IWASHITA, S., Y. TAKENO, K. OKAZAKI, J. ITOH, Y. KAMIJO, S. MASUKI, Y. YANAGIDAIRA, and H. NOSE. Triaxial Accelerometry to Evaluate Walking Efficiency in Older Subjects. Med. Sci. Sports Exerc., Vol. 35, No. 10, pp. 1766–1772, 2003.
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 (V̇O2, 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, V̇O2 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.
The accuracy of accelerometry to estimate energy expenditure has been evaluated during daily life by indirect calorimetry (5,7) and during walking and jogging by the oxygen consumption rate (V̇O2) (4,7,10,12,14). Although these previous results support the suitability of the method of calorimetry in the field, there have been few studies to apply this method to estimate walking efficiency.
The vertical displacement during walking as measured by triaxial accelerometry is likely associated with decreased walking efficiency. Eston et al. (7) measured three-dimensional accelerations in 9-yr-old children with a triaxial accelerometer placed on their back waist during graded walking and running on a treadmill at 4–10 km·h−1, suggesting that the ratio of vertical to total acceleration at a given walking velocity was twofold higher in children than that reported in adults elsewhere (4), because the higher energy expenditure at a given walking velocity of 4–5 km·h−1 reported in children 9 yr of age compared with adults may be partially explained by the energy waste in the vertical direction (14). Bouten et al. (4) measured three-dimensional accelerations in adults during walking at a graded velocity of 3–7 km·h−1 on a treadmill and reported that the sum of accelerations in all directions increased with walking velocity, which was highly correlated with V̇O2. They also reported that the increasing rate of acceleration with walking velocity was highest in the vertical direction, but they did not suggest the involvement in walking efficiency. Because the mechanical energy in the vertical direction does not drive the body forth, the increase in acceleration rate in the vertical direction suggests a decrease in walking efficiency.
It has been suggested that thigh-muscle strength is closely associated with maximal walking velocity in older subjects (8,16,17). Moreover, the vertical displacement of energy expenditure was reportedly improved by preventing decline in thigh-muscle strength for older subjects (13). So far, these biomechanical parameters have been investigated using video and/or force plate systems in laboratories (6,11,15), which are expensive and not readily available in the field. The purposes of the present study was to therefore assess the ability of triaxial accelerometry to accurately represent baseline walking efficiency and to detect improvements of walking efficiency after an exercise training program.