The Structural Adaptations That Mediate Disuse-Induced Atrophy of Skeletal Muscle

The maintenance of skeletal muscle mass plays a fundamental role in health and issues associated with quality of life. Mechanical signals are one of the most potent regulators of muscle mass, with a decrease in mechanical loading leading to a decrease in muscle mass. This concept has been supported by a plethora of human- and animal-based studies over the past 100 years and has resulted in the commonly used term of 'disuse atrophy'. These same studies have also provided a great deal of insight into the structural adaptations that mediate disuse-induced atrophy. For instance, disuse results in radial atrophy of fascicles, and this is driven, at least in part, by radial atrophy of the muscle fibers. However, the ultrastructural adaptations that mediate these changes remain far from defined. Indeed, even the most basic questions, such as whether the radial atrophy of muscle fibers is driven by the radial atrophy of myofibrils and/or myofibril hypoplasia, have yet to be answered. In this review, we thoroughly summarize what is known about the macroscopic, microscopic, and ultrastructural adaptations that mediated disuse-induced atrophy and highlight some of the major gaps in knowledge that need to be filled.

Energy transfer in reactive movements as a function of individual stretch load

Background: By directly recording electromyographic activity profiles and muscle-tendon interaction, this study aimed to elucidate the mechanisms why well-trained track and field athletes (experts) are able to outperform untrained individuals without former systematic experience in reactive jump training (novices). In particular, reactive power output and the elastic recoil properties of the muscle-tendon unit (MTU) were of special interest. For this purpose, stiffness regulation on muscle and joint level, energy management in terms of storing or dissipating elastic energy were compared between experts and novices during various stretch loads. Methods: Experts were compared with novices during reactive drop jumps (DJs) from drop heights ranging between 25 and 61 cm. Delta kinetic energy (Ekin) was calculated as the difference between the Ekin at take-off and ground contact (GC) to determine energy management. By recording electromyography of the lower limb muscles, in vivo fascicle dynamics (gastrocnemius medialis) and by combining kinematics and kinetics in a 3D inverse dynamics approach to compute ankle and knee joint kinetics, this study aimed to compare reactive jump performance, the neuromuscular activity and muscle-tendon interaction between experts and novices among the tested stretch loads. Results: Experts demonstrated significantly higher power output during DJs. Among all drop heights experts realized higher delta Ekin compared to novices. Consequently, higher reactive jump performance shown for experts was characterized by shorter GC time (GCT), higher jump heights and higher neuromuscular activity before and during the GC phase compared to novices. Concomitantly, experts were able to realize highest leg stiffness and delta Ekin in the lowest stretch load; however, both groups compensated the highest stretch load by prolonged GCT and greater joint flexion. On muscle level, experts work quasi-isometrically in the highest stretch load, while in novices GM fascicles were forcefully stretched. Conclusion: Group-specific stiffness regulation and elastic recoil properties are primarily influenced by the neuromuscular system. Due to their higher neuromuscular activity prior and during the GC phase, experts demonstrate higher force generating capacity. A functionally stiffer myotendinous system through enhanced neuromuscular input enables the experts loading their elastic recoil system more efficiently, thus realizing higher reactive power output and allowing a higher amount of energy storage and return. This mechanism is regulated in a stretch load dependent manner.

Ultrasonographic measurements of fascicle length overestimate adaptations in serial sarcomere number

Ultrasound-derived measurements of muscle fascicle length (FL) are often used to infer increases (chronic stretch or training) or decreases (muscle disuse or aging) in serial sarcomere number (SSN). Whether FL adaptations measured via ultrasound can truly approximate SSN adaptations has not been investigated. We casted the right hindlimb of 15 male Sprague-Dawley rats in a dorsiflexed position (i.e., stretched the plantar flexors) for 2 weeks, with the left hindlimb serving as a control. Ultrasound images of the soleus, lateral gastrocnemius (LG), and medial gastrocnemius (MG) were obtained with the ankle at 90° and full dorsiflexion for both hindlimbs pre and post-cast. Following post-cast ultrasound measurements, legs were fixed in formalin with the ankle at 90°, then muscles were dissected and fascicles were teased out for measurement of sarcomere lengths via laser diffraction and calculation of SSN. Ultrasound detected an 11% increase in soleus FL, a 12% decrease in LG FL, and an 8-11% increase in MG FL for proximal fascicles and at full dorsiflexion. These adaptations were partly reflected by SSN adaptations, with a 6% greater soleus SSN in the casted leg than the un-casted leg, but no SSN differences for the gastrocnemii. Weak relationships were observed between ultrasonographic measurements of FL and measurements of FL and SSN from dissected fascicles. Our results showed that ultrasound-derived FL measurements can overestimate an increase in SSN by ∼5%. Future studies should be cautious when concluding a large magnitude of sarcomerogenesis from ultrasound-derived FL measurements, and may consider applying a correction factor. NEW FINDINGS: What is the central question of this study? Measurements of muscle fascicle length via ultrasound are often used to infer changes in serial sarcomere number, such as increases following chronic stretch or resistance training, and decreases with ageing: does ultrasound-derived fascicle length accurately depict adaptations in serial sarcomere number? What is the main finding and its importance? Ultrasound detected an ∼11% increase in soleus fascicle length, but measurements on dissected fascicles showed the actual serial sarcomere number increase was only ∼6%; therefore, measurements of ultrasound-derived fascicle length can overestimate serial sarcomere number adaptations by as much as 5%.

Quadriceps Muscle Action and Association With Knee Joint Biomechanics in Individuals with Anterior Cruciate Ligament Reconstruction

Insufficient quadriceps force production and altered knee joint biomechanics after anterior cruciate ligament reconstruction (ACLR) may contribute to a heightened risk of osteoarthritis. Quadriceps muscle lengthening dynamics affect force production and knee joint loading; however, no study to our knowledge has quantified in vivo quadriceps dynamics during walking in individuals with ACLR or examined correlations with joint biomechanics. Our purpose was to quantify bilateral vastus lateralis (VL) fascicle length change and the association thereof with gait biomechanics during weight acceptance in individuals with ACLR. The authors hypothesized that ACLR limbs would exhibit more fascicle lengthening than contralateral limbs. The authors also hypothesized that ACLR limbs would exhibit positive correlations between VL fascicle lengthening and knee joint biomechanics during weight acceptance in walking. The authors quantified VL contractile dynamics via cine B-mode ultrasound imaging in 18 individuals with ACLR walking on an instrumented treadmill. In partial support of our hypothesis, ACLR limb VL fascicles activated without length change on average during weight acceptance while fascicle length on the contralateral limb decreased on average. The authors found a positive association between fascicle lengthening and increase in knee extensor moments in both limbs. Our results suggest that examining quadriceps muscle dynamics may elucidate underlying mechanisms relevant to osteoarthritis.

Median and ulnar nerve fascicle imaging using MR microscopy and high-resolution ultrasound

BACKGROUND AND PURPOSE

Understanding nerve microanatomy is important as different neuropathies and some nerve neoplasms present with fascicle enlargement. The aim of our study was to gain clinically oriented knowledge on nerve fascicular anatomy using imaging modalities.

METHODS

On a cadaveric upper extremity, high-resolution ultrasound (HRUS) scan with 22 MHz probe was performed. Sections of the median and ulnar nerves were excised at the level of the distal arm and after magnetic resonance microscopy (MRM), histological cross-sections (HCS) were prepared. Cross-referencing of the MRM and HRUS images with HCS was performed. Fascicle and nerve contouring was performed with morphometric software in order to assess nerve and fascicular cross-sectional area (CSA), fascicle count, and interfascicular distances. Based on fascicle differentiation, factual fascicle (FF) group and fascicular cluster (FC) group were defined.

RESULTS

On the cross-referenced imaging material, fascicles were differentiated in 92.7% on MRM and in 57.3% on HRUS. High to very high positive correlation among imaging material was observed for the fascicle CSA. FF depiction was 30.1% on HRUS. In comparison to the FF group, the FC group had significantly larger fascicle CSA and shorter interfascicular distances.

DISCUSSION

The findings of our study contribute to understanding of fascicle depiction on imaging modalities. HRUS offers good visualization of fascicles. The capability of differentiating fascicles is modality specific and depends on the fascicle CSA and the amount of interfascicular epineurium.

Is Muscle Architecture Different in Athletes with a Previous Hamstring Strain? A Systematic Review and Meta-Analysis

Hamstring strains are a frequent injury in sports and are characterized by a high recurrence rate. The aim of this review was to examine the muscle and tendon architecture in individuals with hamstring injury. A systematic literature search in four databases yielded eleven studies on architecture following injury. Differences in the fascicle length (FL), pennation angle (PA) and muscle size measures (volume, thickness and physiological cross-sectional area) at rest were not significantly different between the previously injured limb and the contralateral limb (p > 0.05). There was moderate evidence that biceps femoris long head (BFlh) FL shortening was greater during contraction in the injured compared to the contralateral limb. The BFlh FL was smaller in athletes with a previous injury compared to uninjured individuals (p = 0.0015) but no differences in the FL and PA of other muscles as well as in the aponeurosis/tendon size were observed (p > 0.05). An examination of the FL of both leg muscles in individuals with a previous hamstring strain may be necessary before and after return to sport. Exercises that promote fascicle lengthening of both injured and uninjured leg muscles may be beneficial for athletes who recover from a hamstring injury.

Intrafascicular chondroid-like bodies in the ageing equine superficial digital flexor tendon comprise glycosaminoglycans and type II collagen

The superficial digital flexor tendon (SDFT) is considered functionally equivalent to the human Achilles tendon. Circular chondroid depositions scattered amongst the fascicles of the equine SDFT are rarely reported. The purpose of this study was the detailed characterization of intrafascicular chondroid-like bodies (ICBs) in the equine SDFT, and the assessment of the effect of ageing on the presence and distribution of these structures. Ultrahigh field magnetic resonance imaging (9.4T) series of SDFT samples of young (1-9 years) and aged (17-25 years) horses were obtained, and three-dimensional reconstruction of ICBs was performed. Morphological evaluation of the ICBs included histology, immunohistochemistry and transmission electron microscopy. The number, size, and position of ICBs was determined and compared between age groups. There was a significant difference (p = .008) in the ICB count between young and old horses with ICBs present in varying number (13-467; median = 47, mean = 132.6), size and distribution in the SDFT of aged horses only. There were significantly more ICBs in the tendon periphery when compared with the tendon core region (p = .010). Histological characterization identified distinctive cells associated with increased glycosaminoglycan and type II collagen extracellular matrix content. Ageing and repetitive strain frequently cause tendon micro-damage before the development of clinical tendinopathy. Documentation of the presence and distribution of ICBs is a first step towards improving our understanding of the impact of these structures on the viscoelastic properties, and ultimately their effect on the risk of age-related tendinopathy in energy-storing tendons.

A ketogenic supplement improves white matter energy supply and processing speed in mild cognitive impairment

INTRODUCTION

White matter (WM) energy supply is crucial for axonal function and myelin maintenance. An exogenous source of ketones, the brain's alternative fuel to glucose, bypasses the brain's glucose-specific energy deficit and improves cognitive outcomes in mild cognitive impairment (MCI). How an additional supply of ketones affects glucose or ketone uptake in specific WM fascicles in MCI has not previously been reported.

METHODS

This 6-month interventional study included MCI participants randomized to a placebo (n = 16) or ketogenic medium chain triglyceride (kMCT; n = 17) drink. A neurocognitive battery and brain imaging were performed pre- and post-intervention. WM fascicle uptake of ketone and glucose and structural properties were assessed using positron emission tomography and diffusion imaging, respectively.

RESULTS

Ketone uptake was increased in the kMCT group by 2.5- to 3.2-fold in all nine WM fascicles of interest (P < .001), an effect seen both in deep WM and in fascicle cortical endpoints. Improvement in processing speed was positively associated with WM ketone uptake globally and in individual fascicles, most importantly the fornix (r = +0.61; P = .014).

DISCUSSION

A 6-month kMCT supplement improved WM energy supply in MCI by increasing ketone uptake in WM fascicles. The significant positive association with processing speed suggests that ketones may have a role in myelin integrity in MCI.

Effects of plyometric training on muscle-tendon mechanical properties and behavior of fascicles during jumping

The purpose of this study was to investigate the effects of plyometric training on the muscle-tendon mechanical properties and behavior of fascicles during jumping in order to elucidate the mechanisms of improved jump performance due to plyometric training. Eleven subjects completed a 12-week unilateral training program for plantar flexors. Active muscle stiffness with (100°·s-1 ) and without (250°·s-1 ) stretch reflex were calculated according to changes in muscle force and fascicle length during fast stretching after submaximal isometric contractions. Stiffness and hysteresis of tendon were measured using ultrasonography during ramp and ballistic contractions. Three kinds of unilateral jump heights using only ankle joint (no counter-movement jump: no-CMJ; counter-movement jump: CMJ; drop jump: DJ) on sledge apparatus were measured. During jumping, electromyographic activities (mEMG) of plantar flexors and fascicle length of the medial gastrocnemius muscle were measured. Active muscle stiffness at 250 and 100°·s-1 and maximal tendon elongation during ballistic contraction significantly increased after training. Tendon hysteresis during ballistic contraction significantly decreased after training, whereas that during ramp contraction did not. The heights of three jump tests, the ratio of mEMG during eccentric to that during concentric phases for CMJ, and the amount of fascicle shortening and shortening velocity during eccentric phase of DJ significantly increased after training. These results suggest that an increase in CMJ height was associated with changes in the muscle-tendon mechanical properties and muscle activation strategy, whereas an increase in DJ height could be explained by changes in the muscle-tendon mechanical properties, but not muscle activation strategy.

Serial sarcomere number is substantially decreased within the paretic biceps brachii in individuals with chronic hemiparetic stroke

A muscle's structure, or architecture, is indicative of its function and is plastic; changes in input to or use of the muscle alter its architecture. Stroke-induced neural deficits substantially alter both input to and usage of individual muscles. We combined in vivo imaging methods (second-harmonic generation microendoscopy, extended field-of-view ultrasound, and fat-suppression MRI) to quantify functionally meaningful architecture parameters in the biceps brachii of both limbs of individuals with chronic hemiparetic stroke and in age-matched, unimpaired controls. Specifically, serial sarcomere number (SSN) and physiological cross-sectional area (PCSA) were calculated from data collected at three anatomical scales: sarcomere length, fascicle length, and muscle volume. The interlimb differences in SSN and PCSA were significantly larger for stroke participants than for participants without stroke (P = 0.0126 and P = 0.0042, respectively), suggesting we observed muscle adaptations associated with stroke rather than natural interlimb variability. The paretic biceps brachii had ∼8,200 fewer serial sarcomeres and ∼2 cm² smaller PCSA on average than the contralateral limb (both P < 0.0001). This was manifested by substantially smaller muscle volumes (112 versus 163 cm³), significantly shorter fascicles (11.0 versus 14.0 cm; P < 0.0001), and comparable sarcomere lengths (3.55 versus 3.59 μm; P = 0.6151) between limbs. Most notably, this study provides direct evidence of the loss of serial sarcomeres in human muscle observed in a population with neural impairments that lead to disuse and chronically place the affected muscle at a shortened position. This adaptation is consistent with functional consequences (increased passive resistance to elbow extension) that would amplify already problematic, neurally driven motor impairments.

Nerve Ultrasound in Traumatic and Iatrogenic Peripheral Nerve Injury

Peripheral nerve injury is a potentially debilitating disorder that occurs in an estimated 2–3% of all patients with major trauma, in a similar percentage of medical procedures. The workup of these injuries has traditionally been clinical, combined with electrodiagnostic testing. However, this has limitations, especially in the acute phase of the trauma or lack of any recovery, when it is very important to determine nerve continuity and perform surgical exploration and repair in the case of the complete transection or intraneural fibrosis. Ultrasound can help in those situations. It is a versatile imaging technique with a high sensitivity of 93% for detecting focal nerve lesions. Ultrasound can assess the structural integrity of the nerve, neuroma formation and other surrounding abnormalities of bone or foreign bodies impeding the nerve. In addition, this can help to prevent iatrogenic nerve injury by marking the nerve before the procedure. This narrative review gives an overview of why and how nerve ultrasound can play a role in the detection, management and prevention of peripheral nerve injury.

Ultrasound-based speckle-tracking in tendons: a critical analysis for the technician and the clinician

Ultrasound has risen to the forefront as one of the primary tools in tendon research, with benefits including its relatively low cost, ease of use, and high safety. Moreover, it has been shown that cine ultrasound can be used to evaluate tendon deformation by tracking the motion of anatomical landmarks during physical movement. Estimates from landmark tracking, however, are typically limited to global tissue properties, such that clinically relevant regional nonuniformities may be missed. Fortunately, advancements in ultrasound scanning have led to the development of speckle-tracking algorithms, which enable the noninvasive measurement of in vivo local deformation patterns. Despite the successes in other fields, the adaptation of speckle-tracking to tendon research has presented some unique challenges as a result of tissue anisotropy and microstructural changes under load. With no generally accepted standards for its use, current methodological approaches vary substantially between studies and research groups. Therefore, the goal of this paper is to provide a summative review of the technical complexities and variations of speckle-tracking approaches being used and the impact these decisions may have on measured results and their interpretation. Variations in these approaches currently being used with relevant technical aspects are discussed first (for the technician), followed by a discussion of the more clinical considerations (for the clinician). Finally, a summary table of common challenges encountered when implementing speckle-tracking is provided, with suggested recommendations for minimizing the impact of such potential sources of error.

Mechanical properties of muscle and tendon at high strain rate in sprinters

The aim of the present study was to compare the mechanical properties of muscles and tendons at high strain rates between sprinters and untrained men. Fifteen sprinters and 18 untrained men participated in this study. Active muscle stiffness of the medial gastrocnemius muscle was calculated according to changes in the estimated muscle force and fascicle length during fast stretching at five different angular velocities (100, 200, 300, 500, and 600 deg·s-1 ) after submaximal isometric contractions. Stiffness and hysteresis of tendon structures were measured during ramp and ballistic contractions. Active muscle stiffness at 500 deg·s-1 (p = .070) and 600 deg·s-1 (p = .041) was greater in sprinters than untrained men, whereas no differences in those at 100, 200, and 300 deg·s-1 were found between the two groups. There were no differences in stiffness or hysteresis of tendon structures measured during ramp and ballistic contractions between the two groups. These results suggest that, for sprinters, greater active muscle stiffness at a high angular velocity is caused by exercising with a high angular velocity that is typical of their training.

Effects of Surface Properties on Gastrocnemius Medialis and Vastus Lateralis Fascicle Mechanics During Maximal Countermovement Jumping

Interactions between human movement and surfaces have previously been studied to understand the influence of surface properties on the mechanics and energetics of jumping. However, little is known about the muscle-tendon unit (MTU) mechanics associated with muscle activity and leg adjustments induced by different surfaces during this movement. This study aimed to examine the effects of three surfaces with different properties (artificial turf, hybrid turf, and athletic track) on the muscle mechanics and muscle excitation of the gastrocnemius medialis (GM) and vastus lateralis (VL) during maximal countermovement jumping (CMJ). Twelve participants performed maximal CMJs on the three sport surfaces. GM and VL muscle fascicles were simultaneously imaged using two ultrafast ultrasound systems (500 Hz). MTUs lengths were determined based on anthropometric models and two-dimensional joint kinematics. Surface electromyography (EMG) was used to record GM and VL muscle activity. Surface mechanical testing revealed systematic differences in surface mechanical properties (P = 0.006, η²: 0.26–0.32, large). Specifically, the highest force reduction and vertical deformation values have been observed on artificial turf (65 ± 2% and 9.0 ± 0.3 mm, respectively), while athletic track exhibited the lowest force reduction and vertical deformation values (28 ± 1% and 2.1 ± 0.1 mm, respectively) and the highest energy restitution (65 ± 1%). We observed no significant difference in CMJ performance between the three surfaces (∼35–36 cm, P = 0.66). GM and VL fascicle shortening (P = 0.90 and P = 0.94, respectively) and shortening velocity (P = 0.13 and P = 0.65, respectively) were also unaffected by the type of surface. However, when jumping from greater deformable surface, both GM muscle activity (P = 0.022, η² = 0.18, large) and peak shortening velocity of GM MTU (P = 0.042, η² = 0.10, medium) increased during the push-off phase. This resulted in a greater peak plantar flexion velocity late in the jump (P = 0.027, η² = 0.13, medium). Our findings suggest that maximal vertical jumping tasks in humans is not affected by common sport surfaces with different mechanical properties. However, internal regulatory mechanisms exist to compensate for differences in surface properties.

Novel mapping algorithm during catheter ablation for ventricular parasystole originating from left anterior fascicle

A 17-year-old woman presented with frequent palpitations and shortness of breath and was diagnosed with drug-refractory ventricular parasystole. We predicted that the parasystole originated from the left anterior fascicle (LAF). Detailed activation maps of both conduction systems, including the LAF, during sinus rhythm and ventricular parasystole were obtained using a parallel mapping system. We confirmed the earliest fascicular potential of the parasystole and performed catheter ablation with no complications. This novel mapping algorithm for simultaneous acquisition of multiple maps aided effective treatment of ventricular parasystole originating from the LAF.

Identifying the Structural Adaptations that Drive the Mechanical Load-Induced Growth of Skeletal Muscle: A Scoping Review

The maintenance of skeletal muscle mass plays a critical role in health and quality of life. One of the most potent regulators of skeletal muscle mass is mechanical loading, and numerous studies have led to a reasonably clear understanding of the macroscopic and microscopic changes that occur when the mechanical environment is altered. For instance, an increase in mechanical loading induces a growth response that is mediated, at least in part, by an increase in the cross-sectional area of the myofibers (i.e., myofiber hypertrophy). However, very little is known about the ultrastructural adaptations that drive this response. Even the most basic questions, such as whether mechanical load-induced myofiber hypertrophy is mediated by an increase in the size of the pre-existing myofibrils and/or an increase in the number myofibrils, have not been resolved. In this review, we thoroughly summarize what is currently known about the macroscopic, microscopic and ultrastructural changes that drive mechanical load-induced growth and highlight the critical gaps in knowledge that need to be filled.

High-Resolution Nerve Ultrasound to Assess Nerve Echogenicity, Fascicular Count, and Cross-Sectional Area Using Semiautomated Analysis

BACKGROUND AND PURPOSE

Little is known about echogenicity and fascicular structure observed in high-resolution nerve ultrasound (HRUS) in both healthy subjects and patients with peripheral nerve disease. The aim of this study was to evaluate the reliability of echogenicity, fascicle count, and fascicle size analysis, to create standard values and compare these parameters to patients with chronic inflammatory demyelinating polyneuropathy (CIDP).

METHODS

Median, ulnar, radial, tibial, and fibular nerve of 79 healthy subjects and patients were scanned by one examiner using HRUS. Image analysis regarding echogenicity, fascicle count, and fascicle cross-sectional area (CSA) was performed by two independent raters semiautomatically using ImageJ. Pearson correlation coefficient r reflected interrater reliability (IR), and intraclass correlation coefficient (ICC) determined intrarater reliability (IAR). Results of healthy subjects were compared to 20 patients with CIDP by analysis of variance.

RESULTS

IR was very good for echogenicity (r = .9) and good for fascicle count and size of the largest fascicle (r = .64/.56). IAR was very good for all three parameters (ICC = .9/.83/.74). Healthy subjects had a wide range of values. CIDP patients were in range of healthy subjects. Clinically progressive CIDP patients (defined as an increase in Overall Disability Sum Score by ≥1 point) had a lower fraction of black than healthy controls and stable CIDP patients (P < .001).

CONCLUSION

Semiautomated evaluation of echogenicity, fascicle count, and fascicle CSA is reliable. Cutoff values to differentiate between healthy persons and CIDP do not exist. Echogenicity is useful for detecting clinically progressive CIDP patients and should be used in clinical context or intraindividual course.

Ultrasound imaging to assess skeletal muscle architecture during movements: a systematic review of methods, reliability, and challenges

B-mode ultrasound is often used to quantify muscle architecture during movements. Our objectives were to 1) systematically review the reliability of fascicle length (FL) and pennation angles (PA) measured using ultrasound during movements involving voluntary contractions; 2) systematically review the methods used in studies reporting reliability, discuss associated challenges, and provide recommendations to improve the reliability and validity of dynamic ultrasound measurements; and 3) provide an overview of computational approaches for quantifying fascicle architecture, their validity, agreement with manual quantification of fascicle architecture, and advantages and drawbacks. Three databases were searched until June 2019. Studies among healthy human individuals aged 17-85 yr that investigated the reliability of FL or PA in lower-extremity muscles during isoinertial movements and that were written in English were included. Thirty studies (n = 340 participants) were included for reliability analyses. Between-session reliability as measured by coefficient of multiple correlations (CMC), and coefficient of variation (CV) was FL CMC: 0.89-0.96; CV: 8.3% and PA CMC: 0.87-0.90; CV: 4.5-9.6%. Within-session reliability was FL CMC: 0.82-0.99; CV: 0.0-6.7% and PA CMC: 0.91; CV: 0.0-15.0%. Manual analysis reliability was FL CMC: 0.89-0.96; CV: 0.0-15.9%; PA CMC: 0.84-0.90; and CV: 2.0-9.8%. Computational analysis FL CMC was 0.82-0.99, and PA CV was 14.0-15.0%. Eighteen computational approaches were identified, and these generally showed high agreement with manual analysis and high validity compared with phantoms or synthetic images. B-mode ultrasound is a reliable method to quantify fascicle architecture during movement. Additionally, computational approaches can provide a reliable and valid estimation of fascicle architecture.

Effects of the Functional Heel Drop Exercise on the Muscle Architecture of the Gastrocnemius

CONTEXT

The architectural characteristics of a muscle determine its function.

OBJECTIVE

To determine the architectural adaptations of the lateral gastrocnemius (LG) and medial gastrocnemius (MG) muscles after a functional eccentric strength training protocol consisting of heel drop exercises, followed by a subsequent detraining period.

DESIGN

Pretest and posttest.

SETTING

Training rooms and laboratory.

PARTICIPANTS

The participants (N = 45) who were randomly divided into an experimental group (EG, n = 25) and a control group (CG, n = 20).

INTERVENTIONS

The 13-week intervention included participants (N = 45) who were randomly divided into an EG (n = 25) and a CG (n = 20). The EG performed a week of control and training, 8 weeks of eccentric training, and 4 weeks of detraining. The CG did not perform any type of muscular training. The architectural characteristics of the LG and MG muscles were evaluated at rest in both groups using 2-D ultrasound before (pretest-week 1) and after (posttest-week 9) the training, and at the end of the detraining period (retest-week 13).

MAIN OUTCOME MEASURES

One-way repeated measures analysis of variance was used to determine training-induced changes in each of the variables of the muscle architecture.

RESULTS

After the training period, the members of the EG experienced a significant increase in the fascicle length of LG (t = -9.85, d = 2.78, P < .001) and MG (t = -8.98, d = 2.54, P < .001), muscle thickness (t = -6.71, d = 2.86, P < .001) and (t = -7.85, d = 2.22, P < .001), and the pennation angle (t = -10.21, d = 1.88, P < .05) and (t = -1.87, d = 0.53, P < .05), respectively. After the detraining period, fascicle length, muscle thickness, and pennation angle showed a significant decrease. In the CG, no significant changes were observed in any of the variables.

CONCLUSIONS

The heel drop exercise seems to generate adaptations in the architectural conditions of LG and MG, which are also reversible after a detraining period. These results may have practical implications for injury prevention and rehabilitation programs.

Ultrasound as a Tool to Study Muscle-Tendon Functions during Locomotion: A Systematic Review of Applications

Movement science investigating muscle and tendon functions during locomotion utilizes commercial ultrasound imagers built for medical applications. These limit biomechanics research due to their form factor, range of view, and spatio-temporal resolution. This review systematically investigates the technical aspects of applying ultrasound as a research tool to investigate human and animal locomotion. It provides an overview on the ultrasound systems used and of their operating parameters. We present measured fascicle velocities and discuss the results with respect to operating frame rates during recording. Furthermore, we derive why muscle and tendon functions should be recorded with a frame rate of at least 150 Hz and a range of view of 250 mm. Moreover, we analyze why and how the development of better ultrasound observation devices at the hierarchical level of muscles and tendons can support biomechanics research. Additionally, we present recent technological advances and their possible application. We provide a list of recommendations for the development of a more advanced ultrasound sensor system class targeting biomechanical applications. Looking to the future, mobile, ultrafast ultrasound hardware technologies create immense opportunities to expand the existing knowledge of human and animal movement.

Medial gastrocnemius muscle remodeling correlates with reduced plantarflexor kinetics 14 weeks following Achilles tendon rupture

Deficits in plantarflexor kinetics are associated with poor outcomes in patients following Achilles tendon rupture. In this longitudinal study, we analyzed the fascicle length and pennation angle of the medial gastrocnemius muscle and the length of the Achilles tendon using ultrasound imaging. To determine the relationship between muscle remodeling and deficits in plantarflexor kinetics measured at 14 wk after injury, we correlated the reduction in fascicle length and increase in pennation angle with peak torque measured during isometric and isokinetic plantarflexor contractions. We found that the medial gastrocnemius underwent an immediate change in structure, characterized by decreased length and increased pennation of the muscle fascicles. This decrease in fascicle length was coupled with an increase in tendon length. These changes in muscle-tendon structure persisted throughout the first 14 wk following rupture. Deficits in peak plantarflexor torque were moderately correlated with decreased fascicle length at 120 degrees per second (R² = 0.424, P = 0.057) and strongly correlated with decreased fascicle length at 210 degrees per second (R² = 0.737, P = 0.003). However, increases in pennation angle did not explain functional deficits. These findings suggest that muscle-tendon structure is detrimentally affected following Achilles tendon rupture. Plantarflexor power deficits are positively correlated with the magnitude of reductions in fascicle length. Preserving muscle structure following Achilles tendon rupture should be a clinical priority to maintain plantarflexor kinetics.NEW & NOTEWORTHY In our study, we found that when the Achilles tendon ruptures due to excessive biomechanical loading, the neighboring skeletal muscle undergoes rapid changes in its configuration. The magnitude of this muscle remodeling explains the amount of ankle power loss demonstrated by these patients once their Achilles tendons are fully healed. These findings highlight the interconnected relationship between muscle and tendon. Isolated injuries to the tendon stimulate detrimental changes to the muscle, thereby limiting joint-level function.

Investigating the Effect of Aging on the Viscosity of Tendon Fascicles and Fibers

In the current work, we investigate the effect of aging on the viscosity of tendon subunits. To that scope, we make use of experimental relaxation curves of healthy and aged tendon fascicles and fibers, upon which we identify the viscosity parameters characterizing the time-dependent behavior of each tendon subunit. We subsequently combine the obtained results with analytical viscoelastic homogenization analysis methods to extract information on the effective viscous contribution of the embedding matrix substance at the fiber scale. The results suggest that the matrix substance plays a significant role in the relaxation process of the upper tendon subunits both for aged and healthy specimens. What is more, the viscosity coefficients computed for the fibrillar components indicate that aging leads to a viscosity reduction that is statistically significant for both fascicles and fibers. Its impact is more prominent for the lower hierarchical scale of fibers. As such, the reduced stress relaxation capability at the tendon macroscale is to be primarily attributed to the modified viscosity of its inner fibrillar subunits rather than to the matrix substance.

A reduction in compliance or activation level reduces residual force depression in human tibialis anterior

AIM

We investigated if residual force depression (rFD) is present during voluntary fixed-end contractions of human tibialis anterior (TA) and whether reducing TA's activation level after active shortening could reduce rFD.

METHODS

Ten participants performed fixed-end dorsiflexion contractions to a low, moderate or high level while electromyography (EMG), dorsiflexion force and TA ultrasound images were recorded. Contractions were force- or EMG-matched and after the low or high contraction level was attained, participants respectively increased or decreased their force/EMG to a moderate level. Participants also performed moderate level contractions while the TA muscle-tendon unit (MTU) was lengthened during the force/EMG rise to the reference MTU length.

RESULTS

Equivalent fascicle shortening over moderate and low to moderate level contractions did not alter EMG (P = 0.45) or dorsiflexion force (P = 0.47) at the moderate level. Greater initial fascicle shortening magnitudes (1.7 mm; P ≤ 0.01) to the high contraction level did not alter EMG (P = 0.45) or dorsiflexion force (P = 0.30) at the subsequent moderate level compared with moderate level contractions. TA MTU lengthening during the initial force/EMG rise reduced TA fascicle shortening (-2.5 mm; P ≤ 0.01), which reduced EMG (-3.9% MVC; P < 0.01) and increased dorsiflexion force (3.7% MVC; P < 0.01) at the moderate level compared with fixed-end moderate level contractions.

CONCLUSION

rFD is present during fixed-end dorsiflexion contractions because fascicles actively shorten as force/EMG increases and rFD can be reduced by reducing the effective MTU compliance. A reduction in muscle activation level also reduces rFD by potentially triggering residual force enhancement-related mechanisms as force drops and some fascicles actively lengthen.

Comparative multi-scale hierarchical structure of the tail, plantaris, and Achilles tendons in the rat

Rodent tendons are widely used to study human pathologies such as tendinopathy and repair, and to address fundamental physiological questions about development, growth, and remodeling. However, how the gross morphology and multi-scale hierarchical structure of rat tendons, such as the tail, plantaris, and Achilles tendons, compare with that of human tendons are unknown. In addition, there remains disagreement about terminology and definitions. Specifically, the definitions of fascicle and fiber are often dependent on diameter sizes, not their characteristic features, and these definitions impair the ability to compare hierarchical structure across species, where the sizes of the fiber and fascicle may change with animal size and tendon function. Thus, the objective of the study was to select a single species that is commonly used for tendon research (rat) and tendons with varying mechanical functions (tail, plantaris, Achilles) to evaluate the hierarchical structure at multiple length scales using histology, SEM, and confocal imaging. With the exception of the specialized rat tail tendon, we confirmed that in rat tendons there are no fascicles and the fiber is the largest subunit. In addition, we provided a structurally based definition of a fiber as a bundle of collagen fibrils that is surrounded by elongated cells, and this definition was supported by both histologically processed and unprocessed samples. In all rat tendons studied, the fiber diameters were consistently between 10 and 50 μm, and this diameter range appears to be conserved across larger species. Specific recommendations were made highlighting the strengths and limitations of each rat tendon as a research model. Understanding the hierarchical structure of tendon can advance the design and interpretation of experiments and development of tissue-engineered constructs.

Resistance Training Combined With Stretching Increases Tendon Stiffness and Is More Effective Than Stretching Alone in Children With Cerebral Palsy: A Randomized Controlled Trial

Aim: Stretching is often used to increase/maintain muscle length and improve joint range of motion (ROM) in children with cerebral palsy (CP). However, outcomes at the muscle (remodeling) and resulting function appear to be highly variable and often unsatisfactory. During passive joint rotation, the Achilles tendon lengthens more than the in-series medial gastrocnemius muscle in children with CP, which might explain the limited effectiveness of stretching interventions. We aimed to ascertain whether increasing tendon stiffness, by performing resistance training, improves the effectiveness of passive stretching, indicated by an increase in medial gastrocnemius fascicle length. Methods: Sixteen children with CP (Age median [IQR]: 9.6 [8.6, 10.5]) completed the study. Children were randomly assigned to a combined intervention of stretching and strengthening of the calf muscles (n = 9) or a control (stretching-only) group (n = 7). Medial gastrocnemius fascicle length at a resting ankle angle, lengthening during passive joint rotations, and tendon stiffness were assessed by combining dynamometry and ultrasound imaging. The study was registered on clinicaltrials.gov (NCT02766491). Results: Resting fascicle length and tendon stiffness increased more in the intervention group compared to the control group (median [95% CI] increase fascicle length: 2.2 [1.3, 4.3] mm; stiffness: 13.6 [9.9, 17.7] N/mm) Maximum dorsiflexion angle increased equally in both groups. Conclusion: This study provides proof of principle that a combined resistance and stretching intervention can increase tendon stiffness and muscle fascicle length in children with CP. This demonstrates that remodeling of muscle structure is possible with non-invasive interventions in spastic CP.

Do triceps surae muscle dynamics govern non-uniform Achilles tendon deformations?

The human Achilles tendon (AT) consists of sub-tendons arising from the gastrocnemius and soleus muscles that exhibit non-uniform tissue displacements thought to facilitate some independent actuation. However, the mechanisms governing non-uniform displacement patterns within the AT, and their relevance to triceps surae muscle contractile dynamics, have remained elusive. We used a dual-probe ultrasound imaging approach to investigate triceps surae muscle dynamics (i.e., medial gastrocnemius-GAS, soleus-SOL) as a determinant of non-uniform tendon tissue displacements in the human AT. We hypothesized that superficial versus deep differences in AT tissue displacements would be accompanied by and correlate with anatomically consistent differences in GAS versus SOL muscle shortening. Nine subjects performed ramped maximum voluntary isometric contractions at each of five ankle joint angles spanning 10° dorsiflexion to 30° plantarflexion. For all conditions, SOL shortened by an average of 78% more than GAS during moment generation. This was accompanied by, on average, 51% more displacement in the deep versus superficial region of the AT. The magnitude of GAS and SOL muscle shortening positively correlated with displacement in their associated sub-tendons within the AT. Moreover, and as hypothesized, superficial versus deep differences in sub-tendon tissue displacements positively correlated with anatomically consistent differences in GAS versus SOL muscle shortening. We present the first in vivo evidence that triceps surae muscle dynamics may precipitate non-uniform displacement patterns in the architecturally complex AT.

The effect of muscle-tendon unit vs. fascicle analyses on vastus lateralis force-generating capacity during constant power output cycling with variable cadence

The maximum force-generating capacity of a muscle is dependent on the lengths and velocities of its contractile apparatus. Muscle-tendon unit (MTU) length changes can be estimated from joint kinematics; however, contractile element length changes are more difficult to predict during dynamic contractions. The aim of this study was to compare vastus lateralis (VL) MTU and fascicle level force-length and force-velocity relationships, and dynamic muscle function while cycling at a constant submaximal power output (2.5 W/kg) with different cadences. We hypothesized that manipulating cadence at a constant power output would not affect VL MTU shortening, but significantly affect VL fascicle shortening. Furthermore, these differences would affect the predicted force capacity of the muscle. Using an isokinetic dynamometer and B-mode ultrasound (US), we determined the force-length and force-velocity properties of the VL MTU and its fascicles. In addition, three-dimensional kinematics and kinetics of the lower limb, as well as US images of VL fascicles were collected during submaximal cycling at cadences of 40, 60, 80, and 100 rotations per minute. Ultrasound measures revealed a significant increase in fascicle shortening as cadence decreased (84% increase across all conditions, P < 0.01), whereas there were no significant differences in MTU lengths across any of the cycling conditions (maximum of 6%). The MTU analysis resulted in greater predicted force capacity across all conditions relative to the force-velocity relationship ( P < 0.01). These results reinforce the need to determine muscle mechanics in terms of separate contractile element and connective tissue length changes during isokinetic contractions, as well as dynamic movements like cycling. NEW & NOTEWORTHY We demonstrate that vastus lateralis (VL) muscle tendon unit (MTU) length changes do not adequately reflect the underlying fascicle mechanics during cycling. When examined across different pedaling cadence conditions, the force-generating potential measured only at the level of MTU (or joint) overestimated the maximum force capacity of VL compared with analysis using fascicle level data.

Muscle-tendon length and force affect human tibialis anterior central aponeurosis stiffness in vivo

The factors that drive variable aponeurosis behaviors in active versus passive muscle may alter the longitudinal stiffness of the aponeurosis during contraction, which may change the fascicle strains for a given muscle force. However, it remains unknown whether these factors can drive variable aponeurosis behaviors across different muscle-tendon unit (MTU) lengths and influence the subsequent fascicle strains during contraction. Here, we used ultrasound and elastography techniques to examine in vivo muscle fascicle behavior and central aponeurosis deformations of human tibialis anterior (TA) during force-matched voluntary isometric dorsiflexion contractions at three MTU lengths. We found that increases in TA MTU length increased both the length and apparent longitudinal stiffness of the central aponeurosis at low and moderate muscle forces (P < 0.01). We also found that increased aponeurosis stiffness was directly related to reduced magnitudes of TA muscle fascicle shortening for the same change in force (P < 0.01). The increase in slope and shift to longer overall lengths of the active aponeurosis force-length relationship as MTU length increased was likely due to a combination of parallel lengthening of aponeurosis and greater transverse aponeurosis strains. This study provides in vivo evidence that human aponeurosis stiffness is increased from low to moderate forces and that the fascicle strains for a given muscle force are MTU length dependent. Further testing is warranted to determine whether MTU length-dependent stiffness is a fundamental property of the aponeurosis in pennate muscles and evaluate whether this property can enhance muscle performance.

Bionic intrafascicular interfaces for recording and stimulating peripheral nerve fibers

The network of peripheral nerves presents extraordinary potential for modulating and/or monitoring the functioning of internal organs or the brain. The degree to which these pathways can be used to influence or observe neural activity patterns will depend greatly on the quality and specificity of the bionic interface. The anatomical organization, which consists of multiple nerve fibers clustered into fascicles within a nerve bundle, presents opportunities and challenges that may necessitate insertion of electrodes into individual fascicles to achieve the specificity that may be required for many clinical applications. This manuscript reviews the current state-of-the-art in bionic intrafascicular interfaces, presents specific concerns for stimulation and recording, describes key implementation considerations and discusses challenges for future designs of bionic intrafascicular interfaces.

Generation of a Motor Nerve Organoid with Human Stem Cell-Derived Neurons

During development, axons spontaneously assemble into a fascicle to form nerves and tracts in the nervous system as they extend within a spatially constrained path. However, understanding of the axonal fascicle has been hampered by lack of an in vitro model system. Here, we report generation of a nerve organoid composed of a robust fascicle of axons extended from a spheroid of human stem cell-derived motor neurons within our custom-designed microdevice. The device is equipped with a narrow channel providing a microenvironment that facilitates the growing axons to spontaneously assemble into a unidirectional fascicle. The fascicle was specifically made with axons. We found that it was electrically active and elastic and could serve as a model to evaluate degeneration of axons in vitro. This nerve organoid model should facilitate future studies on the development of the axonal fascicle and drug screening for diseases affecting axon fascicles.

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Axons spontaneously assembled into a unidirectional fascicle within a microchannel

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The axon fascicles were electrically active and elastic

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The axon fascicle can model degeneration of axons in vitro

Plyometric Training Favors Optimizing Muscle-Tendon Behavior during Depth Jumping

The purpose of the present study was to elucidate how plyometric training improves stretch–shortening cycle (SSC) exercise performance in terms of muscle strength, tendon stiffness, and muscle–tendon behavior during SSC exercise. Eleven men were assigned to a training group and ten to a control group. Subjects in the training group performed depth jumps (DJ) using only the ankle joint for 12 weeks. Before and after the period, we observed reaction forces at foot, muscle–tendon behavior of the gastrocnemius, and electromyographic activities of the triceps surae and tibialis anterior during DJ. Maximal static plantar flexion strength and Achilles tendon stiffness were also determined. In the training group, maximal strength remained unchanged while tendon stiffness increased. The force impulse of DJ increased, with a shorter contact time and larger reaction force over the latter half of braking and initial half of propulsion phases. In the latter half of braking phase, the average electromyographic activity (mEMG) increased in the triceps surae and decreased in tibialis anterior, while fascicle behavior of the gastrocnemius remained unchanged. In the initial half of propulsion, mEMG of triceps surae and shortening velocity of gastrocnemius fascicle decreased, while shortening velocity of the tendon increased. These results suggest that the following mechanisms play an important role in improving SSC exercise performance through plyometric training: (1) optimization of muscle–tendon behavior of the agonists, associated with alteration in the neuromuscular activity during SSC exercise and increase in tendon stiffness and (2) decrease in the neuromuscular activity of antagonists during a counter movement.

Faster Movement Speed Results in Greater Tendon Strain during the Loaded Squat Exercise

INTRODUCTION

Tendon dynamics influence movement performance and provide the stimulus for long-term tendon adaptation. As tendon strain increases with load magnitude and decreases with loading rate, changes in movement speed during exercise should influence tendon strain.

METHODS

Ten resistance-trained men [squat one repetition maximum (1RM) to body mass ratio: 1.65 ± 0.12] performed parallel-depth back squat lifts with 60% of 1RM load at three different speeds: slow fixed-tempo (TS: 2-s eccentric, 1-s pause, 2-s concentric), volitional-speed without a pause (VS) and maximum-speed jump (JS). In each condition joint kinetics, quadriceps tendon length (LT), patellar tendon force (FT), and rate of force development (RFDT) were estimated using integrated ultrasonography, motion-capture, and force platform recordings.

RESULTS

Peak LT, FT, and RFDT were greater in JS than TS (p < 0.05), however no differences were observed between VS and TS. Thus, moving at faster speeds resulted in both greater tendon stress and strain despite an increased RFDT, as would be predicted of an elastic, but not a viscous, structure. Temporal comparisons showed that LT was greater in TS than JS during the early eccentric phase (10-14% movement duration) where peak RFDT occurred, demonstrating that the tendon's viscous properties predominated during initial eccentric loading. However, during the concentric phase (61-70 and 76-83% movement duration) differing FT and similar RFDT between conditions allowed for the tendon's elastic properties to predominate such that peak tendon strain was greater in JS than TS.

CONCLUSIONS

Based on our current understanding, there may be an additional mechanical stimulus for tendon adaptation when performing large range-of-motion isoinertial exercises at faster movement speeds.

An Alternative Bundle-to-Bundle Suturing Technique for Repairing Fresh Achilles Tendon Rupture

The main concern about conventional Achilles tendon repair surgical techniques is how to maintain the initial strength of the ruptured Achilles tendon through complicated suturing methods. The primary surgical problem lies in the properties of the soft tissue; the deterioration of the Achilles tendon, especially in its elasticity; and the surface lubricity of the local tissues. In the present study, we describe an innovative bundle-to-bundle suturing method that addresses these potential problems.

A functional model and simulation of spinal motor pools and intrafascicular recordings of motoneuron activity in peripheral nerve

Decoding motor intent from recorded neural signals is essential for the development of effective neural-controlled prostheses. To facilitate the development of online decoding algorithms we have developed a software platform to simulate neural motor signals recorded with peripheral nerve electrodes, such as longitudinal intrafascicular electrodes (LIFEs). The simulator uses stored motor intent signals to drive a pool of simulated motoneurons with various spike shapes, recruitment characteristics, and firing frequencies. Each electrode records a weighted sum of a subset of simulated motoneuron activity patterns. As designed, the simulator facilitates development of a suite of test scenarios that would not be possible with actual data sets because, unlike with actual recordings, in the simulator the individual contributions to the simulated composite recordings are known and can be methodically varied across a set of simulation runs. In this manner, the simulation tool is suitable for iterative development of real-time decoding algorithms prior to definitive evaluation in amputee subjects with implanted electrodes. The simulation tool was used to produce data sets that demonstrate its ability to capture some features of neural recordings that pose challenges for decoding algorithms.

Lifespan maturation and degeneration of human brain white matter

Properties of human brain tissue change across the lifespan. Here we model these changes in the living human brain by combining quantitative magnetic resonance imaging (MRI) measurements of R1 (1/T1) with diffusion MRI and tractography (N=102, ages 7-85). The amount of R1 change during development differs between white-matter fascicles, but in each fascicle the rate of development and decline are mirror-symmetric; the rate of R1 development as the brain approaches maturity predicts the rate of R1 degeneration in aging. Quantitative measurements of macromolecule tissue volume (MTV) confirm that R1 is an accurate index of the growth of new brain tissue. In contrast to R1, diffusion development follows an asymmetric time-course with rapid childhood changes but a slow rate of decline in old age. Together, the time-courses of R1 and diffusion changes demonstrate that multiple biological processes drive changes in white-matter tissue properties over the lifespan.

X-ray computed tomography of the anterior cruciate ligament and patellar tendon

The effect of phosphotungstic acid (PTA) and iodine solution (IKI) staining was investigated as a method of enhancing contrast in the X-ray computed tomography of porcine anterior cruciate ligaments (ACL) and patellar tendons (PT). We show that PTA enhanced surface contrast, but was ineffective at penetrating samples, whereas IKI penetrated more effectively and enhanced contrast after 70 hours of staining. Contrast enhancement was compared when using laboratory and synchrotron based X-ray sources. Using the laboratory source, PT fascicles were tracked and their alignment was measured. Individual ACL fascicles could not be identified, but identifiable features were evident that were tracked. Higher resolution scans of fascicle bundles from the PT and ACL were obtained using synchrotron imaging techniques. These scans exhibited greater contrast between the fascicles and matrix in the PT sample, facilitating the identification of the fascicle edges; however, it was still not possible to detect individual fascicles in the ACL.

Fascicles from energy-storing tendons show an age-specific response to cyclic fatigue loading

Some tendons, such as the human Achilles and equine superficial digital flexor tendon (SDFT), act as energy stores, stretching and recoiling to increase efficiency during locomotion. Our previous observations of rotation in response to applied strain in SDFT fascicles suggest a helical structure, which may provide energy-storing tendons with a greater ability to extend and recoil efficiently. Despite this specialization, energy-storing tendons are prone to age-related tendinopathy. The aim of this study was to assess the effect of cyclic fatigue loading (FL) on the microstructural strain response of SDFT fascicles from young and old horses. The data demonstrate two independent age-related mechanisms of fatigue failure; in young horses, FL caused low levels of matrix damage and decreased rotation. This suggests that loading causes alterations to the helix substructure, which may reduce their ability to recoil and recover. By contrast, fascicles from old horses, in which the helix is already compromised, showed greater evidence of matrix damage and suffer increased fibre sliding after FL, which may partially explain the age-related increase in tendinopathy. Elucidation of helix structure and the precise alterations occurring owing to both ageing and FL will help to develop appropriate preventative and repair strategies for tendinopathy.

Enhanced force production in old age is not a far stretch: an investigation of residual force enhancement and muscle architecture

In older adults, isometric force production is enhanced following a voluntary lengthening contraction when compared with isometric force produced at the same muscle length without a prior lengthening contraction. This phenomenon is termed residual force enhancement (RFE), and appears to be related to the age-related maintenance of eccentric (ECC) strength. However, it is unknown whether age-related changes in muscle architecture contribute to greater RFE at short and long muscle lengths in old age. Neuromuscular properties of the knee extensors were assessed on a HUMAC NORM dynamometer. Torque was examined in young (26 ± 3 year, n = 11) and old men (77 ± 6 year, n = 11) during brief maximal voluntary isometric contractions (MVC) at 80° and 120° (180° representing full knee extension) and then compared with torque during a steady-state phase at the same joint angle following a maximal voluntary lengthening contraction at 30°/sec over a 60° joint excursion; either from 140 to 80° (long), or from 180 to 120° (short). Ultrasound images were obtained from the vastus lateralis during the isometric phase for each condition. When comparing the ECC torque with the MVC isometric torque, old men had 17% greater ECC:MVC ratios than young men, confirming an age-related maintenance of ECC strength. The extent of RFE was greater at long versus short but independent of age. At rest, old had shorter (∼18%) and less pennated (∼22%) fascicles. However, changes in fascicle length and pennation during contraction did not contribute to RFE in either group. Thus, age-related changes in muscle architecture may not contribute to RFE.

Intraoperative electrophysiological studies to predict the efficacy of neurolysis after nerve injury-experiment in rats

Compound muscle action potentials (CMAPs) can be used to analyze injury and recovery of nerve. This standardized study evaluates the value of CMAP analysis in predicting the long-term efficacy of neurolysis. CMAP amplitude is also used to determine the optimal extent of neurolysis. The left peroneal nerves of 30 rats were crushed. CMAPs were recorded for both crushed (left) and control (right) nerves. Fifteen rats underwent neurolysis 3 months post crush injury; the remaining 15 were sham controls and did not undergo neurolysis. CMAP measurements were taken after: (1) release of the nerve from the fascia, (2) opening the epineurium, and (3) opening the perineurium. At 3 months post crush injury, opening the epineurium resulted in a statistically significant increase in CMAP. CMAP increase with perineurial neurolysis was greater than with fascial release of the nerve but was not statistically different from that of epineurial release. At 5 months post crush injury, recovery of crushed nerves that underwent neurolysis was 90% and significantly less at 70.5% in rats not treated with neurolysis, according to CMAP analysis. Two conclusions can be made from this study. First, intraoperative neurophysiologic studies can monitor the immediate results of neurolysis and predict long-term results in the injured nerve. Second, epineurotomy is important in neurolysis, improves the function of the nerve, less invasive, and a slightly more effective technique than perineurotomy.