Effect of simplifying the body model to compute the energy parameters in pole vaulting.

This study compared changes in the energy-time profiles in pole vaulting using several body models. Two-dimensional kinematics were collected from 20 successful vaults (5.20-6.01 m) performed by 10 athletes during a national meet. The linear and angular kinetic, potential, and total mechanical energy-time profiles were obtained from three pole vaulter models composed of 12, 5, and 3 segments (M12, M5, and M3, respectively), as well as calculated and approximated centre of mass models. One-dimensional statistical parametric mapping was used to compare these energy-time profiles from the models, while agreements of discrete energy parameters were assessed. For all the studied energy-time profiles, there was a main effect (0.05 < p < 0.001) of the models, but pairwise comparisons showed that M5 presented the lowest differences with M12 in comparison with the other models (M3 and approximated centre of mass models). In addition, M5 showed better agreement (lower bias and small effect size) with M12 for the studied energy parameters compared to the other models. Therefore, M5 may be a reliable option to simplify the body model and speed up the computation of the energy-time profiles of the pole vaulter.

Postural disorders induced by cochlear implantation in normo-reflexic patients: A potential origin of a transient geocentric perception disorder.

BACKGROUND: Profound hearing loss is a public health problem with serious consequences for patient's quality of life. Some of them, submitted to cochlear implantation, revealed various postural disorders such as balance and spatial perception disorders without detail on their vestibular status. RESEARCH QUESTION: The purpose of this preliminary study was to analyze the evolution of the balance control and geocentric perception after cochlear implantation procedure in normo-reflexic patients before the implant activation. METHODS: We assessed balance control of five patients with profound hearing loss and five healthy participants by means of computerized dynamic posturography and their geocentric perception by the subjective visual vertical test before surgery, three days and forty-five days after surgery (prior to implant activation). RESULTS: Before surgery, the patients showed some difficulties to control their balance in challenged postural context without geocentric perception disorder. Patients presented an improvement in their postural accuracy, but their balance control remained inappropriate in challenging environment. Moreover, their geocentric perception was deviated towards their healthy ear immediately after cochlear implantation. This misperception naturally fades before the implant activation. SIGNIFICANCE: This transient spatial perception alteration might probably cause the perceived postural discomforts and the daily difficulties often reported by these patients in their clinical records early after cochlear implantation. This preliminary study allows for the first time the distinction between the both components of posture: balance control and geocentric perception. Therefore, a specific therapeutic care targeting the rehabilitation of spatial cognition could be proposed to these patients in order to reduce their transient postural disorders.

Biomechanical Pole Vault Patterns Were Associated With a Higher Proportion of Injuries.

Background: Pole vault is a highly demanding sport where many physical and technical requirements are engaged in performance process. Considering level of energy transferred from athlete's horizontal speed to the pole during pole bending, we can imagine that associated musculoskeletal tensions, in addition to trials accumulation, can increase the risk of (specific) injuries. Given the multiple morphological, physical and technical characteristics of vaulters and ways of pole vaulting, we can hypothesis that some patterns of pole vaults can lead to higher injury risk than others. Aim: To analyze the potential association between the biomechanical patterns of pole vault and the history of injuries. Method: We conducted a study over national-level pole vaulters including the prospective collection of pole vault biomechanical data during competition at the national elite indoor championship and youth national indoor championship (U17 and U20), associated with the retrospective collection of their injuries during the 12 preceding months through an online questionnaire. Results: Among the 88 pole vaulters participating in these championships, 62 (70.5%) accepted to participated in this study, and their pole vault biomechanical and injury data were collected. 77.4% reported having presented at least one injury during the 12 preceding months. One biomechanical parameter related to the take-off phase (lower H2, i.e., height of the grip (superior) hand from the ground when the athlete subsequently took off from the ground) and some biomechanical parameters related to the terminal phase of the run-up phase (higher Spd [i.e., speed between 10 and 5 meters to the box), SLadj (last stride adjustment), SLvar (stride length variation), tc (contact time)] were significantly associated with higher proportions of all injuries. Conclusion: Biomechanical pole vault patterns during the competition day were associated with a higher proportion of history of all injuries. Although the injury data collection was retrospective leading to recall bias risk, and do not allow determining cause-consequence relationships regarding biomechanical patterns and injury occurrence, this present study is the first to analyze potential association between the biomechanical pole vault patterns and injury occurrence, which is of great help to provide hypotheses/ideas to design future studies and to move forward into prevention measures.

You are better off running than walking revisited: Does an acute vestibular imbalance affect muscle synergies?

It has been suggested that vestibular cues are inhibited for the benefit of spinal locomotor centres in parallel with the increase in locomotion speed. This study aimed at quantifying the influence of a transient vestibular tone imbalance (TVTI) on gait kinematics, muscle activity and muscle synergies during walking and running. Twelve participants walk or run at a self-selected speed with or without TVTI, which was generated by 10 body rotations just prior the locomotion task. Three-dimensional lower-limb kinematic was recorded simultaneously with the surface electromyographic (EMG) activity of 8 muscles to extract muscle synergies via non-negative matrix factorization. Under TVTI, there was an increased gait deviation in walking compared to running (22.8 ±â€¯8.4° and 8.5 ±â€¯3.6°, respectively; p < 0.01), while the number (n = 4) and the composition of the muscle synergies did not differ across conditions (p = 0.78). A higher increase (p < 0.05) in EMG activity due to TVTI was found during walking compared to running, especially during stance. These findings confirmed that the central nervous system inhibited misleading vestibular signals according to the increase in locomotion speed for the benefit of spinal mechanisms, expressed by the muscle synergies.

Does the postural variable affect the determination of balance compensation level in vestibular schwannoma patients?

Previous sensory organization test (SOT) outcomes provided evidences that the vestibular schwannoma (VS) removal led to acute and slow changes in the ability to use vestibular cues for balance control. However, the assumptions behind the equilibrium score (ES) are somewhat controversial within the literature. Therefore, we compared the time-course of balance control in eighteen VS patients across different postural variables. Analyses of variance and unsupervised clustering (k-means) were used to compare the whole dataset of four postural variables: ES, a modified ES which factored in the time before a fall (cES), the mean amplitude (MA) and the mean velocity (MV) of center of pressure displacements. Early after surgery, postural performances significantly decreased (p < 0.01), especially when vestibular cues are predominant, with lower ES (12.5 ± 22.8%) and cES (26.6 ± 16.7%) and higher MA (27.7 ± 7.1 mm) and MV (95.2 ± 53.2 mm.s-1) than before or three months after surgery. For each postural variable, the k-means clustering divided the whole dataset into two clusters: cluster #1 corresponded to a SOT with low sway amplitude and cluster #2 with high sway amplitude and falls. Overall, whatever the selected postural variable, the main recovery profile of VS patients was highlighted, thus surpassing the ambiguities inherent of the ES calculation.

Spectral properties of multiple myoelectric signals: New insights into the neural origin of muscle synergies.

It is still unclear if muscle synergies reflect neural strategies or mirror the underlying mechanical constraints. Therefore, this study aimed to verify the consistency of muscle groupings between the synergies based on the linear envelope (LE) of muscle activities and those incorporating the time-frequency (TF) features of the electromyographic (EMG) signals. Twelve healthy participants performed six 20-m walking trials at a comfort and fast self-selected speed, while the activity of eleven lower limb muscles was recorded by means of surface EMG. Wavelet-transformed EMG was used to obtain the TF pattern and muscle synergies were extracted by non-negative matrix factorization. When five muscle synergies were extracted, both methods defined similar muscle groupings whatever the walking speed. When accounting the reconstruction level of the initial dataset, a new TF synergy emerged. This new synergy dissociated the activity of the rectus femoris from those of the vastii muscles (synergy #1) and from the one of the tensor fascia latae (synergy #5). Overall, extracting TF muscle synergies supports the neural origin of muscle synergies and provides an opportunity to distinguish between prescriptive and descriptive muscle synergies.

Dynamical analysis of balance in vestibular schwannoma patients.

The analysis of the complexity of postural fluctuations is a recent method for assessing postural control. Complexity relates to the irregularity of the center of pressure time series and characterizes the ability of postural control to meet a changing environment. In our study, we used the sample entropy (SampEn) parameter to evaluate the complexity of postural sway velocity time series in patients with vestibular schwannoma (n=19) compared to healthy controls (n=20), using the sensory organization test. Patients performed postural assessments three days before surgical ablation of the tumor, then three times after surgery, at eight, thirty, and ninety days. The control group underwent posturographic tests only once. Our results demonstrated that SampEn values distinguished both groups before surgery only in postural tasks where vestibular afferences significantly contribute to maintaining balance. We also found an immediate decrease of complexity after the surgical resection of the tumor. Our results are in line with the theory of complexity loss of physiological systems stating that reducing the number of their structural components or altering their coupling leads to a decrease in complexity. Finally, our findings showed that progressive restoration of complexity over time was such that no difference was found between the two groups ninety days after surgery, due to the implementation of central adaptive mechanisms and the substitution by other sensory afferences. Thus, the SampEn parameter can highlight the postural effects of vestibular pathology, and complexity analysis appears to be a valuable tool for investigating the temporal structure of CoP time series.

Correlations between postural control and psychological factors in vestibular schwannoma patients.

BACKGROUND: Various individual factors have been described to influence postural performances related to vestibular schwannoma. However, psychological factors may also be involved in postural variations. OBJECTIVE: To identify relationships between postural performances, illness perceptions, coping, anxiety-depression and quality of life of patients with vestibular schwannoma. METHODS: Twenty-six patients who were scheduled for a surgical removal of a vestibular schwannoma underwent posturography tests and were asked to complete psychological questionnaires three days prior to surgery.The Sensory Organization Test, the Illness Perceptions Questionnaire-Revised, the Brief-COPE, the Hospital Anxiety Depression Scale and the World Health Organization Quality of Life instrument were used for assessments. Correlations between posturography and psychological questionnaires were calculated. RESULTS: Balance disorders were associated with (i) impaired quality of life of patients, (ii) anxiety and depression affects, (iii) greater daily consequences, and with (iv) denial coping response. CONCLUSIONS: Given the association between balance disorders and psychological factors, health practitioners should be attentive to the deterioration of both aforementioned issues.

Sit to stand in elderly fallers vs non-fallers: new insights from force platform and electromyography data.

BACKGROUND: The sit-to-stand movement requires balance control and coordination between the trunk and lower limbs. For these reasons, it is commonly used in clinics for evaluating lower limb muscle function in the elderly. The aim of the present study was to point out re levant biomechanical and neurophysiological sit-to-stand parameters allowing comparison between elderly fallers and non-fallers. METHODS: Ten elderly fallers and thirty non-fallers performed sit-to-stand movements. Sit-to-stand mechanical (maximal and mean force, impulse) and temporal parameters were measured in the vertical and anteroposterior axes using force platforms. Activity of rectus femoris, vastus lateralis, and gastrocnemius lateralis muscles was bilaterally recorded by surface electromyography. RESULTS: Time to realize sit-to-stand movements was significantly longer in elderly fallers compared to non-fallers (p < 0.05). In the same way, maximal vertical force and mean posterior force applied on force platform were significantly lower (p < 0.05) in fallers than in non-fallers individual. At muscular activity level, results showed a main statistical difference in gastrocnemius lateralis muscle activity patterns between faller and non-faller groups. CONCLUSION: Vertical and anteroposterior data from force platform, and gastrocnemius lateralis muscle activity determined during sit-to-stand movement are the most relevant parameters to differentiate fallers and non-fallers. Moreover, these factors highlight different strategies to rise from a chair between faller and non-faller group, suggesting that fallers would constantly adjust their control balance during the sit-to-stand movement.

Prediction of Balance Compensation After Vestibular Schwannoma Surgery.

Background Balance compensation after vestibular schwannoma (VS) surgery is under the influence of specific preoperative patient and tumor characteristics. Objective To prospectively identify potential prognostic factors for balance recovery, we compared the respective influence of these preoperative characteristics on balance compensation after VS surgery. Methods In 50 patients scheduled for VS surgical ablation, we measured postural control before surgery (BS), 8 (AS8) days after, and 90 (AS90) days after surgery. Based on factors found previously in the literature, we evaluated age, body mass index and preoperative physical activity (PA), tumor grade, vestibular status, and preference for visual cues to control balance as potential prognostic factors using stepwise multiple regression models. Results An asymmetric vestibular function was the sole significant explanatory factor for impaired balance performance BS, whereas the preoperative PA alone significantly contributed to higher performance at AS8. An evaluation of patients' balance recovery over time showed that PA and vestibular status were the 2 significant predictive factors for short-term postural compensation (BS to AS8), whereas none of these preoperative factors was significantly predictive for medium-term postoperative postural recovery (AS8 to AS90). Conclusions We identified specific preoperative patient and vestibular function characteristics that may predict postoperative balance recovery after VS surgery. Better preoperative characterization of these factors in each patient could inform more personalized presurgical and postsurgical management, leading to a better, more rapid balance recovery, earlier return to normal daily activities and work, improved quality of life, and reduced medical and societal costs.

Preoperative balance control compensation in patients with a vestibular schwannoma: does tumor size matter?

OBJECTIVE: The influence of tumor size on postural control of patients with vestibular schwannoma (VS) remains to be determined. This study aimed to compare the postural performances of VS patients, according to the size of the tumor, with healthy subjects. METHODS: The six conditions (C1-C6) of the sensory organization test (SOT) were carried out in 87 patients, split into four groups according to the Koos classification (stage I-IV), and in 72 aged-matched controls to evaluate postural control. The vestibular reflectivity and compensation were estimated with videonystagmography. RESULTS: Among patients, lower C5 and C6 scores were found in stage I and IV patients than in stage II and III patients, whereas vestibular compensation did not impact the tumor size influence on the postural control. The scores were significantly (p<0.001) lower for all the groups of patients than the controls in the vestibular-related SOT conditions (C5-C6). CONCLUSIONS: Patients with an unilateral VS displayed altered postural performances compared to the control subjects and tumor size had a bell-like pattern effect on balance control. SIGNIFICANCE: The tumor size could be seen as a determining factor in the implementation of adaptive mechanisms that lead to the postural compensation and might be dissociated from vestibular compensation.

Quality of life and audiologic performance through the ability to phone of cochlear implant users.

This study aimed to evaluate the impact of cochlear implantation on quality of life (QoL), using general and cochlear implant (CI) specific questionnaires and to determine the relationship of phone ability with QoL, speech recognition abilities and tinnitus. Twenty-six adult volunteers with a post-lingual profound deafness, unilaterally implanted with a CI, were included in this study. All subjects had used a CI for at least 1 year. The Glasgow benefit inventory (GBI) and Nijmegen cochlear implant questionnaire (NCIQ) were administered to assess QoL. Speech recognition was tested using phonemic Lafon's lists. The subjective tinnitus severity scale (STSS) questionnaire was used to determine the effects of tinnitus. CI users were split into four groups according to their phone ability. There was an improvement in QoL after cochlear implantation. The NCIQ showed significant (p < 0.001) improvements in the total score and in all subdomains after CI. A significant relationship between phone ability, QoL and speech recognition was found. Improving phone ability led to higher QoL (p < 0.05) and speech recognition (p < 0.01) scores. The CI use decreased significantly the occurrence of tinnitus, but its severity was not correlated with QoL. Post-surgery assessment should include speech recognition measures and QoL evaluation. The NCIQ appeared more effective than the GBI in its ability to detect improvements in QoL. Assessing phone ability represents an easy and fast approach to evaluate hearing performances and QoL, and may reflect global outcomes of CI.

Prediction of time-to-exhaustion in the first dorsal interosseous muscle from early changes in surface electromyography parameters.

INTRODUCTION: In this study we evaluated the precision of the time-to-exhaustion (T(lim)) prediction from the early changes in surface electromyography (sEMG) of the first dorsal interosseous muscle. METHODS: Thirty subjects performed an index finger isometric abduction at 35% of maximal voluntary contraction (MVC) until exhaustion. Ten participants performed the same exercise at 50% MVC 1 week later. Changes in sEMG parameters across time were modeled using the area-ratio and the linear regression slope. T(lim) was plotted as a function of each of these indices of change, and the coefficient of determination (R(2)) was determined. RESULTS: Null to moderate R(2) (0.22 and 0.56 at 35% and 50% MVC, respectively) values were calculated. The best T(lim) estimation led to a high prediction error (21.6 ± 15.0% of T(lim) for the 50% MVC task). CONCLUSIONS: Although the prediction of time-to-exhaustion is an appealing research topic, these results suggest that it cannot be done solely from sEMG.

Shoulder muscles recruitment during a power backward giant swing on high bar: a wavelet-EMG-analysis.

This study aimed at determining the upper limb muscles coordination during a power backward giant swing (PBGS) and the recruitment pattern of motor units (MU) of co-activated muscles. The wavelet transformation (WT) was applied to the surface electromyographic (EMG) signal of eight shoulder muscles. Total gymnast's body energy and wavelet synergies extracted from the WT-EMG by using a non-negative matrix factorization were analyzed as a function of the body position angle of the gymnast. A cross-correlation analysis of the EMG patterns allowed determining two main groups of co-activated muscles. Two wavelet synergies representing the main spectral features (82% of the variance accounted for) discriminated the recruitment of MU. Although no task-group of MU was found among the muscles, it appeared that a higher proportion of fast MU was recruited within the muscles of the first group during the upper part of the PBGS. The last increase of total body energy before bar release was induced by the recruitment of the muscles of the second group but did not necessitate the recruitment of a higher proportion of fast MU. Such muscle coordination agreed with previous simulations of elements on high bar as well as the findings related to the recruitment of MU.

Catapult effect in pole vaulting: is muscle coordination determinant?

This study focused on the phase between the time of straightened pole and the maximum height (HP) of vaulter and aimed at determining the catapult effect in pole vaulting on HP. Seven experienced vaulters performed 5-10 vaults recorded by two video cameras, while the surface electromyography (sEMG) activity of 10 upper limbs muscles was recorded. HP was compared with an estimated maximum height (HP(est)) allowing the computation of a push-off index. Muscle synergies were extracted from the sEMG activity profiles using a non-negative matrix factorization algorithm. No significant difference (p>0.47) was found between HP(est) (4.64±0.21m) and HP (4.69±0.23m). Despite a high inter-individual variability in sEMG profiles, two muscle synergies were extracted for all the subjects which accounted for 96.1±2.9% of the total variance. While, the synergy activation coefficients were very similar across subjects, a higher variability was found in the muscle synergy vectors. Consequently, whatever the push-off index among the pole vaulters, the athletes used different muscle groupings (i.e., muscle synergy vectors) which were activated in a similar fashion (i.e., synergy activation coefficients). Overall, these results suggested that muscle coordination adopted between the time of straightened pole and the maximum height does not have a major influence on HP.

Effect of the upper limbs muscles activity on the mechanical energy gain in pole vaulting.

The shoulder muscles are highly solicited in pole vaulting and may afford energy gain. The objective of this study was to determine the bilateral muscle activity of the upper-limbs to explain the actions performed by the vaulter to bend the pole and store elastic energy. Seven experienced athletes performed 5-10 vaults which were recorded using two video cameras (50Hz). The mechanical energy of the centre of gravity (CG) was computed, while surface electromyographic (EMG) profiles were recorded from 5 muscles bilateral: deltoideus, infraspinatus, biceps brachii, triceps, and latissimus dorsi muscles. The level of intensity from EMG profile was retained in four sub phases between take-off (TO1) and complete pole straightening (PS). The athletes had a mean mechanical energy gain of 22% throughout the pole vault, while the intensities of deltoideus, biceps brachii, and latissimus dorsi muscles were sub phases-dependent (p<0.05). Stabilizing the glenohumeral joint (increase of deltoideus and biceps brachii activity) and applying a pole bending torque (increase of latissimus dorsi activity) required specific muscle activation. The gain in mechanical energy of the vaulter could be linked to an increase in muscle activation, especially from latissimusdorsi muscles.

Influence of the scale function on wavelet transformation of the surface electromyographic signal.

The scale function in wavelet transformation (WT) determines wavelet dilation and optimises the processing of a given signal. Here, the objective was to determine the influence of the scale function on the WT of 160 surface electromyograms using second-degree polynomial (WT(poly)) and exponential (WT(exp)) scale functions. For each WT, a mean frequency (MNF) was calculated from the original wavelet spectrum and from the cubic spline interpolated wavelet spectrum, and these were compared with the MNF obtained from a fast Fourier transform (FFT). The total intensity (Tp) for each WT was compared with the root mean square (RMS). The MNFs computed from the original wavelet spectra were significantly (P < 0.05) lower and higher when computed from the reconstructed wavelet spectra than those from the FFT. The Tp computed from WT(poly) showed significantly higher agreement with the RMS than the Tp from WT(exp). Finally, the WT(poly) may serve as a reference in electromyography.

Between-subject variability of muscle synergies during a complex motor skill.

The purpose of the present study was to determine whether subjects who have learned a complex motor skill exhibit similar neuromuscular control strategies. We studied a population of experienced gymnasts during backward giant swings on the high bar. This cyclic movement is interesting because it requires learning, as untrained subjects are unable to perform this task. Nine gymnasts were tested. Both kinematics and electromyographic (EMG) patterns of 12 upper-limb and trunk muscles were recorded. Muscle synergies were extracted by non-negative matrix factorization (NMF), providing two components: muscle synergy vectors and synergy activation coefficients. First, the coefficient of correlation (r) and circular cross-correlation (r(max)) were calculated to assess similarities in the mechanical patterns, EMG patterns, and muscle synergies between gymnasts. We performed a further analysis to verify that the muscle synergies (in terms of muscle synergy vectors or synergy activation coefficients) extracted for one gymnast accounted for the EMG patterns of the other gymnasts. Three muscle synergies explained 89.9 ± 2.0% of the variance accounted for (VAF). The coefficients of correlation of the muscle synergy vectors among the participants were 0.83 ± 0.08, 0.86 ± 0.09, and 0.66 ± 0.28 for synergy #1, #2, and #3, respectively. By keeping the muscle synergy vectors constant, we obtained an averaged VAF across all pairwise comparisons of 79 ± 4%. For the synergy activation coefficients, r(max)-values were 0.96 ± 0.03, 0.92 ± 0.03, and 0.95 ± 0.03, for synergy #1, #2, and #3, respectively. By keeping the synergy activation coefficients constant, we obtained an averaged VAF across all pairwise comparisons of 72 ± 5%. Although variability was found (especially for synergy #3), the gymnasts exhibited gross similar neuromuscular strategies when performing backward giant swings. This confirms that the muscle synergies are consistent across participants, even during a skilled motor task that requires learning.

Mechanics of pole vaulting: a review.

A good understanding of the mechanics of pole vaulting is fundamental to performance because this event is quite complex, with several factors occurring in sequence and/or in parallel. These factors mainly concern the velocities of the vaulter-pole system, the kinetic and potential energy of the vaulter and the strain energy stored in the pole, the force and torque applied by the athlete, and the pole design. Although the pole vault literature is vast, encompassing several fields such as medicine, sports sciences, mechanics, mathematics, and physics, the studies agree that pole vault performance is basically influenced by the energy exchange between the vaulter and pole. Ideally, as the athlete clears the crossbar, the vaulter mechanical energy must be composed of high potential energy and low kinetic energy, guaranteeing the high vertical component of the vault. Moreover, the force and torque applied by the vaulter influences this energy exchange and these factors thus must be taken into consideration in the analysis of performance. This review presents the variables that influence pole vault performance during the run-up, take-off, pole support, and free flight phases.