title: Muscle Strength and Body Weight Mediate the Relationship Between Physical Activity and Usual Gait Speed.
abstract: Usual gait speed (UGS) is recognized as a good indicator of a variety of health conditions as well as a predictor of future disability and mortality. There is evidence that UGS increases with physical activity. Muscle function and body composition changes may mediate these changes. However, we do not know exactly which of these factors contribute to the effect of physical activity on gait speed or the magnitude of their contribution.
  
  
  
  Data are from 1378 women aged 75 years and older recruited in the Toulouse EPIDémiologie de l'OStéoporose cohort. Body weight and composition (dual energy X-ray absorptiometry), knee extension strength, and physical activity habits were assessed. The INDIRECT macro for SPSS (SPSS Inc, Chicago, IL) was used to determine total and specific indirect effects of physical activity on UGS through body weight (BW) and composition as well as muscle mass and strength.
  
  
  
  Knee extension strength [95% confidence interval (CI) 0.0091, 0.0231] and BW (95% CI 0.0037, 0.0412), but not fat mass or muscle mass, were mediators of the relationship between physical activity and gait speed. However, muscle mass significantly mediated the relationship between physical activity and muscle strength (95% CI -3.0722, -0.6265).
  
  
  
  Results suggest that muscle strength and BW are the most significant mediators of the relationship between physical activity and UGS. Although the specific effect of muscle mass appears negligible at first sight, its role should not be overlooked given its impact on muscle strength.
authors.affiliation: Département de Biologie, Université du Québec à Montréal, Montréal, Canada; Groupe de Recherche en Activité Physique Adaptée, Université du Québec à Montréal, Montréal, Canada; Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal, Montréal, Canada.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Barbat-Artigas
authors.affiliation: Groupe de Recherche en Activité Physique Adaptée, Université du Québec à Montréal, Montréal, Canada; Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal, Montréal, Canada; Département des sciences de l'activité physique, Université du Québec à Montréal, Montréal, Canada.
authors.forename: Lívia
authors.initials: L
authors.lastname: Pinheiro Carvalho
authors.affiliation: Service de Médecine interne et de Gérontologie Clinique, Hôpital La Grave-Casselardit, Toulouse, France; Unité Inserm 558, Faculté de Médecine de Toulouse, Toulouse, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Rolland
authors.affiliation: Service de Médecine interne et de Gérontologie Clinique, Hôpital La Grave-Casselardit, Toulouse, France; Unité Inserm 558, Faculté de Médecine de Toulouse, Toulouse, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Vellas
authors.affiliation: Groupe de Recherche en Activité Physique Adaptée, Université du Québec à Montréal, Montréal, Canada; Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal, Montréal, Canada; Département des sciences de l'activité physique, Université du Québec à Montréal, Montréal, Canada. Electronic address: aubertin-leheudre.mylene@uqam.ca.
authors.forename: Mylène
authors.initials: M
authors.lastname: Aubertin-Leheudre
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001835:Body Weight / Q000502:physiology*; D015444:Exercise; D005260:Female; D005602:France; D006801:Humans; D053580:Muscle Strength / Q000502:physiology*; D011446:Prospective Studies; D057566:Self Report; D000072797:Walking Speed / Q000502:physiology*
keywords: Walking speed; leisure-time physical activity; mediation factors; older adults