Achilles tendon and triceps surae muscle properties in athletes.

PURPOSE: The aim of this study was to investigate internal Achilles tendon (AT) displacement, AT shear wave velocity (SWV), and triceps surae (TS) muscle shear modulus in athletes. METHODS: Internal AT displacement was assessed using ultrasound during isometric contraction. Shear wave elastography was used to assess AT SWV (m × s-1) at rest and TS muscle shear modulus (kPa) during passive ankle dorsiflexion. RESULTS: A total of 131 athletes participated in this study. Athletes who had not exercised within two days had greater AT non-uniformity and mean anterior tendon displacement, and lower SWV at the proximal AT measurement site (mean difference [95% CI]: 1.8 mm [0.6-2.9], p = 0.003; 1.6 mm [0.2-2.9], p = 0.021; - 0.9 m × s-1 [- 1.6 to - 0.2], p = 0.014, respectively). Male basketball players had a lower mean AT displacement compared to gymnasts (- 3.7 mm [- 6.9 to - 0.5], p = 0.042), with the difference localised in the anterior half of the tendon (- 5.1 mm [- 9.0 to - 1.1], p = 0.022). Male gymnasts had a smaller absolute difference in medial gastrocnemius-minus-soleus shear modulus than basketball players (59.6 kPa [29.0-90.2], p < 0.001) and track and field athletes (52.7 kPa [19.2-86.3], p = 0.004). Intraclass correlation coefficients of measurements ranged from 0.720 to 0.937 for internal AT displacement, from 0.696 to 0.936 for AT SWE, and from 0.570 to 0.890 for TS muscles. CONCLUSION: This study provides a reliability assessment of muscle and tendon SWV. The relative differences in passive TS muscle shear modulus suggest sport-specific adaptation. Importantly, in healthy individuals, lower AT displacement after exercise may reflect the time required for tendon recovery.

Preoperative Rehabilitation Enhances Mental and Physical Well-Being in Anterior Cruciate Ligament-Injured Individuals: A Mixed Methods Study.

CONTEXT: Rehabilitation after an anterior cruciate ligament injury is recommended to be started soon after the injury. When surgery is required, research supports the delivery of physiotherapy before anterior cruciate ligament reconstruction (prehabilitation) to optimize recovery and positive outcomes. Individuals attending prehabilitation have never been questioned regarding their adherence to prehabilitation, perception of utility in meeting needs, upcoming events, or anticipated recovery goals. DESIGN: Mixed methods cross-sectional study: Methods: 25 individuals before anterior cruciate ligament reconstruction (43% of eligible individuals from 12 clinics during the delivery period) were surveyed on their mindset and recovery expectancies. Semistructured interviews conducted in 9 of 25 participants assessed their lived experience of prehabilitation. RESULTS: Participants reported that preventing a reinjury (96% of responses) and feeling confident during daily activities about their knee (92%) were the higher rating expectations at this stage of their treatment course. Three themes were developed from the interviews and analyses. (1) Participants reported that prehabilitation was a period full of challenges with memories of the injury and uncertainties. (2) They viewed prehabilitation as a step to move forward by finding support and self-motivating. (3) They believed that prehabilitation would have positive impacts on the treatment outcomes. Participants were confident that prehabilitation would accelerate the recovery of muscle volume (88%) and strength (84%). CONCLUSION: Participants had positive experiences of prehabilitation, aligning with the findings on functional outcomes in the existing literature on prehabilitation.

In vivo assessment of the elastic properties of the external anal sphincter in term pregnant women using shear wave elastography.

INTRODUCTION AND HYPOTHESIS: The objective was to assess the intraobserver intersession and interobserver intrasession reliability of shear wave elastography applied to the external anal sphincter in term pregnant women. METHODS: This prospective study involved nulliparous pregnant women at 37 weeks or more with two visits (V1: one observer; V2 two observers) planned within a 12-h to 7-day interval. Measurements were performed using an Aixplorer V12® device with an SL 18-5 linear probe using a transperineal approach, allowing a measurement of the shear modulus (SM) in kPa. Measures were performed at rest, Valsalva maneuver, and maximal contraction. Reliability was assessed using the intraclass correlation coefficient (ICC). The study was approved by an ethics committee (ID RCB: 2020-A00764-65). RESULTS: A total of 37 women were included. Intraobserver reliability was excellent at rest (ICC = 0.91 [0.84-0.95) and good during the Valsalva maneuver (ICC = 0.83 [0.72-0.90]) and contraction (ICC = 0.85 [0.75-0.91]). Interobserver reliability was good at rest (ICC = 0.79 [0.66-0.87]) and during Valsalva (ICC = 0.84 [0.73-0.90]), but moderate during contraction (ICC = 0.70 [0.53-0.82]). CONCLUSIONS: Shear wave elastography is a reliable tool for assessing the elastic properties of the external anal sphincter in term pregnant women.

Mild to moderate damage in knee extensor muscles accumulates after two bouts of maximal eccentric contractions.

PURPOSE: This study aimed to determine whether mild to moderate muscle damage accumulates on the knee extensors after two bouts of maximal eccentric contractions performed over two consecutive days. METHODS: Thirty participants performed an initial bout of maximal eccentric contractions of knee extensors during the first day of the protocol (ECC1). Then, they were separated in two groups. The Experimental (EXP) group repeated the eccentric bout 24 h later (ECC2) while the Control (CON) group did not. Indirect markers of muscle damage (i.e., strength loss, muscle soreness, and shear modulus) were measured to quantify the amount of muscle damage and its time course. RESULTS: Two days after the initial eccentric session, participants from EXP had a higher strength deficit (- 14.5 ± 10.6%) than CON (- 6.6 ± 8.7%) (P = 0.017, d = 0.9). Although both groups exhibited an increase in knee extensors shear modulus after ECC1, we found a significant increase in muscle shear modulus (+ 13.3 ± 22.7%; P < 0.01; d = 0.5) after ECC2 for the EXP group, despite the presence of mild to moderate muscle damage (i.e., strength deficit about 16%). CONCLUSION: Although the markers of muscle damage used in the current study were indirect, they suggest that the repetition of two bouts of maximal eccentric contractions with 24 h apart induces additional muscle damage in the knee extensors in presence of mild to moderate muscle damage.

In vivo measurement of the elastic properties of pelvic floor muscles in pregnancy using shear wave elastography.

OBJECTIVE: We aimed to investigate changes in the elastic properties of levator ani muscle (LAM) and external anal sphincter (EAS) during pregnancy using shear wave elastography (SWE). Our secondary objective was to examine the association between the elastic properties of pelvic floor muscles (PFM) and perineal tears at childbirth. METHODS: This was a prospective monocentric study, including nulliparous women. Three visits were planned (14-18, 24-28, and 34-38 weeks) with a SWE assessment of the LAM and EAS at rest and during Valsalva maneuver. Then, we collected data about the delivery's characteristics. Assessments were performed using an Aixplorer V12® device (SL 18-5 linear probe) using a transperineal approach, reporting the shear modulus in kPa. We looked for changes in PFM's elastic properties during pregnancy using one-way ANOVA for repeated measures. We compared the mean shear modulus in late pregnancy for each muscle and condition between women with an intact perineum at delivery and those with a perineal tear using Student's t test. RESULTS: Forty-seven women were considered. Forty-five women had vaginal delivery of which 38 (84.4%) had perineal tears. We did not report any significant changes in the elastic properties of PFM during pregnancy. Women with an intact perineum at delivery had a stiffer EAS at Valsalva maneuver in late pregnancy (27.0 kPa vs. 18.2 kPa; p < 0.005). CONCLUSIONS: There were no significant changes in the elastic properties of the PFM in pregnancy. Stiffer EAS in late pregnancy appears to be associated with a lower incidence of perineal tears.

Handedness is associated with less common input to spinal motor neurons innervating different hand muscles.

Whether the neural control of manual behaviors differs between the dominant and nondominant hand is poorly understood. This study aimed to determine whether the level of common synaptic input to motor neurons innervating the same or different muscles differs between the dominant and the nondominant hand. Seventeen participants performed two motor tasks with distinct mechanical requirements: an isometric pinch and an isometric rotation of a pinched dial. Each task was performed at 30% of maximum effort and was repeated with the dominant and nondominant hand. Motor units were identified from two intrinsic (flexor digitorum interosseous and thenar) and one extrinsic muscle (flexor digitorum superficialis) from high-density surface electromyography recordings. Two complementary approaches were used to estimate common synaptic inputs. First, we calculated the coherence between groups of motor neurons from the same and from different muscles. Then, we estimated the common input for all pairs of motor neurons by correlating the low-frequency oscillations of their discharge rate. Both analyses led to the same conclusion, indicating less common synaptic input between motor neurons innervating different muscles in the dominant hand than in the nondominant hand, which was only observed during the isometric rotation task. No between-side differences in common input were observed between motor neurons of the same muscle. This lower level of common input could confer higher flexibility in the recruitment of motor units, and therefore, in mechanical outputs. Whether this difference between the dominant and nondominant arm is the cause or the consequence of handedness remains to be determined.NEW & NOTEWORTHY How the neural control of manual behaviors differs between the dominant and nondominant hand remains poorly understood. This study shows that there is less common synaptic input between motor neurons innervating different muscles in the dominant than in the nondominant hand during isometric rotation tasks. This lower level of common input could confer higher flexibility in the recruitment of motor units.

Analysis of elite road-cycling sprints in relation to maximal power-velocity-endurance profile: a longitudinal one-case study.

The aims of the present study were to characterize the mechanical output of final road sprints of an elite sprinter during international competitions in relation to his power-velocity-endurance characteristics and to investigate the relationship between this sprint performance and the power produced during preceding phases of the race. The sprinter performed a set of short and long sprints (5 to 15-s) on a cycle ergometer to determine his maximal power-velocity-endurance profile. Based on eleven races, the distribution of power throughout each race, peak and mean power (Ppeak and Pmean ) and associated pedaling rates (vPpeak and vPmean ) during the final sprint were analyzed. The power-velocity-endurance profile of the sprinter indicated that his theoeretical mean maximal power and corresponding optimal pedaling rate ranged from 20.0 W.kg-1 (124 rpm) for a 1-s sprint to 15.0 W.kg-1 (109 rpm) for 20 s. Race data showed that final road sprints were mainly performed on the ascending limb of the power-velocity relationship (vPpeak , 104 ± 8 and vPmean , 101 ± 8 rpm). Additionally, Ppeak and Pmean were lower than the theoretical maximal power determined from the power-velocity-endurance profile (9.9 ± 7.0% and 10.6 ± 9.8%, respectively), which highlighted a significant state of fatigue induced by the race. Finally, sprint power exhibited a high variability between races and was strongly related to the level of power produced during the last minute before the sprint. These findings show the importance of considering both the power-velocity-endurance qualities and the power demand of the last lead-up phase before the sprint in order to optimize final sprint performance.

Hamstring muscle activation strategies during eccentric contractions are related to the distribution of muscle damage.

Large inter-individual variability of activation strategies is observed during hamstring strengthening exercises but their consequences remain unexplored. The objective of this study was to determine whether individual activation strategies are related to the distribution of damage across the hamstring muscle heads semimembranosus (SM), semitendinosus (ST), and biceps femoris (BF) after eccentric contractions. 24 participants performed 5 sets of 15 maximal eccentric contractions of knee flexors on a dynamometer, while activation of each muscle head was assessed using surface electromyography. Knee flexion maximal isometric strength was assessed before exercise and 48 h afterward. Shear modulus was measured using shear wave elastography before exercise and 30 min afterward to quantify the distribution of damage across the hamstring muscle heads. At 48 h, maximal knee flexion torque had decreased by 15.9% ± 16.9% (p < 0.001). Although no differences between activation ratios of each muscle were found during the eccentric exercise (all p > 0.364), we reported a heterogeneous distribution of damage, with a larger change in shear modulus of ST/Hams than SM/Hams (+70.8%, p < 0.001) or BF/Hams (+50.3%, p < 0.001). A large correlation was found between the distribution of activation and the distribution of damage for ST/Hams (r = 0.69; p < 001). This study provides evidence that the distribution of activation during maximal eccentric contractions has mechanical consequences for synergist muscles. Further studies are needed to understand whether individual activation strategies influence the distribution of structural adaptations after a training program.

A Gel Pad Designed to Measure Muscle Volume Using Freehand 3-Dimensional Ultrasonography.

We developed an innovative gel pad that covers the entire lower leg to remove artifacts due to the pressure of the transducer in freehand 3-dimensional ultrasonography. In comparison to the reference method in water, this study showed that this new method was valid (bias, 3.4 mL; limit of agreement, 7.7 mL for a volume of ≈220 mL) and reliable (coefficient of variation, <1.1%) for the measurement of gastrocnemius medialis muscle volume. Considering that it is easier to use than the water tank technique, it has much promise for volumetric measurement of many muscles.

Hamstring muscle elasticity differs in specialized high-performance athletes.

The effect of training on hamstring flexibility has been widely assessed through the measurement of the maximal range of motion or passive torque. However, these global measures do not provide direct information on the passive muscle mechanical properties of individual muscle. This characterization is crucial to better understand the effect of interventions as selective adaptations may occur among synergist muscles. Taking advantage of shear wave elastography, we aimed to determine whether elite sport athletes exhibit different passive shear modulus of hamstring heads compared to controls. Passive shear modulus was measured on semitendinosus (ST), semimembranosus (SM), and biceps femoris (BF) using shear wave elastography with the knee flexed at 60° and 90°, and 90° of hip flexion. A total of 97 elite athletes from various sports including running sprint, figure skating, fencing, field hockey, taekwondo, basketball, and soccer and 12 controls were evaluated. The shear modulus measured at 60° of knee flexion was lower in SM for figure skating (P < .001; d = 1.8), taekwondo (P < .001; d = 2.1), fencing (P = .024; d = 1.0), and soccer (P = .011; d = 0.9) compared to controls, while no difference was found for athletic sprinters, field hockey, and basketball players. Shear modulus of the BF and ST muscle was not significantly different between controls and elite athletes, regardless of the sport specialization (all P values = 1). We provide evidence that the shear modulus of the SM is altered in athletes involved in elite sport practice performed over large range of motion and/or including substantial stretching program in training content (taekwondo, figure skating, fencing, and soccer).

Surface properties affect the interplay between fascicles and tendinous tissues during landing.

PURPOSE: Muscle-tendon units are forcefully stretched during rapid deceleration events such as landing. Consequently, tendons act as shock absorbers by buffering the negative work produced by muscle fascicles likely to prevent muscle damage. Landing surface properties can also modulate the amount of energy dissipated by the body, potentially effecting injury risk. This study aimed to evaluate the influence of three different surfaces on the muscle-tendon interactions of gastrocnemius medialis (GM), and vastus lateralis (VL) during single- and double-leg landings from 50 cm. METHODS: Ultrasound images, muscle activity and joint kinematics were collected for 12 participants. Surface testing was also performed, revealing large differences in mechanical behavior. RESULTS: During single-leg landing, stiffer surfaces increased VL fascicle lengthening and velocity, and muscle activity independent of joint kinematics while GM length changes showed no difference between surfaces. Double-leg landing resulted in similar fascicle and tendon behavior despite greater knee flexion angles on stiffer surfaces. CONCLUSION: This demonstrates that VL fascicle lengthening is greater when the surface stiffness increases, when performing single-leg landing. This is due to the combination of limited knee joint flexion and lower surface absorption ability which resulted in greater mechanical demand mainly withstood by fascicles. GM muscle-tendon interactions remain similar between landing surfaces and types. Together, this suggests that surface damping properties primarily affect the VL muscle-tendon unit with a potentially higher risk of injury as a result of increased surface stiffness when performing single-leg landing tasks.

Shear Wave Elastographic Investigation of the Immediate Effects of Slump Neurodynamics in People With Sciatica.

OBJECTIVES: Neurodynamic techniques are often used to treat people with sciatica pain, but their mechanical effects on the sciatic nerve are unknown. Shear wave elastography (SWE) has been shown to effectively estimate the stiffness of peripheral nerves in real time. The aim of this study was to use SWE to assess the effects of slump neurodynamics in the sciatic stiffness of people with sciatica. METHODS: Sixteen participants volunteered for this study. The sciatic stiffness of 8 patients with unilateral chronic sciatica and 8 healthy control participants was measured by SWE, with the participants in a prone position and during a dynamic condition (ie, ankle dorsiflexion). These measurements were performed before and immediately after the neurodynamic intervention, which consisted of a static slump position applied to the symptomatic limb of the patients with sciatica and in a randomly chosen limb of the healthy participants. RESULTS: The 8 patients with sciatica included 6 male and 2 female patients, and the 8 healthy control participants included 5 male and 3 female volunteers. Slump neurodynamics resulted in an immediate decrease in the sciatic nerve stiffness of the symptomatic limb in people with sciatica by 16.1% (effect size = 0.65; P = .019). The intervention showed no significant changes in the sciatic nerve stiffness of the healthy participants (effect size = 0.05; P = .754). CONCLUSIONS: Slump neurodynamics have the potential of decreasing the sciatic nerve stiffness in people with sciatica, and this effect can be quantified by SWE, which may provide valuable information for health professionals.

In vivo assessment of the elastic properties of women's pelvic floor during pregnancy using shear wave elastography: design and protocol of the ELASTOPELV study.

BACKGROUND: Animal studies have reported an increase in pelvic floor muscle stiffness during pregnancy, which might be a protective process against perineal trauma at delivery. Our main objective is to describe the changes in the elastic properties of the pelvic floor muscles (levator ani, external anal sphincter) during human pregnancy using shear wave elastography (SWE) technology. Secondary objectives are as follows: i) to look for specific changes of the pelvic floor muscles compared to peripheral muscles; ii) to determine whether an association between the elastic properties of the levator ani and perineal clinical and B-mode ultrasound measures exists; and iii) to provide explorative data about an association between pelvic floor muscle characteristics and the risk of perineal tears. METHODS: Our prospective monocentric study will involve three visits (14-18, 24-28, and 34-38 weeks of pregnancy) and include nulliparous women older than 18 years, with a normal pregnancy and a body mass index (BMI) lower than 35 kg.m- 2. Each visit will consist of a clinical pelvic floor assessment (using the Pelvic Organ Prolapse Quantification system), an ultrasound perineal measure of the anteroposterior hiatal diameter and SWE assessment of the levator ani and the external anal sphincter muscles (at rest, during the Valsalva maneuver and during pelvic floor contraction), and SWE assessment of both the biceps brachii and the gastrocnemius medialis (at rest, extension and contraction). We will collect data about the mode of delivery and the occurrence of perineal tears. We will investigate changes in continuous variables collected using the Friedman test. We will look for an association between the elastic properties of the levator ani muscle and clinical / ultrasound measures using a Spearman test at each trimester. We will investigate the association between the elastic properties of the pelvic floor muscles and perineal tear occurrence using a multivariate analysis with logistic regression. DISCUSSION: This study will provide original in vivo human data about the biomechanical changes of pregnant women's pelvic floor. The results may lead to an individualized risk assessment of perineal trauma at childbirth. TRIAL REGISTRATION: This study was registered on https://clinicaltrials.gov on July 26, 2018 (NCT03602196).

In vivo assessment of the levator ani muscles using shear wave elastography: a feasibility study in women.

INTRODUCTION AND HYPOTHESIS: We hypothesized that shear wave elastography (SWE) technology might be useful for assessing the elastic properties of the pelvic floor in women. Our primary objective was to evaluate the feasibility of assessing the levator ani muscles using SWE in women. Our secondary aim was to investigate the changes in their elastic properties from rest to Valsalva maneuver. METHODS: During this prospective feasibility study in nonpregnant female volunteers, we collected data on participant age, body mass index (BMI), parity, and time since the delivery. The levator ani muscles of each participant were assessed using SWE technology at rest and during a Valsalva maneuver by measuring the shear modulus (in kilopascals). We then assessed the changes in the shear modulus at rest and during the Valsalva maneuver using a Wilcoxon test. RESULTS: Twelve parous women participated in this study. The mean time since the last delivery was 14 months, the mean age was 31 years, and mean BMI was 28 kg.m-2. All the assessments performed at rest were successfully completed, but we encountered two failures during the Valsalva maneuver. The mean shear modulus increased by a factor of more than 2 from rest to the Valsalva maneuver for both the right (16.0 vs 35.4 kPa) and left side (17.1 vs 37.6 kPa). CONCLUSIONS: An assessment of the elastic properties of the levator ani muscles is feasible for nonpregnant women. The reproducibility of the technique and its application in pregnant women and women with pelvic floor disorders must be investigated.

Interactions between fascicles and tendinous tissues in gastrocnemius medialis and vastus lateralis during drop landing.

Animal tendons have been shown to act as shock absorbers to protect muscle fascicles from exercise-induced damage during landing tasks. Meanwhile, the contribution of tendinous tissues to damping activities such as landing has been less explored in humans. The aim of this study was to analyze in vivo fascicle-tendon interactions during drop landing to better understand their role in energy dissipation. Ultrafast ultrasound images of the gastrocnemius medialis (GM) and vastus lateralis (VL), lower limb electromyographic activity, 2-D kinematics, and ground reaction forces were collected from twelve participants during single- and double-leg drop landings from various heights. For both muscles, length changes were higher in tendinous tissues than in fascicles, demonstrating their key role in protecting fascicles from rapid active lengthening. Increasing landing height increased lengthening and peak lengthening velocity of VL fascicle and GM architectural gear ratio, whereas GM fascicle displayed similar length and velocity patterns. Single-leg landing lengthens the tendinous tissues of GM and, to a greater degree, VL muscles, without affecting the fascicles. These findings demonstrate the adjustment in fascicle-tendon interactions to withstand mechanical demand through the tendon buffer action and fascicle rotation. The higher VL fascicle contribution to negative work as the drop height increases would suggest muscle-specific damping responses during drop landing. This can originate from the distal-to-proximal sequence of joint kinetics, from differences in muscle and tendon functions (one- and two-joint muscles), architectural and morphological properties (eg, tendon stiffness), as well as from the muscle activity of the GM and VL muscles.

Is reaction time altered by mental or physical exertion?

PURPOSE: Reaction time, classically divided into premotor time and electromechanical delay (EMD), can be determinant in daily life or sport situations. While some previous studies reported a negative impact of both muscle and mental fatigue on reaction time, the respective contributions of premotor time and EMD to the changes of reaction time remains unclear. The aim of the study was, therefore, to assess the effects of both muscle and mental effort on reaction time and its components. METHODS: Thirteen subjects performed three conditions (mental effort condition, i.e., 14 min of a mathematical cognitive task; muscle effort condition, i.e., intermittent contractions of the biceps brachii; control condition, i.e., watching a documentary). Before and after each condition, reaction time, premotor time and EMD were measured during voluntary contractions of the biceps brachii. EMD was also measured during evoked contractions of the biceps brachii to separate the parts due to the onset of muscle fascicle motion and the onset of force production. RESULTS: Reaction time and premotor time remained stable regardless of the condition considered (all P values > 0.05). EMD increased only after the muscle effort condition (+ 25% during voluntary contractions, no significant; + 17% during evoked contractions, P = 0.001), mainly due to an increase in the passive part of the series elastic component. CONCLUSION: Our study showed that neither mental nor muscle effort has a negative effect on simple reaction time during voluntary contractions.

Noninvasive Measurement of Sciatic Nerve Stiffness in Patients With Chronic Low Back Related Leg Pain Using Shear Wave Elastography.

OBJECTIVES: The purpose of this study was to determine whether sciatic nerve stiffness is altered in people with chronic low back-related leg pain by using shear wave elastography. METHODS: In this cross-sectional study, the sciatic nerve shear wave velocity (ie, an index of stiffness) was measured in both legs of 16 participants (8 with unilateral low back-related leg pain and 8 healthy controls). Sciatic stiffness was measured during a passive ankle dorsiflexion motion performed at 2°/s in an isokinetic dynamometer. The ankle range of motion and passive torque, as well as muscle activity, were also measured. RESULTS: In people with low back-related leg pain, the affected limb showed higher sciatic nerve stiffness compared to the unaffected limb (+11.3%; P = .05). However, no differences were observed between the unaffected limb of people with low back-related leg pain and the healthy controls (P = .34). CONCLUSIONS: People with chronic low back-related leg pain have interlimb differences in sciatic nerve stiffness, as measured by a safe and noninvasive method: shear wave elastography. The changes found may be related to alterations in nerve mechanical properties, which should be confirmed by future investigations.

Tissue biomechanical behavior should be considered in the risk assessment of perineal trauma at childbirth.

Perineal trauma at childbirth is associated with strong negative impacts on a woman's health but remains unpredictable. Pregnancy induces several changes in biomechanical behavior in humans as in animals, namely, an increase in ligamentous laxity and an increase in vaginal distensibility. Pelvic floor muscles in rats are reported to exhibit specific behaviors during pregnancy. Increases in both stiffness and the number of sarcomeres in series are observed and might process that protect against perineal trauma at childbirth. Some data in humans have shown that the risk of perineal trauma is highly linked to the intrinsic characteristics of the tissue, suggesting the potential benefit of incorporating intrinsic biomechanical characteristics in the risk prediction for perineal trauma. Shear wave elastography might be a useful noninvasive tool to investigate the elastic properties of these tissues in pregnant women in vivo, with the goal of implementing these properties as a predictive strategy.

Neuromechanical coupling within the human triceps surae and its consequence on individual force-sharing strategies.

Little is known about the factors that influence the coordination of synergist muscles that act across the same joint, even during single-joint isometric tasks. The overall aim of this study was to determine the nature of the relationship between the distribution of activation and the distribution of force-generating capacity among the three heads of the triceps surae [soleus (SOL), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL)]. Twenty volunteers performed isometric plantarflexions, during which the activation of GM, GL and SOL was estimated using electromyography (EMG). Functional muscle physiological cross-sectional area (PCSA) was estimated using imaging techniques and was considered as an index of muscle force-generating capacity. The distribution of activation and PCSA among the three muscles varied greatly between participants. A significant positive correlation between the distribution of activation and the distribution of PCSA was observed when considering the two bi-articular muscles at intensities ≤50% of the maximal contraction (0.51