Startling acoustic stimuli (SAS) can accelerate reaction times ("StartReact" effect), but the underlying mechanism remains unclear. Both direct release of a subcortically stored motor program and a subcortically mediated trigger for a cortically stored motor program have been hypothesized. To distinguish between these hypotheses, we examined the StartReact effect in humans with pure hereditary spastic paraplegia (HSP). Delayed reaction times in HSP patients in trials both with and without a SAS would argue in favor of a cortically stored response.We instructed 12 HSP patients and 12 matched controls to respond as rapidly as possible to a visual imperative stimulus, in two different conditions: dorsiflexion of the dominant ankle; or flexion of the dominant wrist. In 25% of trials, a SAS was delivered simultaneously with the imperative stimulus. Before these tests, subjects received five SAS while standing to verify normal function of the reticulospinal tract in HSP.Latencies of startle responses in sternocleidomastoid and tibialis anterior muscles were comparable between patients and controls. During the ankle dorsiflexion task, HSP patients had an average 19 ms delay in reaction times compared with controls. Administration of a SAS accelerated ankle dorsiflexion in both groups, but more so in the patients, which completely normalized their latencies. The wrist flexion task yielded no differences in onset latencies between HSP patients and controls.The reticulospinal tract seems unaffected in HSP patients, because startle reflex onsets were normal. The corticospinal tract was affected, as reflected by delayed ankle dorsiflexion reaction times. These delayed onsets in HSP were normalized when the imperative stimulus was combined with a SAS, presumably through release of a subcortically stored motor program conveyed by the preserved reticulospinal tract.

Stroke survivors are at high risk for falls in all poststroke stages. Falls may have severe consequences, both physically and psychosocially. Individuals with stroke have an increased risk for hip fractures, and after such a fracture, they less often regain independent mobility. In addition, fear of falling is a common consequence of falls, which may lead to decreased physical activity, social deprivation and, eventually, loss of independence. Important risk factors for falls are balance and gait deficits. Stroke-related balance deficits comprise reduced postural stability during quiet standing and delayed and less coordinated responses to both self-induced and external balance perturbations. Gait deficits include reduced propulsion at push-off, decreased hip and knee flexion during the swing phase, and reduced stability during the stance phase. Interventions addressing these deficits can be expected to prevent falls more successfully. Preliminary evidence shows that task-specific exercise programs targeting balance and gait deficits can indeed reduce the number of falls in individuals with stroke. Technological advances in assistive devices are another promising area. More research is needed, however, to provide conclusive evidence of the efficacy of these interventions regarding the prevention of falls in individuals with stroke.

AimThis study aims to establish evidence-based accelerometer data reduction criteria to accurately assess total sedentary time and sedentary patterns in children.MethodsParticipants (n = 1057 European children; 9–13 yrs) were invited to wear an accelerometer for at least 6 consecutive days. We explored 1) non-wear time criteria; 2) minimum daily valid wear time; 3) differences between weekday and weekend day; and 4) minimum number of days of accelerometer wear by comparing the effects of commonly used data reduction decisions on total sedentary time, and duration and number of prolonged sedentary bouts.ResultsMore than 60 consecutive minutes of zero counts was the optimal criterion for non-wear time. Increasing the definition of a valid day from 8 to 10 hours wear time hardly influenced the sedentary outcomes, while the sample size of children with more than 4 valid days increased from 69 to 81%. On weekdays, children had on average 1 hour more wear time, 50 minutes more total sedentary time, 26 minutes more sedentary time accumulated in bouts, and 1 more sedentary bout. At least 6 days of accelerometer data were needed to accurately represent weekly sedentary time and patterns.ConclusionsBased on our results we recommend 1) a minimum of 60 minutes of consecutive zeros as the most realistic criterion for non-wear time; and 2) including at least six days with minimum eight valid hours to characterize children's usual total sedentary time and patterns, preferably including one weekend day.

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a b s t r a c t a r t i c l e i n f oObjective. This study examined the occurrence and duration of sedentary bouts and explored the crosssectional association with health indicators in children applying various operational definitions of sedentary bouts.Methods. Accelerometer data of 647 children (10-13 years old) were collected in five European countries. We analyzed sedentary time (b 100 cpm) accumulated in bouts of at least 5, 10, 20 or 30 min based on four operational definitions, allowing 0, 30 or 60 s ≥100 cpm within bouts. Health indicators included anthropometrics (i.e. waist circumference and body mass index (BMI)) and in a subsample from two European countries (n = 112) fasting capillary blood levels of glucose, C-peptide, high-density-and low-density cholesterol, and triglycerides. Data collection took place from March to July 2010. Associations were adjusted for age, gender, moderate-to-vigorous physical activity, total wear time and country.Results. Occurrence of sedentary bouts varied largely between the various definitions. Children spent most of their sedentary time in bouts of ≥5 min while bouts of ≥20 min were rare. Linear regression analysis revealed few significant associations of sedentary time accumulated in bouts of ≥5-30 min with health indicators. Moreover, we found that more associations became significant when allowing no tolerance time within sedentary bouts.Conclusion. Despite a few significant associations, we found no convincing evidence for an association between sedentary time accumulated in bouts and health indicators in 10-13 year old children. IntroductionRecent experimental studies in normal weight young (Altenburg et al., 2013;Peddie et al., 2013) and overweight adults (Dunstan et al., 2012) indicate that, compared to uninterrupted sitting, brief, light-or moderate-intensity breaks during prolonged sitting (i.e. 1 min 40 s breaks every 30 min) may attenuate cardiometabolic risk. These studies support the hypothesized mechanism that prolonged sitting leads to the loss of contractile stimulation in weight-bearing muscles, which suppresses skeletal muscle lipoprotein lipase (LPL) activity, leading to a prolonged time in which cellular metabolism substrates are present in the vascular compartments (Bey and Hamilton, 2003;Hamilton et al., 2004). These effects may contribute to the development of cardiovascular diseases. In contrast to studies in adults, brief light-intensity interruptions in sitting did not result in measurable changes in cardiometabolic indicators in 10-14 year old children (Saunders et al., 2013a).Currently, few epidemiological studies have examined accelerometerbased sedentary bouts and breaks in sedentary time in children (Colley Preventive Medicine 71 (2015)