The Combined Effects of Body Weight Support and Gait Speed on Gait Related Muscle Activity: A Comparison between Walking in the Lokomat Exoskeleton and Regular Treadmill Walking

Background

For the development of specialized training protocols for robot assisted gait training, it is important to understand how the use of exoskeletons alters locomotor task demands, and how the nature and magnitude of these changes depend on training parameters. Therefore, the present study assessed the combined effects of gait speed and body weight support (BWS) on muscle activity, and compared these between treadmill walking and walking in the Lokomat exoskeleton.

Methods

Ten healthy participants walked on a treadmill and in the Lokomat, with varying levels of BWS (0% and 50% of the participants’ body weight) and gait speed (0.8, 1.8, and 2.8 km/h), while temporal step characteristics and muscle activity from Erector Spinae, Gluteus Medius, Vastus Lateralis, Biceps Femoris, Gastrocnemius Medialis, and Tibialis Anterior muscles were recorded.

Results

The temporal structure of the stepping pattern was altered when participants walked in the Lokomat or when BWS was provided (i.e. the relative duration of the double support phase was reduced, and the single support phase prolonged), but these differences normalized as gait speed increased. Alternations in muscle activity were characterized by complex interactions between walking conditions and training parameters: Differences between treadmill walking and walking in the exoskeleton were most prominent at low gait speeds, and speed effects were attenuated when BWS was provided.

Conclusion

Walking in the Lokomat exoskeleton without movement guidance alters the temporal step regulation and the neuromuscular control of walking, although the nature and magnitude of these effects depend on complex interactions with gait speed and BWS. If normative neuromuscular control of gait is targeted during training, it is recommended that very low speeds and high levels of BWS should be avoided when possible.     

Effects of Aging on Arm Swing during Gait: The Role of Gait Speed and Dual Tasking

Healthy walking is characterized by pronounced arm swing and axial rotation. Aging effects on gait speed, stride length and stride time variability have been previously reported, however, less is known about aging effects on arm swing and axial rotation and their relationship to age-associated gait changes during usual walking and during more challenging conditions like dual tasking. Sixty healthy adults between the ages of 30–77 were included in this study designed to address this gap. Lightweight body fixed sensors were placed on each wrist and lower back. Participants walked under 3 walking conditions each of 1 minute: 1) comfortable speed, 2) walking while serially subtracting 3’s (Dual Task), 3) walking at fast speed. Aging effects on arm swing amplitude, range, symmetry, jerk and axial rotation amplitude and jerk were compared between decades of age (30–40; 41–50; 51–60; 61–77 years). As expected, older adults walked slower (p = 0.03) and with increased stride variability (p = 0.02). Arm swing amplitude decreased with age under all conditions (p = 0.04). In the oldest group, arm swing decreased during dual task and increased during the fast walking condition (p<0.0001). Similarly, arm swing asymmetry increased during the dual task in the older groups (p<0.004), but not in the younger groups (p = 0.67). Significant differences between groups and within conditions were observed in arm swing jerk (p<0.02), axial rotation amplitude (p<0.02) and axial jerk (p<0.001). Gait speed, arm swing amplitude of the dominant arm, arm swing asymmetry and axial rotation jerk were all independent predictors of age in a multivariate model. These findings suggest that the effects of gait speed and dual tasking on arm swing and axial rotation during walking are altered among healthy older adults. Follow-up work is needed to examine if these effects contribute to reduced stability in aging.     

Altering meal timing to improve cognitive performance during simulated nightshifts

ABSTRACT

Altering meal timing could improve cognition, alertness, and thus safety during the nightshift. This study investigated the differential impact of consuming a meal, snack, or not eating during the nightshift on cognitive performance (ANZCTR12615001107516). 39 healthy participants (59% male, age mean±SD: 24.5 ± 5.0y) completed a 7-day laboratory study and underwent four simulated nightshifts. Participants were randomly allocated to: Meal at Night (MN; n= 12), Snack at Night (SN; n = 13) or No Eating at Night (NE; n = 14). At 00:30 h, MN consumed a meal and SN consumed a snack (30% and 10% of 24 h energy intake respectively). NE did not eat during the nightshift. Macronutrient intake was constant across conditions. At 20:00 h, 22:30 h, 01:30 h, and 04:00 h, participants completed the 3-min Psychomotor Vigilance Task (PVT-B), 40-min driving simulator, post-drive PVT-B, subjective sleepiness scale, 2-choice Reaction Time task, and Running Memory task. Objective sleep was recorded for each of the day sleeps using Actigraphy and for the third day sleep, Polysomnography was used. Performance was compared between conditions using mixed model analyses. Significant two-way interactions were found. At 04:00 h, SN displayed increased time spent in the safe zone (p < .001; percentage of time spent within 10 km/h of the speed limit and 0.8 m of lane center), and decreases in speed variability (p < .001), lane variability (p < .001), post-drive PVT-B lapses (defined as RT > 355 ms; p < .001), and reaction time on the 2-choice reaction time task (p < .001) and running memory task (p < .001) compared to MN and NE. MN reported greater subjective sleepiness at 04:00 h (p < .001) compared to SN and NE. There was no difference in objective sleep between eating conditions. Eating a large meal during the nightshift impairs cognitive performance and sleepiness above the effects of time of night alone. For improved performance, shiftworkers should opt for a snack at night.     

Gait in Very Preterm School-Aged Children in Dual-Task Paradigms

Objective

The control of gait requires executive and attentional functions. As preterm children show executive and attentional deficits compared to full-term children, performing concurrent tasks that impose additional cognitive load may lead to poorer walking performance in preterm compared to full-term children. Knowledge regarding gait in preterm children after early childhood is scarce. We examined straight walking and if it is more affected in very preterm than in full-term children in dual-task paradigms.

Study design

Twenty preterm children with very low birth-weight (≤ 1500 g), 24 preterm children with birth-weight > 1500 g, and 44 full-term children, born between 2001 and 2006, were investigated. Gait was assessed using an electronic walkway system (GAITRite) while walking without a concurrent task (single-task) and while performing one concurrent (dual-task) or two concurrent (triple-task) tasks. Spatio-temporal gait parameters (gait velocity, cadence, stride length, single support time, double support time), normalized gait parameters (normalized velocity, normalized cadence, normalized stride length) and gait variability parameters (stride velocity variability, stride length variability) were analyzed.

Results

In dual- and triple-task conditions children showed decreased gait velocity, cadence, stride length, as well as increased single support time, double support time and gait variability compared to single-task walking. Further, results showed systematic decreases in stride velocity variability from preterm children with very low birth weight (≤ 1500 g) to preterm children with birth weight > 1500 g to full-term children. There were no significant interactions between walking conditions and prematurity status.

Conclusions

Dual and triple tasking affects gait of preterm and full-term children, confirming previous results that walking requires executive and attentional functions. Birth-weight dependent systematic changes in stride velocity variability indicate poorer walking performance in preterm children who were less mature at birth.     

Effect of napping opportunity at different times of day on vigilance and shuttle run performance

ABSTRACT

The aim of the present study was to examine the effect of a nap opportunity during the daytime realized at different times of day on physical and mental performance. Eighteen physically active males (age: 20.5 ± 3.0 years, height: 175.3 ± 5.9 cm, body-mass: 70.0 ± 8.6 kg) were tested under four experimental conditions: no-nap condition, nap at 13h00, nap at 14h00 and nap at 15h00. All nap durations were of 25-min and all tests were performed at 17h00. They performed a 5-m shuttle run test, which generated measures of the highest distance (HD) and total distance (TD). The rating of perceived exertion (RPE) was recorded after each of the six sprints in the 5-m shuttle run test. Vigilance was measured using a digit cancellation test. The results showed that TD at 17h00 was 4% greater after a nap at 14h00 than in the no-nap condition (+28 m, p < .05) or after the nap at 13h00 (+29 m, p < .05). HD was 8% higher (+9 m, p < .001) after a nap at 14h00 than in the no-nap condition and 7% higher after nap at 15h00 than in the no-nap condition (+7 m, p < .05). In addition, HD was 6% higher after nap at 14h00 (+7 m, p < .01) and 5% higher after nap at 15h00 (+9 m, p < .01) than HD after a nap at 13h00. Napping at 13h00 had no effect on physical performance at 17h00. No significant differences were observed between RPE and vigilance scores in the nap and no-nap conditions. In conclusion, napping for 25 min at 14h00 and 15h00 produces meaningful improvements in responses during repeated short-term maximal exercise tests performed at 17h00. Napping at 13h00 does not. Vigilance, as measured using a digit cancellation test, and RPE scores are not influenced by any of the nap opportunities.     

The effects of sleep deprivation and time of day on cognitive performance

The extent to which the diurnal fluctuations of different cognitive processes could be affected by sleep loss may be explored to predict performance decrements observed in the real world. Twenty healthy male subjects voluntarily took part in 8 test sessions at 06:00, 10:00, 14:00, and 18:00 h, following either a night with or without sleep in random order. Measurements included oral temperature, simple reaction time, sign cancelation, Go/NoGo, and the Purdue pegboard test. The results indicate that simple reaction time and motor coordination had morning–afternoon variations closely following the rhythms of temperature and vigilance. Inhibitory attention (Go/NoGo) presented no morning–afternoon variations. Sleep deprivation may affect the profiles of cognitive performance depending on the processes solicited. Sustained and inhibitory attention are particularly affected in the morning (after 24 and 28 waking hours), while a complex task (visuo-motor coordination) would be affected after 32 waking hours only.     

Visuospatial Tasks Affect Locomotor Control More than Nonspatial Tasks in Older People

Background

Previous research has shown that visuospatial processing requiring working memory is particularly important for balance control during standing and stepping, and that limited spatial encoding contributes to increased interference in postural control dual tasks. However, visuospatial involvement during locomotion has not been directly determined. This study examined the effects of a visuospatial cognitive task versus a nonspatial cognitive task on gait speed, smoothness and variability in older people, while controlling for task difficulty.

Methods

Thirty-six people aged ≥75 years performed three walking trials along a 20 m walkway under the following conditions: (i) an easy nonspatial task; (ii) a difficult nonspatial task; (iii) an easy visuospatial task; and (iv) a difficult visuospatial task. Gait parameters were computed from a tri-axial accelerometer attached to the sacrum. The cognitive task response times and percentage of correct answers during walking and seated trials were also computed.

Results

No significant differences in either cognitive task type error rates or response times were evident in the seated conditions, indicating equivalent task difficulty. In the walking trials, participants responded faster to the visuospatial tasks than the nonspatial tasks but at the cost of making significantly more cognitive task errors. Participants also walked slower, took shorter steps, had greater step time variability and less smooth pelvis accelerations when concurrently performing the visuospatial tasks compared with the nonspatial tasks and when performing the difficult compared with the easy cognitive tasks.

Conclusions

Compared with nonspatial cognitive tasks, visuospatial cognitive tasks led to a slower, more variable and less smooth gait pattern. These findings suggest that visuospatial processing might share common networks with locomotor control, further supporting the hypothesis that gait changes during dual task paradigms are not simply due to limited attentional resources but to competition for common networks for spatial information encoding.     

Diurnal variations of postural stability and attentional capacities in 5–6-year-old tennis players

The present study aimed to investigate the diurnal variation of postural stability, attentional capacities, and oral temperature in 5–6-year-old tennis players. A total of 24 young children were divided into two groups: Twelve tennis players with 2 years of training experience and twelve sedentary children without previous experience in any type of sport. They were asked to maintain an upright bipedal stance on a static force platform with eyes open (EO) and eyes closed (EC) at 07:00, 10:00, 14:00, and 18:00 h. Postural stability was evaluated by the center of pressure (CoP), surface area (CoP_Area), CoP mean velocity (CoP_Vm), and Romberg’s index (RI). Oral temperature and simple reaction time (SRT) were also recorded at the beginning of each test session. Postural stability in 5–6-year-old tennis players was low at 07:00 h and improved at 10:00 h (p < 0.001); then, it worsened at 14:00 h (p < 0.001) and improved again at 18:00 h (p < 0.001) as found in sedentary children. This rhythm was also close to that of SRT in both groups. Body temperature increased significantly (p < 0.001) from the morning to the afternoon in both groups. However, the peak of postural performance, the peak of attentional capacities, and the greatest vision contribution to maintain balance observed at 18:00 h were only found in the trained group. Moreover, young tennis players were more stable (p < 0.001) and more attentive (p < 0.01) than sedentary ones at 18:00 h. The amplitude of the diurnal rhythm of CoP parameters was significantly larger (p < 0.01) in trained children compared to sedentary ones (43.1 ± 8.5 vs 31.7 ± 8.3 for the CoP_Area; 27.5 ± 7.4 vs 17.7 ± 8.2 for the CoP_Vm). Therefore, time-of-day has a significant effect on static postural stability and attentional capacities in young tennis players with better performances in the late afternoon (habitual hour of training). Thus, we recommend planning some training sessions at 07:00 and/or 14:00 h to optimize postural stability at the time of its batyphase and to reduce the incidence of fall-related injury risks during this critical age in athletic environments.     

Walking kinematics and kinetics following eccentric exercise-induced muscle damage

The goal of this investigation was to investigate how walking patterns are affected following muscle-damaging exercise by quantifying both lower limb kinematics and kinetics. Fifteen young women conducted a maximal isokinetic eccentric exercise (EE) muscle damage protocol (5 × 15) of the knee extensors and flexors of both legs at 60°/s. Three-dimensional motion data and ground reaction forces (GRFs) were collected 24 h pre-EE while the participants walked at their preferred self-selected walking speed (SWS). Participants were asked to perform two gait conditions 48 h post-EE. The first condition (COND1) was to walk at their own speed and the second condition (COND2) to maintain the SWS (±5%) they had 24 h pre-EE. Walking speed during COND1 was significantly lower compared to pre-exercise values. When walking speed was controlled during COND2, significant effects of muscle damage were noticed, among other variables, for stride frequency, loading rate, lateral and vertical GRFs, as well as for specific knee kinematics and kinetics. These findings provide new insights into how walking patterns are adapted to compensate for the impaired function of the knee musculature following muscle damage. The importance to distinguish the findings caused by muscle damage from those exhibited in response to changes in stride frequency is highlighted.     

Walking speed changes in response to novel user-driven treadmill control

Implementing user-driven treadmill control in gait training programs for rehabilitation may be an effective means of enhancing motor learning and improving functional performance. This study aimed to determine the effect of a user-driven treadmill control scheme on walking speeds, anterior ground reaction forces (AGRF), and trailing limb angles (TLA) of healthy adults. Twenty-three participants completed a 10-m overground walking task to measure their overground self-selected (SS) walking speeds. Then, they walked at their SS and fastest comfortable walking speeds on an instrumented split-belt treadmill in its fixed speed and user-driven control modes. The user-driven treadmill controller combined inertial-force, gait parameter, and position based control to adjust the treadmill belt speed in real time. Walking speeds, peak AGRF, and TLA were compared among test conditions using paired t-tests (α = 0.05). Participants chose significantly faster SS and fast walking speeds in the user-driven mode than the fixed speed mode (p > 0.05). There was no significant difference between the overground SS walking speed and the SS speed from the user-driven trials (p < 0.05). Changes in AGRF and TLA were caused primarily by changes in walking speed, not the treadmill controller. Our findings show the user-driven treadmill controller allowed participants to select walking speeds faster than their chosen speeds on the fixed speed treadmill and similar to their overground speeds. Since user-driven treadmill walking increases cognitive activity and natural mobility, these results suggest user-driven treadmill control would be a beneficial addition to current gait training programs for rehabilitation.     

Diurnal variation in gait characteristics and transition speed

The aim of this study was to investigate the effect of time-of-day on Preferred Transition Speed (PTS) and spatiotemporal organization of walking and running movements. Twelve active male subjects participated in the study (age: 27.2?±?4.9 years; height: 177.9?±?5.4?cm; body mass: 75.9?±?5.86?kg). First, PTS was determined at 08:00?h and 18:00?h. The mean of the two PTS recorded at the two times-of-day tested was used as a reference (PTS_m). Then, subjects were asked to walk and run on a treadmill at three imposed speeds (PTS_m, PTS_m?+?0.3?m.s^?1, and PTS_m???0.3?m.s^?1) at 08:00?h and 18:00?h. Mean stride length, temporal stride, spatial stride variability, and temporal stride variability were used for gait analysis. The PTS observed at 08:00?h (2.10?±?0.17?m.s^?1) tends to be lower (p?=?0.077) than that recorded at 18:00?h (2.14?±?0.19?m.s^?1). Stride lengths recorded while walking (p?=?0.038) and running (p?=?0.041) were shorter at 08:00?h than 18:00?h. No time-of-day effect was observed for stride frequency during walking and running trials. When walking, spatial stride variability (p?=?0.020) and temporal stride variability (p?=?0.028) were lower at 08:00?h than at 18:00?h. When running, no diurnal variation of spatial stride variability or temporal stride variability was detected.     

Gait patterns of Japanese pedestrians

Gait patterns of adult Japanese were observed while walking on a sidewalk at Fukuoka city under natural conditions on clear days during December 1987. Pedestrians were recorded by means of video recorder for eleven 1-hr observations. From the measurements of the number of steps and the time required for each subject to traverse 50 m, walking speed was calculated for 479 women and 139 men, and step length and cadence for 292 women and 117 men. The following factors were taken into account in the data analysis: footwear, accompanist, time of day, estimated age and sex. Normal values for walking speed, step length, and cadence information on present-day adult Japanese were documented. The range for the total sample was from 49 to 119 m/min in walking speed, from 51 to 91 cm in step length, and from 95 to 160 steps/min in cadence. There were no significant differences in walking speed, step length, and cadence of the women between wearing flat shoes and heeled shoes. Walking velocity and step length were greater in single walking than in group walking. As compared with the values in the daytime (10:00-15:30) velocity, step length, and cadence tended to be higher in the morning (7:30-10:00) and lower in the evening (15:30-18:00). Older people walked at a slower speed with shorter steps than younger people. For younger pedestrians no significant sex difference was observed in walking speed. Women required a higher cadence than men because of their shorter step lengths. Older men walked faster than older women.     

Melatonin suppression during a simulated night shift in medium intensity light is increased by 10-minute breaks in dim light and decreased by 10-minute breaks in bright light

ABSTRACT

Exposure to light at night results in disruption of endogenous circadian rhythmicity and/or suppression of pineal melatonin, which can consequently lead to acute or chronic adverse health problems. In the present study, we investigated whether exposure to very dim light or very bright light for a short duration influences melatonin suppression, subjective sleepiness, and performance during exposure to constant moderately bright light. Twenty-four healthy male university students were divided into two experimental groups: Half of them (mean age: 20.0 ± 0.9 years) participated in an experiment for short-duration (10 min) light conditions of medium intensity light (430 lx, medium breaks) vs. very dim light (< 1 lx, dim breaks) and the other half (mean age: 21.3 ± 2.5 years) participated in an experiment for short-duration light conditions of medium intensity light (430 lx, medium breaks) vs. very bright light (4700 lx, bright breaks). Each simulated night shift consisting of 5 sets (each including 50-minute night work and 10-minute break) was performed from 01:00 to 06:00 h. The subjects were exposed to medium intensity light (550 lx) during the night work. Each 10-minute break was conducted every hour from 02:00 to 06:00 h. Salivary melatonin concentrations were measured, subjective sleepiness was assessed, the psychomotor vigilance task was performed at hourly intervals from 21:00 h until the end of the experiment. Compared to melatonin suppression between 04:00 and 06:00 h in the condition of medium breaks, the condition of dim breaks significantly promoted melatonin suppression and the condition of bright breaks significantly diminished melatonin suppression. However, there was no remarkable effect of either dim breaks or bright breaks on subjective sleepiness and performance of the psychomotor vigilance task. Our findings suggest that periodic exposure to light for short durations during exposure to a constant light environment affects the sensitivity of pineal melatonin to constant light depending on the difference between light intensities in the two light conditions (i.e., short light exposure vs. constant light exposure). Also, our findings indicate that exposure to light of various intensities at night could be a factor influencing the light-induced melatonin suppression in real night work settings.     

Effect of time of day on the offensive capability and aerobic performance in football game

The purpose of this study was to examine the time-of-day effects on the offensive capability and aerobic performance in football game in young subjects. In a randomized order, participants realized the Yo–Yo intermittent recovery test in two test sessions and a football game situations (two 15-min games), interspersed by a verbalization sequence (3 min) at 08:00 and 17:00 h on separate days. A recovery period of 24 h was permitted between two consecutive test sessions. The results revealed diurnal variations on the maximal aerobic velocity during the Yo–Yo test (MAV) and the oral temperature with higher values in the afternoon than morning (p < 0.05). Concerning offensive capability, the numbers of scored goals were significantly higher at 17:00 h in comparison with 08:00 h (p < 0.05). However, there was no significant difference between 08:00 and 17:00 h for the kicked balls (shooting parameter). In conclusion, our findings suggest that performance was improved in the evening and the parameters (shooting and Scored goals) can be used as a model to describe the offensive capacity in football game depending on the time of day.     

Interactions between cognitive and sensory load while planning and controlling complex gait adaptations in Parkinson’s disease

Background

Recent research has argued that removal of relevant sensory information during the planning and control of simple, self-paced walking can result in increased demand on central processing resources in Parkinson’s disease (PD). However, little is known about more complex gait tasks that require planning of gait adaptations to cross over an obstacle in PD.

Methods

In order to understand the interaction between availability of visual information relevant for self-motion and cognitive load, the current study evaluated PD participants and healthy controls while walking toward and stepping over an obstacle in three visual feedback conditions: (i) no visual restrictions; (ii) vision of the obstacle and their lower limbs while in complete darkness; (iii) vision of the obstacle only while in complete darkness; as well as two conditions including a cognitive load (with a dual task versus without a dual task). Each walk trial was divided into an early and late phase to examine changes associated with planning of step adjustments when approaching the obstacle.

Results

Interactions between visual feedback and dual task conditions during the obstacle approach were not significant. Patients with PD had greater deceleration and step time variability in the late phase of the obstacle approach phase while walking in both dark conditions compared to control participants. Additionally, participants with PD had a greater number of obstacle contacts when vision of their lower limbs was not available specifically during the dual task condition. Dual task performance was worse in PD compared to healthy control participants, but notably only while walking in the dark regardless of visual feedback.

Conclusions

These results suggest that reducing visual feedback while approaching an obstacle shifts processing to somatosensory feedback to guide movement which imposes a greater demand on planning resources. These results are key to fully understanding why trips and falls occur in those with PD.

     

Diurnal and circadian variations in indole contents in the goose pineal gland

ABSTRACT

The diurnal and circadian profiles of pineal indoles, except melatonin, are poorly characterized in birds. Moreover, there are no data on the effect of sudden changes in the light–dark cycle on these profiles. Therefore, we investigated the diurnal (Experiment I) and circadian variation (Experiment II) of nine pineal indoles (tryptophan, 5-hydroxytryptophan, serotonin, N-acetylserotonin, melatonin, 5-hydroxyindole acetic acid, 5-methoxytryptophol, 5-methoxyindole acetic acid, 5-methoxytryptamine) in geese, as well as the changes in the profiles of these substances in geese subjected to a reversed light–dark cycle (Experiment III). For the first 12 weeks of life, all geese were kept under a diurnal cycle of 12 h of light and 12 h of darkness (12L:12D). In Experiment I (n = 48), they were kept under these conditions for another 14 days before being sacrificed at 2-h intervals for sampling of the pineal glands. In Experiment II, the geese (n = 48) were divided into three groups (12L:12D, 24L:0D, 0L:24D) for 10 days before sampling at 6-h intervals. In Experiment III, 24 geese were exposed to a reversed light–dark cycle before sampling at 14:00 and 02:00 on the first, second and third days after light–dark cycle reversal. To determine the content of the indoles in the goose pineals, HPLC with fluorescence detection was used. We found that, with the exception of tryptophan, all the investigated indoles showed statistically significant diurnal variation. When geese were kept in constant darkness, most of the indoles continued to show this variation, but when geese were kept in constant light, the indoles did not show significant variation. When the light–dark cycle was reversed (12L:12D to 12D:12L), the profiles of NAS, melatonin, 5-MTAM and 5-MTOL reflected the new cycle within 2 days. The content of serotonin in geese in 12L:12D was higher than that observed in other birds under these conditions, which suggests that this compound may play a special role in the pineal physiology of this species. In conclusion, our results show that the daily variations in the metabolism of melatonin-synthesis–related indoles in the goose pineal gland are generated endogenously and controlled by environmental light conditions, as in other birds. However, comparison of the results obtained with the goose to those obtained with other species (chicken, duck) unambiguously shows that the profiles of pineal indoles differ markedly between species, in both the quantitative proportions of the compounds and the characteristics of the diurnal changes. These findings provide strong arguments for the need for comparative studies.     

Circadian variations in self-monitoring,a component of executive functions

The objective of this study was to identify circadian rhythms in self-monitoring, a component of executive functions. Participants were 10 undergraduate students, age: 18.5 ± 2.68 years, two male and eight female. They were recorded on a 30-h constant routine protocol; rectal temperature was recorded every minute and performance on a tracking task was assessed every 100 min. Self-monitoring indicators were adjustments of responses to random changes of speed and trajectory of a circle moving on the computer screen. Participants showed better accuracy during the afternoon, with decreases in the morning (06:20 and 08:00 h). These variations showed a phase delay of 2:29 ± 2:19 h with respect to the circadian rhythm of body temperature. In conclusion, there are circadian variations in self-monitoring. The decline in this component of executive functions could cause serious accidents among people working or studying during a morning shift, as well as commuting to and from work or school.     

Maintaining Gait Performance by Cortical Activation during Dual-Task Interference: A Functional Near-Infrared Spectroscopy Study

In daily life, mobility requires walking while performing a cognitive or upper-extremity motor task. Although previous studies have evaluated the effects of dual tasks on gait performance, few studies have evaluated cortical activation and its association with gait disturbance during dual tasks. In this study, we simultaneously assessed gait performance and cerebral oxygenation in the bilateral prefrontal cortices (PFC), premotor cortices (PMC), and supplemental motor areas (SMA), using functional near-infrared spectroscopy, in 17 young adults performing dual tasks. Each participant was evaluated while performing normal-pace walking (NW), walking while performing a cognitive task (WCT), and walking while performing a motor task (WMT). Our results indicated that the left PFC exhibited the strongest and most sustained activation during WCT, and that NW and WMT were associated with minor increases in oxygenation levels during their initial phases. We observed increased activation in channels in the SMA and PMC during WCT and WMT. Gait data indicated that WCT and WMT both caused reductions in walking speed, but these reductions resulted from differing alterations in gait properties. WCT was associated with significant changes in cadence, stride time, and stride length, whereas WMT was associated with reductions in stride length only. During dual-task activities, increased activation of the PMC and SMA correlated with declines in gait performance, indicating a control mechanism for maintaining gait performance during dual tasks. Thus, the regulatory effects of cortical activation on gait behavior enable a second task to be performed while walking.     

Fan-precooling effect on heat strain while wearing protective clothing

This study compared heat strain during walking while wearing impermeable protective suits between fan-precooling and nonprecooling conditions. Six males engaged in 60 min of walking at a moderate speed (～2.5 km/h) in a hot environment (37 °C, 40 % relative humidity). Fanning using a fan (4.5 m/s) and spraying water over the body before wearing the suits produced significantly lower rectal temperature before the walking (37.3?±?0.1 °C vs. 37.0?±?0.1 °C, P?P?相似文献   

The Effect of Pedal Rate and Time of Day on the Time to Exhaustion from High‐Intensity Exercise

The aim of this study was to examine the supposed influence of pedal rate on the diurnal fluctuation of the time to exhaustion from high‐intensity exercise. Eleven male cyclists performed three tests at 06:00 h and three at 18:00 h at a free pedal rate (FPR) and two imposed pedal rates (80% and 120% of the FPR). They performed the tests until exhaustion using a power output corresponding to 95% maximal power (P_max). Time to exhaustion, rectal temperature, oxygen consumption (V˙O₂), M. quadriceps, vastus medialis, M. biceps femoris electromyographic Root Mean Square activity rise (RMS slope), and blood lactate concentration were measured. The mean time to exhaustion recorded at 18:00 h (270.6±104.8 sec) was greater than at 06:00 h (233.9±84.9 sec). The time to exhaustion was significantly greater when the pedal rate was imposed at 80% versus 120% FPR. The blood lactate concentration and absolute core temperature at the point of exhaustion were significantly higher during tests done at 18:00 h. There was no diurnal variation in core temperature increase, V˙O₂, and RMS slope. The time‐of‐day effect for every variable did not depend on pedal rate. Diurnal variations in maximal aerobic endurance cannot be explained by a change in aerobic metabolism or in muscular fatigue. The origin of the diurnal variation in the time to exhaustion is likely to lie in greater participation in anaerobic metabolism. Also, the influence of temperature on neuromuscular functioning as an explanation for the diurnal variation in performance cannot be excluded in this study. The hypothesis on the basis of which pedal rate would influence diurnal variations in time to exhaustion in cycling was not validated by this research.