Muscle-tendon Unit Research Articles

Ultrasound and surface electromyography analyses reveal an intensity dependent active stretch-shortening cycle of the vastus lateralis muscle during ergometer rowing

ABSTRACT A rowing cycle is characterised by a stretch-shortening cycle (SSC) at the quadriceps femoris muscle-tendon unit (MTU) level. However, due to the associated decoupling between MTU and muscle fascicle length changes, it remains unclear whether a rowing cycle causes active stretch at the muscle level. Fifteen young, sub-elite, male rowers (19.5 ± 1.6 yr; 1.94 ± 0.06 m; 91.9 ± 5.4 kg; rowing experience: 7.5 ± 2.8 yr) performed randomised 60-s rowing intervals using a traditional style at a low (LiR) and high intensity (HiR) and a micro-pause style at a low intensity (MpR). Muscle activity, knee joint angles, and muscle fascicle length changes from the left-sided vastus lateralis (VL) muscle were quantified using surface electromyography, inertial measurement units, and B-mode ultrasound imaging, respectively. All rowing conditions showed active fascicle stretch during late knee flexion (p≤0.001, standardised mean difference (SMD) ≥0.72) and subsequent active fascicle shortening throughout knee extension. Active fascicle stretch duration, amplitude and velocity (rANOVA: p≤0.001, ηp 2 = 0.49) were not significantly different (p≥0.174; SMD≤0.26) between LiR and MpR, but were significantly increased during HiR (p≤0.001; SMD≥0.70). The percentage of rowing cycles that involved active fascicle stretch (rANOVA: p≤0.001, ηp 2 = 0.95; post-hoc: p≤0.001, SMD≥0.87) was also significantly higher for HiR (98.3 ±12.9%) compared with both LiR (65.0 ± 48.1%) and MpR (68.3 ± 46.9%). In conclusion, rowing involves SSC at the VL muscle fascicle level, but the amount of active stretch differs between rowing intensities, with the longest, largest, and fastest active stretch occurring during HiR. SSC-based mechanisms may therefore contribute more to rowing performance during HiR than LiR or MpR. Highlights Surface electromyography and ultrasound imaging revealed stretch-shortening cycles (SSCs) of the vastus lateralis muscle fascicles during rowing Increased active fascicle stretch duration, amplitude and velocity from low- to high-intensity rowing indicate that SSC-based mechanisms likely contribute more to performance during high-intensity rowing The SSC within the vastus lateralis muscle was independent of the rowing style at the same low rowing intensity

Medial gastrocnemius muscle–tendon unit ratios of young females and males

A muscle’s contractile element length relative to its muscle–tendon unit (MTU) length is a fundamental design feature affecting MTU function, with high (0.9) or low ratios (0.1) favouring either rapid or economical force production, respectively. Despite the importance for MTU function, little in vivo work has been done to understand contractile element-MTU length ratio variability between individuals and sexes. We therefore compared the medial gastrocnemius (MG) MTU ratios of thirteen females and eighteen males, and explored whether individual ratios could be predicted based on anatomical features.At the presumed tendon slack length ankle joint angle, lengths of MG’s MTU, Achilles tendon, muscle belly and its muscle fascicles were measured from B-mode ultrasound images. Contractile element length was represented by the in-series muscle fascicle length (FL) and was calculated by multiplying FL by the cosine of fascicle angle.The mean ± standard deviation in-series FL-MTU length ratio was 0.09 ± 0.02 and ranged from 0.06 to 0.11, whereas the muscle belly length-MTU length ratio was 0.54 ± 0.38 and ranged from 0.47 to 0.60. Neither ratio was significantly different between females and males (p ≥ 0.116). In-series FL was not significantly correlated with MTU length (r = -0.115, p =.538), muscle belly length (r = 0.05, p =.788), or shank length (r = 0.169, p =.364), but MTU length was significantly correlated with muscle belly length (r = 0.641, p <.001), and shank length (r = 0.575, p =.001).A low in-series FL-MTU length ratio suggests that the MG of young, healthy individuals is specialised for energy-efficient stretch–shortening cycles. These findings provide useful inputs for the MTU actuator design of Hill-type models.

The Effect Of Static Stretching Calf Muscle Tendon Unit With Theraband Toward Range Of Motion Dorsi Flexion Ankle On Elderly Person

Background: Aging is a natural process. One problem that often occurs in the elderly is a decrease in the range of motion in the calf muscle tendons, which can interfere with their physical activities. Purpose: Knowing the effect of static stretching calf muscle tendon unit with theraband toward range of motion dorsi flexion ankle on elderly person. Method: Analytical study with a control group design. The sampling technique uses purposive sampling, with 60 respondents: 30 as the treatment group and 30 as the control group. A goniometer measured ROM. Static stretching can be done using theraband. Result: Dependent T-Test (p &lt; 0.05) It means that there is an effect on the treatment and control groups. Independent T-Test (p &lt; 0.05) it means a significant difference between the treatment and control groups. Conclusion: The research results showed a positive influence.

Fused ultrasound and electromyography-driven neuromuscular model to improve plantarflexion moment prediction across walking speeds

BackgroundImproving the prediction ability of a human-machine interface (HMI) is critical to accomplish a bio-inspired or model-based control strategy for rehabilitation interventions, which are of increased interest to assist limb function post neurological injuries. A fundamental role of the HMI is to accurately predict human intent by mapping signals from a mechanical sensor or surface electromyography (sEMG) sensor. These sensors are limited to measuring the resulting limb force or movement or the neural signal evoking the force. As the intermediate mapping in the HMI also depends on muscle contractility, a motivation exists to include architectural features of the muscle as surrogates of dynamic muscle movement, thus further improving the HMI’s prediction accuracy.ObjectiveThe purpose of this study is to investigate a non-invasive sEMG and ultrasound (US) imaging-driven Hill-type neuromuscular model (HNM) for net ankle joint plantarflexion moment prediction. We hypothesize that the fusion of signals from sEMG and US imaging results in a more accurate net plantarflexion moment prediction than sole sEMG or US imaging.MethodsTen young non-disabled participants walked on a treadmill at speeds of 0.50, 0.75, 1.00, 1.25, and 1.50 m/s. The proposed HNM consists of two muscle-tendon units. The muscle activation for each unit was calculated as a weighted summation of the normalized sEMG signal and normalized muscle thickness signal from US imaging. The HNM calibration was performed under both single-speed mode and inter-speed mode, and then the calibrated HNM was validated across all walking speeds.ResultsOn average, the normalized moment prediction root mean square error was reduced by 14.58 % (p=0.012) and 36.79 % (p<0.001) with the proposed HNM when compared to sEMG-driven and US imaging-driven HNMs, respectively. Also, the calibrated models with data from the inter-speed mode were more robust than those from single-speed modes for the moment prediction.ConclusionsThe proposed sEMG-US imaging-driven HNM can significantly improve the net plantarflexion moment prediction accuracy across multiple walking speeds. The findings imply that the proposed HNM can be potentially used in bio-inspired control strategies for rehabilitative devices due to its superior prediction.

Effects of simulated reduced gravity and walking speed on ankle, knee, and hip quasi-stiffness in overground walking.

Quasi-stiffness characterizes the dynamics of a joint in specific sections of stance-phase and is used in the design of wearable devices to assist walking. We sought to investigate the effect of simulated reduced gravity and walking speed on quasi-stiffness of the hip, knee, and ankle in overground walking. 12 participants walked at 0.4, 0.8, 1.2, and 1.6 m/s in 1, 0.76, 0.54, and 0.31 gravity. We defined 11 delimiting points in stance phase (4 each for the ankle and hip, 3 for the knee) and calculated the quasi-stiffness for 4 phases for both the hip and ankle, and 2 phases for the knee. The R2 value quantified the suitability of the quasi-stiffness models. We found gravity level had a significant effect on 6 phases of quasi-stiffness, while speed significantly affected the quasi-stiffness in 5 phases. We concluded that the intrinsic muscle-tendon unit stiffness was the biggest determinant of quasi-stiffness. Speed had a significant effect on the R2 of all phases of quasi-stiffness. Slow walking (0.4 m/s) was the least accurately modelled walking speed. Our findings showed adaptions in gait strategy when relative power and strength of the joints were increased in low gravity, which has implications for prosthesis and exoskeleton design.

2021 ISB World Athletics Award for Biomechanics: The Subtalar Joint Maintains "Spring-Like" Function While Running in Footwear That Perturbs Foot Pronation.

Humans have the remarkable ability to run over variable terrains. During locomotion, however, humans are unstable in the mediolateral direction and this instability must be controlled actively-a goal that could be achieved in more ways than one. Walking research indicates that the subtalar joint absorbs energy in early stance and returns it in late stance, an attribute that is credited to the tibialis posterior muscle-tendon unit. The purpose of this study was to determine how humans (n = 11) adapt to mediolateral perturbations induced by custom-made 3D-printed "footwear" that either enhanced or reduced pronation of the subtalar joint (modeled as motion in 3 planes) while running (3m/s). In all conditions, the subtalar joint absorbed energy (ie,negative mechanical work) in early stance followed by an immediate return of energy (ie,positive mechanical work) in late stance, demonstrating a "spring-like" behavior. These effects increased and decreased in footwear conditions that enhanced or reduced pronation (P ≤ .05), respectively. Of the recorded muscles, the tibialis posterior (P ≤ .05) appeared to actively change its activation in concert with the changes in joint energetics. We suggest that the "spring-like" behavior of the subtalar joint may be an inherent function that enables the lower limb to respond to mediolateral instabilities during running.

Validity and reliability of a novel 3D ultrasound approach to assess static lengths and the lengthening behavior of the gastrocnemius medialis muscle and the Achilles tendon in vivo

PurposeHuman muscle–tendon units (MTUs) are highly plastic and undergo changes in response to specific diseases and disorders. To investigate the pathological changes and the effects of therapeutic treatments, the use of valid and reliable examination methods is of crucial importance. Therefore, in this study, a simple 3D ultrasound approach was developed and evaluated with regard to: (1) its validity in comparison to magnetic resonance imaging (MRI) for the assessment of the gastrocnemius medialis (GM) MTU, muscle belly, and Achilles tendon lengths; and (2) its reliability for static and dynamic length measurements.MethodsSixteen participants were included in the study. To evaluate the validity and reliability of the novel 3D ultrasound approach, two ultrasound measurement sessions and one MRI assessment were performed. By combining 2D ultrasound and 3D motion capture, the tissue lengths were assessed at a fixed ankle joint position and compared to the MRI measurements using Bland–Altman plots. The intra-rater and inter-rater reliability for the static and dynamic length assessments was determined using the coefficient of variation, standard error of measurement (SEM), minimal detectable change (MDC95), and intraclass correlation coefficient (ICC).ResultsThe 3D ultrasound approach slightly underestimated the length when compared with MRI by 0.7%, 1.5%, and 1.1% for the GM muscle belly, Achilles tendon, and MTU, respectively. The approach showed excellent intra-rater as well as inter-rater reliability, with high ICC (≥ 0.94), small SEM (≤ 1.3 mm), and good MDC95 (≤ 3.6 mm) values, with even better reliability found for the static length measurements.ConclusionThe proposed 3D ultrasound approach was found to be valid and reliable for the assessment of the GM MTU, muscle belly, and Achilles tendon lengths, as well as the tissue lengthening behavior, confirming its potential as a useful tool for investigating the effects of training interventions or therapeutic treatments (e.g., surgery or conservative treatments such as stretching and orthotics).Level of evidenceLevel II.

Altered countermovement jump force profile and muscle-tendon unit kinematics following combined ballistic training.

Combined heavy‐ and light‐load ballistic training is often employed in high‐performance sport to improve athletic performance and is accompanied by adaptations in muscle architecture. However, little is known about how training affects muscle‐tendon unit (MTU) kinematics during the execution of a sport‐specific skill (e.g., jumping), which could improve our understanding of how training improves athletic performance. The aim of this study was to investigate vastus lateralis (VL) MTU kinematics during a countermovement jump (CMJ) following combined ballistic training. Eighteen young, healthy males completed a 10‐week program consisting of weightlifting derivatives, plyometrics, and ballistic tasks under a range of loads. Ultrasonography of VL and force plate measurements during a CMJ were taken at baseline, mid‐test, and post‐test. The training program improved CMJ height by 11 ± 13%. During the CMJ, VL's MTU and series elastic element (SEE) length changes and velocities increased from baseline to post‐test, but VL's fascicle length change and velocity did not significantly change. It is speculated that altered lower limb coordination and increased force output of the lower limb muscles during the CMJ allowed more energy to be stored within VL's SEE. This may have contributed to enhanced VL MTU work during the propulsion phase and an improved CMJ performance following combined ballistic training.

Triceps surae muscle force potential and force demand shift with altering stride frequency in running.

While it is well recognized that the preferred stride frequency (PSF) in running closely corresponds to the metabolically optimal frequency, the underlying mechanisms are still unclear. Changes in joint kinematics when altering stride frequency will affect the muscle-tendon unit lengths and potentially the efficiency of muscles crossing these joints. Here, we investigated how fascicle kinematics and forces of the triceps surae muscle, a highly energy consuming muscle, are affected when running at different stride frequencies. Twelve runners ran on a force measuring treadmill, adopting five different frequencies (PSF; PSF ± 8%; PSF ± 15%), while we measured joint kinematics, whole-body energy expenditure, triceps surae muscle activity, and soleus (SOL; N=10) and gastrocnemius medialis (GM; N=12) fascicle kinematics. In addition, we used dynamic optimization to estimate SOL and GM muscle forces. We found that SOL and GM mean muscle fascicle length during stance followed an inverted U-relationship with the longest fascicle lengths occurring at PSF. Fascicle lengths were shortest at frequencies lower than PSF. In addition, average SOL force was greater at PSF-15% compared with PSF. Overall, our results suggest that reduced SOL and GM muscle fascicle lengths, associated with reduced muscle force potential, together with greater SOL force demand, contribute to the increased whole-body energy expenditure when running at lower than PSF. At higher stride frequencies, triceps surae muscle kinematics and force production were less affected suggesting that increased energy expenditure is rather related to higher cost of leg swing and greater cost of force production.

Examining the intrinsic foot muscles’ capacity to modulate plantar flexor gearing and ankle joint contributions to propulsion in vertical jumping

BackgroundDuring human locomotion, a sufficiently stiff foot allows the ankle plantar flexors to generate large propulsive powers. Increasing foot stiffness (e.g., via a carbon plate) increases the ankle's external moment arm in relation to the internal moment arm (i.e., increasing gear ratio), reduces plantar flexor muscles’ shortening velocity, and enhances muscle force production. In contrast, when activation of the foot's intrinsic muscles is impaired, there is a reduction in foot and ankle work and metatarsophalangeal joint stiffness. We speculated that the reduced capacity to actively control metatarsophalangeal joint stiffness may impair the gearing function of the foot at the ankle. MethodsWe used a tibial nerve block to examine the direct effects of the intrinsic foot muscles on ankle joint kinetics, in vivo medial gastrocnemius’ musculotendinous dynamics, and ankle gear ratio on 14 participants during maximal vertical jumping. ResultsUnder the nerve block, the internal ankle plantar flexion moment decreased (p = 0.004) alongside a reduction in external moment arm length (p = 0.021) and ankle joint gear ratio (p = 0.049) when compared to the non-blocked condition. Although medial gastrocnemius muscle–tendon unit and fascicle velocity were not different between conditions, the Achilles tendon was shorter during propulsion in the nerve block condition (p < 0.001). ConclusionIn addition to their known role of regulating the energetic function of the foot, our data indicate that the intrinsic foot muscles also act to optimize ankle joint torque production and leverage during the propulsion phase of vertical jumping.

Biomechanical Modeling of Brachialis-to-Wrist Extensor Muscle Transfer Function for Daily Activities in Tetraplegia.

A model of the transferred BRA-ECRB muscle-tendon unit was developed to calculate isometric elbow and wrist joint torque as a function of elbow and wrist angles resulting from different BRA reattachment locations from 50 to 80 mm proximal to the wrist joint crease. Using this model, mathematical optimization predicted the optimal location for BRA reattachment in order to perform each of a number of important upper extremity tasks as well as to calculate a global optimum for performing all of the tasks. Analysis of active joint torque showed that the entire elbow torque-angle curve surface shifted "diagonally" toward elbow flexion and wrist extension as the attachment location approached the wrist joint; peak wrist torque was produced at extended wrist angles. Our model predicted that the optimal attachment location for each different task ranged from 54.3 to 74.6 mm proximal to the wrist joint, which is feasible given the anatomy of the muscle-tendon unit. The attachment location to optimize performing all tasks was calculated as 63.5 mm proximal to the wrist joint. This study clearly demonstrates that the BRA, which is underused as a donor in tetraplegia surgery, is an excellent donor muscle to provide wrist extension. Biomechanical simulation further highlighted the need to consider not only donor-muscle appropriateness but the patient's desired function when planning surgical tendon transfers. Quantitative evaluation of the way that surgery affects daily tasks rather than simply matching muscle properties may be a more appropriate approach for surgeons to use when choosing and tensioning donor muscles.

A Scientific Perspective of the Three Harmony Principle of Taijiquan

The Three Harmony Principle helps to regulate whole-body motion in harmony by balancing and aligning the movements of the body segments. Taijiquan uses the fangsong-relaxtion modality to resolve the switching back and forth of the active muscle forces and the passive tensional forces of tendons, ligaments and fascial tissues. Fangsong induces the modulation of the muscles to resettle in a better state of balance, thus is necessarily a manipulation of the fascial tissues enveloping the muscles, organs and structures. In so doing, fangsong-relaxation cultivates the cognition and sensation of the fascial tensional network, which traditional Taiji theory refers to as Qi. Taijiquan harnesses Qi in the discipline of body motion to balance and align the momenta of the body segments in force transmission. This gives rise to maximal force potential in balance—the force of neijin (internal strength)—in response of application. Crucially, the settling into balance by fangsong functions as a neutral countermovement in the stretch-shorten cycle that primes the muscle-tendon unit in an ever-ready state of action, which endows neijin with the liveliness of response. Secondly, the fangsong manipulation of the fascial tissues serves as a fascial massage and release that provides relief to chronic pain syndrome caused by tenseness of muscles and fascia, a therapy that accrues with the many health benefits of Taijiquan. Lastly, but not least, the attentiveness required in the fangsong process develops into the meditation component of the practice which brings tranquility and the insight of mindfulness. Taijiquan thus bestows the triple gems of neijin, health well-being, and equanimity.

Predictive Simulations of Human Sprinting: Effects of Muscle-Tendon Properties on Sprint Performance.

We combined a full-body musculoskeletal model with dynamic optimization theory to predict the biomechanics of maximum-speed sprinting and evaluate the effects of changes in muscle-tendon properties on sprint performance. The body was modeled as a three-dimensional skeleton actuated by 86 muscle-tendon units. A simulation of jogging was used as an initial guess to generate a predictive dynamic optimization solution for maximum-speed sprinting. Nominal values of lower-limb muscle strength, muscle fascicle length, muscle intrinsic maximum shortening velocity (fiber-type composition), and tendon compliance were then altered incrementally to study the relative influence of each property on sprint performance. Model-predicted patterns of full-body motion, ground forces, and muscle activations were in general agreement with experimental data recorded for maximum-effort sprinting. Maximum sprinting speed was 1.3 times more sensitive to a change in muscle strength compared with the same change in muscle fascicle length, 2.0 times more sensitive to a change in muscle fascicle length compared with the same change in muscle intrinsic maximum shortening velocity, and 9.1 times more sensitive to a change in muscle intrinsic maximum shortening velocity compared with the same change in tendon compliance. A 10% increase in muscle strength increased maximum sprinting speed by 5.9%, whereas increasing muscle fascicle length, muscle intrinsic maximum shortening velocity, and tendon compliance by 10% increased maximum sprinting speed by 4.7%, 2.4%, and 0.3%, respectively. Sprint performance was most sensitive to changes in muscle strength and least affected by changes in tendon compliance. Sprint performance was also more heavily influenced by changes in muscle fascicle length than muscle intrinsic maximum shortening velocity. These results could inform training methods aimed at optimizing performance in elite sprinters.

Achilles Tendon Mechanical Behavior and Ankle Joint Function at the Walk-to-Run Transition.

Simple SummaryIn this study we investigated the ankle joint functional indexes and the Achilles tendon mechanical behaviour (changes in AT force and power as a function of speed and gait) during walking and running at speeds close to transition speed (about 7.2–7.5 km/h in healthy adults), to better elucidate the mechanical determinants of the walk-to-run transition. Our results indicate that, when walking at speeds faster than the typical transition speed (7.5–8.5 km/h), the Achilles tendon mechanical behavior is impaired: the force acting along its line of action is reduced, as well as its contribution in determining the total mechanical power of the muscle–tendon unit. Moreover, our data suggest that the walk-to-run transition could be partially explained by the need to preserve the spring-like function of the ankle joint (which is indeed lower in walking than in running at speeds > 7.5 km/h).Walking at speeds higher than transition speed is associated with a decrease in the plantar-flexor muscle fibres’ ability to produce force and, potentially, to an impaired behaviour of the muscle–tendon unit (MTU) elastic components. This study aimed to investigate the ankle joint functional indexes and the Achilles tendon mechanical behaviour (changes in AT force and power) to better elucidate the mechanical determinants of the walk-to-run transition. Kinematics, kinetic and ultrasound data of the gastrocnemius medialis (GM) were investigated during overground walking and running at speeds ranging from 5–9 km·h−1. AT and GM MTU force and power were calculated during the propulsive phase; the ankle joint function indexes (damper, strut, spring and motor) were obtained using a combination of kinetic and kinematic data. AT force was larger in running at speeds > 6.5 km/h. The contribution of AT to the total power provided by the GM MTU was significantly larger in running at speeds > 7.5 km/h. The spring and strut indexes of the ankle were significantly larger in running at speeds > 7.5 km/h. These data suggest that the walk-to-run transition could (at least partially) be explained by the need to preserve AT mechanical behaviour and the ankle spring function.

The effects of calf muscle self-massage on ankle joint range of motion and tendon-muscle morphology

IntroductionSelf-massage using a foam roller (foam rolling) has been used to improve joint range of motion (ROM). However, the effect of foam rolling on the morphology of a targeted muscle, tendon, and muscle-tendon unit (MTU) has not been fully clarified. This study aimed to investigate extensibility changes in the gastrocnemius muscle (GM), MTU, and the Achilles tendon (AT) in terms of maximum ankle dorsiflexion (max-DF) following a foam rolling intervention. This was an interventional study with no controls. MethodsStudy participants comprised 10 male and female students (mean [standard deviation]: 22.7 [2.5] years; height, 164.2 [6.7] cm; weight, 57.9 [7.9] kg). The foam rolling intervention was performed on the right leg plantar flexor muscles for 3 min. The outcomes were max-DF with specified resistance values (ROM-SR) and non-specified resistance values (ROM-NSR) and GM, MTU, and AT extensibility. An ultrasound device was used to determine the rate of change by subtracting the value in a neutral ankle joint position (0°) from the ankle max-DF to identify GM, MTU, and AT extensibility. All outcomes were measured pre- and post-intervention. ResultsThe range of ankle joint dorsiflexion increased significantly following the foam rolling intervention (Δ: ROM-SR, +4.35 [5.79]; ROM-NSR, +4.18 [4.43]), whereas GM extensibility increased 4.0 mm, although no significant difference was observed pre- and post-intervention. ConclusionFoam rolling was effective in increasing ankle joint dorsiflexion ROM. Moreover, it was suggested that the GM morphology might be affected by the intervention.

A muscle control strategy to alter pedal force direction under multiple constraints: A simulation study

Humans can quickly adapt to different task demands in cycling. The motor system continuously manipulates applied pedal forces under the influence of gravitational and inertial forces, but the muscular control strategy remains unknown. The aim of this study was to investigate muscular control and coordination when altering pedal force patterns, using a musculoskeletal model with dynamic tracking optimization and induced acceleration analysis (IAA). The tracking data were pedaling kinematics and kinetics in recreational cyclists before and after learning to apply pedal force toward a tangential target direction in one-legged pedaling (Park et al., 2021). The gravity and inertial force contributions to pedal forces were relatively unchanged after practice due to the consistent rider posture and pedaling mechanics. Pedal force contributions induced by individual muscle–tendon units (MTUs) were also relatively consistent in direction before and after practice, likely due to similar joint positions and task constraints in the two conditions. However, the total applied pedal force from the sum of IAA component contributions was more closely directed towards the target due to coordinated changes in the magnitudes of contributions of the resultant pedal force by individual MTUs. The improvement in pedal force targeting seen in this complex coordination task may be possible through a control strategy of scaling muscle activity level. The rapid adaptation to a new pedal force pattern in this constrained task is facilitated by a relatively simple strategy of scaling muscle activation amplitude.

Recovery of the medial gastrocnemius muscle after calcaneus fracture differs between contractile and elastic components.

BackgroundCalcaneal fractures result in severe functional impairments and walking restrictions. Postoperative evaluation mainly focusses on the restoration of calcaneal anatomy while ankle plantar flexor insufficiency remains largely neglected. This study aims to investigate biomechanical and morphologic adaptions of elastic and contractile components of the gastrocnemius medialis after unilateral calcaneal fracture. Methods20 Patients (BMI: 27.6 ± 3.1 kgm−2, Age: 50 ± 12 years) were measured using gait analysis and portable ultrasound over a follow-up of three, six and twelve months after surgery. Data comparison was performed using 20 matched healthy controls (BMI: 26.2 ± 2.9 kgm−2, Age: 48 ± 11 years). Static and dynamic behavior of the gastrocnemius muscle tendon unit, muscle fascicle and the serial-elastic element as well ankle joint kinematics and kinetics were analyzed. FindingsWithin patients, a significant (p < 0.05) increase in fascicle length (by 67%) during single support and a decrease of serial elastic element shortening (by 20%) during push off was found between three and twelve months follow-up comparisons. Patients showed differences for fascicle lengthening and pennation angle increase during single support after three and six months compared to healthy controls. A smaller shortening of the serial-elastic element (by 29%) and muscle-tendon unit (by 16%) persisted even for the twelve month comparisons. InterpretationPatients with calcaneal fracture showed an incomplete restoration of the medial gastrocnemius dynamic morphological behavior. While muscle fascicle contraction almost recovered, the serial elastic component still showed restrictions regarding its shortening behavior. Limited foot mobility and plantarflexor strength as well as lowered responsiveness of elastic tissues to mechanical loading are regarded as key mechanisms.

Isometric fascicle behaviour of the biceps femoris long head muscle during Nordic hamstring exercise variations

ObjectivesTo compare biceps femoris long head (BFlh) muscle tendon unit and fascicle function during Nordic hamstring exercise (NHE) variations with different hip range of motion. DesignCross-sectional. MethodsTwelve healthy volunteers (age: 24 ± 4 years; mass: 77 ± 6 kg; height: 177 ± 4 cm) performed two NHE variations: NHE with hips in neutral (fixed) position (conventional NHE); and NHE with hip flexion/extension. BFlh fascicle length behaviour was assessed using a dual transducer ultrasound configuration. BFlh and semitendinosus muscle electromyography, lower limb kinematics and knee flexion moment were also recorded. A biomechanical model was used to estimate BFlh muscle-tendon unit (MTU) length. Statistical Parametric Mapping was used to assess timing differences in outcome variables across the movement. ResultsIn both variations, during much of the exercise (~30–80% of movement phase), BFlh fascicles undergo little length change (isometric) while the MTU lengthens. Fascicles stretched considerably just in the last ~20% of the exercise, and changes in fascicle length (<2 cm stretch) were smaller in comparison to changes in MTU length (<4 cm stretch). Hip flexion resulted in the muscle tendon unit and fascicles operating at longer lengths until approximately 80% of the movement phase. ConclusionsThe decoupling between fascicle and MTU length seen during the NHE variations suggests that stretch of the elastic tissue of the MTU has an important role in absorbing energy during Nordic hamstring exercises. This may be important when considering adaptations to BFlh muscle and connective tissues that might occur from NHE training.

Role of Knee and Ankle Extensors' Muscle-Tendon Properties in Dynamic Balance Recovery from a Simulated Slip.

Participants exposed to a simulated slip with forward loss of balance (FLB) develop large lower limb joint moments which may be a limiting factor for those whose muscle-tendon units’ (MTUs) properties are deteriorated. Whether the age-related decline in these properties limits participants’ capacity to recover their balance following a slip with FLB remains unclear. We combined isokinetic dynamometry, ultrasound and EMG to understand how knee extensor and ankle plantarflexor muscle strength and power, rate of moment development, electromechanical delay, and tendon stiffness affected the balance of young (25.3 ± 3.9 years) and older adults (62.8 ± 7.1 years) when recovering from a single slip with FLB triggered whilst walking on a split-belt instrumented treadmill. Except for the patellar tendon’s stiffness, knee extensor and ankle plantarflexor electromechanical delays, older adults’ MTUs properties were deteriorated compared to those of young participants (p < 0.05). We found no significant relationship between age or the MTUs properties of participants and balance recovery. These findings provide additional support that neither maximal nor explosive strength training are likely to be successful in preventing a fall for healthy older adults, and that other type of interventions, such as task-specific training that has already proved efficacious in reducing the risk of falling, should be developed.

Multi-Day EMG-Based Knee Joint Torque Estimation Using Hybrid Neuromusculoskeletal Modelling and Convolutional Neural Networks.

Proportional control using surface electromyography (EMG) enables more intuitive control of a transfemoral prosthesis. However, EMG is a noisy signal which can vary over time, giving rise to the question what approach for knee torque estimation is most suitable for multi-day control. In this study we compared three different modelling frameworks to estimate knee torque in non-weight-bearing situations. The first model contained a convolutional neural network (CNN) which mapped EMG to knee torque directly. The second used a neuromusculoskeletal model (NMS) which used EMG, muscle tendon unit lengths and moment arms to compute knee torque. The third model (Hybrid) used a CNN to map EMG to specific muscle activation, which was used together with NMS components to compute knee torque. Multi-day measurements were conducted on ten able-bodied participants who performed non-weight bearing activities. CNN had the best performance in general and on each day (Normalized Root Mean Squared Error (NRMSE) 9.2 ± 4.4%). The Hybrid model (NRMSE 12.4 ± 3.4%) was able to outperform NMS (NRMSE 14.3 ± 4.2%). The NMS model showed no significant difference between measurement days. The CNN model and Hybrid models had significant performance differences between the first day and all other days. CNNs are suited for multi-day torque estimation in terms of error rate, outperforming the other two model types. NMS was the only model type which was robust over all days. This study investigated the behavior of three model types over multiple days, giving insight in the most suited modelling approach for multi-day torque estimation to be used in prosthetic control.