared to the values reported by Nordeen-Snyder (1977). Similar results were found by Hull and Gonzalez (1990) with an optimisation model for cycling. For a cyclist of average height (1.78m) and weight (72.5kg), Hull and Gonzalez (1990) determined that the optimal seat height plus crank arm length should be 97% of trochanteric leg length to minimise the cycling cost function. In a comparison of lower limb electromyographic activity between 2 seat heights (105 vs 95% of pubic symphysis height) for national level male cyclists, Despires (1974) reported no significant differences in muscle activity. Similarly, Houtz and Fischer (1959) state that varying the height of the bicycle seat from 21 inches (53cm) to 24 inches (61cm) does not affect, in general, the timing of muscle activity; although the exercise is performed with less effort at 24 inches. In using 2 specified seat heights for all subjects, Houtz and Fischer (1959) did not account for individual differences in lower limb lengths. The optimal seat to pedal distance for nonconventional human powered vehicles is unknown. 3.2 Crank Arm Length Changing the crank length, instead of the seat height will also alter the seat-to-pedal distance. But, there appear to be certain differences between the 2 methods. First, altering crank lengths will result in greater torques being attained with longer cranks

Factors Affecting Cycling Performance

whereas raising the seat to obtain a greater seat-topedal distance will not. Secondly, there is decreasing muscle tension with increasing crank lengths, which would affect the amount of muscular fatigue experienced over time. Finally, with increasing crank lengths force patterns can change and deviate from the optimal pattern (lnbar et al. 1983). There appears to be a limitation regarding the length of the crank arm. Simpson (1979) states the crank arm length is limited by the fact that the pedal at the bottom of the arc must clear the ground on turns. The pedal at its farthest forward point, must not interfere with the turning of the front wheel (the wheel must not hit the toe-cage). Other considerations regarding the selection of a crank length include: (a) the cyclists' leg length (i.e. the reach of the leg on the downstroke, the angle of the leg on the upstroke); (b) the type of terrain involved and the gearing ratio selected; and (c) the nature of the competition (longer cranks for hill climbs and shorter cranks for pursuits and sprints where fast rotations are required). From the available literature, the crank lengths which have been investigated ranged from 3.1 inches (7.9cm) to 9.45 inches (24cm) [Goto et al 1976]. To maintain the same seat-to-pedal distances with different crank lengths, the seat-to-pedal distance is elevated or lowered correspondingly to the increase or decrease in crank length (Astrand 1953; Inbar et al. 1983). Inbar et al. (1983) state seat height variation will only affect the muscle force application angle to the pe<;lals while crank length alteration will simultaneously involve other factors as well. Since the effects of these factors is not believed to be parallel or even unidirectional, the exact nature of the combined effect is difficult to predetermine. For instance, a 5cm deviation in crank length from the optimum can produce a 1% power output fall-off whereas a similar 5cm change from the optimal seat height can result in a 5 to 8% decrement in efficiency or power in both aerobic and anaerobic cycle ergometry (Inbar et al. 1983). The most commonly used bicycle pedal crank length is 6.5 inches (16.5cm) [Dickinson 1929]. Whitt (1969) states that the optimum pedal crank

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length appears to be approximately 6.5 inches (16.5cm) to 7 inches (17.8cm). The use of long cranks, such as those 9 inches long (22.9cm), results in inefficient muscle usage and is analogous to cycling in a seat height that is too low. Inbar et al. (1983) reported that the optimal crank length for peak power and mean power in an all-out anaerobic test (3O-second Wingate) was 16.6cm and 16.4cm, respectively. Inbar et al. (1983) state the optimal crank lengths for shorter or taller individuals (leg lengths of92 to 97cm and 100 to 107.2cm, respectively) should vary from the standard crank length (17.5cm) by lcm for approximately every 6.3cm difference in leg length. For aerobic work, Carmichael (1981) indicate that the crank length minimising oxygen consumption is dependent upon the upper thigh length and determined by the equation: Optimal crank length (mm) = 2.33 (upper leg length in cm) + 55.8. In an aerobic test involving 9 male competitive cyclists tested at 75% of maximal oxygen consumption with cranks 15, 16, 17, 18, 19,and20cm in length, Carmichael (1981) reported optimal crank length was correctly predicted by the upper leg length with 80% accuracy. These results were limited to subjects with heights between 169.3 to 195.5cm, total leg length between 84.0 to 102.9cm, upper leg lengths between 41.0 to 50.8cm, and lower leg lengths between 43.0 to 53.8cm. Depending on the size of the. cyclist, Hull and Gonzalez (1990), found that a crank arm length of 14cm minimised the cost function in cycling for a rider of average anthropometry (height 1.78m, weight 72.5kg). However, with increasing size, the optimal crank arm length will also increase. In other studies, Goto et al. (1976) found that oxygen consumption and electromyographic activity increased only slightly for cranks 3.1 inches (7.9cm) and 6.3 inches (16cm) in length, whereas marked increases were found for cranks 9.45 inches (24cm) in length. Astrand (1953), using 16,18, and 20cm crank lengths, reported an energy output of 12.5 kcal/min when cycling at 20 km/h on a treadmill with a 2% slope. No significant differences in

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efficiency (as measured by oxygen consumption) were found among the various crank lengths. Optimal crank lengths for boys 6, 8, and 10 years of age were reported by Klimt and Voigt (1974) to be 14, 15 and 16cm, respectively. Whether similar results will be found with the same crank arm lengths when tested in nonconventional cycling positions is unknown.

4. Factors Affecting Cycling Energy Expenditure There appears to be some optimal pedalling frequency for different workloads which would minimise energy for some power output (Cavanagh & Kram 1985a,b). The number of investigations involving manipulation of these variables are quite large and varied. Some investigators have examined the effect of altering workload and power output on energy expenditure while maintaining a constant pedalling frequency (Coast & Welch 1985; Gaesser & Brooks 1975; Gollnick et al. 1974; Hagberg et al. 1978; Henry & DeMoor 1950; HughJones 1947). Other investigators have examined the effect of altering pedalling frequency on energy expenditure while maintaining: (a) a constant resistance (Benedict & Cathcart 1913; Dickinson 1929; Girandola & Henry 1976); (b) the frictional load, while keeping the total work constant (Croisant 1975); or (c) the same power output by simultaneously changing the workload (Faria et a1. 1982; McKay & Banister 1976; Michielli & Stricevic 1977; Moffatt & Stamford 1978; Stamford 1973). Still others have examined the effect of different pedalling frequencies on energy expenditure while working at a certain percentage of maximum oxygen uptake (Cafarelli 1978; Gueli & Shephard 1976; Hagberg Giese, & Mullin 1975; Hagberg et al. 1981; Jordan & Merrill 1979; Lollgen et al. 1980; Merrill & White 1984; Patterson & Pearson 1983), altering both the pedalling frequency and power output (Banister & Jackson 1967; Boning et al. 1984; Croisant 1979; Croisant & Boileau 1984; Hagberg et al. 1975; Knuttgen et a1. 1971; Pugh 1974; Seabury et a1. 1975, 1977), or manipulations with other combinations of pedalling rates, workloads, and

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power outputs (Garry & Wishart 1931; Kroon 1983; McCartney et al. 1983; Pandolf & Noble 1973). Manipulations of the pedalling rate, frictional load, power output, and/or total work accomplished can affect the amount of energy expended for a given cycling task. 4.1 Workload, Power Output and Pedalling Rate The optimal pedalling rate to minimise energy expenditure and maximise efficiency is believed by many investigators to vary with the workload selected. Croisant and Boileau (1984) indicate there is a significant interaction between workload and pedalling frequency; and with an increase in workload and power output, a nonlinear increase in the optimal pedalling rate is required to minimise energy expenditure. Croisant (1979) states the relation between workload and pedalling frequency is fairly linear between the loads of 1 and 3kp for rates of 20, 40, 60 and 80 rpm, but is more sharply curvilinear above 3kp and below 1kp. This is supported by Boning et al. (1984), who reported nonlinear relations with pedalling frequencies and stated that the lowest oxygen uptake and the highest efficiency shifted to higher pedalling frequencies with increasing workload. However, it appears that increasing the pedalling frequency without increasing the workload may increase the relative energy expended rather than decrease it. It would also appear that depending on the workload selected, an increase in pedalling frequency accompanied by a corresponding decrease in frictional resistance (to maintain an equivalent power output) will result in: (a) a significant increase in oxygen consumption at moderate power outputs [i.e. 800 kg • m/min (131W)]; and (b) a significant decrease in oxygen consumption at high power outputs [i.e. 1800 kg • m/min (294W)] (Faria et al. 1982). This suggests a definite interaction between pedalling frequency, power output, and energy expenditure, and a most efficient pedalling rate for different power outputs. This was confirmed by Seabury et al. (1977), who found that: (a) a most efficient pedalling rate

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Factors Affecting Cycling Performance

exists for each power output studied; (b) the most efficient pedalling rate increases with power output; (c) the increase in energy expenditure when pedalling slower than optimal is greater at high power outputs than at lower power outputs; and (d) the increase in energy expenditure when pedalling faster than optimal is greater at low power outputs than at high power outputs. Contrary to the data reported by Seabury et al. (1977), Hagberg et al. (1981) stated that if the cyclist is unsure of his optimal pedalling rate, pedalling speed that is less than the optimal level is more efficient than one that is above. It is unknown whether these differences were attributed to the use of a different subject population, the test protocol, or both because competitive cyclists were used by Hagberg et al. (1981) and testing involved riding their own racing bicycles on a treadmill. Finally, Hull and Gonzalez (1990) determined, with an optimisation model, the optimal pedalling rate to be 115 rpm at a constant average power of 200W. But, the optimal pedalling rate was stated to decrease as the rider's size increased. It is difficult to determine whether optimal pedalling frequencies reported in the literature for different workloads and power outputs are also appropriate for different body positions, configurations, and orientations in nonconventional bicycles. Based on the available information, it is logical to assume some optimal pedalling frequencies do exist for different power outputs which would maximise efficiency and minimise energy expenditure for both submaximal and maximal workloads in nonstandard cycling positions.

5. Conclusion There are a large number of factors affecting cycling performance and a gap still exists between cycling research in the various disciplines. To bridge this gap requires cooperation and interdisciplinary research between the engineers and kinesiologists. To maximise and/or optimise cycling performance requires a definition of performance, the criterion for performance and the constraints imposed upon it. If the criterion is development of an 'ultimate'

human-powered vehicle to establish unprecedented speed and/or distance records on land, air, and/or sea, then information must be obtained regarding the interaction of environmental factors with mechanical and human factors. This would involve the design and development of a humanpowered vehicle to not only account for aerodynamic and/or hydrodynamic drag, but also to seat and position an individual in an orientation and configuration that would optimise interaction of the various neurological, biomechanical and physiological variables related to power, work, energy, and efficiency. Further interdisciplinary research needs to be undertaken before final solutions to these issues can be obtained.

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Correspondence and reprints: Dr Danny Too. Department of Health. Physical Education and Recreation. California State University Fullerton. 800 N. State College. Fullerton. CA 92634-4080. USA.