Motion envelopes: unfolding longitudinal rotation data from walking stick-figures

Abstract

This work presents Motion Envelopes (ME), a simple method to estimate the missing longitudinal rotations of minimal stick figures, which is based on the spatial-temporal surface traced by line segments that connect contiguous pairs of joints. We validate ME by analyzing the gait patterns of 6 healthy subjects, comprising a total of 18 gait cycles. A strong correlation between experimental and estimated data was obtained for lower limbs and upper arms, indicating that ME can predict their longitudinal orientation in normal gait, hence, ME can be used to complement the kinematic information of stick figures whenever it is incomplete.

Keywords:

• Inverse kinematics
• stick figures
• longitudinal rotations
• markerless systems
• gait

Disclosure statement

No potential conflict of interest was reported by the authors.

Ethics approval

Ethical approval for this study was obtained from ethics committee of Instituto Superior Técnico in January 2020 with reference number 1/2020 (CE-IST).

Additional information

Funding

This research was supported by the Fundação para a Ciência e a Tecnologia through grants with references UIDB/50022/2020, UIDB/50021/2020, UTAP-EXPL/CA/0065/2017, and PTDC/CCI-COM/30274/2017.