Neural Correlates of Balance Skill Learning in Young and Older Individuals: A Systematic Review and Meta-analysis.

BACKGROUND: Despite the increasing number of research studies examining the effects of age on the control of posture, the number of annual fall-related injuries and deaths continues to increase. A better understanding of how old age affects the neural mechanisms of postural control and how countermeasures such as balance training could improve the neural control of posture to reduce falls in older individuals is therefore necessary. The aim of this review is to determine the effects of age on the neural correlates of balance skill learning measured during static (standing) and dynamic (walking) balance tasks in healthy individuals. METHODS: We determined the effects of acute (1-3 sessions) and chronic (> 3 sessions) balance skill training on balance in the trained and in untrained, transfer balance tasks through a systematic review and quantified these effects by robust variance estimation meta-analysis in combination with meta-regression. We systematically searched PubMed, Web of Science, and Cochrane databases. Balance performance and neural plasticity outcomes were extracted and included in the systematic synthesis and meta-analysis. RESULTS: Forty-two studies (n = 622 young, n = 699 older individuals) were included in the systematic synthesis. Seventeen studies with 508 in-analysis participants were eligible for a meta-analysis. The overall analysis revealed that acute and chronic balance training had a large effect on the neural correlates of balance skill learning in the two age groups combined (g = 0.79, p < 0.01). Both age groups similarly improved balance skill performance in 1-3 training sessions and showed little further improvements with additional sessions. Improvements in balance performance mainly occurred in the trained and less so in the non-trained (i.e., transfer) balance tasks. The systematic synthesis and meta-analysis suggested little correspondence between improved balance skills and changes in spinal, cortical, and corticospinal excitability measures in the two age groups and between the time courses of changes in balance skills and neural correlates. CONCLUSIONS: Balance skill learning and the accompanying neural adaptations occur rapidly and independently of age with little to no training dose-dependence or correspondence between behavioral and neural adaptations. Of the five types of neural correlates examined, changes in only spinal excitability seemed to differ between age groups. However, age or training dose in terms of duration did not moderate the effects of balance training on the changes in any of the neural correlates. The behavioral and neural mechanisms of strong task-specificity and the time course of skill retention remain unclear and require further studies in young and older individuals. REGISTRATION: PROSPERO registration number: CRD42022349573.

Immediate effects of visuomotor tracking with the head on cervical sensorimotor function and pain in chronic neck pain patients.

BACKGROUND: Working in awkward and sustained postures is, besides psychosocial risk factors, the most reported physical risk factor for neck pain. Accurate proprioception is fundamental to correcting awkward head-to-trunk positions, but impaired proprioceptive performance has been found in patients with chronic neck pain. OBJECTIVE: The aim was to compare the effectiveness of two different interventions in a workplace set-up on sensorimotor performance and pain sensitivity in people with chronic neck pain. METHODS: A total of 25 patients with chronic neck pain participated in this double-blind study. Patients were randomly allocated to the visuomotor tracking task group or the video group (watching a massage video, imagining themselves being massaged). The primary outcomes were cervical joint position sense acuity and pressure pain threshold of the cervical spine, evaluated by a blinded assessor. RESULTS: There were significant time by group interactions for cervical joint position sense acuity (F1;23: 4.38; p= 0.048) and pressure pain threshold (F1;23: 5.78; p= 0.025), with the tracking task group being more accurate in cervical joint position sense testing and less pain sensitive for pressure pain threshold. CONCLUSIONS: The visuomotor tracking task improves cervical joint position sense acuity and reduces pressure pain threshold immediately after intervention in people with chronic neck pain.

What interventions can treat arthrogenic muscle inhibition in patients with chronic ankle instability? A systematic review with meta-analysis.

PURPOSE: To identify, critically appraise, and synthesize the existing evidence regarding the effects of therapeutic interventions on arthrogenic muscle inhibition (AMI) in patients with chronic ankle instability (CAI). MATERIALS AND METHODS: Two reviewers independently performed exhaustive database searches in Web of Science, PubMed, Medline, CINAHL, and SPORTDiscus. RESULTS: Nine studies were finally included. Five types of disinhibitory interventions were identified: focal ankle joint cooling (FAJC), manual therapy, fibular reposition taping (FRT), whole-body vibration (WBV), and transcranial direct current stimulation (tDCS). There were moderate effects of FAJC on spinal excitability in ankle muscles (g = 0.55, 95% CI = 0.03-1.08, p = 0.040 for the soleus and g = 0.54, 95% CI = 0.01-1.07, p = 0.046 for the fibularis longus). In contrast, manual therapy, FRT, WBV were not effective. Finally, 4 weeks of tDCS combined with eccentric exercise showed large effects on corticospinal excitability in 2 weeks after the intervention (g = 0.99, 95% CI = 0.14-1.85 for the fibularis longus and g = 1.02, 95% CI = 0.16-1.87 for the tibialis anterior). CONCLUSIONS: FAJC and tDCS may be effective in counteracting AMI. However, the current evidence of mainly short-term studies to support the use of disinhibitory interventions is too limited to draw definitive conclusions.

Therapeutic interventions on arthrogenic muscle inhibition (AMI) in patients with chronic ankle instability are scarce.Current studies incorporate mainly short-term therapeutic interventions.Focal ankle joint cooling seems effective to treat AMI.Several weeks of transcranial direct current stimulation may also be effective to counteract arthrogenic muscle inhibition but more studies are needed.

Probing the link between cortical inhibitory and excitatory processes and muscle fascicle dynamics.

During movements, neural signals are translated into muscle fibre shortening, lengthening or they remain isometric. This study investigated cortical excitatory and inhibitory processes in relation to muscle fascicle dynamics during fixed-end rapid contractions. Fourteen adults performed submaximal and maximal ankle dorsiflexions. Single and paired pulse transcranial magnetic stimulation over the cortical representation projecting to the tibialis anterior (TA) was applied during rest, the activation and deactivation phase of contractions to test for short- (SICI) and long-interval intracortical inhibition (LICI) and intracortical facilitation (ICF). Ultrasound images were taken to measure muscle fascicle dynamics of the superficial (TASF) and deep (TADP) TA compartments. The results show significantly greater maximal shortening velocities (p = 0.003, d = 0.26, CI [4.89, 18.52]) and greater maximal fascicle shortening (p = 0.003, d = 0.86, CI [0.29, 3.13]) in TASF than TADP during submaximal dorsiflexions. Significantly lower SICI levels during activation compared to deactivation (p = 0.019, d = 1.12, CI [19.82, 1.76]) and at rest (p < 0.0001) were observed. ICF was significantly greater during activation (p = 0.03) than during rest while LICI did not modulate significantly. Maximal TASF but not TADP shortening velocity correlated with SICI levels at activation (p = 0.06) and with the rate of torque development (p = 0.02). The results suggest that SICI might be related to muscle fascicle behavior and that intracortical inhibition and excitation are phase-dependently modulated.

How to benefit from augmented feedback? The influence of motivational and informational content of augmented feedback and the influence of task complexity.

Augmented feedback (aF) positively influences motor performance by enhancing motivation and/or by providing information about task execution. It was speculated that aF-induced performance increments that rely on motivation should also occur when providing incorrect aF, while performance increments that rely on guidance towards "successful executions" (i.e. improved performances) should only occur when aF is correct. We further hypothesised that the informational content of aF is more important in more complex motor tasks. Thus, 32 participants received two forms of aF (correct, incorrect) during maximal voluntary contractions (MVC's; maximise force without time constraints; less complex) and maximal explosive contractions (MEC's; maximise force in the shortest possible way; more complex) of the knee extensors. Peak torque (MVC), peak rate of torque development (MEC) and EMG signals of rectus femoris (RF) and vastus lateralis were recorded. Correct and incorrect aF significantly enhanced MVC performance, indicating that performance improvements resulted mainly from the motivational property of aF. The observed trend towards increased RF muscle activity supports this conclusion. In contrast, while correct aF positively impacted MEC performance, incorrect aF had a negative influence. This indicates that the informational property of aF guided participants towards movement executions resulting in improved (correct aF) or decreased (incorrect aF) performances. The observed simultaneous decrease in muscle activity suggests that participants changed motor strategy, supporting the guiding role of aF. Our results demonstrate that the motivational aspect of aF dominates in maximal tasks with lower complexity (MVC), while the informational aspect is used during more complex maximal tasks (MEC).

Augmented feedback (aF) can influence performance by enhancing the motivation and/or by providing information about the execution of a task.Our results demonstrate that over the short-term, the motivational aspect of aF dominates in maximal tasks with lower complexity (maximal voluntary contractions). In contrast, the informational aspect will predominantly be used during more complex maximal tasks (maximal explosive contractions).This is the first study distinguishing between the motivational and informational aspects of aF during maximal motor tasks. Future research should focus on the long-term effects of these two separate aspects of aF.

Knowledge of results during vertical jump testing: an effective method to increase the performance but not the consistency of vertical jumps.

This study aimed to determine whether the provision of jump height feedback (knowledge of result; KR) can increase the performance and the consistency of output variables. In a randomised order, sixteen participants performed six squat or countermovement jumps (three from a 90º knee angle and three from a self-preferred knee angle) with or without KR over four sessions. The provision of KR significantly increased peak force (p = 0.046, 1.83%), mean force (p = 0.037, 1.45%), peak velocity (p < 0.001, 3.71%), mean velocity (p = 0.004, 3.44%), peak power (p < 0.001, 4.22%) and mean power (p = 0.001, 4.69%). A high within-session reliability was observed for all variables (coefficient of variation [CV] ≤ 5.62%, intraclass correlation coefficient [ICC] ≥ 0.95). No systematic differences in reliability were detected between the jumps performed without KR (CV = 3.00 ± 1.38%, ICC = 0.97 ± 0.03) and with KR (CV = 3.04 ± 1.49%, ICC = 0.97 ± 0.04). These results suggest that the provision of jump height feedback during vertical jump testing is effective to enhance vertical jump performance but it does not reduce the variability between jumps.

The effects of normobaric and hypobaric hypoxia on cognitive performance and physiological responses: A crossover study.

This partially randomised controlled, crossover study sought to investigate the effects of normobaric hypoxia (NH) and hypobaric hypoxia (HH) on cognitive performance, the physiological response at rest and after a 3-min step-test. Twenty healthy participants (10 females and 10 males, 27.6±6.2yrs, 73.6±13.7kg, 175.3±8.9cm) completed a cognitive performance test, followed by the modified Harvard-step protocol, in four environments: normobaric normoxia (NN; PiO2: 146.0±1.5mmHg), NH (PiO2: 100.9±1.3mmHg), HH at the first day of ascent (HH1: PiO2 = 105.6±0.4mmHg) and HH after an overnight stay (HH2: PiO2 = 106.0±0.5mmHg). At rest and/or exercise, SpO2, NIRS, and cardiovascular and perceptual data were collected. The cerebral tissue oxygenation index and the cognitive performance (throughput, accuracy, and reaction time) were not different between the hypoxic conditions (all p>0.05). In NH, SpO2 was higher compared to HH1 (ΔSpO2 NH vs HH1: 1.7±0.5%, p = 0.003) whilst heart rate (ΔHR NH vs HH2: 5.8±2.6 bpm, p = 0.03) and sympathetic activation (ΔSNSi NH vs HH2: 0.8±0.4, p = 0.03) were lower in NH compared to HH2. Heart rate (ΔHR HH1 vs HH2: 6.9±2.6 bpm, p = 0.01) and sympathetic action (ΔSNSi HH1 vs HH2: 0.9±0.4, p = 0.02) were both lower in HH1 compared to HH2. In conclusion, cognitive performance and cerebral oxygenation didn't differ between the hypoxic conditions. SpO2 was only higher in NH compared to HH1. In HH2, heart rate and sympathetic activation were higher compared to both NH and HH1. These conclusions account for a PiO2 between 100-106 mmHg.

Sex differences during a cold-stress test in normobaric and hypobaric hypoxia: A randomized controlled crossover study.

Cold and hypoxia are two stressors that are frequently combined and investigated in the scientific literature. Despite the growing literature regarding normobaric hypoxia (NH) and hypobaric hypoxia (HH), responses between females and males are less often evaluated. Therefore, this study aims to investigate the physiological sex differences following a cold-stress test under normoxia, normobaric- and hypobaric hypoxia. A total of n = 10 females (24.8 ± 5.1 years) and n = 10 males (30.3 ± 6.3 years) from a university population volunteered for this study. The cold-stress test (CST) of the right hand (15°C for 2 min) was performed using a randomised crossover design in normobaric normoxia, NH and HH. The change (∆) from baseline to post-CST up to 15 min was analysed for cutaneous vascular conductance (CVC) and the hands' skin temperature, whilst the mean values across time (post-CST up to 15 min) were assessed for peripheral oxygen saturation (SpO2), thermal sensation- and comfort. Pressure pain threshold (PPT) was assessed after the post-CST 15 min period. The hands' skin temperature drop was higher (p = 0.01) in the female group (∆3.3 ± 1.5°C) compared to the male group (∆1.9 ± 0.9°C) only in NH. Females (-0.9 ± 0.5) rated this temperature drop in NH to feel significantly colder (p = 0.02) compared to the males (-0.2 ± 0.7). No differences were observed between sexes in NN, NH, and HH for ∆CVC, SpO2, thermal comfort and PPT. In conclusion, females and males show similar reactions after a CST under normoxia and hypoxia. Sex differences were observed in the local skin temperature response and thermal sensation only in NH.

The Methodological Quality of Studies Investigating the Acute Effects of Exercise During Hypoxia Over the Past 40 years: A Systematic Review.

Exercise under hypoxia and the physiological impact compared to normoxia or hypoxia has gained attention in the last decades. However, methodological quality assessment of articles in this area is lacking in the literature. Therefore, this article aimed to evaluate the methodologic quality of trials studying exercise under hypoxia. An electronic search was conducted until December 2021. The search was conducted in PubMed, CENTRAL, and PEDro using the PICO model. (P) Participants had to be healthy, (I) exercise under normobaric or hypobaric hypoxia had to be (C) compared to exercise in normoxia or hypoxia on (O) any physiological outcome. The 11-item PEDro scale was used to assess the methodological quality (internal validity) of the studies. A linear regression model was used to evaluate the evolution of trials in this area, using the total PEDro score of the rated trials. A total of n = 81 studies met the inclusion criteria and were processed in this study. With a mean score of 5.1 ± 0.9 between the years 1982 and 2021, the mean methodological quality can be described as "fair." Only one study reached the highest score of 8/10, and n = 2 studies reached the lowest observed value of 3/10. The linear regression showed an increase of the PEDro score of 0.1 points per decade. A positive and small tendency toward increased methodologic quality was observed. The current results demonstrate that a positive and small tendency can be seen for the increase in the methodological quality in the field of exercise science under hypoxia. A "good" methodological quality, reaching a PEDro score of 6 points can be expected in the year 2063, using a linear regression model analysis. To accelerate this process, future research should ensure that methodological quality criteria are already included during the planning phase of a study.

A Comparison of the Effects of Stochastic Resonance Therapy, Whole-Body Vibration, and Balance Training on Pain Perception and Sensorimotor Function in Patients With Chronic Nonspecific Neck Pain: Protocol for a Randomized Controlled Trial.

BACKGROUND: Neck pain is a prevalent pathological condition, and together with low back pain, it presents as the leading cause of years lived with disability worldwide in 2015 and continues to contribute substantially to the global burden of disease. OBJECTIVE: This study will investigate and compare the effects of stochastic resonance therapy (SRT), whole-body vibration (WBV), and balance training (BLT) in the management of chronic nonspecific neck pain. METHODS: In total, 45 participants with chronic neck pain will be randomly allocated into SRT, WBV, and BLT groups. Pain intensity, pressure pain threshold, neck disability, and cervical joint position sense will be measured before, immediately after, and 15 minutes after the first intervention session and after 4 weeks of intervention. A follow-up postintervention measurement would be taken after 4 weeks. The SRT group will train on an SRT device (SRT Zeptor Medical plus noise, Zeptoring). The WBV group will train on a Galileo vibration device (Novotec Medical), while the BLT group will perform balance exercises. All participants shall train 3 times a week for a period of 4 weeks. Mixed ANOVA will be used to determine the main and effects of interactions within (before intervention, post intervention 1, post intervention 2, post intervention 3, and follow-up) and between (SRT, WBV, and BLT) factors on the study outcome variables. RESULTS: Recruitment of participants started in May 2021, and as of May 2022, a total of 20 patients have been enrolled in the study. All participants are expected to have completed the trial by the end of 2022, and data analysis will commence thereafter. CONCLUSIONS: The outcome of this study will shed closer light on the effects of SRT, WBV, and BLT on pain and function in patients with chronic neck pain. TRIAL REGISTRATION: German Clinical Trials Register DRKS00023881; https://tinyurl.com/ycxuhj37. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/34430.

Brain Activation During Active Balancing and Its Behavioral Relevance in Younger and Older Adults: A Functional Near-Infrared Spectroscopy (fNIRS) Study.

Age-related deterioration of balance control is widely regarded as an important phenomenon influencing quality of life and longevity, such that a more comprehensive understanding of the neural mechanisms underlying this process is warranted. Specifically, previous studies have reported that older adults typically show higher neural activity during balancing as compared to younger counterparts, but the implications of this finding on balance performance remain largely unclear. Using functional near-infrared spectroscopy (fNIRS), differences in the cortical control of balance between healthy younger (n = 27) and older (n = 35) adults were explored. More specifically, the association between cortical functional activity and balance performance across and within age groups was investigated. To this end, we measured hemodynamic responses (i.e., changes in oxygenated and deoxygenated hemoglobin) while participants balanced on an unstable device. As criterion variables for brain-behavior-correlations, we also assessed postural sway while standing on a free-swinging platform and while balancing on wobble boards with different levels of difficulty. We found that older compared to younger participants had higher activity in prefrontal and lower activity in postcentral regions. Subsequent robust regression analyses revealed that lower prefrontal brain activity was related to improved balance performance across age groups, indicating that higher activity of the prefrontal cortex during balancing reflects neural inefficiency. We also present evidence supporting that age serves as a moderator in the relationship between brain activity and balance, i.e., cortical hemodynamics generally appears to be a more important predictor of balance performance in the older than in the younger. Strikingly, we found that age differences in balance performance are mediated by balancing-induced activation of the superior frontal gyrus, thus suggesting that differential activation of this region reflects a mechanism involved in the aging process of the neural control of balance. Our study suggests that differences in functional brain activity between age groups are not a mere by-product of aging, but instead of direct behavioral relevance for balance performance. Potential implications of these findings in terms of early detection of fall-prone individuals and intervention strategies targeting balance and healthy aging are discussed.

Effects of an external compared to an internal focus of attention on the excitability of fast and slow(er) motor pathways.

The neurophysiological mechanisms underlying the behavioural improvements usually associated with an external (EF) compared with an internal focus of attention (IF) remain poorly investigated. Surround inhibition in the primary cortex has been shown to be more pronounced with an EF, indicating a more spatial restriction of the motor command. However, the influence of different foci on the temporal aspect of the motor command, such as the modulation of fast versus slow(er) motor pathways, remains unknown and was therefore investigated in this study. Fourteen participants were asked to press on a pedal with the right foot to match its position with a target line displayed on a screen. The deviation of the pedal from the target line was used as a behavioural parameter and compared between both foci (EF vs IF). Additionally, conditioned H-reflexes were evoked during the motor task to assess the excitability of fast (direct) and slower (more indirect) motor pathways when adopting an EF or IF. With an EF compared to an IF, the motor performance was enhanced (P = .001; + 24%) and the activation of slow(er) motor pathways was reduced (P < 0.001, - 11.73%). These findings demonstrate for the first time that using different attentional strategies (EF and IF) has an influence on the excitability of slow(er) motor pathways. Together with the increased intracortical inhibition and surround inhibition known from previous studies, the diminished activation in the slow(er) motor pathways further explains why using an EF is a more economic strategy.

Intramuscular Temperature Changes in the Quadriceps Femoris Muscle After Post-Exercise Cold-Water Immersion (10°C for 10 min): A Systematic Review With Meta-Analysis.

Post-exercise cold-water immersion (CWI) is a widely accepted recovery strategy for maintaining physical performance output. However, existing review articles about the effects of CWI commonly pool data from very heterogenous study designs and thus, do rarely differentiate between different muscles, different CWI-protocols (duration, temperature, etc.), different forms of activating the muscles before CWI, and different thickness of the subcutaneous adipose tissue. This systematic review therefore aimed to investigate the effects of one particular post-exercise CWI protocol (10°C for 10 min) on intramuscular temperature changes in the quadriceps femoris muscle while accounting for skinfold thickness. An electronic search was conducted on PubMed, LIVIVO, Cochrane Library, and PEDro databases. Pooled data on intramuscular temperature changes were plotted with respect to intramuscular depth to visualize the influence of skinfold thickness. Spearman's rho (rs) was used to assess a possible linear association between skinfold thickness and intramuscular temperature changes. A meta-analysis was performed to investigate the effect of CWI on pre-post intramuscular temperature for each measurement depth. A total of six articles met the inclusion criteria. Maximum intramuscular temperature reduction was 6.40°C with skinfold thickness of 6.50 mm at a depth of 1 cm, 4.50°C with skinfold thickness of 11.00 mm at a depth of 2 cm, and only 1.61°C with skinfold thickness of 10.79 mm at a depth of 3 cm. However, no significant correlations between skinfold thickness and intramuscular temperature reductions were observed at a depth of 1 cm (r s = 0.0), at 2 cm (r s = -0.8) and at 3 cm (r s = -0.5; all p > 0.05). The CWI protocol resulted in significant temperature reductions in the muscle tissue layers at 1 cm (d = -1.92 [95% CI: -3.01 to -0.83] and 2 cm (d = -1.63 [95% CI: -2.20 to -1.06]) but not at 3 cm (p < 0.05). Skinfold thickness and thus, subcutaneous adipose tissue, seems to influence temperature reductions in the muscle tissue only to a small degree. These findings might be useful for practitioners as they demonstrate different intramuscular temperature reductions after a specific post-exercise CWI protocol (10°C for 10 min) in the quadriceps femoris muscle.

How far from the gold standard? Comparing the accuracy of a Local Position Measurement (LPM) system and a 15 Hz GPS to a laser for measuring acceleration and running speed during team sports.

PURPOSE: This study compared the validity and inter- and intra-unit reliability of local (LPM) and global (GPS) position measurement systems for measuring acceleration during team sports. METHODS: Devices were attached to a remote-controlled car and validated against a laser. Mean percentage biases (MPBs) of maximal acceleration (amax) and maximal running speed (vmax) were used to measure validity. Mean between-device and mean within-device standard deviations of the percentage biases (bd-SDs and wd-SDs) of amax and vmax were used to measure inter- and intra-unit reliability, respectively. RESULTS: Both systems tended to underestimate amax similarly (GPS: -61.8 to 3.5%; LPM: -53.9 to 9.6%). The MPBs of amax were lower in trials with unidirectional linear movements (GPS: -18.8 to 3.5%; LPM: -11.2 to 9.6%) than in trials with changes of direction (CODs; GPS: -61.8 to -21.1%; LPM: -53.9 to -35.3%). The MPBs of vmax (GPS: -3.3 to -1.0%; LPM: -12.4 to 1.5%) were lower than those of amax. The bd-SDs and the wd-SDs of amax were similar for both systems (bd-SDs: GPS: 2.8 to 12.0%; LPM 3.7 to 15.3%; wd-SDs: GPS: 3.7 to 28.4%; LPM: 5.3 to 27.2%), whereas GPS showed better bd-SDs of vmax than LPM. CONCLUSION: The accuracy depended strongly on the type of action measured, with CODs displaying particularly poor validity, indicating a challenge for quantifying training loads in team sports.

What to train first: Balance or explosive strength? Impact on performance and intracortical inhibition.

Explosive strength and balance training are commonly applied to enhance explosive strength and balance performance. Even though both training methods are frequently implemented, ordering effects have largely been neglected. Therefore, the present study aimed to investigate ordering effects of balance and explosive strength training on explosive strength and balance performance as well as changes in short-interval intracortical inhibition (SICI). Two groups of subjects either participated in 4 weeks of balance training followed by 4 weeks of explosive strength training (BT-ET) or vice versa (ET-BT). Before, after 4 and 8 weeks, balance performance, as well as explosive strength, was tested. Additionally, SICI was tested during rest as well as during balance perturbations and explosive contractions. The results show a training specific increase in performance with an increase in balance control followed by an increase in explosive strength in the BT-ET, while the ET-BT increased its balance and explosive strength in the opposite order. There were no significant ordering effects. Both groups showed a significant decrease in SICI during the explosive contractions after the eight weeks of training. When SICI was tested during the balance perturbations, SICI initially increased after the first 4 weeks of training but returned to baseline until the end of the eight weeks. It is suggested that the decrease in SICI with prolonged training might show a disengagement of the motor cortex during the balance task. During the explosive contractions, the low SICI levels are beneficial to provide the necessary level of excitatory cortical drive.

Testing-Specific Skating Performance in Ice Hockey.

ABSTRACT: Hajek, F, Keller, M, Taube, W, von Duvillard, SP, Bell, JW, and Wagner, H. Testing-specific skating performance in ice hockey. J Strength Cond Res 35(12S): S70-S75, 2020-Skating performance generally determines overall performance in ice hockey but has not been measured adequately in the past. Consequently, the aim of the study was to develop and validate a specific overall skating performance test for ice hockey (SOSPT) that includes similar movements and intensities as in competition. Ten male elite under-14-year and under-18-year old ice hockey players performed the SOSPT (2 heats only) and a 40-m on-ice sprinting test twice within 8 days. Additionally, 14 under-15, 18 under-17, and 20 under-20 male elite ice hockey players performed only the SOSPT (4 heats). Time was measured from the first subject's movement during a V-start until crossing the line (40-m on-ice sprinting test), first touch of the shoulder on the mat (heat #1 in the SOSPT) or first touch of the puck with the stick (heat #2 in the SOSPT) using a hand stopwatch. We found a high test-retest reliability of the SOSPT and 40-m on-ice sprinting test (interclass correlation coefficient, >0.7; coefficient of variation, <5%) with highly significant differences (p < 0.001) between the under-15, under-17, and under-20 players, a high correlation (r > 0.70) between an expert rating and the SOSPT, and a low correlation between the 40-m on-ice sprinting test and the SOSPT in the under-14 and under-18 players. The results of the study reveal that the SOSPT is a reliable and valid test to determine the specific overall skating performance in ice hockey players and is more suitable compared with straight skating tests of the 40-m on-ice sprinting test.

How to Serve Faster in Tennis: The Influence of an Altered Focus of Attention and Augmented Feedback on Service Speed in Elite Players.

ABSTRACT: Keller, M, Kuhn, YA, Lüthy, F, and Taube, W. How to serve faster in tennis: the influence of an altered focus of attention and augmented feedback on service speed in elite players. J Strength Cond Res 35(4): 1119-1126, 2021-Different approaches, such as providing augmented feedback (AF) or adopting an external focus of attention (EF), have been shown to directly enhance performance in recreational athletes. Furthermore, research has shown that combining AF with EF (AF + EF) results in superior performance compared to AF and EF alone. Here, we tested the influence of AF, EF, AF + EF, and an internal focus of attention (IF) on service speed in elite tennis players. High-level national tennis players (19.2 ± 3.7 years) were asked to serve flat serves to a target zone with maximum speed. With respect to service speed, a significant main effect of condition was found (p ≤ 0.001). Post hoc comparisons revealed faster serves for AF compared to control serves without instruction/feedback (p < 0.01) and compared to EF (p < 0.05), whereas no significant difference was found between EF and IF (p = 0.81). The fastest service speeds were found in the AF condition, whereas the combination of AF + EF did not further promote performance. The number of serves landed in the target zone did not differ between conditions (p = 0.17). Thus, no speed-accuracy trade-off was found, indicating that enhanced service speeds did not result in less serves landed in the target zone. Augmented feedback seems most beneficial to instantly enhance tennis serve performance. In contrast to previous studies with recreational sportsmen, EF did not differ from IF, providing further evidence that expertise level and task-relevant instructions mediate the influence of attentional focus on motor performance.

Functional relevance of resistance training-induced neuroplasticity in health and disease.

Repetitive, monotonic, and effortful voluntary muscle contractions performed for just a few weeks, i.e., resistance training, can substantially increase maximal voluntary force in the practiced task and can also increase gross motor performance. The increase in motor performance is often accompanied by neuroplastic adaptations in the central nervous system. While historical data assigned functional relevance to such adaptations induced by resistance training, this claim has not yet been systematically and critically examined in the context of motor performance across the lifespan in health and disease. A review of muscle activation, brain and peripheral nerve stimulation, and imaging data revealed that increases in motor performance and neuroplasticity tend to be uncoupled, making a mechanistic link between neuroplasticity and motor performance inconclusive. We recommend new approaches, including causal mediation analytical and hypothesis-driven models to substantiate the functional relevance of resistance training-induced neuroplasticity in the improvements of gross motor function across the lifespan in health and disease.

Sedentary Behavior in Children by Wearable Cameras: Development of an Annotation Protocol.

INTRODUCTION: There is increasing evidence that not all types of sedentary behavior have the same harmful effects on children's health. Hence, there has been a growing interest in the use of wearable cameras. The aim of this study is to develop a protocol to categorize children's wearable camera data into sedentary behavior components. METHODS: Wearable camera data were collected in 3 different samples of children in 2014. A development sample (3 children aged 4-8 years) was used to design the annotation protocol. A training sample (4 children aged 10 years) was used to train 3 different coders. The independent reliability sample (14 children aged 9-11 years) was used for independent coding of wearable camera images and to estimate inter-rater agreement. Data were analyzed in 2018. Cohen's κ was calculated for every rater pair on a per-participant basis. Means and SDs were then calculated across per-participant κ scores. RESULTS: A total of 41,651 images from 14 participants were considered for analysis. Inter-rater agreement over all raters over all the sedentary behavior components was almost perfect (mean κ=0.85, 95% CI=0.83, 0.87). Inter-rater reliability for screen-based sedentary behavior (mean κ=0.72, 95% CI=0.62, 0.82) and nonscreen sedentary behavior (κ=0.69, 95% CI=0.65, 0.72) showed substantial agreement. Inter-rater reliability for location (κ=0.91, 95% CI=0.88, 0.93) showed almost perfect agreement. CONCLUSIONS: A reliable annotation protocol to categorize wearable camera data of children into sedentary behavior components was developed. Once applied to larger samples in children, this protocol can ultimately help to better understand the potential harms of screen time and sedentary behavior in children.

Countermovement Jump Training Is More Effective Than Drop Jump Training in Enhancing Jump Height in Non-professional Female Volleyball Players.

The aim of the present study was to compare the effects of countermovement jump (CMJ) and drop jump (DJ) training on the volleyball-specific jumping ability of non-professional female volleyball players. For that purpose, 26 female volleyball players (15-32 years) were assigned to either a CMJ (20.4 ± 3.1 years, 171.0 ± 3.0 cm) or a DJ training group (22.0 ± 4.4 years, 168.2 ± 5.0 cm), which performed a six-week jump training (two sessions per week, 60 jumps per session). Each group performed 20% of the jumps in the jump type of the other group in order to minimize the influence of enhanced motor coordination on the differences between groups regarding the improvements of jump performance. Before and after the training, jump height was assessed in four jump types, including the trained and volleyball-specific jump types. Although both training forms substantially improved jump height, the CMJ training was significantly more effective in all jump types (17 vs. 7% on average; p < 0.001). This suggests that, at least for non-professional female volleyball players and a training duration of six weeks, training with a high percentage of CMJs is more effective than one with a high percentage of DJs. We hypothesize that this might be related to the slower stretch-shortening cycle during CMJs, which seems to be more specific for these players and tasks. These findings should support volleyball coaches in designing optimal jump trainings.