title: Pooling sexes when assessing ground reaction forces during walking: Statistical Parametric Mapping versus traditional approach.
abstract: Ground reaction force (GRF) data from men and women are commonly pooled for analyses. However, it may not be justifiable to pool sexes on the basis of discrete parameters extracted from continuous GRF gait waveforms because this can miss continuous effects. Forty healthy participants (20 men and 20 women) walked at a cadence of 100 steps per minute across two force plates, recording GRFs. Two statistical methods were used to test the null hypothesis of no mean GRF differences between sexes: (i) Statistical Parametric Mapping-using the entire three-component GRF waveform; and (ii) traditional approach-using the first and second vertical GRF peaks. Statistical Parametric Mapping results suggested large sex differences, which post-hoc analyses suggested were due predominantly to higher anterior-posterior and vertical GRFs in early stance in women compared to men. Statistically significant differences were observed for the first GRF peak and similar values for the second GRF peak. These contrasting results emphasise that different parts of the waveform have different signal strengths and thus that one may use the traditional approach to choose arbitrary metrics and make arbitrary conclusions. We suggest that researchers and clinicians consider both the entire gait waveforms and sex-specificity when analysing GRF data.
authors.affiliation: Centre of Research, Education, Innovation and Intervention in Sport, School of Sport, University of Porto, Portugal; Activity and Human Movement Study Centre, School of Allied Health Science, Polytechnic Institute of Porto, Portugal. Electronic address: marcelo.peduzzi.castro@gmail.com.
authors.forename: Marcelo P
authors.initials: MP
authors.lastname: Castro
authors.affiliation: Department of Bioengineering, Shinshu University, Japan.
authors.forename: Todd C
authors.initials: TC
authors.lastname: Pataky
authors.affiliation: School of Physiotherapy, University of Otago, New Zealand.
authors.forename: Gisela
authors.initials: G
authors.lastname: Sole
authors.affiliation: Centre of Research, Education, Innovation and Intervention in Sport, School of Sport, University of Porto, Portugal; Porto Biomechanics Laboratory, University of Porto, Portugal.
authors.forename: Joao Paulo
authors.initials: JP
authors.lastname: Vilas-Boas
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D005684:Gait; D006801:Humans; D008297:Male; D012680:Sensitivity and Specificity; D012727:Sex Characteristics; D018709:Statistics, Nonparametric; D016138:Walking; D055815:Young Adult
keywords: Biomechanics; Force plate; Gender; Random field theory; Walking