Walking variability, oxygen uptake and physical activity in older women

INTRODUCTION Walking is an automatic motor task and healthy form of physical activity that can be performed at light, moderate or vigorous intensity. There are significant changes in gait across the life span, especially in older adults. In particular, motion patterns deteriorate with age [1], with a decrement of variability, being reported as a potential predictor of falling risk. Gait variability was associated with many factors related to falls, such as strength and balance [2], but less is known about the influence of other physical function components like aerobic fitness and physical activity levels. Principal component analysis (PCA) allows splitting kinematic walking data into a main (regular) and a residual (irregular) pattern of whole-body motion. Walking irregularity can be then quantified by the residual variance (RV), that is, the relative amount of variance in the residual patterns [3]. Hence, the purpose of the current work was to investigate if a relationship exists between gait variability, physical activity levels and oxygen uptake during walking in older women. METHODS Six minutes of treadmill walking performed at 4.5 km/h by a group of old women (n=13, 684 y, BMI 26.42.2 kg/m2) was recorded by a motion analyzer (BTS Spa, Italy). During the trial, oxygen uptake (VO2, ml/kg/min) was measured with a portable spirometer (K4b2, Cosmed Spa, Italy) and subtracted to the standing rate (VO2 SMR). The 3D coordinates of 23 markers of each participant were assembled in a posture matrix P, after shape registration and subtraction of the mean posture, to filter out anthropometric differences between subjects and take into account only the movement patterns. P was submitted to PCA, getting the principal components (PC), each characterized by its proportion of explained variance. Kinematic walking data are highly structured, with two or three PCs typically explaining the vast majority of variance. The first three PCs explained 97.290.46% of the overall variance, and were chosen as representative of the regular pattern. RV was defined as the percentage of total variance present in the residual pattern and was used as a holistic measure of gait variability [2]. To provide an accurate estimation of physical activity level during free-living activities, the subjects worn an activity monitor (Actiheart, CamNtech, UK) for almost 7 complete and consecutive days, inferring time spent in sedentary (SED), light, moderate (MOD) or vigorous (VIG) physical activity. To assess the extent to which RV was correlated with VO2 and activity levels, Pearson’s correlations (r) were computed. RESULTS The residual variance of the assessed old women was 2.700.46%. Significant moderate correlations were found with VO2 (r=-0.507, p=0.047) and VIG (0.546, p=0.045). Non-significant correlations were computed for VO2 SMR, SED, LIGHT and MOD (p>0.05). DISCUSSION As expected, older adults showed lower variability (RV: 2.7%) than a matched group of young women (223 y; RV: 3.040.44%, unpublished data). This is consistent with previous literature reporting that older subjects exhibit a more conservative gait pattern [1]. A moderate negative correlation between VO2 and RV was obtained. This could be the evidence that the deterioration of movement patterns produces a worsening in walking economy, that could in turn be avoided or relieved increasing the amount of vigorous activities. Even though correlations were moderate, a large number of subjects may allow to focus on physical activities that can help in maintaining a healthy gait pattern and ensure functional independence throughout life.