title: Triaxial accelerometry to evaluate walking efficiency in older subjects.
abstract: OBJECTIVE
  We tested the suitability of triaxial accelerometry to evaluate walking efficiency in older subjects.
  
  
  METHODS
  First, we verified the accuracy to estimate the oxygen consumption rate (.VO2, mL.min-1) from the total impulse (Itotal, N.min-1), the square root of summed accelerations of each direction, during graded walking on a flat ground in 13 male and 27 female older subjects (61 +/- 6 yr, mean +/- SD). Second, to examine the effects of endurance/resistance training on walking efficiency, we assessed the relations of maximal isometric knee extension force (Fmax, N.m), maximal walking velocity (Vmax, m.min-1), and three-dimensional impulses (Ix, anterior-posterior; Iy, mediolateral; Iz, vertical) in 13 male and 40 female older subjects (62 +/- 7 yr) before and after 6 and 9 months of training.
  
  
  RESULTS
  The following analyses were performed in all the data from the male and female groups. First, .VO2 was highly correlated with Itotal (r = 0.958, P < 0.0001) over the range of 250-2200 mL.min-1. Second, Fmax and Vmax increased by 48 +/- 7% (P < 0.001) and 21 +/- 2% (P < 0.001), respectively, after 9 months of training. Ix/Itotal and Iy/Itotal increased by 18 +/- 2% (P < 0.001) and 10 +/- 2%, respectively, after 9 months of training (P < 0.001), whereas Iz/Itotal decreased by 14 +/- 2% (P < 0.001). Vmax was negatively correlated with Iz/Itotal (r = -0.522, P < 0.0001) while positively correlated with Ix/Itotal (r = 0.561, P < 0.0001) and Iy/Itotal in the pooled data from before, after 6 and 9 months of training. Similarly, the product of Vmax and body weight was positively correlated with Fmax (r = 0.633, P < 0.0001).
  
  
  CONCLUSIONS
  These results suggest that increased Fmax improved walking efficiency by increasing energy utilization in the anterior-posterior/mediolateral directions while decreasing energy loss in the vertical direction.
authors.affiliation: Department of Sports Medical Sciences, Institute on Aging and Adaptation, Shinshu University Graduate School of Medicine, Matsumoto 390-8621, Japan.
authors.forename: Soh
authors.initials: S
authors.lastname: Iwashita
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Takeno
authors.forename: Kazunobu
authors.initials: K
authors.lastname: Okazaki
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Itoh
authors.forename: Yoshi-ichiro
authors.initials: Y
authors.lastname: Kamijo
authors.forename: Shizue
authors.initials: S
authors.lastname: Masuki
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Yanagidaira
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nose
mesh_terms: D000054:Acceleration; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D010101:Oxygen Consumption; D010806:Physical Education and Training; D016138:Walking