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ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

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to represent a body-segments-coordination, only the combinations of 2 and 3<br />

accelerations were considered, reducing thus the number of possible combinations to<br />

680. To evaluate which one of these 680 possible combinations accelerations could be<br />

used to characterise the PA, the Hausdorff Distance (HD) was computed for each of the<br />

680 combinations between trials of a same PA (intra-activity HDs), whatever the<br />

subject or the intensity of the exercise, but also between trials representing two different<br />

PAs (inter-activity HD). HDs were then classified in 6 different categories:<br />

HDw representing HDs computed between two trials of “walking”<br />

HDr representing HDs computed between two trials “running”<br />

HDc representing HDs computed between two trials “cycling”<br />

HDwr representing HDs computed between a trial “walking” and a trial “running”<br />

HDwc representing HDs computed between a trial “walking” and a trial “cycling”<br />

HDrc, which represents HDs computed between a trial “running” and a trial<br />

“cycling”.<br />

The best combination of the n accelerations to identify the PA is that of the intraactivity<br />

HDs significantly inferior to inter-activity HDs. Normal distribution of the HDs<br />

was assessed using the Shapiro-Wilkinson test. Differences between HD categories<br />

were compared for the 680 accelerations combinations using a one-way ANOVA. When<br />

a significant difference has been noticed, post-hoc analysis with Bonferoni-correction<br />

was performed to compare the intra-activity HD with each inter-activity HD including<br />

the activity. For all the statistical tests, the level of significance was set at 0.05. In<br />

addition to this, for each combination of accelerations tested, were computed the<br />

percentage of intra-activity HDs superior to the inter-activity HDs including the activity<br />

(e.g. the percentage of HDw superior to HDwr and of HDw superior HDwc). Based on<br />

this analysis the best acceleration combination to distinguish the physical activity has be<br />

deduced and definitively implemented in the PA recognition sub-routine.<br />

4. RESULTS<br />

Table 1 : Five best accelerations combinations to<br />

provide the highest percentage (in mean) of intra-<br />

activity HDs inferior to inter-activities HDs.<br />

%<br />

KNEz<br />

oKNEz<br />

KNEz<br />

ANKz<br />

KNEz<br />

ANKz<br />

oKNEz<br />

KNEz<br />

ANKz<br />

oANKz<br />

KNEz<br />

oANKz<br />

HDw

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