Rapid Dual-Task Decrements After a Brief Period of Manual Tracking in Simulated Weightlessness by Water Submersion.

OBJECTIVE: Investigating dual-task (DT) performance during simulated weightlessness by water submersion, using a manual tracking and a choice reaction task. In contrast to previous work, we focus on performance changes over time. BACKGROUND: Previous research showed motor tracking and choice reaction impairments under DT and single-task (ST) conditions in shallow water submersion. Recent research analyzed performance as average across task time, neglecting potential time-related changes or fluctuations of task-performance. METHOD: An unstable tracking and a choice reaction task was performed for one minute under ST and DT conditions in 5 m water submersion and on dry land in 43 participants. Tracking and choice reaction time performance for both tasks were analyzed in blocks of 10 seconds. RESULTS: Tracking performance deteriorated underwater compared to dry land conditions during the second half while performing one minute in DT conditions. Choice reaction time increased underwater as well, but independent of task time and type. CONCLUSION: Tracking error increased over time when performing unstable tracking and choice reaction together. Potentially, physiological and psychological alterations under shallow submersion further strain the human system during DT operations, exceeding available recourse capacities such that DT performance deteriorated over time. APPLICATION: Humans operating in simulated weightlessness underwater should be aware of substantial performance declines that can occur within a short amount of time during DT situations that include continuous tracking.

Cognitive and motor task performance under single- and dual-task conditions: effects of consecutive versus concurrent practice.

The concurrent execution of two or more tasks simultaneously results in performance decrements in one or both conducted tasks. The practice of dual-task (DT) situations has been shown to decrease performance decrements. The purpose of this study was to investigate the effects of consecutive versus concurrent practice on cognitive and motor task performance under single-task (ST) and DT conditions. Forty-five young adults (21 females, 24 males) were randomly assigned to either a consecutive practice (INT consecutive) group, a concurrent practice (INT concurrent) group or a control (CON) group (i.e., no practice). Both INT groups performed 2 days of acquisition, i.e., practicing a cognitive and a motor task either consecutively or concurrently. The cognitive task required participants to perform an auditory stroop task and the number of correct responses was used as outcome measure. In the motor task, participants were asked to stand on a stabilometer and to keep the platform as close to horizontal as possible. The time in balance was calculated for further analysis. Pre- and post-practice testing included performance assessment under ST (i.e., cognitive task only, motor task only) and DT (i.e., cognitive and motor task simultaneously) test conditions. Pre-practice testing revealed no significant group differences under ST and DT test conditions neither for the cognitive nor the motor task measure. During acquisition, both INT groups improved their cognitive and motor task performance. The post-practice testing showed significantly better cognitive and motor task values under ST and DT test conditions for the two INT groups compared to the CON group. Further comparisons between the two INT groups revealed better motor but not cognitive task values in favor of the INT consecutive practice group (ST: p = 0.022; DT: p = 0.002). We conclude that consecutive and concurrent practice resulted in better cognitive (ST condition) and motor (ST and DT test conditions) task performance than no practice. In addition, consecutive practice resulted in superior motor task performance (ST and DT test conditions) compared to concurrent practice and is, therefore, recommended when executing DT practice schedules.

Will We Do If We Can? Habitual Qualitative and Quantitative Physical Activity in Multi-Morbid, Older Persons with Cognitive Impairment.

This study aimed to identify determinants of quantitative dimensions of physical activity (PA; duration, frequency, and intensity) in community-dwelling, multi-morbid, older persons with cognitive impairment (CI). In addition, qualitative and quantitative aspects of habitual PA have been described. Quantitative PA and qualitative gait characteristics while walking straight and while walking turns were documented by a validated, sensor-based activity monitor. Univariate and multiple linear regression analyses were performed to delineate associations of quantitative PA dimensions with qualitative characteristics of gait performance and further potential influencing factors (motor capacity measures, demographic, and health-related parameters). In 94 multi-morbid, older adults (82.3 ± 5.9 years) with CI (Mini-Mental State Examination score: 23.3 ± 2.4), analyses of quantitative and qualitative PA documented highly inactive behavior (89.6% inactivity) and a high incidence of gait deficits, respectively. The multiple regression models (adjusted R2 = 0.395-0.679, all p < 0.001) identified specific qualitative gait characteristics as independent determinants for all quantitative PA dimensions, whereas motor capacity was an independent determinant only for the PA dimension duration. Demographic and health-related parameters were not identified as independent determinants. High associations between innovative, qualitative, and established, quantitative PA performances may suggest gait quality as a potential target to increase quantity of PA in multi-morbid, older persons.

Effects of Drop-height and Surface Instability on Jump Performance and Knee Kinematics.

The purpose of this study was to examine the combined effects of drop-height and surface condition on drop jump (DJ) performance and knee joint kinematics. DJ performance, sagittal and frontal plane knee joint kinematics were measured in jump experienced young male and female adults during DJs on stable, unstable and highly unstable surfaces using different drop-heights (20, 40, 60 cm). Findings revealed impaired DJ performance (Δ5-16%; p<0.05; 1.43≤d≤2.82), reduced knee valgus motion (Δ33-52%; p<0.001; 2.70≤d≤3.59), and larger maximum knee flexion angles (Δ13-19%; p<0.01; 1.74≤d≤1.75) when using higher (60 cm) compared to lower drop-heights (≤40 cm). Further, lower knee flexion angles and velocity were found (Δ8-16%; p<0.01; 1.49≤d≤2.38) with increasing surface instability. When performing DJs from high (60 cm) compared to moderate drop-heights (40 cm) on highly unstable surfaces, higher knee flexion velocity and maximum knee valgus angles were found (Δ15-19%; p<0.01; 1.50≤d≤1.53). No significant main and/or interaction effects were observed for the factor sex. In conclusion, knee motion strategies were modified by the factors 'drop-height' and/or 'surface instability'. The combination of high drop-heights (>40 cm) together with highly unstable surfaces should be used cautiously during plyometrics because this may increase the risk of injury due to higher knee valgus stress.

Effects of Different Footwear Properties and Surface Instability on Neuromuscular Activity and Kinematics During Jumping.

Lesinski, M, Prieske, O, Borde, R, Beurskens, R, and Granacher, U. Effects of different footwear properties and surface instability on neuromuscular activity and kinematics during jumping. J Strength Cond Res 32(11): 3246-3257, 2018-The purpose of this study was to examine sex-specific effects of different footwear properties vs. barefoot condition during the performance of drop jumps (DJs) on stable and unstable surfaces on measures of jump performance, electromyographic (EMG) activity, and knee joint kinematics. Drop jump performance, EMG activity of lower-extremity muscles, as well as sagittal and frontal knee joint kinematics were tested in 28 healthy male (n = 14) and female (n = 14) physically active sports science students (23 ± 2 years) during the performance of DJs on stable and unstable surfaces using different footwear properties (elastic vs. minimal shoes) vs. barefoot condition. Analysis revealed a significantly lower jump height and performance index (Δ7-12%; p < 0.001; 2.22 ≤ d = 2.90) during DJs on unstable compared with stable surfaces. This was accompanied by lower thigh/shank muscle activities (Δ11-28%; p < 0.05; 0.99 ≤ d = 2.16) and knee flexion angles (Δ5-8%; p < 0.05; 1.02 ≤ d = 2.09). Furthermore, knee valgus angles during DJs were significantly lower when wearing shoes compared with barefoot condition (Δ22-32%; p < 0.01; 1.38 ≤ d = 3.31). Sex-specific analyses indicated higher knee flexion angles in females compared with males during DJs, irrespective of the examined surface and footwear conditions (Δ29%; p < 0.05; d = 0.92). Finally, hardly any significant footwear-surface interactions were detected. Our findings revealed that surface instability had an impact on DJ performance, thigh/shank muscle activity, and knee joint kinematics. In addition, the single factors "footwear" and "sex" modulated knee joint kinematics during DJs. However, hardly any significant interaction effects were found. Thus, additional footwear-related effects can be neglected when performing DJs during training on different surfaces.

Effects of Standardized Home Training in Patients with Cognitive Impairment following Geriatric Rehabilitation: A Randomized Controlled Pilot Study.

BACKGROUND: Post-ward geriatric rehabilitation programs have hardly been developed and validated, which leaves a substantial gap in rehabilitative care in older adults and hinders full exploitation of maintained, but often unrecognized rehabilitation potentials. Geriatric rehabilitation patients with cognitive impairment represent a highly vulnerable population which is often affected by a lack of an ongoing support at the intersection between ward-based and post-ward rehabilitation. OBJECTIVE: To determine the effect of a standardized home-based training program in geriatric patients with cognitive impairment following ward-based rehabilitation. METHODS: A randomized controlled, single-blinded intervention trial (RCT) with wait list control design was used. Geriatric patients (n = 34; age: 81.9 ± 5.7 years) with cognitive impairment (MMSE: 18.8 ± 4.7), identified by predefined in- and exclusion criteria, were consecutively recruited from a geriatric rehab ward. Patients in the intervention group (IG, n = 17) performed a 6-week strength and functional home training. The control group (CG, n = 17) started an identical training 6 weeks later with an initial usual care period during the intervention for the IG. Functional performance (Short Physical Performance Battery; SPPB), clinically relevant functional deficits (Performance Oriented Assessment; POMA), and physical activity (Assessment of Physical Activity For Older Persons questionnaire; APAFOP) represented primary outcome measurements complemented by additional secondary outcome parameters. RESULTS: The IG significantly increased functional performances in SPPB (total score: p = 0.012; chair rise: p = 0.007, balance: p = 0.066), reduced gait and balance deficits in POMA (total score: p = 0.006; balance: p = 0.034; gait: p = 0.019), and increased physical activity (APAFOP; p = 0.05) compared to the CG. Effect sizes showed medium to large effects for significant parameters (eta2 = 0.14-0.45). Training benefits and adherence were more pronounced following the immediate onset of post-ward training compared to a delayed start (eta2 = 0.06-0.23). CONCLUSION: Results of this pilot study show that a feasible and easy to handle, home-based rehabilitation program increased functional performance and physical activity in a vulnerable, multimorbid patient group with cognitive impairment, in particular when the post-ward training onset was not postponed.

Effects of Power Training on Mobility and Gait Biomechanics in Old Adults with Moderate Mobility Disability: Protocol and Design of the Potsdam Gait Study (POGS).

BACKGROUND: Walking speed decreases in old age. Even though old adults regularly participate in exercise interventions, we do not know how the intervention-induced changes in physical abilities produce faster walking. The Potsdam Gait Study (POGS) will examine the effects of 10 weeks of power training and detraining on leg muscle power and, for the first time, on complete gait biomechanics, including joint kinematics, kinetics, and muscle activation in old adults with moderate mobility disability. METHODS/DESIGN: POGS is a randomized controlled trial with two arms, each crossed over, without blinding. Arm 1 starts with a 10-week control period to assess the reliability of the tests and is then crossed over to complete 25-30 training sessions over 10 weeks. Arm 2 completes 25-30 exercise sessions over 10 weeks, followed by a 10-week follow-up (detraining) period. The exercise program is designed to improve lower extremity muscle power. Main outcome measures are: muscle power, gait speed, and gait biomechanics measured at baseline and after 10 weeks of training and 10 weeks of detraining. DISCUSSION: It is expected that power training will increase leg muscle power measured by the weight lifted and by dynamometry, and these increased abilities become expressed in joint powers measured during gait. Such favorably modified powers will underlie the increase in step length, leading ultimately to a faster walking speed. POGS will increase our basic understanding of the biomechanical mechanisms of how power training improves gait speed in old adults with moderate levels of mobility disabilities.

Neural Correlates of Dual-Task Walking: Effects of Cognitive versus Motor Interference in Young Adults.

Walking while concurrently performing cognitive and/or motor interference tasks is the norm rather than the exception during everyday life and there is evidence from behavioral studies that it negatively affects human locomotion. However, there is hardly any information available regarding the underlying neural correlates of single- and dual-task walking. We had 12 young adults (23.8 ± 2.8 years) walk while concurrently performing a cognitive interference (CI) or a motor interference (MI) task. Simultaneously, neural activation in frontal, central, and parietal brain areas was registered using a mobile EEG system. Results showed that the MI task but not the CI task affected walking performance in terms of significantly decreased gait velocity and stride length and significantly increased stride time and tempo-spatial variability. Average activity in alpha and beta frequencies was significantly modulated during both CI and MI walking conditions in frontal and central brain regions, indicating an increased cognitive load during dual-task walking. Our results suggest that impaired motor performance during dual-task walking is mirrored in neural activation patterns of the brain. This finding is in line with established cognitive theories arguing that dual-task situations overstrain cognitive capabilities resulting in motor performance decrements.

Association of dual-task walking performance and leg muscle quality in healthy children.

BACKGROUND: Previous literature mainly introduced cognitive functions to explain performance decrements in dual-task walking, i.e., changes in dual-task locomotion are attributed to limited cognitive information processing capacities. In this study, we enlarge existing literature and investigate whether leg muscular capacity plays an additional role in children's dual-task walking performance. METHODS: To this end, we had prepubescent children (mean age: 8.7 ± 0.5 years, age range: 7-9 years) walk in single task (ST) and while concurrently conducting an arithmetic subtraction task (DT). Additionally, leg lean tissue mass was assessed. RESULTS: Findings show that both, boys and girls, significantly decrease their gait velocity (f = 0.73), stride length (f = 0.62) and cadence (f = 0.68) and increase the variability thereof (f = 0.20-0.63) during DT compared to ST. Furthermore, stepwise regressions indicate that leg lean tissue mass is closely associated with step time and the variability thereof during DT (R(2) = 0.44, p = 0.009). These associations between gait measures and leg lean tissue mass could not be observed for ST (R(2) = 0.17, p = 0.19). CONCLUSION: We were able to show a potential link between leg muscular capacities and DT walking performance in children. We interpret these findings as evidence that higher leg muscle mass in children may mitigate the impact of a cognitive interference task on DT walking performance by inducing enhanced gait stability.

Age-related decline of peripheral visual processing: the role of eye movements.

Earlier work suggests that the area of space from which useful visual information can be extracted (useful field of view, UFoV) shrinks in old age. We investigated whether this shrinkage, documented previously with a visual search task, extends to a bimanual tracking task. Young and elderly subjects executed two concurrent tracking tasks with their right and left arms. The separation between tracking displays varied from 3 to 35 cm. Subjects were asked to fixate straight ahead (condition FIX) or were free to move their eyes (condition FREE). Eye position was registered. In FREE, young subjects tracked equally well at all display separations. Elderly subjects produced higher tracking errors, and the difference between age groups increased with display separation. Eye movements were comparable across age groups. In FIX, elderly and young subjects tracked less well at large display separations. Seniors again produced higher tracking errors in FIX, but the difference between age groups did not increase reliably with display separation. However, older subjects produced a substantial number of illicit saccades, and when the effect of those saccades was factored out, the difference between young and older subjects' tracking did increase significantly with display separation in FIX. We conclude that the age-related shrinkage of UFoV, previously documented with a visual search task, is observable with a manual tracking task as well. Older subjects seem to partly compensate their deficit by illicit saccades. Since the deficit is similar in both conditions, it may be located downstream from the convergence of retinal and oculomotor signals.

Age-related deficits of dual-task walking: a review.

This review summarizes our present knowledge about elderly people's problems with walking. We highlight the plastic changes in the brain that allow a partial compensation of these age-related deficits and discuss the associated costs and limitations. Experimental evidence for the crucial role of executive functions and working memory is presented, leading us to the hypothesis that it is difficult for seniors to coordinate two streams of visual information, one related to navigation through visually defined space, and the other to a visually demanding second task. This hypothesis predicts that interventions aimed at the efficiency of visuovisual coordination in the elderly will ameliorate their deficits in dual-task walking.

Effects of fixed versus variable task prioritization during short-term dual task practice on motor and cognitive task performance in young adults.

OBJECTIVE: It has been shown that variable compared to fixed task prioritization during dual task practice more effectively improves motor (i.e., postural control) and cognitive (i.e., memory) performance in older adults. However, it is unclear whether this finding is also valid in young adults. Thus, the present study examined the effect of fixed (allocate equal priority on both tasks) versus variable (vary priority between both tasks) priority during short-term motor-cognitive dual task practice on single and dual task performance in healthy young adults (age range: 20-30 years). RESULTS: During two days of practice, significant improvements of motor (i.e., balance task: reduced root mean square error; p < 001, ηp2 = .72) and cognitive (i.e., arithmetic task: increased serial three subtractions; p < .001, ηp2 = .78) task performance were observed and that was irrespective of group ("fixed priority" and "variable priority"). Further, the statistical analysis of post-practice single and dual task performance revealed no significant differences between groups, irrespective of task (i.e., motor or cognitive). This indicates that in young as opposed to old adults, single and dual task performance improvements are independent of task prioritization (i.e., fixed or variable priority) during short-term motor-cognitive dual task practice.

Effects of a Home-Based Physical Training and Activity Promotion Program in Community-Dwelling Older Persons with Cognitive Impairment after Discharge from Rehabilitation: A Randomized Controlled Trial.

BACKGROUND: Older people with cognitive impairment (CI) are at high risk for mobility limitations and adverse outcomes after discharge from geriatric rehabilitation settings. The aim was to estimate the effects of a specifically designed home-based physical training and activity promotion program on physical capacity, different aspects of physical activity (PA), and psychosocial status. METHODS: Patients with mild to moderate CI (Mini-Mental State Examination [MMSE]: 17-26 points) discharged home after rehabilitation were included in this randomized, double-blind, placebo-controlled trial with a 12-week intervention and 12-week follow-up period. The intervention group performed a CI-specific, autonomous, home-based strength, balance, and walking training supported by tailored motivational strategies to foster training adherence and promote PA. The control group participated in an unspecific motor placebo activity. Primary outcomes were physical capacity (Short Physical Performance Battery [SPPB]) and PA (sensor-based activity time). RESULTS: Among 118 randomized participants (82.3 ± 6.0 years) with CI (MMSE: 23.3 ± 2.4) and high levels of multimorbidity, those participants undergoing home-based training demonstrated superior outcomes to the control group in SPPB (mean difference between groups 1.9 points; 95% CI: 1.0-2.8; p < .001), with persistent benefits over the follow-up (1.3 points; 95% CI: 0.4-2.2; p < .001). There were no differences in PA across any time points. Among secondary outcomes, fear of falling and activity avoidance behavior were reduced in the intervention group at all time points, life-space mobility improved short-term. CONCLUSIONS: The results demonstrate clinically important benefits of an individually tailored autonomous physical training and activity promotion program on physical capacity and secondary outcomes in different domains in a vulnerable, multimorbid population. CLINICAL TRIAL REGISTRATION: ISRCTN82378327.

Discriminative validity of the lower and upper quarter Y balance test performance: a comparison between healthy trained and untrained youth.

BACKGROUND: The Lower (YBT-LQ) and Upper (YBT-UQ) Quarter Y Balance Test have been widely used for the assessment of dynamic balance and shoulder mobility/stability, respectively. However, investigations on the validity of the two tests in youth are lacking. Therefore, we performed two studies to determine discriminative validity of the YBT-LQ (study 1) and the YBT-UQ (study 2) in healthy youth. METHODS: Sixty-nine male soccer players (age: 14.4 ± 1.9 yrs) and 69 age-matched untrained male subjects (14.3 ± 1.6 yrs) participated in study 1 and 37 young swimmers (age: 12.3 ± 2.1 yrs) as well as 37 age-/sex-matched individuals (age: 12.5 ± 2.0 yrs) took part in study 2. Absolute (cm) and relative (% leg/arm length) maximal reach distances per reach direction and the composite score of the YBT-LQ/UQ were used as outcome measures. One-way analysis of variance and the receiver operator characteristic curve analysis (i.e., calculating the area under the curve [AUC]) were conducted to assess discriminative validity. RESULTS: Concerning the relative values, youth athletes showed significantly better YBT-LQ (study 1: p < 0.001, d = 0.86-1.21) and YBT-UQ (study 2: p < 0.001, d = 0.88-1.48) test performances compared to age- and sex-matched untrained subjects. Further, AUC-values indicated a chance of ≥74% (YBT-LQ) and ≥ 71% (YBT-UQ) to discriminate between youth athletes and controls. These findings were confirmed when using the absolute data for analysis. CONCLUSIONS: According to our results, the YBT-LQ and the YBT-UQ seem to be useful test instruments to discriminate trained and untrained healthy youth performance for dynamic balance and shoulder mobility/stability, respectively.

Effects of Motor Versus Cognitive Task Prioritization During Dual-Task Practice on Dual-Task Performance in Young Adults.

Background: Previous studies have reported positive effects of concurrent motor and cognitive task practice compared to motor or cognitive task practice only on dual-task performance in young adults. Knowledge about the effect of motor vs. cognitive task prioritization during practice on dual-task performance remains unclear and has not been investigated in depth so far. Thus, we examined the effects of motor task compared to cognitive task prioritization during dual-task practice on motor-cognitive performance in healthy young adults. Methods: Healthy young adults were randomly assigned to dual-task (DT; i.e., concurrent motor and cognitive practice) or single-task (ST; i.e., motor or cognitive task practice only) practice groups. In DT practice, subjects were instructed to either prioritize the motor or the cognitive task. The motor task required subjects to keep a stabilometer in a horizontal position. The cognitive task involved serial three subtractions. Outcome variables were the root-mean-square error (RMSE) for the motor task and the total number of correct calculations for the cognitive task. All participants practiced for 2 consecutive days under their respective treatment condition and were tested under DT condition 24 h later (i.e., retention on day 3) without providing instructions on task prioritization. Results: Irrespective of prioritization (i.e., prioritize the motor task or the cognitive task), the DT practice groups similarly improved their DT motor and cognitive task performance. The ST groups also improved motor or cognitive performance depending on their respective training contents (i.e., motor practice improved RMSE and cognitive practice improved number of correct calculations but not vice versa). Conclusion: We conclude that DT compared to ST practice is well-suited to improve DT performance, irrespective of task-prioritization. DT but not ST practice resulted in an improved modulation of both domains (i.e., motor and cognitive) during DT performance. Our findings might be explained by freeing up central resources following DT practice that can be used to effectively perform the concurrent execution of motor and cognitive processing demands. However, this process is not further enhanced by the prioritized task domain.

Lower Quarter Y Balance Test performance: Reference values for healthy youth aged 10 to 17 years.

BACKGROUND: The Lower Quarter Y Balance Test (YBT-LQ) has been widely used to register dynamic balance performance in children and adolescents. However, studies evaluating age- and sex-specific normative data to assess and classify YBT-LQ performance for these age-cohorts are missing. OBJECTIVE: Thus, we investigated YBT-LQ performance in healthy youth to provide age- and sex-specific reference values. METHODS: Six-hundred and sixty-nine individuals (286 female, 383 male) aged 10-17 years performed the YBT-LQ with their left and right leg. Normalized maximal reach distances (% leg length) for all three directions (i.e., anterior, posterolateral, posteromedial) and the composite score were calculated. Further, age- and sex-specific percentile values (i.e., 10th to 90th percentile) were computed and plotted. RESULTS: In boys, the oldest age group (16-17 years) performed better than the younger ones (14-15, 12-13, and 10-11 years). In girls, the youngest age group (10-11 years) often achieved better values compared to the 12-13-year olds. Further, 16-17-year old boys compared to the same aged girls showed better YBT-LQ performance in all but one measure (except left leg reach in posterolateral direction). For both sexes, curvilinear shaped curves were detected for percentile values across the reach directions. CONCLUSIONS: The generated age- and sex-specific reference values for the YBT-LQ can be used by practitioners to evaluate dynamic balance performance in healthy youth aged 10-17 years.

Effects of Supervised vs. Unsupervised Training Programs on Balance and Muscle Strength in Older Adults: A Systematic Review and Meta-Analysis.

BACKGROUND: Balance and resistance training can improve healthy older adults' balance and muscle strength. Delivering such exercise programs at home without supervision may facilitate participation for older adults because they do not have to leave their homes. To date, no systematic literature analysis has been conducted to determine if supervision affects the effectiveness of these programs to improve healthy older adults' balance and muscle strength/power. OBJECTIVES: The objective of this systematic review and meta-analysis was to quantify the effectiveness of supervised vs. unsupervised balance and/or resistance training programs on measures of balance and muscle strength/power in healthy older adults. In addition, the impact of supervision on training-induced adaptive processes was evaluated in the form of dose-response relationships by analyzing randomized controlled trials that compared supervised with unsupervised trials. DATA SOURCES: A computerized systematic literature search was performed in the electronic databases PubMed, Web of Science, and SportDiscus to detect articles examining the role of supervision in balance and/or resistance training in older adults. STUDY ELIGIBILITY CRITERIA: The initially identified 6041 articles were systematically screened. Studies were included if they examined balance and/or resistance training in adults aged ≥65 years with no relevant diseases and registered at least one behavioral balance (e.g., time during single leg stance) and/or muscle strength/power outcome (e.g., time for 5-Times-Chair-Rise-Test). Finally, 11 studies were eligible for inclusion in this meta-analysis. STUDY APPRAISAL: Weighted mean standardized mean differences between subjects (SMDbs) of supervised vs. unsupervised balance/resistance training studies were calculated. The included studies were coded for the following variables: number of participants, sex, age, number and type of interventions, type of balance/strength tests, and change (%) from pre- to post-intervention values. Additionally, we coded training according to the following modalities: period, frequency, volume, modalities of supervision (i.e., number of supervised/unsupervised sessions within the supervised or unsupervised training groups, respectively). Heterogeneity was computed using I 2 and χ 2 statistics. The methodological quality of the included studies was evaluated using the Physiotherapy Evidence Database scale. RESULTS: Our analyses revealed that in older adults, supervised balance/resistance training was superior compared with unsupervised balance/resistance training in improving measures of static steady-state balance (mean SMDbs = 0.28, p = 0.39), dynamic steady-state balance (mean SMDbs = 0.35, p = 0.02), proactive balance (mean SMDbs = 0.24, p = 0.05), balance test batteries (mean SMDbs = 0.53, p = 0.02), and measures of muscle strength/power (mean SMDbs = 0.51, p = 0.04). Regarding the examined dose-response relationships, our analyses showed that a number of 10-29 additional supervised sessions in the supervised training groups compared with the unsupervised training groups resulted in the largest effects for static steady-state balance (mean SMDbs = 0.35), dynamic steady-state balance (mean SMDbs = 0.37), and muscle strength/power (mean SMDbs = 1.12). Further, ≥30 additional supervised sessions in the supervised training groups were needed to produce the largest effects on proactive balance (mean SMDbs = 0.30) and balance test batteries (mean SMDbs = 0.77). Effects in favor of supervised programs were larger for studies that did not include any supervised sessions in their unsupervised programs (mean SMDbs: 0.28-1.24) compared with studies that implemented a few supervised sessions in their unsupervised programs (e.g., three supervised sessions throughout the entire intervention program; SMDbs: -0.06 to 0.41). LIMITATIONS: The present findings have to be interpreted with caution because of the low number of eligible studies and the moderate methodological quality of the included studies, which is indicated by a median Physiotherapy Evidence Database scale score of 5. Furthermore, we indirectly compared dose-response relationships across studies and not from single controlled studies. CONCLUSIONS: Our analyses suggest that supervised balance and/or resistance training improved measures of balance and muscle strength/power to a greater extent than unsupervised programs in older adults. Owing to the small number of available studies, we were unable to establish a clear dose-response relationship with regard to the impact of supervision. However, the positive effects of supervised training are particularly prominent when compared with completely unsupervised training programs. It is therefore recommended to include supervised sessions (i.e., two out of three sessions/week) in balance/resistance training programs to effectively improve balance and muscle strength/power in older adults.

Postural Control in Dual-Task Situations: Does Whole-Body Fatigue Matter?

Postural control is important to cope with demands of everyday life. It has been shown that both attentional demand (i.e., cognitive processing) and fatigue affect postural control in young adults. However, their combined effect is still unresolved. Therefore, we investigated the effects of fatigue on single- (ST) and dual-task (DT) postural control. Twenty young subjects (age: 23.7 ± 2.7) performed an all-out incremental treadmill protocol. After each completed stage, one-legged-stance performance on a force platform under ST (i.e., one-legged-stance only) and DT conditions (i.e., one-legged-stance while subtracting serial 3s) was registered. On a second test day, subjects conducted the same balance tasks for the control condition (i.e., non-fatigued). Results showed that heart rate, lactate, and ventilation increased following fatigue (all p < 0.001; d = 4.2-21). Postural sway and sway velocity increased during DT compared to ST (all p < 0.001; d = 1.9-2.0) and fatigued compared to non-fatigued condition (all p < 0.001; d = 3.3-4.2). In addition, postural control deteriorated with each completed stage during the treadmill protocol (all p < 0.01; d = 1.9-3.3). The addition of an attention-demanding interference task did not further impede one-legged-stance performance. Although both additional attentional demand and physical fatigue affected postural control in healthy young adults, there was no evidence for an overadditive effect (i.e., fatigue-related performance decrements in postural control were similar under ST and DT conditions). Thus, attentional resources were sufficient to cope with the DT situations in the fatigue condition of this experiment.

Effects of Backpack Carriage on Dual-Task Performance in Children During Standing and Walking.

Primary school children perform parts of their everyday activities while carrying school supplies and being involved in attention-demanding situations. Twenty-eight children (8-10 years old) performed a 1-legged stance and a 10 m walking test under single- and dual-task situations in unloaded (i.e., no backpack) and loaded conditions (i.e., backpack with 20% of body mass). Results showed that load carriage did not significantly influence children's standing and walking performance (all p > .05), while divided attention affected all proxies of walking (all p < .001). Last, no significant load by attention interactions was detected. The single application of attentional but not load demand negatively affects children's walking performance. A combined application of both did not further deteriorate their gait behavior.

Effects of heavy-resistance strength and balance training on unilateral and bilateral leg strength performance in old adults.

The term "bilateral deficit" (BLD) has been used to describe a reduction in performance during bilateral contractions when compared to the sum of identical unilateral contractions. In old age, maximal isometric force production (MIF) decreases and BLD increases indicating the need for training interventions to mitigate this impact in seniors. In a cross-sectional approach, we examined age-related differences in MIF and BLD in young (age: 20-30 years) and old adults (age: >65 years). In addition, a randomized-controlled trial was conducted to investigate training-specific effects of resistance vs. balance training on MIF and BLD of the leg extensors in old adults. Subjects were randomly assigned to resistance training (n = 19), balance training (n = 14), or a control group (n = 20). Bilateral heavy-resistance training for the lower extremities was performed for 13 weeks (3 × / week) at 80% of the one repetition maximum. Balance training was conducted using predominately unilateral exercises on wobble boards, soft mats, and uneven surfaces for the same duration. Pre- and post-tests included uni- and bilateral measurements of maximal isometric leg extension force. At baseline, young subjects outperformed older adults in uni- and bilateral MIF (all p < .001; d = 2.61-3.37) and in measures of BLD (p < .001; d = 2.04). We also found significant increases in uni- and bilateral MIF after resistance training (all p < .001, d = 1.8-5.7) and balance training (all p < .05, d = 1.3-3.2). In addition, BLD decreased following resistance (p < .001, d = 3.4) and balance training (p < .001, d = 2.6). It can be concluded that both training regimens resulted in increased MIF and decreased BLD of the leg extensors (HRT-group more than BAL-group), almost reaching the levels of young adults.