Empirical Evidence for the Functionality Hypothesis in Motor Learning: The Effect of an Attentional Focus Is Task Dependent

A large body of research suggests that during learning motor skills, focusing on environmental effects of the movement (external focus) generally leads to better performance than focusing on one’s own body (internal focus). The functionality hypothesis states, in contrast, that the superiority of any attentional focus is task dependent. The present study aimed to test the predictions of the latter and searched for underlying mechanisms and task characteristics for one or the other focus being more functional. In Experiment 1, we examined whether the internal focus is superior in a difficult body-oriented balance task. In Experiment 2, we added visual feedback and investigated whether this would enhance the functionality of the external focus. In both experiments, the participants stood one-legged on a balance board and had to shift their centre of pressure (COP) to predefined target points. Per instruction, they were asked to interpret their attentional focus on the COP as either internal (the sole of the foot) or external (the platform). In Experiment 1, the external focus was induced through a mental image. The internal focus group performed significantly better, thereby supporting the functionality hypothesis. In Experiment 2, the COP was dynamically visualized on a screen. The internal focus superiority vanished. We suggest that the internal focus is more functional in motor-learning situations that provide more effect information through body-internal senses than through body-external senses. In these cases, the external focus hampers learning because it is associated with additional cognitive load.

Does instructing attentional focus direction affect static single leg balance performance?

Balance and postural control exercises are generally included as a part of exercise programs, during which movement practitioners can provide instructions to facilitate the performance of motor skills. Instructions can be used as cues to direct attentional focus, which has been found to affect the performance of motor skills, including balance and postural control tasks. However, no known studies to date have investigated the effect of both internal and external attentional focus instructions on static single leg balance performance, and it seems unclear whether effects of such instructions are related specifically to the direction of attention. The purpose of this study was to investigate the effect of instructing the direction of attentional focus on single leg static balance performance as reflected by the complexity of the center of pressure (COP) profile. Participants (N = 46) between the ages of 19–28 years old were randomly assigned to one of three group conditions: internal focus (INTn=15), external focus (EXTn=16) and control (CONn=15). Participants performed a thirty-five second static single leg balance task. Outcome measures were the scaling exponent determined from a detrended fluctuation analysis (DFA) to infer complexity of the COP profile in the anterior-posterior (AP) and medial-lateral (ML) directions, and root mean square error (RMSE) of the COP profile in AP and ML directions. A one-way analysis of variance (ANOVA) determined there were no statistically significant differences in the measured variables among groups. The results do not support the claim that manipulating the direction of attentional focus affects static single leg balance performance.

Validity and Application of a Portable Force Platform in Assessment of Dynamic Balance Ability

Background: Dynamic balance assessment, which requires a specialized device, is crucial in clinic to evaluate postural control comprehensively. The Nintendo Wii Balance Board (WBB), a portable force platform may be a suitable alternative to the expensive “gold standard”- the laboratory-grade force platform (FP). However, its validity in assessment of dynamic balance is still unclear. The purpose of this study is to demonstrate the validity of the WBB in dynamic balance assessment.Methods: We performed three static and dynamic balance tests, including open eyes single-leg stand, close eyes single-leg stand and Limitation of Stability, on the WBB for 34 healthy participants. Trajectories of center of pressure (COP) were recorded synchronously and used to compute seven characteristics. To quantify the consistency of the two devices, we used intraclass correlation coefficient (ICC) as well as visual evaluation of Bland–Altman plots.Results: The data showed a high consistency between the two devices (ICC = 0.92-0.98) under static and dynamic balance assessments, and the visual evaluation result from Bland–Altman plot was acceptable between device agreement. Moreover, in the dynamic balance task (Limitation of Stability test), the typical ranges of COP-based postural sway distances for healthy adults in medial-lateral and anterior-posterior measured by the WBB were 27.17 ± 3.88 cm and 21.13 ± 2.33 cm, respectively, indicating the validity of the WBB in assessing COP under both static or dynamic balance tasks. Conclusion: With the advantages of portability and low-cost, the valid WBB can facilitate the popularization of quantitative balance evaluation to basic hospitals. Our results provide valuable reference for clinical evaluation of balance ability.

The Immediate Effects of Intermittent Theta Burst Stimulation of the Cerebellar Vermis on Cerebral Cortical Excitability During a Balance Task in Healthy Individuals: A Pilot Study

Objective: This pilot study aimed to investigate the immediate effects of single-session intermittent theta-burst stimulation (iTBS) on the cerebellar vermis during a balance task, which could unveil the changes of cerebral cortical excitability in healthy individuals.Subjects: A total of seven right-handed healthy subjects (26.86 ± 5.30 years) were included in this study.Interventions: Each subject received single-session iTBS on cerebellar vermis in a sitting position.Main Measures: Before and after the intervention, all subjects were asked to repeat the balance task of standing on the left leg three times. Each task consisted of 15 s of standing and 20 s of resting. Real-time changes in cerebral cortex oxygen concentrations were monitored with functional near-infrared spectroscopy (fNIRS). During the task, changes in blood oxygen concentration were recorded and converted into the mean HbO2 for statistical analysis.Results: After stimulation, the mean HbO2 in the left SMA (P = 0.029) and right SMA (P = 0.043) significantly increased compared with baseline. However, no significant changes of mean HbO2 were found in the bilateral dorsolateral prefrontal lobe (P > 0.05).Conclusion: Single-session iTBS on the cerebellar vermis in healthy adults can increase the excitability of the cerebral cortex in the bilateral supplementary motor areas during balance tasks.Clinical Trial Registration: [www.ClinicalTrials.gov], identifier [ChiCTR2100048915].

The effects of leg preference and leg dominance on static and dynamic balance performance in highly-trained tennis players

In this study, 90 (51 males, 39 females) tennis players performed single-leg quiet stance and single-leg landing tasks. For the static standing task, center-of pressure (CoP) velocities, amplitudes, frequency and area were calculated. For the landing tasks, time to stabilization as well as dynamic postural stability index were considered. The analysis of differences between the legs was done based on two methods for a priori determination of leg preference, one based on the preference of kicking a ball and one based on the preference for single-leg jumping. An additional analysis was done based on the leg dominance (determined post hoc), based on the observed performance of the tasks. In case of the classification based on kicking a ball, there was a statistically significantly lower CoP anterior-posterior velocity and anterior-posterior amplitude in static balance task (p ≤ 0.017; 0.17 ≤ d ≤ 0.28) for the preferred leg. The CoP frequency was higher in the preferred leg for both directions (p ≤ 0.002; 0.10 ≤ d ≤ 0.22). For the landing task, CoP medial-lateral time to stabilization was statistically significantly shorter for the preferred leg (0.28 ± 0.38 s) compared to the non-preferred leg (0.47 ± 0.60 s) (p = 0.012; d = 0.38). There were no differences between the legs for the landing task. Moreover, there were no differences between the legs when we used the preference based on jumping for either of the tasks (d ≤ 0.14). The differences between legs in terms of observed dominance were larger than the differences based on the preference, which stresses the need for clear distinction of limb preference and limb dominance in research and practice. Regarding the effect of leg preference, small differences in static balance may exist between the legs (when the preference is based on kicking a ball).

The Immediate Effect of Static Hamstring Stretching on Dynamic Balance and Gait Biomechanical Variables in Athletes With Hamstring Tightness: A Preliminary Study

Introduction: Flexibility is an essential component of muscle function, and insufficient muscle flexibility may lead to muscle injuries. Decreased hamstring flexibility is one of the frequently reported risk factors for a hamstring strain and diminished athletic performance. Stretching is a commonly used intervention for increasing muscle length. There is a lack of evidence concerning the possible effects of hamstring stretching in balance and gait biomechanics. So, this study was designed to investigate the potential effects of static hamstring stretching on the range of motion (ROM), dynamic balance, and biomechanical variables of gait in athletes with hamstring tightness. Materials and Methods: This study is a single-group, pretest-posttest clinical trial performed on semi-professional female athletes. Twelve female athletes aged 20 to 35 years with bilateral hamstring tightness received a single session of unilateral static hamstring stretching on their randomly selected side. All subjects were assessed for straight leg raise, popliteal angle (using standard goniometry), perceived hamstring tightness (using a visual analog scale). They completed single-leg standing and 15-m walking and running tasks before and immediately after the intervention. The biomechanical parameters, including gait-line length, swing duration, and stance duration in walking tasks, maximum total force and mean total force in running task, and center of pressure (COP) displacement and standard deviation during balance task were measured using OpenGo sensor insole system. The pre-post values were compared using the paired sample t-test, and the level of significance was 0.05. Results: The values for straight leg raise and popliteal angle significantly increased (P<0.05) compared with the baseline, while perceived tightness significantly decreased following stretching (P<0.001). The amplitude (P₌0.006) and standard deviation (P₌0.016) of COP displacement in the mediolateral direction during the single leg stance balance task were significantly decreased after the intervention. Stance duration in slow walking (P₌0.004), as well as stance duration (P₌0.012) and swing duration (P<0.001) in fast walking, were significantly decreased (P<0.05) after stretching. No change was observed in gait biomechanical variables during the running test (P>0.05). Conclusion: The results of this study indicate that static hamstring stretching can be a promising intervention not just for increasing hamstring flexibility but also for improving balance ability.

Cortical and Cerebellar Oscillatory Responses to Postural Instability in Parkinson's Disease

Introduction: Posture and balance dysfunctions critically impair activities of daily living of patients with progressing Parkinson's disease (PD). However, the neural mechanisms underlying postural instability in PD are poorly understood, and specific therapies are lacking. Previous electrophysiological studies have shown distinct cortical oscillations with a significant contribution of the cerebellum during postural control tasks in healthy individuals.Methods: We investigated cortical and mid-cerebellar oscillatory activity via electroencephalography (EEG) during a postural control task in 10 PD patients with postural instability (PDPI+), 11 PD patients without postural instability (PDPI–), and 15 age-matched healthy control participants. Relative spectral power was analyzed in the theta (4–7 Hz) and beta (13–30 Hz) frequency bands.Results: Time-dependent postural measurements computed by accelerometer signals showed poor performance in PDPI+ participants. EEG results revealed that theta power was profoundly lower in mid-frontal and mid-cerebellar regions during the postural control task in PDPI+, compared to PDPI– and control participants. In addition, theta power was correlated with postural control performance in PD subjects. No significant changes in beta power were observed. Additionally, oscillatory changes during the postural control task differed from the resting state.Conclusion: This study underlines the involvement of mid-frontal and mid-cerebellar regions in postural stability during a balance task and emphasizes the important role of theta oscillations therein for postural control in PD.

Effects of Concurrent and Terminal Visual Feedback on Ankle Co-Contraction in Older Adults during Standing Balance

This preliminary investigation studied the effects of concurrent and terminal visual feedback during a standing balance task on ankle co-contraction, which was accomplished via surface electromyography of an agonist–antagonist muscle pair (medial gastrocnemius and tibialis anterior muscles). Two complementary mathematical definitions of co-contraction indices captured changes in ankle muscle recruitment and modulation strategies. Nineteen healthy older adults received both feedback types in a randomized order. Following an analysis of co-contraction index reliability as a function of surface electromyography normalization technique, linear mixed-effects regression analyses revealed participants learned or utilized different ankle co-contraction recruitment (i.e., relative muscle pair activity magnitudes) and modulation (i.e., absolute muscle pair activity magnitudes) strategies depending on feedback type and following the cessation of feedback use. Ankle co-contraction modulation increased when concurrent feedback was used and significantly decreased when concurrent feedback was removed. Ankle co-contraction recruitment and modulation did not significantly change when terminal feedback was used or when it was removed. Neither ankle co-contraction recruitment nor modulation was significantly different when concurrent feedback was used compared to when terminal feedback was used. The changes in ankle co-contraction recruitment and modulation were significantly different when concurrent feedback was removed as compared to when terminal feedback was removed. Finally, this study found a significant interaction between feedback type, removal of feedback, and order of use of feedback type. These results have implications for the design of balance training technologies using visual feedback.