Biomechanical assessment of sports bra performance
thesisposted on 07.10.2016, 11:36 authored by Laura Whittingham
Biomechanical testing has been the cornerstone of sports bra research to date and the quantification of breast kinematics during exercise has received increasing interest. However, comparatively little research has been published regarding the development of biomechanical testing methodology and how this testing may inform the development of sports bra design. Thus, the overall research aim was the ‘Development and application of methods used in the biomechanical assessment of sports bra performance with the end goal of better biomechanical tools for use in the sports bra design process’. Breast kinematics are typically measured relative to the torso, therefore, it is necessary to track both torso and breast motion. The absence of a universally accepted torso tracking model, and information regarding the sensitivity of breast kinematics to the selected torso model were identified as limitations to the existing research. The seven marker torso tracking model presented is the first to be specifically developed for analysing relative breast motion during activities such as treadmill running and is recommended to be implemented in future sports bra research. The torso segment used to calculate relative breast kinematics is assumed to be rigid, however, breast movement resulting from respiration has been reported for a static condition. The effect of breathing on breast kinematics during treadmill running was investigated. Significant differences were observed in the breast kinematics between breathing and non-breathing conditions, notably in the superior-inferior direction; however, they could not definitively be directly linked to breathing since significant differences in running gait were also observed. The results do suggest that increasing the number of gait cycles analysed may reduce any effects of breathing on breast kinematics due to phase-locking, the synchronisation of breathing with running locomotion. Analysing breast kinematics over 30 gait cycles may help minimise any potential effects of phase-locking across all commonly used phase-locking ratios. Further understanding of breast motion and whether markers placed on the bra represent the underlying breast were identified as pertinent to advancing biomechanical assessment of sports bra performance. Motion between the breast and bra (either during an initial bedding in phase or steady state running) has yet to be explored within the existing literature and is assumed to be negligible for a correctly fitted bra. A settling in period of ~30 seconds between the breast and bra was found to occur during the initial phase of treadmill running. Whilst the study is recognised to be exploratory in nature, the findings suggest future breast kinematic study should consider the possibility of a settling in effect. Therefore, experimental protocols may benefit from including a short period of activity after the subject has changed into the bra to help eliminate any settling in effect prior to data capture or application of over bra markers. The results also suggest that motion occurs between the breast and bra irrespective of bra size and that over bra markers underestimate superior-inferior (S-I) breast displacement and anterior-posterior (A-P) displacement at the upper breast. Markers positioned over the bra were found to be less sensitive to variation in A-P and S-I displacement in different regions of the breast. However, use of under bra markers is limited by current motion capture technology and until advances in technology are made the use of over bra markers remains current best practice. Future studies are recommended to state whether breast markers were located over or under the bra and recognise that over bra markers represent bra motion. Bra strap stiffness was identified as a potentially important factor in sports bra performance. The effect was investigated using a modified bra with removable strap sections of three differing stiffness. Bra strap mechanical properties were characterised using a specifically developed tensile testing protocol. Sports bra performance during treadmill running was assessed using biomechanical and perceptual measures. Increasing bra strap stiffness was found to improve sports bra performance with respect to bra kinematics (primarily in the superior-interior direction) and subjective perception ratings (in particular the perception of support), suggesting strap stiffness may have an important role to play in bra design.
- Mechanical, Electrical and Manufacturing Engineering