Gait adaptability and brain activity during unaccustomed treadmill walking in healthy elderly females

This study evaluated brain activity during unaccustomed treadmill walking using positron emission tomography (PET) and [¹⁸F]fluorodeoxyglucose. Twenty-four healthy elderly females (75–82 years) participated in this study. Two PET scans were performed after 25 min of rest and after walking for 25 min at 2.0 km/h on a treadmill. Participants were divided into low and high step-length variability groups according to the median coefficient of variation in step length during treadmill walking. We compared the regional changes in brain glucose metabolism between the two groups. The most prominent relative activations during treadmill walking compared to rest in both groups were found in the primary sensorimotor areas, occipital lobe, and anterior and posterior lobe of the cerebellum. The high step-length variability group showed significant relative deactivations in the frontal lobe and the inferior temporal gyrus during treadmill walking. There was a significant relative activation of the primary sensorimotor area in the low step-length variability group compared to the high step-length variability group (P = 0.022). Compared to the low step-length variability group, the high step-length variability group exhibited a greater relative deactivation in the white matter of the middle and superior temporal gyrus (P = 0.032) and hippocampus (P = 0.034) during treadmill walking compared to resting. These results suggest that activation of the primary sensorimotor area, prefrontal area, and temporal lobe, especially the hippocampus, is associated with gait adaptability during unaccustomed treadmill walking.     

Strategies of healthy adults walking on a laterally oscillating treadmill

We mounted a treadmill on top of a six degree-of-freedom motion base platform to investigate locomotor responses produced by healthy adults introduced to a dynamic walking surface. The experiment examined self-selected strategies employed by participants when exposed to continuous, sinusoidal lateral motion of the support surface while walking. Torso translation and step width were used to classify responses used to stabilize gait in this novel, dynamic environment. Two response categories emerged. Participants tended to either fix themselves in space (FIS), allowing the treadbelt to move laterally beneath them, or fix themselves to the base (FTB), moving laterally as the motion base oscillated. The degree of fixation in both extremes varied across participants. This finding suggests that normal adults have innate and varied preferences for optimizing gait stability, some depending more heavily on vision (FIS group) and others on proprioception (FTB group).     

A kinematic and kinetic comparison of overground and treadmill walking in healthy subjects

INTRODUCTION: Gait evaluation protocols using instrumented treadmills will be increasingly used in the near future. For this reason, it must be shown that using instrumented treadmills will produce measures of the ground reaction force adequate for inverse dynamic analysis, and differences between treadmill and overground gait must be well characterized. METHODS: Overground walking kinetics were estimated with the subjects walking at their self-selected comfortable walking speed. For the treadmill gait trials, the subjects walked on two treadmills, such that heel-strike occurred on the forward treadmill and toe-off occurred on the trailing treadmill. The treadmill was set to the average overground walking speed. Overground and treadmill data were evaluated using Vicon Plug-in Gait. The differences between the maxima and minima of kinematic and kinetic parameters for overground and treadmill gait were evaluated. RESULTS: The kinematics of treadmill and overground gait were very similar. Twelve of 22 kinematic parameter maxima were statistically significantly different (p<0.05), but the magnitude of the difference was generally less than 2 degrees . All GRF maxima were found to be statistically significantly smaller for treadmill versus overground gait (p<0.05) as were 15 of 18 moment, and 3 of 6 power maxima. However, the magnitude of the differences was comparable to the variability in normal gait parameters. The sagittal plane ankle moments were not statistically different for treadmill and overground gait. DISCUSSION: We have shown that treadmill gait is qualitatively and quantitatively similar to overground gait. Differences in kinematic and kinetic parameters can be detected in matched comparisons, particularly in the case of kinetic parameters. However, the magnitudes of these differences are all within the range of repeatability of measured kinematic parameters. Thus, the mechanics of treadmill and overground gait are very similar. CLINICAL SIGNIFICANCE: Having demonstrated the essential equivalence of treadmill and overground gait, it is now possible for clinical movement analysis to take advantage of treadmill-based protocols.     

Dual-task prioritization during overground and treadmill walking in healthy adults

BackgroundThe dual-task effect on walking performance is different during treadmill and overground walking, though the cause of this difference is unknown. This study examined the effects of task prioritization on overground and treadmill dual-task walking.MethodTwenty-two adults walked overground and on a treadmill under three dual-task conditions: prioritization of walking performance, prioritization of cognitive performance (serial subtraction in sevens), or no prioritization.ResultsCompared to single-task walking, stride velocity was reduced and stride time variability was increased during dual-task overground walking. During treadmill walking, there was no dual-task effect on walking performance, but cognitive task performance was improved. Prioritization of the cognitive task reduced the dual-task effect on stride velocity during overground walking only, whilst prioritization of the walking task reduced cognitive task performance in both walking modalities.SignificanceThese results corroborate recent findings that the dual-task effects on treadmill walking are not equivalent to those on overground walking. Healthy adults appear to prioritize cognitive task performance during treadmill dual-task walking without detrimental effects to gait. During overground walking however, allocation of attention to the secondary task reduces gait performance. These results indicate that treadmill based dual-task paradigms should not be used to infer factors which influence the cognitive control of overground walking.     

Postural stability after treadmill and overground walking in young and elderly

BackgroundAgeing commonly disrupts the balance control and compensatory postural responses that contribute to maintaining balance and preventing falls during perturbation of posture. Improvement of compensatory postural responses during walking is one of the main goals in fall prevention programs which often include treadmill walking training. However, during treadmill walking, there is a sensory (visualsomatosensory and vestibular-somatosensory) conflict that can evoke aftereffects of self-motion sensation and could alter postural stability after training.Research questionThe aim of this study was to compare the effect of overground and treadmill walking on postural stability in healthy young and elderly subjects. Methods: Postural responses of 31 Young and 19 healthy Elderly before and after overground and treadmill walking were assessed by a force platform in four stance conditions: firm and foam surface with eyes open and eyes closed.ResultsIn Elderly group, velocity parameters significantly increased after treadmill walking but not after overground walking. This increase was found particularly in the conditions with eyes open in both types of surfaces (firm, foam). The velocity parameters values (expect Vx) were significantly increased in Elderly compared to Young almost in all four conditions after treadmill and overground walking. Significance: Our study suggests that Elderly become more unstable after treadmill walking and have greater difficulties to adapt to new balance circumstances caused by sensory conflict associated with treadmill walking. It seems that during treadmill walking and subsequent stance, vision is the major factor contributing to posture stabilization. Thus, the suitability of treadmill walking as a part of training programs for elderly adults with higher fall risk should be seriously considered.     

Reliability of gait parameters during treadmill walking in community-dwelling healthy seniors

The present study aimed at assessing the between- and within-day-variability of temporal and spatial gait characteristics during treadmill walking in community-dwelling seniors. In 20 active, healthy seniors (10 women, 10 men, age: 64.8 (SD 3.2) years, height: 1.70 (0.10) m, weight: 69.7 (10.9) kg, physical activity: 11 (6) h week(-1)) gait characteristics were assessed on three days in weekly intervals (between-day variability). Either on days two or three, testing was repeated 30 min after the initial trial (within-day variability). We determined routine spatio-temporal gait parameters as well as gait variability during 400 steps at a normal walking speed (5.0 (0.4) km h(-1)) on a one-dimensional ground reaction force measuring treadmill. No significant mean differences occurred in any parameter for between- and within-day comparisons. Between-day ICC were high (ICC≥0.86) for most parameters except for temporal (ICC=0.44) and spatial (ICC=0.22) gait variability. Coefficients of variation (CoV) were also high in the latter parameters (CoV=30.2-36.1%), whereas all other variables showed clearly lower values (CoV<7%). CoV were still lower between days 2 and 3 (CoV<5%). Compared to between-day comparisons, within-day variability was comparable in spatio-temporal gait parameters (CoV<5%, ICC≥0.97) and lower in gait variability parameters (CoV<18%, ICC≥0.72-0.74). In conclusion, most gait parameters were highly reliable during treadmill walking. Changes of less than 10% can be detected with sufficient confidence. Gait variability parameters were less reliable and, thus, should be carefully interpreted.     

Anomalous centre of mass energy fluctuations during treadmill walking in healthy individuals

Motorised treadmills are used to research and rehabilitate gait despite conflicting evidence that treadmill ambulation is equivalent to ground walking. It has been suggested that no mechanical differences should exist between these environments but there is little evidence to support this. During ground walking, the whole body centre of mass (COM) acts like an inverted pendulum recovering energy, thereby reducing the effort of locomotion. The energy recovery has a relationship with speed whereby maximum recovery occurs at intermediate speeds. In order to determine the relationship between energy recovery and speed during treadmill walking, we investigated estimated COM displacement in nine healthy individuals each walking on a treadmill at seven different speeds. In addition, we measured oxygen cost to determine the effort of walking. Our participants formed two distinct groups, those with normal COM energy recovery (N%R) that was similar to ground walking, and those with low COM energy recovery (L%R) that was different from typical ground walking. The low energy recovery in the L%R group was attributed to in-phase potential and kinetic energy fluctuations. Despite the low energy recovery values both groups produced the expected 'U'-shaped oxygen cost speed curve with no significant difference between groups (p<0.05), however, only N%R produced a significant relationship between energy recovery and oxygen cost (p<0.05). Although a useful tool, walking on a treadmill may not be a true representation of ground walking and therefore not the most effective way to research or rehabilitate gait.     

A comparison of muscle activity and heart rate response during backward and forward walking on an underwater treadmill

This investigation compared muscle activities and heart rate (HR) responses while subjects walked backward or forward in water, with and without a water current. Ten healthy males (23.5+/-1.4 years) volunteered for the study. Surface electromyography (EMG) was used to evaluate muscle activities while the subjects walked in water, immersed to the level of the xiphoid process. HR responses were monitored continuously by a telemetry method. A "Flowmill" was used for this study, which involves a treadmill at the base of a water flume. Measurement of maximal voluntary contraction (MVC) of each tested muscle was undertaken prior to gait analysis. The %MVCs obtained from the paraspinal muscles, vastus medialis and tibialis anterior were all significantly greater when walking backward than when walking forward, for every experimental condition (P<0.05). HR responses tended to be greater while walking backward than when walking forward, with a statistical significance at fast speed (P<0.05). In conclusion, walking backward in water resulted in significantly greater muscle activation of the paraspinal muscles, vastus medialis and tibialis anterior compared with walking forward in water. These findings may be helpful in developing water-based exercise programs.     

Attentional demands of cued walking in healthy young and elderly adults

Among a wide range of negative consequences stemming from excess mass in children, recent studies suggest an impairment of postural control, including basic capabilities such as static and dynamic balance. Such impairment may be compounded when additional tasks are performed, such as carrying localized loads as occurs among children using a backpack. To investigate this, postural control was measured among 77 overweight and obese children (6-11 years old), and an equal number of normal-weight children matched for gender, age, and height. Testing was conducted at school, in which center of pressure (COP) time series during quiet standing were obtained in the presence and absence of each student's backpack. A traditional postural control measure derived from COP (mean velocity) did not indicate significant differences between overweight and normal-weight children, regardless of backpack presence. In contrast, a complexity index (derived from multiscale entropy) suggested the existence of different postural strategies and reduced balance capabilities among overweight children, whose consequences need to be further clarified.     

Comparison of neural activation and energy cost during treadmill walking with body weight unloading between frail and healthy older women

The aims of the study were to investigate whether body weight unloading (BWU) enables frail older women to walk on a treadmill without increasing energy and cardiac cost compared to normal gravity conditions and whether BWU affects lower extremity muscle activation levels. Oxygen uptake, heart rate (HR) and surface electromyography (EMG) of vastus medialis (VM) and biceps femoris (BF) of 10 frail older women (mean±SD; 78±3.6 years) and 10 healthy older women (78.5±4.2 years) were measured during various walking conditions overground and on a treadmill with BWU. Frail older women exercising at their self-selected comfortable walking speed on the treadmill at 0% BWU had a higher walking energy cost per unit of time (WECt) compared to overground walking at the same speed (255±46 vs 207±32 J kg(-1) min(-1), P<0.05), whereas healthy older women had similar responses in the two conditions (262±31 vs 260±39 J kg(-1) min(-1)). However, WECt of treadmill walking at self-selected fast walking speed with 40% BWU was not statistically different to overground walking at comfortable walking speed for frail (218±36 vs 207±31 J kg(-1) min(-1)) or healthy older women (265±65 vs 262±32 J kg(-1) min(-1)). EMG of the VM and BF muscles did not significantly change in either group during treadmill walking at any speeds up to 40% BWU (P>0.05). Frail older women could therefore be safely trained on a treadmill with 40% BWU thus achieving faster speeds without increasing energy and cardiac cost and without compromising lower extremity muscle activation levels.     

Upper body accelerations during walking in healthy young and elderly men

The purpose of the present study was to assess whether any differences existed in the upper body accelerations of young and elderly subjects during natural speed walking. Head and trunk accelerations in eight young subjects (aged 23±4 years) and eight healthy elderly subjects (aged 74±3 years) were measured during level walking on a 20 m walkway using a pair of tri-axial accelerometers. Heel contact and toe-off events were determined using a footswitch system embedded in the innersole of the right shoe. Gait measures assessed included; stride, stance and swing durations, cadence, gait velocity, step length and 3D head and trunk accelerations. All acceleration variables were normalised to walking speed before statistical analysis. The main findings of this study were: (1) the peak positive anterior–posterior (AP) trunk acceleration associated with push-off was significantly lower for elderly subjects, (2) the peak negative AP head and trunk accelerations following heel contact was significantly higher for elderly subjects, and (3) the time delay between trunk and head accelerations experienced in the AP direction was significantly lower for the elderly compared to the young group. Together, these results suggest that elderly subjects exhibit different patterns of upper body motion in the direction of travel compared to younger subjects. These differences are probably motivated by the need to maximise dynamic stability during critical parts of the gait cycle.     

Effect of walking speed during gait in water of healthy elderly

BackgroundWalking in water (WW) is frequently used as an aquatic exercise in rehabilitation programs for the elderly. Understanding gait characteristics of WW is of primary importance to effectively design specific water-based rehabilitation programs. Moreover, as walking speed in water is reduced with a possible effect on gait parameters, the age- and environment-related changes during WW have to be investigated considering the effects of instantaneous walking speed. Research question: how do gait kinematic characteristics differ in healthy elderly between WW and on land walking condition (LW)? Do elderly show different walking patterns compared to young adults? Can these kinematic changes be accounted only by the different environment/age or are they also related to walking speed?MethodsNine healthy elderly participants (73.5 ± 5.8 years) were acquired during walking in WW and LW at two different speeds. Kinematic parameters were assessed with waterproofed inertial magnetic sensors using a validated protocol. The influence of environment, age and walking speed on gait parameters was investigated with linear mixed models.ResultsShorter stride distances and longer stride durations were observed in WW compared to LW. In the sagittal plane, hip and knee joint showed larger flexion in WW (>10deg over the whole stride and ∼28deg at foot strike, respectively). Furthermore, lower walking speeds and stride distances were observed in elderly compared to young adults. In the sagittal plane, a slightly more flexed hip joint and a less plantarflexed ankle joint (∼9 deg) were observed in the elderly. Significance: The results showed the importance of assessing the walking speed during WW, as gait parameters can vary not only for the effect environment but also due to different walking speeds.     

Test-retest reliability of stability outcome measures during treadmill walking in patients with balance problems and healthy controls

BackgroundImprovement of balance control is an important rehabilitation goal for patients with motor and sensory impairments. To quantify balance control during walking, various stability outcome measures have described differences between healthy controls and patient groups with balance problems. To be useful for the evaluation of interventions or monitoring of individual patients, stability outcome measures need to be reliable.Research questionWhat is the test-retest reliability of six stability outcome measures during gait?MethodsPatients with balance problems (n = 45) and healthy controls (n = 20) performed two times a two-minute walk test (2MWT). The intraclass correlation coefficient (ICC) and Bland-Altman analysis (coefficient of repeatability; CR) were used to evaluate the test-retest reliability of six stability outcome measures: dynamic stability margin (DSM), margin of stability (MoS), distance between the extrapolated centre of mass (XCoM) and centre of pressure (CoP) in anterior-posterior (XCoM-CoP_AP) and medial-lateral (XCoM-CoP_ML) direction, and inclination angle between centre of mass (CoM) and CoP in anterior-posterior (CoM-CoP_AP-angle) and medial-lateral (CoM-CoP_ML-angle) direction. A two way mixed ANOVA was performed to reveal measurement- and group-effects.ResultsThe ICCs of all stability outcome measures ranged between 0.51 and 0.97. Significant differences between the measurements were found for the DSM (p = 0.017), XCoM-CoP_AP (p = 0.008) and CoM-CoP_AP-angle (p = 0.001). Significant differences between controls and patients were found for all stability outcome measures (p < 0.01) except for the MoS (p = 0.32). For the XCoM-CoP distances and CoM-CoP angles, the CRs were smaller than the difference between patients and controls.SignificanceBased on the ICCs, the reliability of all stability outcome measures was moderate to excellent. Since the XCoM-CoP_ML and CoM-CoP_ML-angle showed no differences between the measurements and smaller CRs than the differences between patients and controls, the XCoM-CoP_ML and CoM-CoP_ML-angle seem the most promising stability outcome measures to evaluate interventions and monitor individual patients.     

Reliability of the long-range power-law correlations obtained from the bilateral stride intervals in asymptomatic volunteers whilst treadmill walking

Stride intervals measured during steady-state walking are irregular. These stride interval fluctuations are not random but exhibit long-range power-law correlation (alpha) such that a given stride interval is 'influenced' by earlier variations in the stride intervals. To estimate alpha, one requires a minute long sequence of right or left side stride interval data. However, to obtain a reliable alpha point estimate, the minimal stride sequence length is unknown. Additionally, it is unknown if the right and left side alpha are equivalent. In this study, the within-day and the right and left side reliabilities of alpha point estimates were examined in 23 volunteers performing three 8-min treadmill walks. In addition, eight volunteers were retested on three additional days to estimate between-day reliability. The standard error of measurement (S.E.M.) and the within- and between-day intraclass correlation (ICC) values, and their 95% confidence intervals, each calculated using the combined right and left leg 8-min alpha estimates were acceptable [0.047 (0.044-0.051); 0.914 (0.882-0.932) and 0.769 (0.689-0.815), respectively]. The left alpha (0.688 +/- 0.93) was greater than the right alpha (0.664 +/- 0.094), albeit this finding was underpowered (0.55). The alpha point estimates obtained from the full 8-min walks provided minimal S.E.M. and maximal within- and between-day ICCs. However, the minimal S.E.M. was statistically indistinguishable from the 6- and 7-min walk durations and all of the within-day and between-day ICCs were similar except for the 3- and 8-min between-day ICCs. This study suggests that data from four 3 min, three 6 min or two 8 min walk duration trials provide reliable alpha point estimates from a short series of short treadmill walks.     

Biomechanical and perceived differences between overground and treadmill walking in children with cerebral palsy

The treadmill is widely used as an instrument for gait training and analysis. The primary purpose of this study was to compare biomechanical variables between overground and treadmill walking in children with cerebral palsy (CP). Perceived differences between the two walking modes were also investigated by comparing self-selected walking speeds. Twenty children with CP performed both overground and treadmill walking at a matched speed for biomechanical comparison using a 3-D motion analysis system. In addition, they were asked to select comfortable and fastest walking speeds under each walking condition to compare perceived differences. Significant differences in spatiotemporal variables were found including higher cadence and shorter stride length during treadmill walking at a matched speed (for all, P < .003). The comparison of joint kinematics demonstrated significant differences between overground and treadmill walking, which showed increases in peak angles of ankle dorsi-flexion, knee flexion/extension, and hip flexion (for all, P < .001), increases in ankle and hip excursions and a decrease in pelvic rotation excursion while walking on treadmill (for all, P < .002). Comparison of perceived difference revealed that children with CP chose significantly slower speeds when asked to select their comfortable and fastest walking speeds on the treadmill as compared to overground (for both, P < .001). Our results suggest that these biomechanical and perceived differences should be considered when using a treadmill for gait intervention or assessment.     

中老年人正常肾脏弥散加权成像对比研究

目的通过测量健康中、老年志愿者肾脏表观弥散系数(ADC)值,研究健康中老年肾脏皮、髓质ADC值差异及随年龄增长的变化。方法选择2010年5月～2012年10月中、老年健康志愿者83例,采用GE 1.5TSigna TwinSpeed磁共振扫描仪进行双肾T1WI、弥散加权成像(DWI)(b=0s/mm2,600s/mm2,1 000s/mm2)扫描,通过配套工作站软件测量肾脏皮质、髓质ADC值。采用SPSS 17.0统计软件进行分析,分别比较中、老年肾脏皮质和髓质ADC值有无统计学差异。结果 b值为600s/mm2时,中、老年组肾脏皮、髓质ADC值分别为(2.24±0.11)×10-3 mm2/s、(2.22±0.12)×10-3 mm2/s、(2.15±0.14)×10-3 mm2/s、(2.12±0.16)×10-3 mm2/s;b值为1 000s/mm2时,中、老年组肾脏皮、髓质ADC值分别为(1.98±0.16)×10-3 mm2/s、(1.89±0.10)×10-3 mm2/s、(1.85±0.19)×10-3 mm2/s、(1.87±0.16)×10-3mm2/s。除b值为1 000s/mm2时中、老年组肾脏髓质ADC值无统计学差异外,同b值下中、老年组肾脏皮质之间、髓质之间ADC值均有统计学差异(P≤0.05);同b值下各组肾脏皮、髓质之间ADC值均无统计学差异(P>0.05)。结论年龄是影响健康中、老年皮、髓质ADC值的重要因素。     

Towards the importance of minimum toe clearance in level ground walking in a healthy elderly population

Tripping is presumed to be the principal cause for falls during walking. At minimum toe clearance, the potential for trip-related falls is considered to be highest. Thus, controlling minimum toe clearance is essential for walking without tripping. In theory, the central nervous system should therefore give priority to accurate control of the variability in minimum toe clearance, as compared to other gait parameters, since people tend to only modify variability in any given task if it interferes with the task performance. The aim of this study was to determine whether elderly individuals show less increase in variability of minimum toe clearance during a dual-task condition (where an increase of gait variability is provoked), while allowing a larger range of variability in the other gait parameters. Forty elderly participants walked back and forth on a 25 m long track for five minutes. They then walked a second time performing an additional cognitive task. The variability in stride time, stride length and minimum toe clearance as well as dual-task costs of each gait parameter were calculated for each walk. The variability in minimum toe clearance did not change during dual task-walking, whereas the variability of stride length and stride time increased, showing dual-task costs of about 66% and 84%, respectively. To avoid additional detrimental load on the central nervous system, the modification of task-irrelevant variability may be tolerated during dual-task conditions, whereas minimum toe clearance is controlled with high priority.     

Towards the importance of minimum toe clearance in level ground walking in a healthy elderly population

Tripping is presumed to be the principal cause for falls during walking. At minimum toe clearance, the potential for trip-related falls is considered to be highest. Thus, controlling minimum toe clearance is essential for walking without tripping. In theory, the central nervous system should therefore give priority to accurate control of the variability in minimum toe clearance, as compared to other gait parameters, since people tend to only modify variability in any given task if it interferes with the task performance. The aim of this study was to determine whether elderly individuals show less increase in variability of minimum toe clearance during a dual-task condition (where an increase of gait variability is provoked), while allowing a larger range of variability in the other gait parameters. Forty elderly participants walked back and forth on a 25 m long track for five minutes. They then walked a second time performing an additional cognitive task. The variability in stride time, stride length and minimum toe clearance as well as dual-task costs of each gait parameter were calculated for each walk. The variability in minimum toe clearance did not change during dual task-walking, whereas the variability of stride length and stride time increased, showing dual-task costs of about 66% and 84%, respectively. To avoid additional detrimental load on the central nervous system, the modification of task-irrelevant variability may be tolerated during dual-task conditions, whereas minimum toe clearance is controlled with high priority.     

A comparison of multi-segment foot kinematics during level overground and treadmill walking

Previous work comparing treadmill and overground walking has focused on lower extremity motion and kinetics, with few identified differences. However, a comparison of multi-segment foot kinematics between these conditions has not been previously reported. Sagittal ankle motion using a single rigid body foot model and three-dimensional hindfoot and forefoot kinematics were compared during barefoot, level, overground walking at a self-selected speed and treadmill walking at a similar speed for 20 healthy adults. Slight differences were seen in ankle plantarflexion and hindfoot plantarflexion during first rocker, as well as peak forefoot eversion and abduction, however all changes were less than 3°, and most were within the day-to-day repeatability. These results indicate that foot mechanics as determined using a multi-segment foot model were similar between overground and treadmill walking at similar speeds in healthy adults. Treadmill protocols may provide a controlled method to analyze a patient's ability to adapt to walking at different speeds and surface slopes, which are encountered often during ambulation of daily living.