title: Step activity and stride-to-stride fluctuations are negatively correlated in individuals with transtibial amputation.
abstract: BACKGROUND
  Variability occurs naturally from stride to stride in healthy gait. It has been shown that individuals with lower limb loss have significantly increased stride-to-stride fluctuations during walking. This is considered indicative of movement disorganization and is associated with less healthy movement. Given that lower limb prosthesis users perform on average less physical activity than able bodied individuals, the purpose of this study was to determine whether increased fluctuations also correspond to a reduced level of activity in daily life.
  
  
  METHODS
  Twenty-two transtibial amputees wore an activity monitor (Actigraph, Pensacola, FL, USA) for 3 weeks. Lower limb kinematics during treadmill walking were measured using a 12-camera motion capture system. The largest Lyapunov exponent (λ) was calculated bilaterally at the ankle, knee and hip to quantify the stride-to-stride fluctuations of the lower limb joints. Pearson correlations were used to identify the relationships between the average daily step count over the 3 week collection period and λ.
  
  
  RESULTS
  Significant, moderate negative correlations between daily step count and λ were found at the intact ankle (r=0.57, P=0.005), and the knee on the affected side (r=0.44, P=0.038). No such correlation was found at any other lower limb joint.
  
  
  CONCLUSIONS
  The negative correlation evident at these two joints demonstrates that increased stride-to-stride fluctuations are related to decreased activity levels, however it remains unclear whether these changes in the stride-to-stride fluctuations promote decreased activity or whether less active individuals do not gain sufficient motor learning experience to achieve a skilled movement.
authors: Biomechanics Research Building, University of Nebraska at Omaha, 6160 University Drive, Omaha, NE 68182-0860, USA. Electronic address: jkent@unomaha.edu.
authors: Jenny A
authors: JA
authors: Kent
authors: Biomechanics Research Building, University of Nebraska at Omaha, 6160 University Drive, Omaha, NE 68182-0860, USA; College of Public Health, 984355 University of Nebraska Medical Center, Omaha, NE 68198-4355, USA. Electronic address: nstergiou@unomaha.edu.
authors: Nicholas
authors: N
authors: Stergiou
authors: Biomechanics Research Building, University of Nebraska at Omaha, 6160 University Drive, Omaha, NE 68182-0860, USA; Hanger Clinics dba Advanced Prosthetics Center, 9109 Blondo St, Omaha, NE 68134, USA. Electronic address: swurdeman@hanger.com.
authors: Shane R
authors: SR
authors: Wurdeman
mesh_terms: D000328:Adult; D000674:Amputees; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena / Q000502:physiology; D005080:Exercise Test; D005260:Female; D005684:Gait / Q000502:physiology*; D006621:Hip Joint / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008297:Male; D008875:Middle Aged; D013977:Tibia / Q000601:surgery; D016138:Walking / Q000502:physiology*
keywords: Amputee; Biomechanics; Human movement variability; Lyapunov exponent; Rehabilitation