Seat Tube Angle Research Articles

Body mass scaling of projected frontal area in competitive cyclists.

The primary purpose of this study was to evaluate the scaling relationship between body mass (mb) and projected frontal area (AP) of competitive male cyclists whilst allowing statistically for the influence of bicycle geometry. A group of 21 cyclists [mean mb 74.4 (SD 7.2) kg, mean height 1.82 (SD 0.06) m, mean age 23.6 (SD 5.1) years] volunteered to have AP determined from photographs at three trunk angles (TA: 5 degrees, 15 degrees, 25 degrees) for each of three seat-tube angles (STA: 70 degrees, 75 degrees, 80 degrees) using a modified cycle ergometer. Using multiple log-linear regression analysis procedures, the following equation was developed: Body AP (meters squared) = 0.00433 x (STA0.172) x (TA0.0965) x (mb0.762) (r2 = 0.73, SEE = 0.017 m2) (n = 183 images total). This equation indicates that after allowing for the independent influence of STA and TA on AP, AP was proportional to mb raised to the +0.762 power (i.e. Ap is directly proportional to 0.762). The 95% confidence interval for this exponent (0.670-0.854) barely included the theoretical two-thirds value but not the +0.55 value for AP or the +0.32 value for submaximal metabolic power (Ws) of outdoor cycling reported in the literature. Further analysis of wind tunnel data reported in the literature suggests that the coefficient of drag (CD) is proportional to mb raised to the -0.45 power. When combined with the present study findings, it is suggested that the drag area (CD x AP), which should be proportional to Ws at submaximal cycling velocities, is proportional to mb to the +0.312 power (i.e. CD x AP is directly proportional to mb-0.45) x (mb+0.762) = mb+0.312), which is consistent with the +0.32 exponent for Ws in the literature.

Effects of bicycle frame ergonomics on triathlon 10-km running performance

It is perceived that, during the triathlon or duathlon, cycling with a steep (>76°) rather than a shallow (≪76°) frame geometry might attenuate the fatigue associated with progression from the cycle to run disciplines and improve subsequent 10-km running performance. This is based on anecdotal testimony from athletes purporting to have experienced improved performance; no empirical evidence exists. To evaluate this view, eight male triathletes completed a counterbalanced, 40-km cycle ride at two frame geometries (73° and 81°) at ~70% VO 2peak . Immediately after completion of each 40-km cycle, a self-paced 10-km treadmill time trial was undertaken, during which physiological, kinematic and performance variables were measured. The 10-km run performance (mean - s : 42:55 - 4:19 vs 46:15 - 4:52 min; P ≪ 0.01) and combined cycle and run performance (1:45:49 - 5:45 vs 1:50:33 - 6:08; P ≪ 0.001) were faster in the 81° than the 73° condition. Improvements in performance were most prominent during the first 5 km of the run (21:41 - 2:15 vs 24:15 - 2:31 min in the 81° and 73° conditions respectively). These improvements were not evident during the second 5 km of the run. No differences in physiological variables were noted, although heart rate, stride length and stride frequency were increased during the 81° condition ( P ≪ 0.05). Modifying frame geometry from a seat tube angle of 73° to 81° improves 10-km running and combined cycle plus run performance. These improvements in performance might relate to alterations during the cycling phase, which minimizes the 'residual effect' of this (i.e. the adverse changes in substrate availability, thermoregulatory, cardiovascular and biomechanical factors felt immediately after transition from cycling to running) and attenuates negative changes in physiological and kinematic responses during the 10-km run.

BODY MASS SCALING OF FRONTAL AREA IN CYCLISTS 1124

Swain (1994) found that projected frontal area (AP, m2) for cyclists in a “racing position” scaled with body mass (MB) to the 0.55 power (ie AP α MB0.55), which is lower than the 0.67 exponent predicted theoretically (˙Astrand and Rodahl, 1986). To evaluate this contradiction, the present study sought to determine how AP scaled with MB after statistically controlling for anthropometric and bicycle geometry covariates in 21 male cyclists(Mean±SD: 23.6±5.1 yrs, 74.4±7.2 kg, 10.8±3.5% fat). AP for each subject was measured at 3 trunk angles (TAs: 5°, 15°, 30°) at each of 3 seat-tube angles (STAs: 70°, 75°, 80°) while seated stationary on a Monark cycle ergometer modified with adjustable seat and handlebar positioning and aerobars. Images from 35 mm film slides of each subject were hand digitized to compute AP using standard planometry procedures (n = 189 slides). Multiple log-linear regression analyses (α = 0.05) were used to determined the MB exponent for AP while using TA, STA, body height (1.82±0.06 m), and biacromial diameter (0.48±0.02 m) as covariates. The resulting regression model (R2=0.84; P<0.001) found that AP scaled with MB to the 0.41 power (95% CI:0.30-0.52). Thus, AP scaled to a lower power than predicted by the literature (0.41 vs 0.55 or 0.67). Clearly, the statistical control of anthropometric and bicycle geometry covariates was very important to determining the MB exponent for AP.

Effect of variation in seat tube angle at different seat heights on submaximal cycling performance in man

The effect of seat tube angle at selected seat heights (96, 100 and 104% trochanteric height) on heart rate, VO 2 and lower limb kinematics was evaluated in 14 competitive male road racing cyclists during discontinuous submaximal exercise (200 W) on an air-resistance ergometer at seat tube angles of 68, 74 and 80 . The tests were randomized to complete the nine combinations (three seat heights, three tube angles) in opposite directions from a starting tube angle of 74 and 100% trochanteric height to avoid any time or sequence bias. Power efficiency was calculated for each combination from work done and VO 2 . All results were analysed using ANOVA for repeated measures. At a seat tube angle of 80 , mean VO 2 was significantly lower and power efficiency significantly higher compared with an angle of 74 at all three seat heights, while heart rate was significantly lower only at a seat height equal to trochanteric height. At a seat tube angle of 74 , mean VO 2 and heart rate were significantly lower and power efficiency significantly higher compared with an angle of 68 at all three seat heights. Hip range of movement and maximum and minimum hip angle were significantly less at an angle of 80 compared with 68 . Further biomechanical analysis suggested that the improvement in cycling efficiency observed at steeper seat tube angles was produced in part by the resultant altered ankling pattern of the cyclist.

The relationship between preferred and optimal positioning during submaximal cycle ergometry.

This study was designed to determine how changes in oxygen uptake (VO2) and heart rate (HR) during submaximal cycle ergometry were determined by changes in cycle geometry and/or lower-limb kinematics. Fourteen trained cyclists [Mean (SD): age, 25.5 (6.4) years; body mass 74.4 (8.8) kg; peak VO2, 4.76 (0.79) 1 x min(-1) peak] were tested at three seat-tube angles (70 degrees, 80 degrees, 90 degrees) at each of three trunk angles (10 degrees, 20 degrees, 30 degrees) using a modified Monark cycle ergometer. All conditions were tested at a power output corresponding to 95% of the VO2 at each subject's ventilatory threshold while pedalling at 90 rpm and using aerodynamic handlebars. Sagittal-view kinematics for the hip, knee, and ankle joints were also recorded for all conditions and for the subjects' preferred positioning on their own bicycles. No combination of seat-tube and trunk angle could be considered optimal since many of the nine conditions elicited statistically similar mean VO2 and HR values. Mean hip angle (HA) was the only kinematic variable that changed consistently across conditions. A regression relationship was not observed between mean VO2 or HR and mean hip angle values (P > 0.45). Significant curvilinear relationships were observed, however, between deltaVO2 (VO2 - minimum VO2) and deltaHA (mean HA - preferred HA) using the data from all subjects (R = 0.45, SEE = 0.13 1 x min(-1)) and using group mean values (R = 0.93, SEE = 0.03 1 x min(-1)). In both cases deltaVO2 minimized at deltaHA = 0, which corresponded to the subjects' preferred HA from their own bicycles. Thus, subjects optimized their VO2 cost at cycle geometries that elicited similar lower-limb kinematics as the preferred geometries from their own bicycles.

Cardiorespiratory responses to seat-tube angle variation during steady-state cycling

The effect of seat-tube angle (STA) variation on oxygen consumption (VO2), heart rate (HR), ventilation (VE), and rating of perceived exertion (RPE) on 25 trained competitive triathletes and cyclists was evaluated during 10-min submaximal tests at each of four STAs (69 degrees, 76 degrees, 83 degrees, 90 degrees). Subjects averaged (mean +/- SD) 26.5 +/- 6.4 yr of age, 68.5 +/- 9.8 kg, 4.26 +/- 0.58 l.min-1 for VO2peak, and 76.2 +/- 1.5 degrees for preferred STA. Tests occurred on a modified cycle ergometer (at each subject's preferred dimensions, except for STA) at a power output that averaged 73% of the subjects' VO2peak and pedaling 90 rpm while using aerodynamic handlebars. Mean VO2, HR, and RPE values at 83 degrees and 90 degrees were significantly lower than values at 69 degrees (3.09, 3.10 vs 3.17 l.min-1; 149.6, 149.9 vs 152.9 bpm; 13.5, 13.5 vs 14.2, respectively; P < 0.05). VE at 83 degrees was significantly lower than VE at 69 degrees (65.2 vs 68.2 l.min-1; P = 0.011). A kinematic analysis found greater hip extension, ankle plantar flexion, and a lower-limb orientation more directly over the crank axis when STA increased. Therefore, only the 69 degrees STA appeared to be a detriment to steady-state cardiorespiratory responses during cycling, whereas the 76 degrees, 83 degrees, and 90 degrees STAs elicited similar cardio-respiratory responses.

Multivariable optimization of cycling biomechanics

Relying on a biomechanical model of the lower limb which treats the leg-bicycle system as a five-bar linkage constrained to plane motion, a cost function derived from the joint moments developed during cycling is computed. At constant average power of 200 W, the effect of five variables on the cost function is studied. The five variables are pedalling rate, crank arm length, seat tube angle, seat height, and longitudinal foot position on the pedal. A sensitivity analysis of each of the five variables shows that pedalling rate is the most sensitive, followed by the crank arm length, seat tube angle, seat height, and longitudinal foot position on the pedal (the least sensitive). Based on Powell's method, a multivariable optimization search is made for the combination of variable values which minimize the cost function. For a rider of average anthropometry (height 1.78 m, weight 72.5 kg), a pedalling rate of 115 rev min −1, crank arm length of 0.140 m, seat tube angle of 76°, seat height plus crank arm length equal to 97% of trochanteric leg length, and longitudinal foot position on the pedal equal to 54% of foot length correspond to the cost function global minimum. The effect of anthropometric parameter variations is also examined and these variations influence the results significantly. The optimal crank arm length, seat height, and longitudinal foot position on the pedal increase as the size of rider increases whereas the optimal cadence and seat tube angle decrease as the rider's size increases. The dependence of optimization results on anthropometric parameters emphasizes the importance of tailoring bicycle equipment to the anthropometry of the individual.