Triaxial accelerometry to evaluate walking efficiency in older subjects

PURPOSE: 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.