Physical activity consists complex behavior, typically structured in
bouts which can consist of one continuous movement (e.g. exercise) or many
sporadic movements (e.g. household chores). Each bout can be represented as a
block of feature vectors corresponding to the same activity type. This paper
introduces a general distance metric technique to use this block representation
to first predict activity type, and then uses the predicted activity to estimate
energy expenditure within a novel framework. This distance metric, dubbed
Bipart, learns block-level information from both training and test sets,
combining both to form a projection space which materializes block-level
constraints. Thus, Bipart provides a space which can improve the bout
classification performance of all classifiers. We also propose an energy
expenditure estimation framework which leverages activity classification in
order to improve estimates. Comprehensive experiments on waist-mounted
accelerometer data, comparing Bipart against many similar methods as well as
other classifiers, demonstrate the superior activity recognition of Bipart,
especially in low-information experimental settings.