Cycling efficiency in trained male and female competitive cyclists

he aim of this study was to examine differences in cycling efficiency between competitive male and female cyclists. Thir- teen trained male (mean + SD: 34 ± 8 yr, 74.1 ± 6.0 kg, Maxi- mum Aerobic Power (MAP) 414 ± 40 W, VO 2max 61.3 ± 5.4 ml·kg -1 ·min -1 ) and 13 trained female (34 ± 9 yr, 60.1 ± 5.2 kg, MAP 293 ± 22 W, VO 2max 48.9 ± 6.1 ml·kg -1 ·min -1 ) competitive cyclists completed a cycling test to ascertain their gross effi- ciency (GE). Leg and lean leg volume of all cyclists was also measured. Calculated GE was significantly higher in female cyclists at 150W (22.5 ± 2.1 vs 19.9 ± 1.8%; p < 0.01) and 180W (22.3 ± 1.8 vs 20.4 ± 1.5%; p = 0.01). Cadence was not significantly different between the groups (88 ± 6 vs 91 ± 5 rev·min -1 ). Lean leg volume was significantly lower for female cyclists (4.04 ± 0.5 vs 5.51 ± 0.8 dm 3 ; p < 0.01) and was in- versely related to GE in both groups at 150 and 180W (r = -0.59 and -0.58; p < 0.05). Lean leg volume was shown to account for the differences in GE between the males and females. During an “unloaded” pedalling condition, male cyclists had a significantly higher O 2 cost than female cyclists (1.0 ± 0.1 vs 0.7 ± 0.1 L·min - 1 ; p < 0.01), indicative of a greater non-propulsive cost of cy- cling. These results suggest that differences in efficiency be- tween trained male and female cyclists can be partly accounted for by sex-specific variation in

pedalling condition, male cyclists had a significantly higher O 2 cost than female cyclists (1.0 ± 0.1 vs 0.7 ± 0.1 L·min - 1 ; p < 0.01), indicative of a greater non-propulsive cost of cy- cling. These results suggest that differences in efficiency be- tween trained male and female cyclists can be partly accounted for by sex-specific variation in lean leg volume. Key words: Gross efficiency, endurance performance, sex- related differences, power output, leg volume. Introduction Whilst there is growing research interest in female cycling (Ashenden et al., 1999), to our knowledge the effect that sex differences have on efficiency remains to be investi- gated in competitive cyclists. Most studies have involved only male participants, with, for example, comparisons being made between trained and untrained riders (Hopker et al., 2007; Hopker et al., 2009). Yasuda et al. (2008) investigated differences between untrained males and females during arm and leg exercise. They found no sig- nificant sex differences in GE, delta efficiency, the ratio of the change in work accomplished or the change in energy expended (Faria et al., 1982) at relative exercise intensities 70-115% of ventilatory threshold. Whipp and Wasserman (1972) have shown this approach to measur- ing efficiency to be problematic as exercise at or above lactate/ventilatory thresholds incurs additional VO 2 due to the slow component of VO 2 kinetics, thereby potentially causing erroneous efficiency values. It has been suggested that gross efficiency (GE) [defined as the ratio of work accomplished to energy expended (Gaesser and Brooks, 1975)] is one of the most important functional abilities of a cyclist (Coyle, 1995) as it determines the amount of power that can be produced for a given O 2 cost and level of energy expenditure. Other methods of calculating efficiency using base-line subtrac- tions (i.e. Net, Work and Delta Efficiency), have all been suggested to be conceptually flawed. For a review see Ettema and Loras (2009). It is, therefore, most appropriate to focus on GE as the primary outcome variable as a measure of the efficiency of whole body exercise. Horowitz et al. (1994) demonstrated that cyclists with a

efficiency using base-line subtrac- tions (i.e. Net, Work and Delta Efficiency), have all been suggested to be conceptually flawed. For a review see Ettema and Loras (2009). It is, therefore, most appropriate to focus on GE as the primary outcome variable as a measure of the efficiency of whole body exercise. Horowitz et al. (1994) demonstrated that cyclists with a high GE were able to generate a greater power output for the same VO 2 than riders possessing a lower GE. Simi- larly Lucia et al. (1998) found that professional riders were able to generate a greater power output than ama- teurs even though their VO 2max values were similar. There are a number of factors which have been shown to affect GE in cycling: cadence (Chavarren et al., 1999; Coast et al., 1986; Samozino et al., 2006), body mass (Berry et al., 1993), cycling position (Browning et al., 1992; Gonzales and Hull, 1989), pedalling technique (Kautz and Neptune, 2002; Korff et al., 2007), prior exercise (Passfield and Doust, 2000), muscle fibre type (Coyle et al., 1992), and training status (Hopker et al., 2007; 2009; 2010). Studies investigating differences between males and females in running economy have produced equivocal findings (Billat et al., 2003; Bransford and Howley, 1979; Davies and Thompson, 1979; Daniels and Daniels, 1992; Joyner, 1993; Maughan and Leiper, 1983). This may, in part, reflect the calibre of the sample populations used. Differences in running economy between sexes in some study populations appear smaller than the intra-individual variation among individual runners (Saunders et al., 2004). On closer analysis of much of this research, it appears that body/limb mass differences could account for a large proportion of any differences found between the sexes. Indeed, Berry et al. (1993) have demonstrated that efficiency during cycling is negatively correlated with body mass over a range of power outputs and cadences in female cyclists. Similarly, Francescato et al. (1995) found that artificially increasing leg mass by the addition of weights strapped to the thighs and lower legs resulted in a significantly higher oxygen cost of cycling across a range of pedal cadences.

demonstrated that efficiency during cycling is negatively correlated with body mass over a range of power outputs and cadences in female cyclists. Similarly, Francescato et al. (1995) found that artificially increasing leg mass by the addition of weights strapped to the thighs and lower legs resulted in a significantly higher oxygen cost of cycling across a range of pedal cadences. To the authors’ knowledge, no study has investi- gated differences in GE between male and female trained competitive cyclists using work rates that are representa- tive of those commonly used during training and racing. Therefore, the aim of the present study was to establish whether gross efficiency differs between trained male and female competitive cyclists. A secondary aim was to Research article

Hopker et al. 333 identify if differences in leg volume could account for any differences found in efficiency between the sexes. Methods A cross-sectional study design was utilized. Twenty six competitive cyclists of regional and national standard were recruited, comprising 13 males (mean ± SD: age 34 ± 8 yr, mass 74.1 ± 6.0 kg, Maximum Aerobic Power (MAP) 414 ± 40 W, VO 2max 61.3 ± 5.4 ml·kg -1 ·min -1 ) and 13 females (34 ± 9 yr, 60.1 ± 5.2 kg, MAP 293 ± 22 W, VO 2max 48.9 ± 6.1 ml·kg -1 ·min -1 ), both with at least 2 years of cycle training/racing experience. Adequate par- ticipant numbers were estimated using a priori statistical power analysis (Hopker et al., 2007). Prior to testing, each cyclist gave written informed consent for this study which had university ethics committee approval. Before partici- pating in the exercise trials, participants underwent ha- bituation sessions in order to familiarise themselves with the testing procedures. The cyclists were instructed not to train in the 24 hours before testing. The female partici- pants performed their tests in the early-follicular phase of the menstrual cycle to standardise hormonal effects influ- encing metabolic responses (Gurd et al., 2007; Janse de Jonge, 2003). Testing of all participants was conducted during the competitive phase of the season as we have previously shown GE to be highest during this period (Hopker et al., 2009). Each rider attended the laboratory for a test of cy- cling efficiency and maximal aerobic power. Upon report- ing to the laboratory, body mass was measured to the nearest 0.1 kg using a beam balance scales (Seca, Ger- many). A stadiometer (Seca, Germany) was used to measure stature to the nearest 0.5 cm. Lower limb dimen- sions and skin fold thicknesses were measured prior to each cyclist’s test to enable the calculation of total and lean leg volume according to the procedures of Winter et al. (1991). Specifically, leg volume was estimated using limb circumference measurements to calculate the volume (v) of a truncated cone: v = 1/3 h (a + √ab +

Lower limb dimen- sions and skin fold thicknesses were measured prior to each cyclist’s test to enable the calculation of total and lean leg volume according to the procedures of Winter et al. (1991). Specifically, leg volume was estimated using limb circumference measurements to calculate the volume (v) of a truncated cone: v = 1/3 h (a + √ab + b) where a and b are the areas of two parallel surfaces derived from circumference measurements, and h is the distance between the surfaces. Lean leg volume was subsequently calculated by subtracting the estimated subcutaneous fat measurements from the leg diameter measurements prior to calculation of lean leg volume. Throughout each trial, laboratory conditions were held constant (ambient temperature 18-22°C, relative humidity 45-55%) and participants were cooled using an electric fan. The cyclists rode an electronically braked ergome- ter (Lode Excalibur Sport, Lode, Groningen, NL) which was calibrated before the start of the study for power outputs of 25-1000 W at cadences of 40, 60, 80, 100 and 120 rev·min -1 and was found to be within 1% of a true value (CV = 1%, CI = 0.7-1.2%). Each cyclist’s bike setup (saddle height, distance between saddle and handle bars, handle bar height, crank lengths) was recorded and reproduced for all tests. Cyclists completed a cycling efficiency test. After an 8-minute period of “unloaded” cycling (for the deter- mination of an unloaded cycling O 2 cost), female cyclists started at a power output of 120W and males at a power output of 150W. In both groups, work rate increased by 30 W every 8 min until the measured concentration of lactate measured in fingertip blood samples (Biosen, EKF, Germany) reached 4 mmol·L -1 . All cyclists used their preferred pedal cadence throughout (rev·min -1 ). During this test Lactate Threshold (LT) was determined as the power preceding 1 mmol·L -1 increase in blood lactate (Coyle, 1999) and OBLA (Onset of Blood Lactate Accumulation) as a measured 4 mmol·L -1 lactate concen- tration (Heck et al., 1985). The power at LT and OBLA was determined from interpolation. Once 4 mmol·L -1

cadence throughout (rev·min -1 ). During this test Lactate Threshold (LT) was determined as the power preceding 1 mmol·L -1 increase in blood lactate (Coyle, 1999) and OBLA (Onset of Blood Lactate Accumulation) as a measured 4 mmol·L -1 lactate concen- tration (Heck et al., 1985). The power at LT and OBLA was determined from interpolation. Once 4 mmol·L -1 was obtained and/or RER exceeded 1.00 the cycling efficiency test was terminated. Expired gases were collected on a breath-by- breath basis (Quark b2, Cosmed, Italy) over the final three minutes of each 8-minute bout of exercise completed for the measurement of VO 2 and RER. Eight-minute stages were used for gas collection as Chuang et al. (1999) sug- gest that during early exercise CO 2 storage in the muscle decreases RER values. As a result CO 2 takes longer to reach steady state, ~4 minutes. CO 2 stability must be ensured prior to sampling due to its influence on RER which is used within the efficiency calculations. Power output was measured and recorded at 1- second intervals. These data were used to calculate GE using the equation: GE = Work accomplished x 100% Energy expended (Gaesser and Brooks, 1975) Following the test to determine GE, participants rested for 5 minutes prior to the commencement of a ramp protocol to determine VO 2max. This protocol started at 150W using a 20W per minute ramp rate and continued until volitional exhaustion. VO 2max was determined as the highest measured 60 second VO 2max achieved during the incremental test. Maximal power output (MAP) was cal- culated as the average power output over the final minute of the ramp test. Data analysis Prior to all statistical analyses, normality of data were confirmed using a Shapiro-Wilk Test. Submaximal VO 2 data were averaged on a minute-by-minute basis and then analysed using an ANOVA to establish the potential in- fluence of the “slow component” of VO 2kinetics. This was because of potential distortion of the linearity of the VO 2-work rate relationship due to additional VO 2consumption after the 3 rd minute of supra-anaerobic threshold exercise

Shapiro-Wilk Test. Submaximal VO 2 data were averaged on a minute-by-minute basis and then analysed using an ANOVA to establish the potential in- fluence of the “slow component” of VO 2kinetics. This was because of potential distortion of the linearity of the VO 2-work rate relationship due to additional VO 2consumption after the 3 rd minute of supra-anaerobic threshold exercise (Whipp, 1972). Comparisons of the mean GE between male and female cyclists were assessed using MANOVA. A MANOVA was used to account for both leg and lean leg volume as uncontrolled covariates influencing the rela- tionship between GE and sex. Subsequently, differences between groups and across intensities were analysed

Male and female cycling efficiency 334 using unadjusted post-hoc analysis (Least Significant Difference). Statistical significance was set at 95% confi- dence (p < 0.05). Differences in GE between the groups were assessed at 0, 150, 180 and 210W, as well as at intensities equivalent to LT and 60% MAP using interpo- lation from the steady state data. Differences in other descriptive physiological data between male and female cyclists were identified using independent student’s t- tests. Relationships between efficiency and leg volumes were assessed using Pearson’s correlation coefficient. Finally the estimated O 2 cost of “unloaded” cycling was calculated from the y-intercept of the relationship be- tween work rate and O 2 uptake. All values are expressed as mean and standard deviation (mean ± SD) unless oth- erwise stated. Results Table 1 presents descriptive and physiological data for male and female cyclists. All variables presented in Table 1 were signifi- cantly higher in male cyclists (p < 0.01) except maximum heart rate and preferred cadence (p > 0.05). Table 1. Descriptive and physiological data for trained male and trained female cyclists. Data presented as mean (±SD). Male Cyclists Female Cyclists Mass (kg) 74.1 (6.0) 60.1 (5.2) * MAP (W) 414 (40) 300 (24) * VO 2max (L·min -1 ) 4.6 (.5) 3.0 (.4) * VO 2max (mL·kg -1 ·min -1 ) 61.3 (5.4) 48.9 (6.1) * Lactate Threshold (W) 267 (25) 159 (14) * OBLA (W) 305 (34) 200 (14) * HR max (b·min -1 ) 184 (10) 185 (12) Leg Volume (dm 3 ) 8.27 (1.2) 7.62 (1.4) * Lean Leg Volume (dm 3 ) 5.51 (.8) 4.04 (.5) * Preferred Cadence (rpm -1 ) 91 (5) 88 (6) * significantly different to male riders (p ≤ 0.01). VO 2 at work rates of 150 and 180W showed no significant differences (mean difference <15.5mL·min -1 ; p = 0.93) between the 3 rd and 8 th minutes of each exercise stage. However, female cyclists demonstrated a signifi- cant “slow component” above 210W. This data was there- fore excluded from the subsequent analysis. Lean leg volume was significantly higher in male

at work rates of 150 and 180W showed no significant differences (mean difference <15.5mL·min -1 ; p = 0.93) between the 3 rd and 8 th minutes of each exercise stage. However, female cyclists demonstrated a signifi- cant “slow component” above 210W. This data was there- fore excluded from the subsequent analysis. Lean leg volume was significantly higher in male cyclists and was inversely related to GE at 150 and 180 W in both male and female cyclists (r = -0.59 and r = -0.58; p < 0.01 respectively). Total leg volume was also higher in male cyclists, although no significant relationships were found with GE at either power output (r = -0.35 and r = -0.36 respectively; p > 0.05). Results for GE at absolute and relative exercise in- tensities are provided in Table 2. VO 2 data for the male and female cyclists are shown in Figure 1. MANOVA analysis identified that female cyclists possessed a sig- nificantly higher GE than males across the common inten- sities of 150 and 180 W (p < 0.01). Including leg volume as a covariate did not alter the difference between groups (for both 150 and 180 W). However, the addition of lean leg volume as a covariate eliminated the GE differences between males and females at both work rates (p = 0.08 and p = 0.43 at 150 W and 180 W respectively). Table 2. GE (%) for trained male and trained female cyclists at absolute power outputs of 150 and 180W and relative to LT and 60%MAP. Data presented as mean (±SD). 150W 180W LT 60%MAP Female22.5 (2.1) * 22.3 (1.8) * 23.2 (3.5) 23.5 (3.5) Male 19.9 (1.8) 20.4 (1.5) 21.9 (1.7) 21.7 (1.6) * significantly different to male value (p < 0.05). Gross efficiency at intensities equivalent to LT and 60%MAP, was not different between male and fe- male cyclists (p = 0.30 and p = 0.07 respectively). The addition of leg volume and lean leg volume as covariates did not alter this finding (p > 0.05). Figure 1. Oxygen uptake (L O 2·min -1 ) plotted against

value (p < 0.05). Gross efficiency at intensities equivalent to LT and 60%MAP, was not different between male and fe- male cyclists (p = 0.30 and p = 0.07 respectively). The addition of leg volume and lean leg volume as covariates did not alter this finding (p > 0.05). Figure 1. Oxygen uptake (L O 2·min -1 ) plotted against the submaximal power output in trained male and trained fe- male cyclists. As leg volume accounted for the differences in ef- ficiency values obtained for males and females, it seemed possible that the O 2 cost of unloaded cycling would be significantly different between groups. Oxygen uptake (L O 2·min -1 ) was plotted against the submaximal power out- puts used for male and female cyclists (see Figure 1). The corresponding intercept of this relationship is an estimate of the ‘unloaded’ O 2 cost of moving the legs, and hence an independent correlate of leg volume. Statistical analy- sis of the data demonstrated a significant difference in the y-intercept of the male and female regression lines (p < 0.01), with no difference in the slope of the two (p = 0.99). However, this predicted “unloaded” cost of cycling was significantly lower than the actual cost measured during the “unloaded” cycling phase of test in both males (0.64 vs 1.0 L·min -1 ; p < 0.01) and females (0.20 vs 0.70 L·min -1 ; p < 0.01). Nevertheless, the main conclusions were consistent, with male cyclists having a significantly higher VO 2 than females during “unloaded” pedalling (1.0 ± 0.1 vs 0.7 ± 0.1 L·min -1 ; p < 0.01). Discussion The main finding of this study was that GE was signifi- cantly higher in female cyclists at each of the absolute power outputs measured. No difference was found in relative values, although female data tended to be higher (~23.5% vs ~21.9%). When lean leg volume was factored into the analysis as a covariate, significant differences in GE between trained male and female cyclists were no longer evident. Therefore, lean leg volume is unlikely to

absolute power outputs measured. No difference was found in relative values, although female data tended to be higher (~23.5% vs ~21.9%). When lean leg volume was factored into the analysis as a covariate, significant differences in GE between trained male and female cyclists were no longer evident. Therefore, lean leg volume is unlikely to

This research investigates cycling efficiency variations based on sex in trained cyclists.