title: Muscular co-contraction during walking and landing from a jump: comparison between genders and influence of activity level.
abstract: BACKGROUND
  Women have higher rates of knee ligament injury than men. Co-contraction of knee muscles is proposed to be an important mechanism to protect the joint from injuries.
  
  
  OBJECTIVE
  Females have lower co-contraction levels when compared to males.
  
  
  METHODS
  Exploratory, cross-sectional design.
  
  
  METHODS
  Thirty-six men and women equally divided into four groups according to gender and activity level (sedentary and athletic) were compared in relation to vastus lateralis and biceps femoris co-contraction before heel strike during level walking and before floor contact during landing from a jump. Muscular co-contraction was assessed by surface electromyography. Correlations between co-contraction and ligament laxity, extensor and flexor work, and flexion/extension torque ratio were also analyzed.
  
  
  RESULTS
  No differences between genders were found in the studied situations (p0.381). During walking, co-contraction was greater in sedentary women compared to athletic women (p=0.002). A moderate inverse correlation was found between co-contraction during walking and women extensor (r=-0.613; p=0.007) and flexor (r=-0.575; p=0.012) work. During landing from a jump, no variables correlated to co-contraction in any of the groups tested (r0.477; p0.061).
  
  
  CONCLUSIONS
  Co-contraction levels were not different between genders. Results suggest that women compensate strength deficits by means of increasing activation levels, possibly to generate adequate joint stiffness to meet stabilization demands. However, this is not evident in a more stressful activity like landing from a jump.
  
  
  CONCLUSIONS
  This study contributes to a better understanding of the factors related to joint protection in females, who are at a greater risk of ligament injuries.
authors.affiliation: Human Performance Laboratory, Department of Physical Therapy, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, Unidade Administrativa II, 3o andar, 31270-010 Belo Horizonte, MG, Brazil. sfonseca@pib.com.br
authors.forename: Sergio Teixeira
authors.initials: ST
authors.lastname: da Fonseca
authors.forename: Daniela Virgínia
authors.initials: DV
authors.lastname: Vaz
authors.forename: Cecília Ferreira
authors.initials: CF
authors.lastname: de Aquino
authors.forename: Rachel Soares
authors.initials: RS
authors.lastname: Brício
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D005684:Gait / Q000502:physiology*; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D012737:Sex Factors; D016138:Walking / Q000502:physiology*