Optical Axis of camera aligned with top of head tubeWhite

background

White groundsheet

Camera & tripod

Minimum camera to subject distance 10 m

Figure 2. Data Collection Experimental setup diagram.

Scaling object (1m Rule)

Introduction

Measurement validity and reliability

Sport specific analysis

Analysis of the Great Britain endurance squad

Guidelines for FSA calculation from digital images

This poster illustrates a project completed as part of the 2002/3 World Class Sport Science Development Programme – a BASES/UKSI project collaboration.The aim of the project was to develop a method of measuring frontal surface area (FSA) to be used by British Cycling with the ultimate aim of improving the performance of British cyclists. It was felt that digital photography and pixel counting using image manipulation software would provide the best vehicle for achieving this aim.The assistance of Dr Andrew Jones (Bases Supervisor) and Andrea Wooles (sport supervisor: British Cycling) are gratefully acknowledged.

A method for measuring the frontal surface area of elite cyclists

Andrew D. MossCRM, Manchester Metropolitan University, Alsager, ST7 2HL.

Measurement validity: using the experimental setup detailed in figure 1, three square pieces of matt black fibreboard were each photographed three times (figure 3). The three pieces of fibreboard had surface areas of 0.25 ± 0.01, 0.56 ± 0.01 and 1.00 ± 0.01 m2. FSA was calculated for each piece of fibreboard. The mean FSA of the three squares calculated from the photographic images analysed in the NIH image software was 0.25 ± 0.00, 0.56 ± 0.00 and 1.00 ± 0.00 m2. The agreement between these vales suggests this is a valid method of assessing FSA.Measurement reliability: the 1 m2 fibreboard shape was photographed 10 times. Each time the setup detailed in figure 1 was repeated as if a separate data collection session were being performed. The mean FSA of the 1 m2 fibreboard square was 0.99 ± 0.01 m2 The coefficient of variation was 0.01 %. The agreement between the vales suggests this is a reliable method of assessing FSA.

Assessment of three riding positions: using the experimental setup detailed in figure 2, data was collected of a subject in three different riding positions (figure 4): Bars – hands on the handlebars next to the stem, hoods – hands positioned as if on the brake hoods, and drops – hands on the drop section of the handlebars. Three photographs were taken of each position. The mean FSA of a subject photographed in three positions was 0.40 ± 0.00, 0.42 ± 0.01 and 0.40 ± 0.00 m2

respectively. The coefficient of variation for each of the three positions was 0.00 0.23 and 0.00 % respectively.Measurement reliability: the subject was photographed 10 times in the Bars position. Each time the setup detailed in figure 2 was repeated as if a separate data collection session was being performed. The mean FSA of a subject photographed ten times was 0.41 ± 0.01 m2. The coefficient of variation was 0.24 %. The agreement between the vales suggests this is a reliable method of assessing FSA.

Import images to be used into Adobe Photoshop image software version 7, crop, and re-size as appropriate (figure 5).

Distinguish subject of analysis using the fill function (figure 6). Save the image as an uncompressed tiff (tagged image format) image.

Import images into NIH image software. Convert individual pixels into real world units using the Set scale function. Measure the FSA using the measure function (figure 7).

Photographs were taken of six members of the Great Britain endurance quad in the standard anatomical position and in aerodynamic position on their cycles. The experimental setup shown in figure 2 was used.Two measurements of FSA were made of each athlete in each of the two positions. The results are shown in table 1. In order to quantify the repeatability of the measurements, the FSA of a subject was calculated twelve times from one image. The mean FSA of the athlete on his cycle in aerodynamic position was 0.33 ± 0.01 m2. The coefficient of variation for each of the three positions was 0.03 % The agreement between the vales suggests this is a reliable method of assessing FSA.

Figure 1. Pilot Work Experimental setup diagram.

Minimum camera to subject distance 10 m

Optical Axis of camera aligned with centre of squareWhite

background

Camera & tripod

White groundsheet

Scaling object (1m Rule)

1m Approx

Figure 4. Three riding positions: Bars, Hoods and Drops.

Figure 3. Fibreboard squares of known FSA used in the assessment of measurement validity and reliability.

Figure 5. Cropped and re-sized image.

Figure 6. Subject distinguished from background with contrasting colour.

Figure 7. FSA measurement in NIH image software.

Table 1. Results of FSA data collection with Great Britain endurance squad.

ConclusionThe data presented above suggest that digital photography and subsequent pixel counting with digital image analysis software is a valid and reliable technique for the assessment of FSA in elite cyclists.