Seat Position on a Bike

Index of contents:

1. Overview 2

2. Goals 2

3. Known Results 3

4. Equipment 4

5. Diagrams & Description 7

6. Analysis & Comparison 9

7. Interpretation 10

1. Overview

This experiment examined the optimal seat position on a bicycle ergometer using the two dimensional SimiMotion Software. The focus was on hip & knee, so the position of the upper body & the foot (angle of the ankle) was totally ignored.

The project includes the matching of certain marker points on the knee, hip & ankle axis, the measurement of the knee angle and the hip movement of our test person on the ergometer.

It should be shown that the optimal saddle height allows the best power output of the thigh muscles (knee angle) & keeps the exposure as low as possible. In addition, we logged the position of the hip axis while pedaling.

2. Goals

By testing different seat positions on the ergometer, the bandwidth of the knee angles and the various hip movements should be shown.

This project should demonstrate that the wrong seat position and the following knee angle bandwidth and movement of the hips causes a not as efficient power output as the optimized seat position.

* Show the hip joint movement

* Show the seat position

* Show the knee angle

3. Known Results

- acquiring knowledge using the available literature:

Specifications (optimal seat position)

HЬGI-Method: 0,893 x length of the inner leg

LEMOND (1987) : saddle height = 0,883 x length of the inner leg

LINDNER (1993): HЬGI - Method

GRESSMANN (2003): LEMOND und HЬGI-Method, knee angle at bottom dead center: 165o-175o (not as far as 180o)

HOWARD: BURKE, Edmund. R. (1995) right seat position: the angle between the straight lines through Femur and Tibia represents 30o in bottom dead center of the pedal-rotation.

PRUITT, HOLMES, WHALEN (1994): BURKE, Edmund. R. (1996): the knee angle is specified via Trochanter, Condylus lateralis und Malleolus lateralis. It should constitute between 25o und 30o.

femur

angle

knee 25o-30o

tibia

Fig. 1: schematic diagram to illustrate the angle between femur and tibia

- state of the scientific and technical knowledge:

Scientific studies of the right seat position

based on distance between bottom and Trochanter:

BORYSEWICZ (1985): 96%

NORDEEN-SNYDER (1977): 100%

based on the length of the inner leg:

THOMAS (1967): 109%

SHENNUM und DE VRIES (1976): 108 -109%

NORDEEN-SNYDER (1977): 107,1%

GREGOR et al. (1981): 106%

(TOO, 1990)

4. Methods & Equipment

Equipment

- Bicycle Ergometer:

Daum electronic (change clipless pedals to normal pedals)

- Software:

SIMI Reality Motion Systems GmbH, SIMI - MOTION 2D, Version 7.0 build 241

Microsoft Excel (Recalculations & Diagrams)

- Hardware:

Desktop PC

- Digital Video camera:

Sony, DV Network Handycam, type:DCR-TRV75EITRV80E

- 3D - Markers (white)

- Calibrating cube (0,98m x 0,98m)

Methods

At first a test layout was configured - the position of the camera (frontal), position of the ergometer, etc. and reflective parts were mask to provide the best matching conditions.

Fig. 2: the experimental set-up (camera in the front; ergometer in the background

Afterwards the white markers were fixed on the test person and the ergometer.

Then a calibrating video was taken. From this moment on, the test layout could not be modified anymore (distance & angle between camera & ergometer).

We used a cube ( 0.98 x 0.98 m ) to calibrate the system (Simi Motion software)

3 different videos were taken - one for each saddle position.

Fig. 3: screenshot of the calibrating video

resolution: 768 x 576

frequency: 50 Hz (50 half pictures were taken per second => Simi Motion interpolates them into 50 complete pictures)

Every single marker