A Case Study of Alpine and Freestyle Snowboard Turn Measurement

Ayuko Saito

, Kazuto Miyawaki

and Naofumi Tsuji

Department of Mechanical Engineering and Robotics, National Institute of Technology, Akita College,

1-1 Iijima-Bunkyo-cho, Akita 011-8511, Japan

Technology Education Support Center, National Institute of Technology, Akita College,

1-1 Iijima-Bunkyo-cho, Akita 011-8511, Japan

Keywords: Alpine Snowboard, Center of Pressure, Force Sensor, Freestyle Snowboard, Reaction Force from Snow

Surface.

Abstract: This study investigated the reaction force from the snow surface affecting a snowboarder during alpine

snowboarding turns and freestyle snowboarding turns. Alpine snowboards and freestyle snowboards have

different widths, shapes, flexes, and hardnesses. Snowboarder motions during turns using an alpine

snowboard and freestyle snowboard differ. Therefore, analyzing the reaction force from the snow surface

affecting the snowboarder gliding on an actual snow field is expected to be valuable for clarifying differences

of snowboarder motions during alpine snowboarding turns and freestyle snowboarding turns. We developed

a new measurement system for this study to measure the reaction force from the snow surface during

snowboarding. Furthermore, we conducted experiments with a professional snowboarder gliding on an actual

snow field using alpine and freestyle snowboards fitted with the measurement system. The center of pressure

during alpine snowboarding showed that the right foot placed on the snowboard in the counter travel direction

side was used mainly to press the snowboard edge during front-side turns. The left foot placed on the

snowboard in the travel direction side was used mainly to press the snowboard edge during back-side turns.

The center of pressure during freestyle snowboarding showed that both feet were used to press the snowboard

edge.

1 INTRODUCTION

Snowboarding, which involves descending a snow-

covered slope on a board attached to both feet,

requires alpine or freestyle snowboards, both of

which are widely used. Alpine snowboarders wear

hard boots similar to those used conventionally for

alpine skiing, with dedicated bindings for hard boots.

Freestyle snowboarders wear soft boots and dedicated

bindings for soft boots. Moreover, alpine snowboards

are narrower than freestyle snowboards. Therefore,

alpine bindings are attached to a board at a much

higher angle in the travel direction to avoid heel or toe

drag. In giant slalom events, alpine snowboards are

used because alpine snowboard characteristics are

suitable for speed and tight curves. By contrast,

freestyle snowboards are suited to jumping and

ground tricks because freestyle snowboarders can

move their ankles freely with soft boots. Alpine and

freestyle boards have numerous points of difference

such as board characteristics, boots, and bindings.

Moreover, snowboard control methods differ among

snowboard types. Clarifying the respective

snowboard turn mechanisms of alpine and freestyle

snowboarding is therefore important for evaluating

snowboarder skills.

Several earlier reports describe studies of skiing

and snowboarding (Subic et al., 2010; Fuss, 2014;

Saito et al., 2015; Korecki et al., 2016). Kagawa et al.

(1998) developed a force sensor incorporating several

strain gauges to measure the six-component forces of

a skier during turns. Other studies have used several

uniaxial load cells or six-component force sensors to

analyze the reaction force from a snow surface on a

skier gliding on an actual snow field (Iwami et al.,

2002; Kiefmann et al., 2006). These studies revealed

how skiers put pressure on the skis during gliding on

an actual snow field. For earlier studies of

snowboarding, force sensors were used to measure

the reaction force from a snow surface on

snowboarders in the same manner as those used for

earlier studies of skiing. Moeyersons et al. (2016)

developed an electronic system to analyze the

reaction force from a snow surface on snowboarders.

Saito, A., Miyawaki, K. and Tsuji, N.

A Case Study of Alpine and Freestyle Snowboard Turn Measurement.

DOI: 10.5220/0007952200150020

In Proceedings of the 7th International Conference on Sport Sciences Research and Technology Support (icSPORTS 2019), pages 15-20

ISBN: 978-989-758-383-4

It alerted the snowboarders when a greater load was

put on the back boot than on the front boot. Hirose et

al. (2013a, 2013b) estimated the joint torques of

snowboarders and skiers during turns using inertial

sensors and six-component force sensors. Kondo et

al. (2014) developed a new system of measuring the

reaction force from a snow surface for snowboarding

using compact three-component force sensors. Other

studies have assessed the six-component force

characteristics of snowboarders during turns and

jumping (Hirose et al., 2016; Fushimi et al., 2017).

Nevertheless, few studies have examined alpine

snowboards. For this study, we conducted

experiments with one professional snowboarder

using an alpine snowboard and a freestyle snowboard

as the first step toward clarifying snowboard turn

mechanisms. This experiment elucidates whether the

reaction force from the snow surface can be different

in alpine snowboarding turns and freestyle

snowboarding turns. The new reaction force

measurement system was developed for this study by

installing six-component force sensors. This

measurement experiment analyzed the six-

component force of a professional snowboarder

during turns made on an actual snow field.

Furthermore, to quantify the difference of each

snowboarding, we compared the center of pressure

(COP) of the snowboarder, as calculated from the six-

component force during alpine and freestyle

snowboarding turns.

2 METHOD

2.1 Measurement System

The snowboarding reaction force measurement

system is presented alone in Fig. 1 and attached to the

snowboard in Fig. 2. The system consists of an upper

plate, a lower plate, and a six-component force sensor

(FFS080YS102U6; Leptrino Co. Ltd.). The upper

plate is attached to a binding. The lower plate is

attached to a snowboard. The six-component force

sensor is installed between the upper plate and the

lower plate. The 120 mm × 120 mm × 34 mm system

had total weight of 970 g including the six-component

force sensor. We developed two measurement

systems: one attached to the travel direction side (left)

binding and one attached to the counter travel

direction side (right) binding. Upper plates were

made of machined aluminum. Using a personal 3D

printer, lower plates were produced from acrylonitrile

butadiene styrene (ABS) resin. The systems were

used with alpine and freestyle snowboards.

The reaction force from the snow surface was

expressed as a six-component force (3-axis force and

3-axis moment) measured using the force sensors.

2.2 Experiment

The measurement experiment assessed a professional

snowboarder (181 cm height, 86 kg weight) gliding

on an actual snow field. The snowboarder, who had

28 years of snowboarding experience, held a Grade-

A instructor license authorized by the Japan

Snowboarding Association. The snowboarder used a

regular stance, with the left foot placed on the

snowboard in the travel direction. Following an

explanation of the purpose and requirements of the

study, the snowboarder gave written informed

consent to participate. Study approval was obtained

from the Research Ethics Board, National Institute of

Akita College. The alpine snowboard used for the

experiment (Eracer 163 cm; Yonex Co., Ltd.) is

depicted in Fig. 3.

Figure 1: Snow surface reaction force measurement system.

Figure 2: Measurement system between the snowboard and

bindings.

The freestyle snowboard (Meister 161 cm; Yonex

Co., Ltd.) is portrayed in Fig. 4. Measurement

systems were installed between the bindings and

snowboards for both feet. The snowboarder with the

measurement system is presented in Fig. 5.

The definitions of binding angles are presented in

Fig. 6. An angle of 0 deg signifies that the binding is

mounted as pointing directly across the snowboard

with no forward or no backward angle. A binding

angle with plus degrees (+) signifies that the binding

is set pointing to the nose of the snowboard. For this

experiment, the travel direction side angle was plus

Upper plate

Lower

plate

Six-component

force sensor

120 mm

34 mm

Measurement system

icSPORTS 2019 - 7th International Conference on Sport Sciences Research and Technology Support

54 deg; the counter travel direction side angle was

plus 48 deg on the alpine snowboard. The travel

direction side angle was plus 21 deg; the counter

travel direction side angle was 0 deg on the freestyle

snowboard.

A schematic view of the slalom slope, with

average inclination of about 12 deg, is presented in

Fig. 7. The snowboarder made periodic carving turns.

The sampling frequency was 100 Hz.

Figure 3: Alpine snowboard used in the experiment.

Figure 4: Freestyle snowboard used in the experiment.

Figure 5: Snowboarder with attached measurement system.

2.3 Analysis Method

The coordinate system of the measurement system is

presented in Fig. 8. The six-component forces of the

snowboarder were compared to clarify their

respective motion characteristics. Furthermore, we

analyzed COP calculated from the six-component

forces. Earlier studies showed that snowboarders

make turns using a moment around the snowboard

length direction (Hirose et al., 2014; Kondo et al.,

2014). For this study, the Y-axis is the snowboard

length direction. Therefore, we specifically examined

the COP of the width direction (X-axis).

The COP of the width direction is represented by

Eq. (1), where a

is the direction from the original

point to the force sensor of z-axis direction, f

and f

respectively represent the x-axis force and y-axis

force, respectively and n

is the y-axis moment.

Figure 6: Definitions of binding angles.

Figure 7: Schematic view of the slalom slope.

Figure 8: Snowboard with attached measurement system.

yzx

naf





(1)

3 RESULTS

Fig. 9 presents results for the reaction force from the

snow surface of turns during alpine snowboarding.

Figure 10 presents results for the reaction force from

Traveling

direction

Travel direction side binding

Counter travel direction side binding

Travel direction side binding

Counter travel direction side binding

A Case Study of Alpine and Freestyle Snowboard Turn Measurement

the snow surface during turns in freestyle

snowboarding. Measurement experiments were

repeated three times for each type of snowboarding.

All results of alpine snowboarding indicated a similar

tendency. All results of freestyle snowboarding also

indicated a similar tendency. The results of the third

trial of both snowboards are presented in Fig. 9 and

Fig. 10, where the horizontal axis is the time axis and

the vertical axis shows the six-component force.

These results represent the outcomes of four turns

as the snowboarder passed from the sixth pole through

the ninth pole. The snowboarder made front-side turns

while passing through the sixth pole and the eighth

pole. Front-side turns were made by pressing on the

toe-side edge. The snowboarder made back-side turns

while passing through the seventh pole and the ninth

pole. Back-side turns were done by pressing on the

heel-side edge.

The switching point between a front-side turn and

a back-side turn was defined as the time when the value

of Y-axis moment became zero. The switching points

of turns on the left foot were defined using the value of

Y-axis moment on the left foot. The switching points

of turns on the right foot were defined using the value

of Y-axis moment on the right foot.

Table 1 presents results for the X-axis coordinate

of the COP of the averages of all trials. The X-axis

coordinate of the COP was calculated using

measurement information of 10% before and after the

midpoint of the time for each turn.

4 DISCUSSION

4.1 Reaction Force from the Snow

Surface

The Z-axis force of the counter travel direction side

foot increased during turns in alpine and freestyle

snowboarding. The Z-axis force of the travel direction

side foot showed little characteristic change during

turns in alpine and freestyle snowboarding. Results

indicate that the counter travel direction side foot was

used mainly to put pressure on the snowboard.

The Y-axis moment of both feet changed

periodically to put pressure on the snowboard edges in

alpine and freestyle snowboarding. The Z-axis

moments of both feet in freestyle snowboarding

changed periodically, whereas the Z-axis moments of

both feet showed only slight changes in alpine

snowboarding. In freestyle snowboarding, the Z-axis

moment of the travel direction side foot increased in

front-side turns. The Z-axis moment of the counter

travel direction side foot increased in back-side turns.

Results demonstrate that the snowboarder moved the

ankles to control the snowboard during freestyle

snowboarding. Presumably, the snowboarder

repositioned the ankles for ease of pressing on the

snowboard.

4.2 Center of Pressure

For alpine and freestyle snowboarding, the X-axis

COP coordinates had plus values during front-side

turns, with X-axis COP coordinates having minus

values during back-side turns. Results show that the X-

axis COP coordinates moved to the inside of turns

during turns to put pressure on the snowboard edges.

In front-side turns of alpine snowboarding, the

COP of the travel direction side foot stayed in the

position close to the origin of the coordinate, although

the COP of the counter travel direction side foot stayed

in the position close to the edge. In back-side turns

during alpine snowboarding, the COP of the travel

direction side foot stayed in the position close to the

snowboard edge, although the COP of the counter

travel direction side foot stayed in the position close to

the origin of the coordinate. Results show that the

counter travel direction side foot was used mainly to

put pressure on the snowboard edge during front-side

turns. The travel direction side foot was used mainly to

put pressure on the snowboard edge during back-side

turns.

However, the COP of both feet stayed in the

position close to the snowboard edge during both

turns in freestyle snowboarding. Results show that both

feet were used to put pressure on the snowboard edge.

5 CONCLUSIONS

Measurement experiments were conducted with a

professional snowboarder to clarify differences in the

reaction force from the snow surface during turns

executed for alpine and freestyle snowboarding. The

results elucidated the characteristics of the three-axis

force and the three-axis moment of a snowboarder

during turns. Furthermore, the COP results reflected

the degree to which the snowboarder put pressure on

the snowboard edge. This study revealed that the

reaction force from the snow surface and the COP are

useful to ascertain the snowboarder motion

characteristics during turns. Additional studies

measuring other snowboarders must be done for

quantitative clarification of reaction forces from the

snow surface and assessment of the differences of

snowboarder motions in alpine snowboarding turns

and freestyle snowboarding turns.

icSPORTS 2019 - 7th International Conference on Sport Sciences Research and Technology Support

(a) Travel direction side (left) force.

(b) Travel direction side (left) moment.

(d) Counter travel direction side (right) moment.

Figure 9: Reaction force from the snow surface of

snowboard turns in alpine snowboarding.

(a) Travel direction side (left) force.

(b) Travel direction side (left) moment.

(d) Counter travel direction side (right) moment.

Figure 10: Reaction force from the snow surface of

snowboard turns in freestyle snowboarding.

A Case Study of Alpine and Freestyle Snowboard Turn Measurement

Table 1: Center of pressure in turns (X-axis coordinate).

Travel direction side (left) foot

Counter travel direction side (right) foot

Turn number

Alpine

Freestyle

Alpine

Freestyle

COP in front side turns

(mm)

6th

139

113

8th

145

104

120

COP in back side turns

(mm)

7th

-98

-153

-74

-106

9th

-96

-154

-88

-113

ACKNOWLEDGMENTS

This work was supported by JSPS KAKENHI Grant

Number JP18K17844.

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