title: The Required Coefficient of Friction for evaluating gait alterations in people with Multiple Sclerosis during gait.
abstract: BACKGROUND
  Required Coefficient of Friction (RCOF) is one of the most critical gait parameters associated to the occurrence of slipping in individuals affected by neurological disorders characterized by balance impairments. This study aims to calculate RCOF in people with Multiple Sclerosis (MS) on the basis of three-dimensional Gait Analysis (GA) data.
  
  
  METHODS
  This study enrolls 22 people with MS (pwMS) who were characterized by an Expanded Disability Status Score in the range 1.5-6 and 10 healthy controls (HC). All participants underwent to three-dimensional GA from which we extracted kinematic and kinetic data (i.e. the Ground Reaction Forces, GRF, and joint moments and powers in the sagittal plane). RCOF was calculated as the ratio of the shear to normal GRF components during the stance phase of gait cycle, and normalized by the walking velocity. Thus, the following variables were extracted: first peak (named P1COF), valley (named V1COF), and second peak (named P2COF) in RCOF curve; also computating the maximum ankle dorsi-plantarflexion moment (MOMmax) and the maximum ankle joint power (PWRmax).
  
  
  RESULTS
  Our data revealed that P2COF results are significantly lower in pwMS when compared to HC (p=0.043; Z=-2.025). In pwMS, the study found a moderate, positive correlation between V1COF and MOMmax (r=0.558; p<0.001) and a moderate, positive correlation between EDSS score and MOMmax (rho=0.622; p=0.001). While, in HC group, the study detected a moderate positive correlation between P1COF and MOM max (r=0.636; p=0.008).
  
  
  CONCLUSIONS
  Friction during mid stance and push off phases is critically important to determine whether the frictional capabilities of foot/floor interface are sufficient to prevent slips in pwMS. The impaired ankle moment in MS group causes increased P2COF in comparison to HC, increasing the risk of slipping in the critical phase of transmission of the developed forces to kinematic chain. Also, the correlation analysis among RCOF values and kinetic variables describe the interplay between V1COF and MOMmax: the higher V1COF is, the higher is MOMmax; and the different correlation the study found between COF and kinetic parameters in MS and HC group highlightes the different gait patterns of the two classes of subjects.
authors.affiliation: Department of Biomedical Sciences for Health, Università degli Studi di Milano, Milan, Italy; Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milan, Italy. Electronic address: ilaria.pacifici@polimi.it.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Pacifici
authors.affiliation: Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milan, Italy; "Motion analysis Lab", IRCCS San Raffaele Pisana, Rome, Italy. Electronic address: manuela.galli@polimi.it.
authors.forename: Manuela
authors.initials: M
authors.lastname: Galli
authors.affiliation: Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milan, Italy. Electronic address: anafrancisca.rozin@polimi.it.
authors.forename: Ana Francisca Rozin
authors.initials: AF
authors.lastname: Kleiner
authors.affiliation: Department of Mechanical, Chemical and Materials Engineering, University of Cagliari, Cagliari, Italy. Electronic address: corona.federic@gmail.com.
authors.forename: Federica
authors.initials: F
authors.lastname: Corona
authors.affiliation: Department of Medical Sciences and Public Health, University of Cagliari, Cagliari, Italy. Electronic address: gccoghe@gmail.com.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Coghe
authors.affiliation: Sport Physiology Lab, Department of Medical Sciences "Mario Aresu", University of Cagliari, Cagliari, Italy. Electronic address: elisamar84@gmail.com.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Marongiu
authors.affiliation: Sport Physiology Lab, Department of Medical Sciences "Mario Aresu", University of Cagliari, Cagliari, Italy. Electronic address: loi@unica.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Loi
authors.affiliation: Sport Physiology Lab, Department of Medical Sciences "Mario Aresu", University of Cagliari, Cagliari, Italy. Electronic address: crisaful@unica.it.
authors.forename: Antonio
authors.initials: A
authors.lastname: Crisafulli
authors.affiliation: Department of Medical Sciences and Public Health, University of Cagliari, Cagliari, Italy. Electronic address: ecocco@unica.it.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Cocco
authors.affiliation: Department of Medical Sciences and Public Health, University of Cagliari, Cagliari, Italy. Electronic address: gmarrosu@unica.it.
authors.forename: Maria Giovanna
authors.initials: MG
authors.lastname: Marrosu
authors.affiliation: Department of Mechanical, Chemical and Materials Engineering, University of Cagliari, Cagliari, Italy. Electronic address: massimiliano.pau@dimcm.unica.it.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Pau
mesh_terms: D000058:Accidental Falls; D000293:Adolescent; D000328:Adult; D000368:Aged; D000843:Ankle Joint / Q000503:physiopathology; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D017276:Friction / Q000502:physiology; D005684:Gait / Q000502:physiology; D006801:Humans; D008875:Middle Aged; D008954:Models, Biological; D009103:Multiple Sclerosis / Q000175:diagnosis* / Q000503:physiopathology*; D012306:Risk; D055815:Young Adult
keywords: Correlation; Kinetic variables; Multiple Sclerosis (MS); Required Coefficient of Friction