Postural Sway Velocity of Deaf Children with and without Vestibular Dysfunction.

BACKGROUND: Sensory information obtained from the visual, somatosensory, and vestibular systems is responsible for regulating postural control, and if damage occurs in one or more of these sensory systems, postural control may be altered. OBJECTIVE: To evaluate and compare the postural sway velocity between children with normal hearing and with sensorineural hearing loss (SNHL), matched by sex and age group, and to compare the postural sway velocity between children with normal hearing and with SNHL, with and without vestibular dysfunction. METHODS: Cross-sectional study that evaluated 130 children (65 with normal hearing and 65 with SNHL), of both sexes and aged between 7 and 11 years, from public schools of the city of Caruaru, Pernambuco state, Brazil. The postural sway velocity of the center of pressure (COP) was assessed by a force platform, in two directions, anteroposterior (AP) and mediolateral (ML)), in three positions, namely bipedal support with feet together and parallel (parallel feet (PF)), bipedal support with one foot in front of the other (tandem foot (TF)), and single-leg support (one foot (OF)), evaluated with the eyes open and closed. RESULTS: Children with SNHL demonstrated greater postural sway velocity compared to children with normal hearing in all the positions evaluated, with significant differences in the AP direction, with the eyes open (PF: p = 0.001; TF: p = 0.000; OF: p = 0.003) and closed (PF: p = 0.050; TF: p = 0.005). The same occurred in the ML direction, with the eyes open (PF: p = 0.001; TF: p = 0.000; OF: p = 0.001) and closed (PF: p = 0.002; TF: p = 0.000). The same occurred in relation to vestibular function, where the children with SNHL with an associated vestibular dysfunction demonstrated greater postural sway velocity compared to children with normal hearing in all the positions evaluated, demonstrating significant differences in the AP direction, with the eyes open (TF: p = 0.001; OF: p = 0.029) and eyes closed (PF: p = 0.036; TF: p = 0.033). The same occurred in the ML direction, with the eyes open (TF: p = 0.000) and with the eyes closed (PF: p = 0.008; TF: p = 0.009). CONCLUSIONS: Children with SNHL demonstrated greater instability of postural control than children with normal hearing in all the directions assessed. Children with SNHL and an associated vestibular dysfunction demonstrated the greatest instability of postural control in this study.

Changes in contractile and elastic properties of the triceps surae muscle induced by neuromuscular electrical stimulation training.

PURPOSE: Neuromuscular electrical stimulation (NMES) training is known to induce improvement in force production capacities and fibre-type transition. The aim of this study was to determine whether NMES training also leads to changes in the mechanical properties of the human triceps surae (TS) muscle. METHODS: Fifteen young male subjects performed a training protocol (4 weeks, 18 sessions, 4-5 sessions per week) based on a high-frequency isometric NMES programme of TS muscle. Quick-release test was used to evaluate Musculo-Tendinous (MT) stiffness index (SIMT) as the slope of the linear MT stiffness-torque relationships under submaximal contraction. Sinusoidal perturbations allowed the assessment of musculo-articular stiffness index (SIMA) as well as the calculation of the maximal angular velocity ([Formula: see text]) of TS muscle using an adaptation of Hill's equation. RESULTS: After NMES training, Maximal Voluntary Contraction under isometric conditions and [Formula: see text] increased significantly by 17.5 and 20.6 %, respectively, while SIMT and SIMA decreased significantly (-12.7 and -9.3 %, respectively). CONCLUSIONS: These changes in contractile and elastic properties may lead to functional changes of particular interest in sport-related activities as well as in the elderly.

Long-term neuromechanical results of selective tibial neurotomy in patients with spastic equinus foot.

BACKGROUND: The neuromechanical consequences of tibial neurotomy have not been extensively studied. METHODS: Fifteen patients were evaluated before and after selective tibial neurotomy (after 2 months and after 15 months) by means of clinical, neurophysiological [tendon (T) reflexes, Hoffmann (H) reflexes and maximum motor response, Mmax] and mechanical parameters (passive stiffness of plantar flexors at the ankle). The neurotomy concerned the soleus (100 % of cases), gastrocnemius (20 % of cases), posterior tibial (60 % of cases) and flexor digitorum longus (47 % of cases) nerves. RESULTS: Neurotomy provided more than 90 % improvement of clinical spasticity scores, 20 % improvement of walking scores and the angle of passive dorsiflexion (APDF) of the ankle (mean angle: 7°), temporary reduction of the soleus Mmax (18 % at 2 months with return to the preoperative value at 15 months), and lasting reduction of the soleus Hmax/Mmax (68 % at 2 months, 78 % at 15 months) and T/Mmax (84 % at 2 months, 80 % at 15 months). M and H responses of the gastrocnemius (whether or not they were included in the neurotomy) were not modified, while T/Mmax decreased to the same degree as for soleus. Passive stiffness was lastingly decreased from 64.0 Nm/rad to 49.0 Nm/rad (2 months) and 49.5 Nm/rad (15 months). CONCLUSION: Selective tibial neurotomy of the soleus nerve induces long-term reduction of reflex hyperexcitability and passive stiffness of plantar flexors in spastic patients, with no lasting impairment of motor efferents. In parallel, it modifies the tendon reflexes of synergistic muscles (gastrocnemius) not concerned by the neurotomy.

Influence of musculo-tendinous stiffness of the plantar ankle flexor muscles upon maximal power output on a cycle ergometre.

The importance of maximal voluntary torque (T (MVC)), maximal rate of torque development (MRTD) and musculo-tendinous stiffness of the triceps surae for maximal power output on a cycle ergometre (Pmax) was studied in 21 healthy subjects by studying the relationships between maximal cycling power related to body mass (Pmax BM(-1)) with T (MVC), MRTD and different indices of musculo-tendinous stiffness of the ankle flexor. Pmax BM(-1) was calculated from the data of an all-out force-velocity test on a Monark cycle ergometre. T (MVC) and MRTD were measured on a specific ankle ergometre. Musculo-tendinous stiffness was estimated by means of quick releases at 20, 40, 60 and 80% T (MVC) on the same ankle ergometre. Pmax BM(-1) was significantly and positively correlated with MRTD related to body mass but the positive correlation between Pmax BM(-1) and T (MVC) did not reach the significance level (0.05). Pmax BM(-1) was significantly and positively correlated with the estimation of stiffness at 40% T (MVC) (S(0.4)), but not with stiffness at 20, 60 and 80% T (MVC). The results of the present study suggest that maximal power output during cycling is significantly correlated with the level of musculo-tendinous stiffness which corresponds to torque range around peak torque at optimal pedal rate. However, the low coefficient of determination (r2 = 0.203) between Pmax BM(-1) and S (0.4) BM(-1) suggested that Pmax BM(-1) largely depended on other factors than the musculo-tendinous stiffness of the only plantar flexors.

Stunting delays maturation of triceps surae mechanical properties and motor performance in prepubertal children.

Malnutrition can lead to possible irreversible consequences in the development of muscle function and some of them are yet poorly characterized. The present study evaluated the mechanical properties of the triceps surae and motor performance in stunted (S) and eutrophic (E) prepubertal children (9 years ± 6 months). Height-for-age ratio was used as indicator of stunting due to early malnutrition, according to the World Health Organization. Torque was determined by maximal voluntary contractions (MVC) and musculotendinous (MT) stiffness was achieved through quick-release tests to obtain MT stiffness index (SI(MT)) and passive stiffness (K (p)) from linear MT stiffness-torque relationships. Percutaneous supramaximal electrically elicited contractions determined twitch torque (Pt) and electromechanical delay (EMD). Motor performance was evaluated by balance test. S group presented significantly lower MVC and a trend of lower Pt values indicating lower capacities to develop force under voluntary or induced conditions. Significantly higher SI(MT) and EMD values were observed, while K (p) and motor performance in balance were significantly lower. Higher SI(MT) values have been reported previously in youngest prepubertal children, indicating that immature activation capacities can mask MT stiffness assessment during voluntary contractions, taking into consideration the higher EMD values as a measure of muscle stiffness contribution. Lower K (p) may indicate a delay in the maturation of tendinous tissue in S group, influencing motor performance in balance. The present study shows that malnutrition leads to adaptation of intrinsic MT elastic properties, but depends on the level of the observed structure.

Repercussions of the Degrees of Hearing Loss and Vestibular Dysfunction on the Static Balance of Children With Sensorineural Hearing Loss.

OBJECTIVE: The purpose of this study was to assess the static balance of children with sensorineural hearing loss (SNHL) according to the degrees of SNHL and the function of the vestibular system. METHODS: This cross-sectional study was conducted in public schools located in Caruaru, Pernambuco state, Brazil, with 130 children (65 with normal hearing and 65 with SNHL as documented by air and bone conduction audiometry) of both sexes between 7 and 11 years old. Static balance was assessed by a stabilometric analysis using a force platform consisting of the circular area of center-of-pressure displacement of the children evaluated in 3 positions: bipedal support with feet together and parallel (PF), tandem feet (TF), and 1 foot (OF), carried out under 2 sensory conditions each, with eyes open and eyes closed. After balance assessments, the children with SNHL received examinations of auditory and vestibular functions-through audiometry and computerized vectoelectronystagmography, respectively-to compose the groups according to degrees of SNHL and vestibular function. RESULTS: The children with severe and profound SNHL demonstrated more static balance instabilities than the children with normal hearing in 5 positions assessed with eyes open (PF, TF, and OF) and eyes closed (PF and TF). The same phenomenon occurred in children with SNHL and associated vestibular dysfunction in all of the positions assessed with eyes open and eyes closed (PF, TF, and OF). CONCLUSION: The larger the degree of SNHL, the greater the balance instability of the children. The children with SNHL and associated vestibular dysfunction showed the highest balance instabilities in this study. IMPACT: Children with larger degrees of SNHL and associated vestibular dysfunction might require prolonged periods to rehabilitate their balance.

Paired changes in electromechanical delay and musculo-tendinous stiffness after endurance or plyometric training.

When measured in vivo electromechanical delay (EMD) depends mainly on the elastic properties of the muscle-tendon unit. Recent studies have shown changes in stiffness of the triceps surae (TS) following a period of training. To confirm the influence of musculo-tendinous stiffness on EMD, this study investigates paired changes in these two parameters after a training period. Two types of training known to induce opposite changes in stiffness were analysed. EMD and musculo-tendinous stiffness were measured on adult subjects before and after 10 weeks of endurance (n = 21) or plyometric (n = 9) trainings. EMD was defined as the time lag between the TS M-wave latency and the onset of muscle twitch evoked at rest by supramaximal electrical stimulations of the posterior tibial nerve. Quick release tests were used to evaluate the musculo-tendinous stiffness of the ankle plantar flexors. The stiffness index was defined as the slope of the relationship between angular stiffness and external torque values. Endurance training, known to preferentially activate the slow, stiffer muscle fibers, leads to a decrease in EMD and to an increase in stiffness index. Following plyometric training, which specifically recruits fast, more compliant fibers, EMD and the stiffness index exhibited adaptations directionally opposite to those seen with endurance training. When pooling the data for the two subject groups, a correlation was found between changes in EMD and changes in musculo-tendinous stiffness indexes. Thus, changes in EMD values are proposed to indirectly link to changes in musculo-tendinous stiffness for subjects involved in muscle training.

A reproducibility study on musculotendinous stiffness quantification, using a new transportable ankle ergometer device.

The use of biomechanical methods to quantify functional/physiological parameters in malnourished humans can provide new insights into the understanding of effects of malnutrition on human muscles. Therefore, a transportable ankle ergometer device was developed, which allows the quantification of mechanical properties of the human plantarflexor muscles in field experiments. More precisely, the ergometer quantifies isometric force in static conditions and musculotendinous stiffness in dynamic conditions. This latter parameter is obtained by the quick-release technique. The aim of the study was first to conduct a reproducibility study on musculotendinous stiffness. Seven healthy subjects were tested three times in alternate days. The results showed the well-known linear relationship between musculotendinous stiffness and torque, where the slope was used as a stiffness index (SI(MT)). Individual regression line comparison indicated that SI(MT) values were not significantly different between the three repeated measurements (P>0.05). Mean coefficient of variation was 4.5+/-1.0%. The individual SI(MT) data were within the range of those reported in the literature. The reproducibility study showed that the quantification of musculotendinous stiffness by means of the quick-release technique is a reliable method, using a transportable ankle ergometer device.

Voluntary activation of the triceps surae in prepubertal children.

The activation capacities and neuromuscular efficiency (NME) of the triceps surae (TS) of prepubescent children (7-11 years) and adults were evaluated during submaximal and maximal (MVC) isometric plantarflexion to determine whether they varied with age. TS-EMG were obtained by summing-up the rectified electromyograms of the soleus and gastrocnemii muscles; these data were quantified using a sliding average method and normalized with reference to the TS maximal compound action potential (TS-M-wave). The maximal EMG increased significantly with age in the children, but less than MVC, what led to a significant increase in NME(Max) (MVC/TS-EMG(max) ratio). The EMG-torque relationship indicated an age-related overactivation of TS at low torque, what led to a lower NME(Sub-max) (inverse of the slope of the EMG-torque relationship) for the youngest children. The overactivation of TS was accompanied by contraction of the TA, which decreased with age. The youngest children were also less able to maintain a target torque and muscle activation. Finally, the twitch interpolated method revealed an age-dependant activation deficit. We conclude that central mechanisms are the main cause of the lower torques developed by children and they appear to vary with age in prepubertal children.

Changes in stretch reflexes and muscle stiffness with age in prepubescent children.

Musculo-articular stiffness of the triceps surae (TS) increases with age in prepubescent children, under both passive and active conditions. This study investigates whether these changes in muscle stiffness influence the amplitude of the reflex response to muscle stretch. TS stiffness and reflex activities were measured in 46 children (7-11 yr old) and in 9 adults. The TS Hoffmann reflex (H reflex) and T reflex (tendon jerk) in response to taping the Achilles tendon were evaluated at rest and normalized to the maximal motor response (Mmax). Sinusoidal perturbations of passive or activated muscles were used to evoke stretch reflexes and to measure passive and active musculoarticular stiffness. The children's Hmax-to-Mmax ratio did not change with age and did not differ from adult values. The T-to-Mmax ratio increased with age but remained significantly lower than in adults. Passive stiffness also increased with age and was correlated with the T-to-Mmax ratio. Similarly, the children's stretch reflex and active musculoarticular stiffness were significantly correlated and increased with age. We conclude that prepubescent children have smaller T reflexes and stretch reflexes than adults, and the lower musculoarticular stiffness is mainly responsible for these smaller reflexes, as indicated by the parallel increases in reflex and stiffness.

Musculotendinous stiffness of triceps surae, maximal rate of force development, and vertical jump performance.

The relationships between ankle plantar flexor musculotendinous stiffness (MTS) and performance in a countermovement vertical jump (CMJ) and maximal rate of torque development (MRTD) were studied in 27 active men. MTS was studied by means of quick releases at 20 (S0.2), 40 (S0.4), 60 (S0.6), and 80% (S0.8) of maximal voluntary torque (T(MVC)). CMJ was not correlated with strength indices but was positively correlated with MRTD/BM, S 0.4/BM. The slope α 2 and intercept ß 2 of the torque-stiffness relationships from 40 to 80% T(MVC) were correlated negatively (α 2) and positively (ß 2) with CMJ. The different stiffness indices were not correlated with MRTD. The prediction of CMJ was improved by the introduction of MRTD in multiple regressions between CMJ and stiffness. CMJ was also negatively correlated with indices of curvature of the torque-stiffness relationship. The subjects were subdivided in 3 groups in function of CMJ (groups H, M, and L for high, medium, and low performers, resp.). There was a downward curvature of the torque-stiffness relationship at high torques in group H or M and the torque-stiffness regression was linear in group L only. These results suggested that torque-stiffness relationships with a plateau at high torques are more frequent in the best jumpers.

Changes in mechanical properties of human plantar flexor muscles in ageing.

Changes in contractile and elastic properties of human plantar flexor muscles in ageing, were investigated in 12 young (19-24 years, YG) and 11 old (61-74 year, OG) men. Maximal isometric and concentric voluntary torques, at several angular velocities, were measured to construct torque-angular velocity relationship. This led to the calculation of an index of maximal shorting velocity (VImax) at low torque. Two methods were then used to calculate musculotendinous (MT, quick-release movements) and musculoarticular (MA, sinusoidal perturbations) stiffness. In both cases, stiffness was linearly related to torque, leading to the calculation of a stiffness index (SI) as the slope of the stiffness-torque relationship: SI(MT) and SI(MA), respectively. MA stiffness under passive conditions (Kp) was also determined. Surface electromyograms were useful to control agonist and antagonist myoelectrical activities. As expected, maximal isometric (P<0.005) and concentric torques (P<0.05) as well as VImax(p<0.05) were lower in OG compared to YG. SI(MT) values were higher for OG compared to YG (P<0.05) leading to a mean difference of 55%, whereas SI(MA) and Kp were not significantly different between the two groups. Thus, older men were weaker and exhibited higher SI(MT) values. These impairments seem to be principally due to muscular atrophy and modifications in both muscle fibre-type distribution and fibre composition, in ageing. Invariance of SI(MA) and Kp would suggest an adaptive mechanism in articular structures to avoid the continuous integration of the ankle joint stiffness by the central nervous system, what may simplify most daily motor tasks.

Gender differences in human muscle and joint mechanical properties during plantar flexion in old age.

Muscle and joint mechanical properties during plantar flexion were investigated in 13 elderly women (EW) (age range 73-83 years) and 15 elderly men (EM) (age range 74-81 years). Maximal torque, at several angular velocities, was measured to construct torque-velocity relationship. This led to the calculation of an index of maximal shortening velocity (VI(max)) at 10% of maximal isometric torque. Two methods were then used to calculate musculotendinous (quick-release movements) and musculoarticular (sinusoidal perturbations) stiffness. In both cases, stiffness was linearly related to torque, and the slope was defined as a stiffness index (SI): SI(MT) and SI(MA), respectively. Maximal torques as well as VI(max) (p <.05) were lower in EW compared with EM. Furthermore, SI(MT) and SI(MA) values were higher for EW than for EM (p <.05). These results are interpreted in terms of possible differences in the muscle mass, fiber-type distribution, and tendons. They may also have implications for daily motor behavior.

Influence of long-term spaceflight on neuromechanical properties of muscles in humans.

Reflex and elastic properties of the triceps surae (TS) were measured on 12 male cosmonauts 28-40 days before a 3- to 6-mo spaceflight, 2 or 3 days after return (R+2/+3) and a few days later (R+5/+6). H reflexes to electrical stimulations and T reflexes to tendon taps gave the reflex excitability at rest. Under voluntary contractions, reflex excitability was assessed by the stretch reflex, elicited by sinusoidal length perturbations. Stiffness measurements concerned the musculoarticular system in passive conditions and the musculotendinous complex in active conditions. Results indicated 1) no changes (P > 0.05) in H reflexes, whatever the day of test, and 2) increase in T reflexes (P < 0.05) by 57%, despite a decrease (P < 0.05) in musculoarticular stiffness (11%) on R+2/+3. T reflexes decreased (P < 0.05) between R+2/+3 and R+5/+6 (-21%); 3) increase in stretch reflexes (P < 0.05) on R+2/+3 by 31%, whereas it decreased (P < 0.05) between R+2/+3 and R+5/+6 (-29%). Musculotendinous stiffness was increased (P < 0.05) whatever the day of test (25%). Links between changes in reflex and stiffness were also studied by considering individual data. At R+2/+3, correlated changes between T reflexes and musculoarticular stiffness suggested that, besides central adaptive phenomena, musculoarticular structures took part in the reflex adaptation. This mechanical contribution was confirmed when data collected at R+2/+3 and R+5/+6 were used because correlations between changes in stretch reflexes and musculotendinous stiffness were improved. In conclusion, the present study shows that peripheral influences take part in reflex changes in gravitational unloaded muscles, but can only be revealed when central influences are reduced.

Evaluation of musculotendinous stiffness in prepubertal children and adults, taking into account muscle activity.

Musculotendinous (MT) stiffness of the triceps surae (TS) muscle group was quantified in 28 prepubertal children (7-10 yr) by using quick-release movements at different levels of submaximal contractions. Surface electromyograms (EMG) of each part of the TS and of the tibialis anterior were also recorded. A stiffness index, defined as the slope of the angular stiffness-torque relationship (SIMT-Torque), was used to quantify changes in MT stiffness with age. Results showed a significant decrease in SIMT-Torque with age, ranging from 4.02 +/- 0.29 to 2.88 +/- 0.31 rad-1 for the youngest to the oldest children. Because an increase in stiffness with age was expected due to the maturation of elastic tissues, overactivation of the TS was suspected to contribute to the higher SIMT-Torque values found in the youngest children. TS EMG-torque analyses confirmed that neuromuscular efficiency was significantly lower for the 7- or 8-yr-old children compared with 10-yr-old children, notably due to a higher degree of tibialis anterior coactivation found in the youngest children. Thus the stiffness index originally defined as the slope of the angular stiffness-EMG relationship increased significantly with age toward adult values. The results underlined the necessity to take into account the capacities of muscle activation to quantify changes in elastic properties of muscles, when those capacities are suspected to be altered.

Neuromechanical assessment of lidocaine test block in spastic lower limbs.

The objective of this study was to quantify in spastic lower limbs the changes in reflex EMGs and in ankle stiffness after a lidocaine block of the soleus nerve to better understand physiological effects of lidocaine. Twenty patients were prospectively included and assessed before and after lidocaine block of the soleus nerve. We studied clinical and neuromechanical parameters of the triceps surae, including quantification of the maximum Hoffmann's reflex (Hmax) and tendinous reflex (T) normalized to the maximum direct motor response (Mmax), and passive ankle stiffness assessed by sinusoidal length perturbations. All patients whatever the aetiology of spasticity were improved in clinical parameters of spasticity after the block (62% reduction of the Ashworth score, 85% reduction of stretch reflex scores, increased score on the Physicians' Rating Scale). All patients presented a reduction of the Hmax-Mmax ratio (mean reduction of 67%) and the T-Mmax ratio (82%). Ankle stiffness was decreased by an average of 23%. Measured stiffness was correlated with the Ashworth score and the T-Mmax ratio. Relatively greater change in the T reflex than in the H reflex suggests that lidocaine block reduces hyperreflexia not only by interfering with generation of afferent volleys in the injected nerve, but also probably by altering generation of the volleys at the level of muscle spindles in the affected spastic muscles, presumably by blocking the transmission along gamma-efferent fibers.

Influence of overweight on the active and the passive fraction of the plantar flexors series elastic component in prepubertal children.

The influence of overweight, as a precursor to obesity, was analyzed on the elastic properties of the triceps surae. Based on body mass index (BMI), children (9 years ± 4 mo) were classified as control (CON; n = 23; BMI -1SD>Z score<1SD) or overweight (OW; n = 21, BMI 1SD>Z score<3SD) with regard to reference data from the World Health Organization. Musculotendinous (MT) stiffness of the series elastic component (SEC) was determined using quick-release tests to obtain 1) the MT stiffness index from the slope of either linear stiffness-torque (SI(MT-Torque)) or stiffness-EMG (SI(MT-EMG)) relationships and 2) passive stiffness from the intercept point with the ordinate. Finally, the SEC active (α(0)) and passive fractions (C(passive)) were separated as described by Morgan (Am J Physiol, 1977), using alpha-torque (α(0-Torque,) C(passive-Torque)) or alpha-EMG (α(0-EMG,) C(passive-EMG)) relationships. No significant differences in SI(MT-Torque) or α(0-Torque) were observed between OW and CON. SI(MT-EMG) or α(0-EMG) values were significantly different between OW and CON, which indicate an increase in MT stiffness. In all cases, passive stiffness (K(p), C(passive-torque), C(passive-EMG)) was significantly greater in OW but independent of the activation capacities. These results indicate that a weight-related additional loading of the MT structures in OW children caused the MT system to response accordingly to the functional demand, i.e., higher stiffness of the MT structures due to a concomitant increase in the stiffness of the SEC passive and active fraction. This study also reveals that possible differences in the activation capacities influence the determination of MT stiffness of the SEC active fraction.

Influence of muscle activity on musculotendinous stiffness quantification in stunted, prepubertal children.

The quick-release technique to estimate musculotendinous (MT) stiffness has been extensively used over the last years, in both animals and humans, to gain insights in the adaptive process of the series elastic component (SEC). Recently, MT stiffness quantification, i.e., SEC behavior, has been revisited for subjects not able to fully activate their muscles (effects of long-term spaceflight or non-mature muscles). Such a phenomenon can also be encountered in stunted children. So, the aim of the present study was to analyze the effect of stunting on MT stiffness taking into account possible defect in muscle activation. For this study, 20 eutrophic children (EU) with an average age of 9years±4months were compared to 11age matched stunted children (S) evaluated by the height-to-age index. The MT stiffness index was obtained with regard to stiffness-torque and stiffness-soleus EMG relationships. The children of the S group presented a significantly lower Maximal Voluntary Contraction (MVC) in plantar flexion in comparison with children of the EU group (-37.8%). The significantly lower MT stiffness index for S children (-42.6%) was evidenced only when quantified with regard to the stiffness-soleus EMG relationship (66.5±42.8 vs. 38.2±19.9 Nmrad(-1)%(-1)). Possible delay in fiber type differentiation or tendinous structure maturation can account for the lower MT stiffness index in S children. In conclusion, stunting during early childhood delays the differentiation and maturation processes of musculotendinous structures as shown by the lower MT stiffness quantified with regards to muscle activity, also altered for stunted prepubertal children.

Acute effects of incremental inspiratory loads on compartmental chest wall volume and predominant activity frequency of inspiratory muscle.

AIM: This research aims to analyze the acute effect of incremental inspiratory loads on respiratory pattern and on the predominant activity frequency of inspiratory muscle, taking into account differences in gender responses. Optoelectronic Plethysmography was performed during loads in 39 healthy subjects (20 women), placing 89 markers on the thoracic-abdominal wall to obtain total and regional volumes. Surface electromyography (SEMG) was taken simultaneously on the Sternocleidomastoid and Diaphragm muscles, to calculate the predominant muscle activity frequency through wavelet analysis. Inspiratory loads were performed using Threshold(®)with 2 min of breathing at different levels, ranging from a load of 10 cmH(2)O plus 5 cmH(2)O to 40 cmH(2)O or fatigue. RESULTS: Inspiratory Time increased during loads. Total and compartmental volumes increased with different regions, changing at different loads. These changes in volume occur earlier in women (20 cmH(2)O) than in men (30 cmH(2)O). The predominant activity frequency of Sternocleidmastoid muscle decreased at 30 cmH(2)O, while Diaphragm activity decreased at 40 cmH(2)O. CONCLUSION: The acute effects of incremental inspiratory loads are increases of total and regional volumes and inspiratory time. As for muscle activity, the predominant activity frequency declined in Sternocleidomastoid and Diaphragm muscles, but at different loads. Such respiratory and SEMG patterns and gender differences should be considered when clinical interventions are performed.

Influence of training background on the relationships between plantarflexor intrinsic stiffness and overall musculoskeletal stiffness during hopping.

The aim of this study was to characterize the influence of intrinsic musculotendinous and musculoarticular stiffness of plantarflexor muscles on (1) the overall musculoskeletal stiffness and (2) the performance during stretch-shortening cycles-type exercise. The influence of plyometric training background on these relationships was also analyzed. Musculotendinous (SIMT), passive (KP) and active (SIMA) musculoarticular stiffnesses were quantified, using quick-release and sinusoidal perturbation tests, on nine French elite long or triple jumpers (athlete group, AG) and nine control subjects (CG). These ergometric parameters were related with the lower-limb stiffness (Kleg) and the maximal performance (Hmax) measured from a force platform during vertical hopping. AG showed a significantly higher SIMT (2.76 rad(-1)), KP (55.6 N m rad(-1)), Kleg (30.3 kN m(-1)) and Hmax (0.48 m) compared to CG (1.83 rad(-1), 37.8 N m rad(-1), 19.6 kN m(-1) and 0.38 m, respectively). Kleg was not significantly correlated with any of the intrinsic stiffness parameters (SIMT, SIMA or KP). For AG, a strong and negative correlation was observed between Hmax and Kleg. These data indicate that, while elite jumpers presented higher stiffness of both musculotendinous and passive musculoarticular structures, a high compliance of musculoskeletal system was beneficial to optimize the performance in vertical hopping for these athletes. We suggested that neuromuscular strategies were designed to counterbalance this higher intrinsic stiffness to solve the problem of the conflicting requirement of the musculotendinous elements: increase in compliance to enhance the elastic recoil and increase in stiffness for a better force transmission to the periphery.