Age-related differences in the loss and recovery of serial sarcomere number following disuse atrophy in rats.

BACKGROUND: Older adults exhibit a slower recovery of muscle mass following disuse atrophy than young adults. At a smaller scale, muscle fibre cross-sectional area (i.e., sarcomeres in parallel) exhibits this same pattern. Less is known, however, about age-related differences in the recovery of muscle fibre length, driven by increases in serial sarcomere number (SSN), following disuse. The purpose of this study was to investigate age-related differences in SSN adaptations and muscle mechanical function during and following muscle immobilization. We hypothesized that older adult rats would experience a similar magnitude of SSN loss during immobilization, however, take longer to recover SSN than young following cast removal, which would limit the recovery of muscle mechanical function. METHODS: We casted the plantar flexors of young (8 months) and old (32 months) male rats in a shortened position for 2 weeks, and assessed recovery during 4 weeks of voluntary ambulation. Following sacrifice, legs were fixed in formalin for measurement of soleus SSN and physiological cross-sectional area (PCSA) with the un-casted soleus acting as a control. Ultrasonographic measurements of pennation angle (PA) and muscle thickness (MT) were conducted weekly. In-vivo active and passive torque-angle relationships were constructed pre-cast, post-cast, and following 4 weeks of recovery. RESULTS: From pre- to post-cast, young and older adult rats experienced similar decreases in SSN (-20%, P < 0.001), muscle wet weight (-25%, P < 0.001), MT (-30%), PA (-15%, P < 0.001), and maximum isometric torque (-40%, P < 0.001), but there was a greater increase in passive torque in older (+ 180%, P < 0.001) compared to young adult rats (+ 68%, P = 0.006). Following cast removal, young exhibited quicker recovery of SSN and MT than old, but SSN recovered sooner than PA and MT in both young and old. PCSA nearly recovered and active torque fully recovered in young adult rats, whereas in older adult rats these remained unrecovered at ∼ 75%. CONCLUSIONS: This study showed that older adult rats retain a better ability to recover longitudinal compared to parallel muscle morphology following cast removal, making SSN a highly adaptable target for improving muscle function in elderly populations early on during rehabilitation.

Muscle structure predictors of vertical jump performance in elite male volleyball players: a cross-sectional study based on ultrasonography.

Objective: The objective of this investigation is to examine the contribution of key muscle groups in the lower limbs to vertical jumping performance in elite male volleyball players. Specifically, the study focuses on the rectus femoris (RF), vastus lateralis (VL), and lateral gastrocnemius (LG), as well as exploring differences between attack jump and other vertical jump types. Methods: To achieve this, we employed B-mode ultrasound to evaluate the anatomical cross-sectional area (ACSA), muscle thickness (MT), pennation angle (PA), and fascicle length (FL) of the RF, VL, and LG in the participants. Fifteen elite male volleyball players were recruited as participants for this study. Jump heights were measured for four types of vertical jumps: attack jump (AJ), countermovement jump (CMJ), squat jump (SJ), and drop jump (DJ). We conducted regression analyses to assess whether the previously mentioned muscle structures could predict jump performance. Results: Our findings reveal that the muscle structure of the RF does not exhibit any significant correlation with the height of any jump. However, VL-ACSA displays a significant and the most potent predictive effect on jump height for all four jump types (AJ: R 2 = 0.32, p = 0.001; CMJ: R 2 = 0.37, p = 0.005; SJ: R 2 = 0.52, p = 0.001; DJ: R 2 = 0.25, p = 0.021). Conversely, LG-FL only demonstrates a significant and stronger predictive effect on AJ jump height (R 2 = 0.18, p = 0.009). Combining VL-ACSA, LG-FL, and training age through multiple linear regression analysis resulted in a highly significant model for predicting AJ jump height (F = 13.86, R 2 = 0.73). Moreover, the model incorporating VL-ACSA and training age is also important for predicting CMJ, SJ, and DJ jump heights (F = 8.41, R 2 = 0.51; F = 13.14, R 2 = 0.63; F = 5.95, R 2 = 0.41; respectively). Conclusion: The muscle structure indicators in the lower limbs significantly predict jump performance among elite male volleyball players. However, different jump types are influenced by distinct indicators, particularly in the case of AJ, which is associated with LG-FL. This suggests that enhancing LG-FL may positively impact AJ ability, thereby emphasizing the importance of specificity in training. To optimize specialized jump performance in volleyball players, practitioners are advised to assess VL-ACSA and LG-FL and incorporate step-up and eccentric strength training targeting the calf muscles to yield considerable benefits.

Interplay of Muscle Architecture, Morphology, and Quality in Influencing Human Sprint Cycling Performance: A Systematic Review.

BACKGROUND: This systematic review aimed to discern the relationships between muscle morphology, architecture, and quality with sprint cycling performance while considering the multifaceted nature of these relationships across diverse studies. METHODS: Employing the PRISMA guidelines, an exhaustive search was performed across four primary databases: MEDLINE/PubMed, Web of Science, CINAHL Complete, and SPORTDiscus. The Methodological Index For Non-Randomised Studies (MINORS) was used to assess the methodological quality of the included studies. Out of 3971 initially identified records, only 10 studies met the eligibility criteria. RESULTS: These investigations underscored the robust relationship of quadriceps muscle volume with peak power output (R2 from 0.65 to 0.82), suggesting its pivotal role in force production. In muscle architecture, the pennation angle and fascicle length showed varied associations with performance. Furthermore, muscle quality, as denoted by echo intensity, showed preliminary evidence of a potential inverse relationship with performance. The methodological quality assessment revealed varied scores, with the most consistent reporting on the aim, endpoints, and inclusion of consecutive patients. However, limitations were observed in the prospective calculation of study size and unbiased assessment of study endpoints. CONCLUSION: Our findings indicate that muscle volume is a major determinant of sprint cycling performance. Muscle architecture and quality also impact performance, although in a more intricate way. The review calls for standardised methodologies in future research for a more comprehensive understanding and comparability of results. PROSPERO REGISTRATION NUMBER: CRD42023432824 ( https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=432824 ).

Sciatic nerve fascicle differentiation on high-resolution ultrasound with histological verification: An ex vivo study.

INTRODUCTION/AIMS: The development of high-resolution ultrasound (HRUS) has enabled the depiction of peripheral nerve microanatomy in vivo. This study compared HRUS fascicle differentiation to the structural depiction in histological cross-sections (HCS). METHODS: A human cadaveric sciatic nerve was marked with 10 surgical sutures, and HRUS image acquisition was performed with a 22-MHz probe. The nerve was excised and cut into five segments for HCS preparation. Selected HCS were cross-referenced to HRUS, with sutures to improve orientation. Sciatic nerve and fascicle contouring were performed to assess nerve and fascicular cross-sectional area (CSA), fascicle count, and interfascicular distances. Three groups were defined based on HRUS fascicle differentiation in comparison to HCS, namely single fascicle (SF), fascicular cluster (FC), and no depiction (ND) group. RESULTS: On cross-referenced HRUS to HCS images, 58% of fascicles were differentiated. On HRUS, significantly larger fascicle CSA and smaller fascicle count were observed compared with HCS. Group analysis showed that 41% of fascicles were defined as SF, 47% as FC, and 12% as ND. The mean fascicle CSA in the ND group was 0.05 mm2. Compared with the SF, the FC had significantly larger fascicle CSA (1.2 ± 0.7 vs. 0.6 ± 0.4 mm2; p < .001) and shorter interfascicular distances (0.1 ± 0.04 vs. 0.5 ± 0.3 µm; p < .001). DISCUSSION: While HRUS can depict fascicular anatomy, only half of the fascicles visualized on HRUS directly correspond to single fascicles observed on HCS. The amount of interfascicular epineurium appears to influence the ability of HRUS to differentiate individual fascicles.

Test-retest reliability of gastrocnemius medialis fascicle force-length relationship.

Fascicle force-length relationship is one major basic mechanical property of skeletal muscle, subsequently influencing movement mechanics. While force-length properties are increasingly described through ultrafast ultrasound imaging, their test-retest reliability remains unknown. Using ultrafast ultrasound, and electrically evoked contractions at various ankle angles, gastrocnemius medialis fascicle force-length relationship was assessed twice, few days apart, in sixteen participants. The test-retest reliability of the resulting fascicle force-length relationship key parameters - i.e., maximal force (Fmax), and optimal fascicle length (L0) - was evaluated considering (i) all the trials obtained at each ankle joint and (ii) the mean of the two trials obtained at each tested angle. Considering all trials, L0 indicated a 'high' test-retest reliability, with intra-class correlation coefficients (ICC) of 0.89 and Fmax a 'moderate' reliability (ICC = 0.71), while when averaging the two trials L0 reliability was 'very-high' (ICC = 0.91), and Fmax reliability 'moderate' (ICC = 0.73). All values of coefficient of variation and standard error of measurement were low, i.e., ≤7.7 % and ≤0.35 cm for L0 and ≤3.4 N for Fmax, respectively. Higher absolute reliability was reported for L0 than Fmax, with better reliability when averaging the two trials at each angle. All these parameters, in accordance with the limit of agreement, demonstrated that L0 and Fmax test-retest reliability is acceptable, particularly when averaging multiple points obtained at a given angle. Interestingly, the shape of the fascicle force-length relationship is more variable. Therefore, L0 and Fmax can be used to compare between days-effects following an intervention, while a comparison of fascicle operating lengths may require more precautions.

Sparse Blind Spherical Deconvolution of diffusion weighted MRI.

Diffusion-weighted magnetic resonance imaging provides invaluable insights into in-vivo neurological pathways. However, accurate and robust characterization of white matter fibers microstructure remains challenging. Widely used spherical deconvolution algorithms retrieve the fiber Orientation Distribution Function (ODF) by using an estimation of a response function, i.e., the signal arising from individual fascicles within a voxel. In this paper, an algorithm of blind spherical deconvolution is proposed, which only assumes the axial symmetry of the response function instead of its exact knowledge. This algorithm provides a method for estimating the peaks of the ODF in a voxel without any explicit response function, as well as a method for estimating signals associated with the peaks of the ODF, regardless of how those peaks were obtained. The two stages of the algorithm are tested on Monte Carlo simulations, as well as compared to state-of-the-art methods on real in-vivo data for the orientation retrieval task. Although the proposed algorithm was shown to attain lower angular errors than the state-of-the-art constrained spherical deconvolution algorithm on synthetic data, it was outperformed by state-of-the-art spherical deconvolution algorithms on in-vivo data. In conjunction with state-of-the art methods for axon bundles direction estimation, the proposed method showed its potential for the derivation of per-voxel per-direction metrics on synthetic as well as in-vivo data.

Myological and osteological approaches to gape and bite force reconstruction in Smilodon fatalis.

Masticatory gape and bite force are important behavioral and ecological variables. While much has been written about the highly derived masticatory anatomy of Smilodon fatalis, there remains a great deal of debate about their masticatory behaviors. To that end, we establish osteological proxies for masticatory adductor fascicle length (FL) based on extant felids and apply these along with previously validated techniques to S. fatalis to provide estimates of fascicle lengths, maximum osteological gapes, and bite force. While the best correlated FL proxies in extant felids do not predict particularly long fascicles, these proxies may be of value for less morphologically distinct felids. A slightly less well correlated proxy predicts a temporalis FL 15% longer than that of Panthera tigris. While angular maximum bony gape is significantly larger in S. fatalis than it is in extant felids, linear gape at the canine tip and carnassial notch were not significantly different from those of extant felids. Finally, we produce anatomical bite force estimates of 1283.74 N at the canine and 4671.41 N at the carnassial, which are similar in magnitude to estimates not of the largest felids but of the much smaller P. onca, with S. fatalis producing slightly less force at the canines and more at the carnassials. These estimates align with previous predictions that S. fatalis may have killed large prey with canine shearing bites produced, in part, by force contributions of the postcranial muscles.

High Velocity Passive Stretching Mimics Eccentric Exercise in Cerebral Palsy and May Be Used to Increase Spastic Muscle Fascicle Length.

Muscle fascicles are shorter and stiffer than normal in spastic Cerebral Palsy (CP). Increasing fascicle length (FL) has been attempted in CP, the outcomes of which have been unsatisfactory. In healthy muscles, FL can be increased using eccentric exercise at high velocities (ECC). Three conditions are possibly met during such ECC: muscle micro-damage, positive fascicle strain, and momentary muscle deactivation during lengthening. Participants with and without CP underwent a single bout of passive stretching at (appropriately) high velocities using isokinetic dynamometry, during which we examined muscle and fascicle behaviour. Vastus lateralis (VL) FL change was measured using ultrasonography and showed positive fascicle strain. Measures of muscle creatine kinase were used to establish whether micro-damage occurred in response to stretching, but the results did not confirm damage in either group. Vastus medialis (VM) and biceps femoris muscle activity were measured using electromyography in those with CP. Results supported momentary spastic muscle deactivation during lengthening: all participants experienced at least one epoch (60 ms) of increased activation followed by activation inhibition/deactivation of the VM during knee flexion. We argue that high-velocity passive stretching in CP provides a movement context which mimics ECC and could be used to increase spastic FL with training.

Bilateral hypogeusia and food aversion due to lacunar infarct in the right dorsomedial pontine tegmentum.

A 70-year-old right-handed housewife suffered an acute loss of taste, an unpleasant change in the taste of foods and liquids, and a strong aversion to all kinds of food due to a small lacune in the right dorsomedial pontine tegmentum. Eating became so unpleasant that she lost 7 kg in three weeks. Olfaction and the sensibility of the tongue were spared. The right medial longitudinal fascicle, the central tegmental tract, or both, were injured by the tegmental lesion. A discrete right-sided lesion in the upper pontine tegmentum may cause a reversible syndrome consisting of bilateral hypogeusia which is more severe ipsilaterally.

Diagnostic value of ultrasonography for injury of anterior talofibular ligament and anterior inferior tibiofibular ligament distal fascicle in patients with ankle fractures. / è¶ å£°è¯„ä¼°è¸å ³èŠ‚éª¨æŠ˜æ‚£è€ è·è “å‰éŸ§å¸¦åŠä¸‹èƒ«è “å‰éŸ§å¸¦è¿œä¾§æŸæŸä¼¤çš„ä»·å€¼.

OBJECTIVES: To explore the diagnostic value of ultrasonography for injuries of anterior talofibular ligament (ATFL) and anterior inferior tibiofibular ligament distal fascicle (ATiFL-DF) in patients with ankle fractures. METHODS: Clinical data of 51 patients with ankle fractures who were clinically suspected of ligament injuries and underwent ankle ultrasonography examination and arthroscopy in Sir Run Run Shaw Hospital, Zhejiang University School of Medicine from April 2019 to March 2023 were retrospectively analyzed. Using arthroscopic findings as the gold standard, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of ultrasonography in diagnosing ATFL and ATiFL-DF injuries were evaluated; and Kappa consistency test was further performed. RESULTS: The sensitivity and specificity of ultrasonography in diagnosis of ATFL injury were 100.0% and 92.3%, with the PPV of 92.6% and NPV of 100.0%. Ultrasonography findings exhibited excellent concordance with arthroscopic results (kappa=0.849). The sensitivity and specificity of ultrasonography in diagnosis of ATiFL-DF injury was 86.7% and 33.3%, with the PPV of 90.7% and NPV of 25.0%. But the consistence between ultrasonography and arthroscopic results was poor (kappa=0.168). CONCLUSIONS: Ultrasonography is a reliable diagnostic modality for assessing injuries to the ATFL in patients with ankle fractures; however, its specificity is limited when evaluating injuries to the ATiFL-DF. Therefore, ankle arthroscopy is necessary for ankle fracture patients with negative findings of ATiFL-DF in ultrasonography.

Narrow QRS ectopy with concealed connections from a para-Hisian origin to the proximal left fascicles.

INTRODUCTION: Catheter ablation of ectopy originating from the vicinity of the His bundle can be challenging. METHODS AND RESULTS: We report a case of a 33-year-old man with narrow QRS ectopy with preferential conduction from a para-Hisian origin to the proximal left fascicles, which was successfully eliminated by radiofrequency ablation in the right coronary cusp, guided by ultrahigh-resolution mapping of the His bundle, bundle branch, and fascicular electrograms. CONCLUSION: Some narrow QRS ectopy may originate from the vicinity of the conduction system, instead of the "true" conduction system, and have concealed connections from its origin to the conduction system.

Acute fatigue-induced alterations in hamstring muscle properties after repeated Nordic hamstring exercises.

This study aimed to investigate the impact of the Nordic hamstring exercises (NHE) on acute fatigue-induced alterations in the mechanical and morphological properties of hamstring muscles. The second aim was to define the blood flow and perfusion after NHE in recreational active volunteers. Twenty-two individuals volunteered to participate in the study. This study investigated fatigue outcomes: rate of perceived exertion (RPE) scale and average force generated during NHE; mechanical properties (stiffness); morphological properties (thickness, pennation angle, and fascicle length), and vascularity index (VI) of the semitendinosus (ST) and biceps femoris long head (BFLH) at baseline, immediately post-exercise and 1-h post-exercise. The NHE fatigue procedure consisted of six bouts of five repetitions. The results showed an increase in thickness and pennation angle of BFLH and ST immediately post-exercise and a decrease in thickness and pennation angle of BFLH and ST 1-h post-exercise. While the fascicle length of BFLH and ST decreased immediately post-exercise and increased 1-h post-exercise. The VI for two muscles increased immediately post-exercise and after 1-h post-exercise. Moreover, we found a relationship between RPE and average force, that is, as RPE increased during NHE, average force decreased. In conclusion, eccentric NHE exercises significantly and acutely affect BFLH and ST. The NHE fatigue protocol significantly affected the mechanical and morphological properties of BFLH and ST muscles, changing their thickness, fascicle length, pennation angle, and VI.

Eccentric exercise ≠ eccentric contraction.

Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series compliance. Therefore, this study investigated the impact of changing the activation timing and level (i.e., preactivation) of the contraction on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were used to assess muscle fascicle kinematics and muscle activity levels, respectively. Although joint kinematics were similar among MTU-stretch-hold contractions (∼40° rotation amplitude), increasing preactivation increased fascicle shortening and stretch amplitudes (9.9-23.2 mm, P ≤ 0.015). This led to increasing positive and negative fascicle work with increasing preactivation. Despite significantly different fascicle kinematics, similar peak fascicle forces during stretch occurred at similar fascicle lengths and joint angles regardless of preactivation. Similarly, residual force enhancement (rFE) following MTU stretch was not significantly affected (6.5-7.6%, P = 0.559) by preactivation, but rFE was strongly correlated with peak fascicle force during stretch (rrm = 0.62, P = 0.003). These findings highlight that apparent eccentric exercise causes shortening-stretch contractions at the fascicle level rather than isolated eccentric contractions. The constant rFE despite different fascicle kinematics and kinetics suggests that a passive element was engaged at a common muscle length among conditions (e.g., optimal fascicle length). Although it remains unclear whether different fascicle mechanics trigger different adaptations to eccentric exercise, this study emphasizes the need to consider MTU series compliance to better understand the mechanical drivers of adaptation to exercise.NEW & NOTEWORTHY Apparent eccentric exercises do not result in isolated eccentric contractions, but shortening-stretch contractions at the fascicle level. The amount of fascicle shortening and stretch depends on the preactivation during the exercise and cannot be estimated from the muscle-tendon unit (MTU) or joint kinematics. As different fascicle mechanics might trigger different adaptations to eccentric exercise, muscle-tendon unit series compliance and muscle preactivation need to be considered when eccentric exercise protocols are designed.

Anterior Talofibular Ligament Repair in Combination With Anterior Tibiofibular Ligament Distal Fascicle Transfer for The Treatment of Chronic Lateral Ankle Instability: A Finite Element Analysis.

In recent years, anterior tibiofibular ligament-distal fascicle transfers for anterior talofibular ligament augmentation repair have proposed. However, a comprehensive biomechanical study on the anterior tibiofibular ligament-distal fascicle transfer is still lacking. We are established four distinct groups, namely the normal, the anterior talofibular ligament rupture, the anterior talofibular ligament repair, and the anterior talofibular ligament repair + anterior tibiofibular ligament-distal fascicle transfer. We assessed the anterior drawer test and varus stress test of the ankle in each group. Moreover, we employed the model to simulate and compute the total displacement and von-Mises stress of the talus cartilage at varying gait phases, including foot strike, tibia vertical, and toe-off phases. The results of the anterior drawer test and varus stress test revealed that the anterior talofibular ligament repair + anterior tibiofibular ligament-distal fascicle transfer group exhibited greater closeness to the normal group. Regarding von-Mises stress in cartilage, the three gait instants had higher values in the anterior talofibular ligament repair + anterior tibiofibular ligament-distal fascicle transfer group than the other groups. Nevertheless, regarding total displacement, the toe-off phases exhibited higher values in the anterior talofibular ligament repair + anterior tibiofibular ligament-distal fascicle transfer group than the other groups. Using ATiFL-DF transfer to augment ATFL repair is a potential feasible procedure. However, this procedure could potentially compromise the anterior tibiofibular ligament's contribution to the dynamic stability of the ankle. Therefore, we recommend conducting further in-depth research to ensure the suitability and success of this technique in a clinical environment.

Chronic lateral ankle instability using anterior tibiofibular ligament distal fascicle transfer augmentation repair: an anatomical, biomechanical, and histological study.

Background: The transfer of the anterior tibiofibular ligament distal fascicle (ATiFL-DF) for the augmentation repair of the anterior talofibular ligament (ATFL) shows potential as a surgical technique. However, evidences on the benefits and disadvantages of this method in relation to ankle joint function are lacking. Purpose: This study aimed to provide comprehensive experimental data to validate the feasibility of ATiFL-DF transfer augmentation repair of the ATFL. Methods: This study included 50 embalmed ankle specimens to measure various morphological features, such as length, width, thickness, and angle, for evaluating similarities between the ATiFL-DF and ATFL. Furthermore, 24 fresh-frozen ankle specimens were examined for biomechanical testing of the ATiFL-DF transfer augmented repair of the ATFL. Finally, 12 pairs of ATiFL-DF and ATFL tissues from fresh-frozen ankle specimens were treated with gold chloride staining to analyze mechanoreceptor densities. Results: Anatomical studies found that the lengths and thicknesses of the ATFL and ATiFL-DF are similar. Biomechanical outcomes showed that performing ATiFL-DF transfer for ATFL repair can improve the stability of the talus and ankle joints. This is evident from the results of the anterior drawer, axial load, and ultimate failure load tests. However, performing ATiFL-DF transfer may compromise the stability of the distal tibiofibular joint, based on the Cotton and axial load tests at an external rotation of 5°. Analysis of the histological findings revealed that mechanoreceptor densities for four types of mechanoreceptors were comparable between the ATiFL-DF and ATFL groups. Conclusion: ATiFL-DF transfer is a viable method for augmenting ATFL repair. This technique helps to improve the stability of the talus and ankle joints while compensating for proprioception loss. Although ATiFL-DF transfer augmented repair of the ATFL may negatively affect the stability of the distal tibiofibular joint, this procedure can enhance the stability of the talus and ankle joints.

Cortico-cortical evoked potentials of language tracts in minimally invasive glioma surgery guided by Penfield stimulation.

OBJECTIVE: We investigated the feasibility of recording cortico-cortical evoked potentials (CCEPs) in patients with low- and high-grade glioma. We compared CCEPs during awake and asleep surgery, as well as those stimulated from the functional Broca area and recorded from the functional Wernicke area (BtW), and vice versa (WtB). We also analyzed CCEP properties according to tumor location, histopathology, and aphasia. METHODS: We included 20 patients who underwent minimally invasive surgery in an asleep-awake-asleep setting. Strip electrode placement was guided by classical Penfield stimulation of positive language sites and fiber tracking of the arcuate fascicle. CCEPs were elicited with alternating monophasic single pulses of 1.1 Hz frequency and recorded as averaged signals. Intraoperatively, there was no post-processing of the signal. RESULTS: Ninety-seven CCEPs from 19 patients were analyzed. There was no significant difference in CCEP properties when comparing awake versus asleep, nor BtW versus WtB. CCEP amplitude and latency were affected by tumor location and histopathology. CCEP features after tumor resection correlated with short- and long-term postoperative aphasia. CONCLUSION: CCEP recordings are feasible during minimally invasive surgery. CCEPs might be surrogate markers for altered connectivity of the language tracts. SIGNIFICANCE: This study may guide the incorporation of CCEPs into intraoperative neurophysiological monitoring.

Reliability of assessing skeletal muscle architecture and tissue organization of the gastrocnemius medialis and vastus lateralis muscle using ultrasound and spatial frequency analysis.

Introduction: The purpose of this study was to investigate inter- and intra-rater reliability as well as the inter-rater interpretation error of ultrasound measurements assessing skeletal muscle architecture and tissue organization of the gastrocnemius medialis (GM) and vastus lateralis (VL) muscle. Methods: The GM and VL of 13 healthy adults (22 ± 3 years) were examined thrice with sagittal B-mode ultrasound: intraday test-retest examination by one investigator (intra-rater) and separate examinations by two investigators (inter-rater). Additionally, images from one investigator were analysed by two interpretators (interpretation error). Muscle architecture was assessed by muscle thickness [MT], fascicle length [FL], as well as superior and inferior pennation angle [PA]. Muscle tissue organization was determined by spatial frequency analysis (SFA: peak spatial frequency radius, peak -6 dB width, PSFR/P6, normalized peak value of amplitude spectrum [Amax], power within peak [PWP], peak power percent). Reliability of ultrasound examination and image interpretation are presented as intraclass correlation coefficient (ICC), test-retest variability, standard error of measurement as well as bias and limits of agreement. Results: GM and VL demonstrated excellent ICCs for inter- and intra-rater reliability, along with excellent ICCs for interpretation error of MT (0.91-0.99), showing minimal variability (<5%) and SEM% (<5%). Systematic bias for MT was less than 1 mm. For PA and FL poor to good ICCs for inter- and intra-rater reliability were revealed (0.41-0.90), with moderate variability (<12%), low SEM% (<10%) and systematic bias between 0.1-1.4°. Tissue organization analysis indicated moderate to good ICCs for inter- and intra-rater reliability. Notably, Amax and PWP consistently held the highest ICC values (0.77-0.87) across all analyses but with higher variability (<24%) and SEM% (<18%), compared to lower variability (<9%) and SEM% (<8%) in other tissue organization parameters. Interpretation error of all muscle tissue organization parameters showed excellent ICCs (0.96-0.999) with very low variability (≤1%) and SEM% (<2%), except Amax & PWP (TRV%: <6%; SEM%: <7%). Conclusion: Our findings demonstrated excellent inter- and intra-rater reliability for MT. However, agreement for PA, FL, and SFA parameters was not as strong. Additionally, MT and all SFA parameters exhibited excellent agreement for inter-rater interpretation error. Therefore, the SFA seems to offer the possibility of objectively and reliably evaluating ultrasound images.

Influence of muscle length on the three-dimensional architecture and aponeurosis dimensions of rabbit calf muscles.

The function of a muscle is highly dependent on its architecture, which is characterized by the length, pennation, and curvature of the fascicles, and the geometry of the aponeuroses. During in vivo function, muscles regularly undergo changes in length, thereby altering their architecture. During passive muscle lengthening, fascicle length (FL) generally increases and the angle of fascicle pennation (FP) and the fascicle curvature (FC) decrease, while the aponeuroses increase in length but decrease in width. Muscles are differently structured, making their change during muscle lengthening complex and multifaceted. To obtain comprehensive data on architectural changes in muscles during passive length, the present study determined the three-dimensional fascicle geometry of rabbit M. gastrocnemius medialis (GM), M. gastrocnemius lateralis (GL), and M. plantaris (PLA). For this purpose, the left and right legs of three rabbits were histologically fixed at targeted ankle joint angles of 95° (short muscle length [SML]) and 60° (long muscle length [LML]), respectively, and the fascicles were tracked by manual three-dimensional digitization. In a second set of experiments, the GM aponeurosis dimensions of ten legs from five rabbits were determined at varying muscle lengths via optical marker tracking. The GM consisted of a uni-pennated compartment, whereas the GL and PLA contained multiple compartments of differently pennated fascicles. In the LML compared to the SML, the GM, GL, and PLA had on average a 41%, 29%, and 41% increased fascicle length, and a 30%, 25%, and 33% decrease in fascicle pennation and a 32%, 11%, and 35% decrease in fascicle curvature, respectively. Architectural properties were also differentiated among the different compartments of the PLA and GL, allowing for a more detailed description of their fascicle structure and changes. It was shown that the compartments change differently with muscle length. It was also shown that for each degree of ankle joint angle reduction, the proximal GM aponeurosis length increased by 0.11%, the aponeurosis width decreased by 0.22%, and the area was decreased by 0.20%. The data provided improve our understanding of muscles and can be used to develop and validate muscle models.

The effects of 6-week home-based static stretching, dynamic stretching, or eccentric exercise interventions on muscle-tendon properties and functional performance in older women.

Background: Joint inflexibility is acknowledged as a significant contributor to functional limitations in the older adult, with lengthening-type exercises identified as a potential remedial approach. Nevertheless, the responses to eccentric exercise in female older adults have not been extensively studied especially in home-based environment. Here, we aimed to assess the effectiveness of home-based static stretching (ST), dynamic closed-chain stretching (DCS), or eccentric exercise (ECC) interventions on flexibility, musculotendinous architecture, and functional ability in healthy older women. Methods: We randomly assigned 51 healthy older women (age 65.9 ± 3.4 years) to one of three interventional exercise groups: DCS (N = 17), ECC (N = 17), or ST (N = 17). The training was performed 3 times a week for 6 weeks. The participants' musculotendinous stiffness, fascicle length, eccentric strength, and functional capacities were measured before the intervention, after 6 weeks of exercise, and at a 1-month follow-up. Results: The results showed that all three interventions improved hamstring flexibility and passive ankle dorsiflexion (p < 0.001), with increased biceps femoris and medial gastrocnemius fascicle length (p < 0.01). However, there was no significant change in musculotendinous stiffness. The ECC intervention produced a greater improvement in knee flexor and calf eccentric peak torque (p < 0.05), and gait speed (p = 0.024) than the other two interventions. The changes in flexibility and knee flexor strength remained for up to 4 weeks after detraining. Conclusion: In conclusion, the present study suggests that home-based ECC may be more beneficial in enhancing physical capacities in older women compared with either DCS or SS interventions.

A shorter R wave peak time in left bundle branch pacing may not be a marker of more physiological ventricular activation: A case report.

Left bundle branch pacing (LBBp) is a promising alternative to conventional biventricular pacing cardiac resynchronization therapy. The left anterior fascicle (LAF) is adjacent to the left ventricular outflow tract, while the left posterior fascicle (LPF) dominates a broader area of the left ventricle. Whether LAF or LPF dominates ventricular activation has not been determined. We present the case of a 76-year-old man who underwent LBBp implantation and propose the left ventricular activation domination in LPF pacing, an alternative when LBBp is unavailable.