Q4E Case Study 6 – Cycle Ergometer

Proposed Subject Usage:

Coaches, Physiotherapy, Strength & Conditioning
Sports Science (1st/2nd and 3rd year), Education Key Stage 4 +

Objective

• To identify difference in the cycling technique induced by seat height.
• To identify differences in the cycling technique induced by frequency (RPM)

Introduction

1) Method 1 - Seat Height

The subject was asked to cycle at a constant rate of 70RPM, at 6 different seat heights (4,6,8,9,10 and 12) marked out on the cycle ergo meter. 30 seconds of 100Hz (Basler High-Speed Camera) video footage was taken per seat height. The video was calibrated using both a vertical and horizontal calibration measurement and automatically digitised. The data was then reduced to 3 complete leg cycles. (One complete cycle is defined as lowest vertical position of the toe, to lowest vertical position of the toe of the same foot on the next cyclic action).

Figure 1: 100fps digitisation trace 1 complete cycle.

Figure 2: Velocity Graph at seat height 4 exported from Quintic Biomechanics v14

 Quintic software functions that were used: Quintic Basler Capture Quintic Automatic Tracking (Biomechanics v14) Quintic Calibration Quintic Linear/Angular Analysis Export Analysis Export Data Image Capture

Results

Table 1: shows the average values for Knee angles at TDC and BDC as well as the angular range of motion.

 Seat Height Knee Angle TDC Maximum Knee Angle BDC Range of Angular Knee Movement 4 51.98 104.99 53.01 6 57.69 111.10 53.40 8 64.13 122.93 58.79 9 67.34 130.96 63.63 10 69.02 133.18 64.16 12 79.06 145.77 66.71

Table one illustrates that as seat height is increased maximum knee flexion increases at top dead centre (TDC ) from 51.98º during the trial at height 4 to 79.06º during the trial at height 12. Maximum knee extension also increases near the BDC from 104.99º to 145º during trial 12.Analysis of the ankle angle during the cycling action shows that, as the seat height increases, so does the range of ankle motion Table 2 illustrates that angular range of motion of the ankle increased from 25.63º at the lowest seat height (4) up to 33.23º at the highest seat height (12). As saddle height increases, ankle plantarflexion increases near bottom dead centre (BDC) from 115.86º at seat height 4 to 118.96º at seat height 12 to prevent the knee from becoming fully extended.

Table 2: shows the average values for Ankle angles at TDC and BDC as well as the angular range of motion

 Seat Height Ankle Angle TDC Ankle Angle BDC Range of Angular Ankle Movement 4 90.23 115.86 25.63 6 87.87 112.45 24.58 8 85.54 110.94 25.39 9 85.01 110.21 25.20 10 81.81 114.36 32.55 12 85.73 118.96 33.23

Although power output was not calculated during this exercise, it it widely recognised that seat height is also linked to power production. If the seat is to high, force transfer through the quariceps and into the pedal crank is not effiecent. If the seat is to low the active muscles are restricted so cannot extend to the optimal force generating length. Alteration of saddle height by only 4% can affect power output by approximately 5%, or 84 seconds on a 28-minute, 15 kilometres time trial. (Lucia et al, 2001)

Future studies could include using varying types of bike frame of set-up, to examine how much different frame set ups, such as racer, triathlon, trial or mountain bike effect the kinematic movements of the cyclist. Future studies could also include the collection of power data to see which frame geometries allow the rider to produce maximum power. A research program like this would allow an athlete to identify which bike set up is efficient for which type of race, whether the race demands explosive power, or strength endurance.

2) Method Frequency (rpm)
The same subject was asked to cycle at his preferred seat height (9) and cycle at 5 different rpm (60,70,80,90,and 100) for 30 seconds. 30 seconds of 100Hz video capture commenced once the subject had signalled that he had reached the designates work rate. The video was then calibrated using both a vertical and horizontal calibration measurement and automatically digitised. The data was then reduced to 3 complete leg cycles for ease of analysis. (One complete cycle is defined as lowest vertical position of the toe, to lowest vertical position of the toe of the same foot on the next cyclic action).

Figure 3: 4 Point (Hip, Knee, Ankle, Toe) Automatic digitisation at 100rpm exported from Quintic Biomechanics v14

Figure 4: Angular Knee Displacement graph at 100rpm exported from Quintic Biomechanics v14.

N.B The black lines on the graphs represent when each trial finished, as each trial was performed at a different rpm, the time to execute 3 complete revolutions was different.

Analysis

Analysis of the cycling action at the various workloads has demonstrated that as the work rate increases there are few technical changes in the subject’s technique. Graph 1 illustrates that as rpm increases, velocity of the toe also increases, this was expected as to increase the rpm the pedal has to complete more revolutions per minute which is achieved by the leg moving faster. Graph 2 shows that although the work rate increases the vertical displacement of the subjects toe stays constant, this again was expected as if vertical displacement increased, revolution time would also increase therefore causing rpm to decrease. During the 100RPM trial Graph 3 illustrates a noticeable decrease in knee extension near the BDC. Graph 4 also illustrates a significant decrease in ankle angle towards the BDC, as rpm increases.

Toe Velocity
m/sec

Vertical Toe Displacement
(m)

Knee Angleº

Ankle Angleº

Trial

TDC

BDC

TDC

BDC

TDC

BDC

TDC

BDC

60rpm

 1.1

1.15

0.67

0.20

70

128

84

117

70rpm

1.24

1.36

0.67

0.22

67

130

85

110

80rpm

1.5

1.65

0.66

0.20

67

128

88

110

90rpm

1.72

1.81

0.66

0.21

68

129

87

112

100rpm

1.94

2.14

0.67

0.21

64

124

84

113

To improve the accuracy of this study, the subjects optimal seat height could have been worked out as well as performing the trials on their current bike by using a turbo trainer set at a specific resisitance. This would have allowed the subject to adopt their natural ride position. To improve this study further power readings could also have been calculated during the different workloads and seat heights. This would allow the subject to design a training program depending on whether they required power for short sprint events or muscle endurance for longer events.

References : Lucia. A., Hoyos. J and Chicharro. J.L. 2001. Physiology of professional road cycling. Journal of Sports Medicine, 31,5,325-337.