Plasticity of the muscle-tendon complex with disuse and aging

Optimal fibre length and maximum isometric force are the most influential parameters when modelling muscular adaptations to unloading using Hill-type muscle models

Introduction: Spaceflight is associated with severe muscular adaptations with substantial inter-individual variability. A Hill-type muscle model is a common method to replicate muscle physiology in musculoskeletal simulations, but little is known about how the underlying parameters should be adjusted to model adaptations to unloading. The aim of this study was to determine how Hill-type muscle model parameters should be adjusted to model disuse muscular adaptations. Methods: Isokinetic dynamometer data were taken from a bed rest campaign and used to perform tracking simulations at two knee extension angular velocities (30°·s-1 and 180°·s-1). The activation and contraction dynamics were solved using an optimal control approach and direct collocation method. A Monte Carlo sampling technique was used to perturb muscle model parameters within physiological boundaries to create a range of theoretical and feasible parameters to model muscle adaptations. Results: Optimal fibre length could not be shortened by more than 67% and 61% for the knee flexors and non-knee muscles, respectively. Discussion: The Hill-type muscle model successfully replicated muscular adaptations due to unloading, and recreated salient features of muscle behaviour associated with spaceflight, such as altered force-length behaviour. Future researchers should carefully adjust the optimal fibre lengths of their muscle-models when trying to model adaptations to unloading, particularly muscles that primarily operate on the ascending and descending limbs of the force-length relationship.

Assessing Muscle Mass in the Orthopedic Clinical Setting: Application of the Ultrasound Sarcopenia Index in Elderly Subjects with a Recent Femoral Fracture

BACKGROUND

Sarcopenia poses a risk factor for falls, disability, mortality, and unfavorable postoperative outcomes. Recently, the Ultrasound Sarcopenia Index (USI) has been validated to assess muscle mass, and this study aimed to apply the USI in the clinical setting.

METHODS

This prospective observational study included 108 patients aged >65 years, hospitalized for proximal femoral traumatic fracture. Patients were divided into two groups based on anamnestic data: patients with independent walking (IW) and patients requiring walking aid (WA) before admission. All the participants received an ultrasound examination. Other parameters evaluated were handgrip strength, limb circumferences, nutrition (MNA), and activity of daily living (ADL) scores.

RESULTS

Fifty-six IW patients (83 ± 6 y; 38 females) and 52 WA patients (87 ± 7 y; 44 females) were recruited. The USI was significantly higher in the IW group compared to the WA group (p = 0.013, Cohen's d = 0.489). Significant correlations were found between the USI and other sarcopenia-associated parameters, such as handgrip strength, MNA, ADLs, other muscle ultrasound parameters, and limb circumferences.

CONCLUSION

The application of the USI in the orthopedic surgery setting is feasible and might support the diagnosis of sarcopenia when combined with other measures of strength and function.

Combined ultrasound of m. quadriceps and diaphragm to determine the occurrence of sarcopenia and prolonged ventilation in a COVID-19 ICU cohort: The COVID-SARCUS trial

OBJECTIVE

The aim of this study was to determine the development of sarcopenia in a COVID-19 intensive care unit population by sequential quadriceps and diaphragm ultrasound and its relationship with hospital outcomes.

METHODS

We assessed muscle thickness, cross-sectional area, fascicle length, pennation angle, and echo intensity within 48 h after intubation, at days 5 and 10 and at discharge from the intensive care unit in 30 critically ill patients with confirmed COVID-19.

RESULTS

A different evolution of muscle thickness of the diaphragm and m. rectus femoris was observed; the changes between the two muscles were not correlated (Pearson's χ2 3.91, P = 0.419). The difference in muscle thickness was linked to the outcome for both m. rectus femoris and diaphragm, with the best survival seen in the group with stable muscle thickness. The greatest loss of muscle thickness occurred between days 5 and 10. The echo intensity was higher in the patients with increased muscle thickness, who also had a worse prognosis. There was a correlation between cross-sectional area on day 5 and handgrip strength (r = 0.290, P = 0.010). Only 31% of patients were able to return to their preadmission residence without any additional rehabilitation.

CONCLUSIONS

Muscle atrophy and decline in muscle strength appear in the earliest stages after admission to the intensive care unit and are related to functional outcome.

3D characterization of the triple-bundle Achilles tendon from in vivo high-field MRI

The Achilles tendon consists of three subtendons that transmit force from the triceps surae muscles to the calcaneus. Individual differences have been identified in Achilles subtendon morphology and twist in cadavers, which may have implications for triceps surae mechanics and function. High-field magnetic resonance imaging (MRI) can be used to identify boundaries within multi-bundle tissues, which could then enable studies of subtendon structure-function relationships in humans. The objective of this study was to use high-field MRI (7T) to image and reconstruct Achilles subtendons arising from the triceps surae muscles. We imaged the dominant lower leg of a cohort of healthy human subjects (n = 10) using a tuned musculoskeletal sequence (double echo steady state sequence, 0.4 mm isotropic voxels). We then characterized the cross-sectional area and orientation of each subtendon between the MTJ and calcaneal insertion. Image collection and segmentation was repeated to assess repeatability. Subtendon morphometry varied across subjects, with average subtendon areas of 23.5 ± 8.9 mm2 for the medial gastrocnemius, 25.4 ± 8.9 mm2 for the lateral gastrocnemius, and 13.7 ± 5.9 mm2 for the soleus subtendons. Repeatable subject-specific variations in size and position of each subtendon were identified over two visits, expanding on prior knowledge that high variability exists in Achilles subtendon morphology across subjects.

Does femoroacetabular impingement syndrome affect range of motion? A systematic review with meta-analysis

BACKGROUND

It is unclear whether femoroacetabular impingement syndrome (FAIS) affect hip range of motion (ROM).

SOURCES OF DATA

We performed a systematic review with meta-analysis searching six electronic databases from inception to March 21, 2022. We included studies assessing hip ROM in FAIS, FAI morphology without symptoms (FAIm), and healthy controls. Mean differences between groups were measured in ROM degrees with 95% confidence interval (CI).

AREAS OF AGREEMENT

A total of 17 studies (1702 hips) were included. Comparison of FAIS patients versus healthy controls showed that hip ROM was clinically and statistically reduced in FAIS for internal rotation (90° hip flexion, -8.01°, 95% CI: -11.21, -4.90; 0° hip flexion -6.38°, 95% CI: -9.79, -2.97); adduction (90° hip flexion, -4.74°, 95% CI: -8.13, -1.34); flexion (-5.41°, 95% CI: -7.05, -3.49), abduction (0° hip flexion, -5.76°, 95% CI: -8.38, -3.23), and external rotation (90° hip flexion, -3.5°, 95% CI: -5.32, -1.67) ranging from low to high certainty of evidence. Comparison of FAIm versus healthy controls showed no statistically significant differences in any direction of movement, albeit with uncertainty of evidence.

AREAS OF CONTROVERSY

The certainty of evidence was unclear, particularly for asymptomatic FAIm.

GROWING POINTS

Hip ROM may be reduced in all directions except extension in FAIS compared to controls. Hip ROM may not be restricted in asymptomatic FAIm.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further studies are needed to resolve the uncertainty of evidence about ROM restrictions in asymptomatic FAIm compared to healthy controls.

Collagen VI in the Musculoskeletal System

Collagen VI exerts several functions in the tissues in which it is expressed, including mechanical roles, cytoprotective functions with the inhibition of apoptosis and oxidative damage, and the promotion of tumor growth and progression by the regulation of cell differentiation and autophagic mechanisms. Mutations in the genes encoding collagen VI main chains, COL6A1, COL6A2 and COL6A3, are responsible for a spectrum of congenital muscular disorders, namely Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and myosclerosis myopathy (MM), which show a variable combination of muscle wasting and weakness, joint contractures, distal laxity, and respiratory compromise. No effective therapeutic strategy is available so far for these diseases; moreover, the effects of collagen VI mutations on other tissues is poorly investigated. The aim of this review is to outline the role of collagen VI in the musculoskeletal system and to give an update about the tissue-specific functions revealed by studies on animal models and from patients' derived samples in order to fill the knowledge gap between scientists and the clinicians who daily manage patients affected by collagen VI-related myopathies.

The effect of specific bioactive collagen peptides on function and muscle remodeling during human resistance training

AIM

Bioactive collagen peptides (CP) have been suggested to augment the functional, structural (size and architecture), and contractile adaptations of skeletal muscle to resistance training (RT), but with limited evidence. This study aimed to determine if CP vs. placebo (PLA) supplementation enhanced the functional and underpinning structural, and contractile adaptations after 15 weeks of lower body RT.

METHODS

Young healthy males were randomized to consume either 15 g of CP (n = 19) or PLA (n = 20) once every day during a standardized program of progressive knee extensor, knee flexor, and hip extensor RT 3 times/wk. Measurements pre- and post-RT included: knee extensor and flexor isometric strength; quadriceps, hamstrings, and gluteus maximus volume with MRI; evoked twitch contractions, 1RM lifting strength, and architecture (with ultrasound) of the quadriceps.

RESULTS

Percentage changes in maximum strength (isometric or 1RM) did not differ between-groups (0.684 ≤ p ≤ 0.929). Increases in muscle volume were greater (quadriceps 15.2% vs. 10.3%; vastus medialis (VM) 15.6% vs. 9.7%; total muscle volume 15.7% vs. 11.4%; [all] p ≤ 0.032) or tended to be greater (hamstring 16.5% vs. 12.8%; gluteus maximus 16.6% vs. 12.9%; 0.089 ≤ p ≤ 0.091) for CP vs. PLA. There were also greater increases in twitch peak torque (22.3% vs. 12.3%; p = 0.038) and angle of pennation of the VM (16.8% vs. 5.8%, p = 0.046), but not other muscles, for CP vs. PLA.

CONCLUSIONS

CP supplementation produced a cluster of consistent effects indicating greater skeletal muscle remodeling with RT compared to PLA. Notably, CP supplementation amplified the quadriceps and total muscle volume increases induced by RT.

Positional and dimensional relation of tendons around the first metatarsal bone with hallux valgus

PURPOSE

It was aimed to reveal whether the positions and dimensions of the extrinsic and intrinsic muscle tendons related to the hallux around the first metatarsal bone are affected by the severity of hallux valgus (HV) and whether tendon positional changes and tendon sizes affect each other.

METHODS

In formalin-fixed 46 feet, three HV angle subgroups (normal, mild, and moderate/severe) were defined. Width, thickness, and cross-sectional area (CSA) of tendons of the extensor hallucis longus (EHL) and brevis (EHB), abductor hallucis (AH), and flexor hallucis longus (FHL) were measured. On the clock model created in coronal plane, positional variations of each tendon were determined.

RESULTS

In the moderate/severe HV group, thickness and CSA of the EHB, width and CSA of the AH were smaller, compared to mild HV. Width and CSA of the FHL were smaller in moderate/severe HV than in the normal. Regardless of HV, the width and CSA of the FHL were greater in cases where the FHL was located more lateral, and the width of both FHL and AT were greater in cases where AH located was more plantar.

CONCLUSION

The smaller tendon size of two intrinsic (one plantar and one dorsal) and one extrinsic muscle in the moderate/severe HV group indicates that changes in the tendons are evident in cases of high severity of HV but not in cases of mild HV. Accordingly, the changes do not appear to be due to a factor limited to only one aspect of the foot. It is recommended to consider the possible biomechanical effects of AH, FHL, and EHB tendon dimensional weakness in surgical planning in moderate/severe HV cases.

Increased incidence of acute achilles tendon ruptures in the peri-pandemic COVID era with parallels to the 2021-22 NFL season

PURPOSE

Acute Achilles tendon ruptures (AATRs) are a common sporting injury, whether for recreational athletes or elite athletes. Prior research has shown returning to physical activity after extended periods of inactivity leads to increased rates of musculoskeletal injuries. The purpose of this study was to investigate rates of acute Achilles' tendon ruptures at a single academic institute in the peri-COVID era, with corollary to the recent NFL season.

METHODS

A retrospective search was conducted using current procedural terminology to identify the total number of Achilles acute primary repair surgeries performed from years 2017 to 2021. Non-operatively managed AATRs were identified from the same electronic medical record using ICD-10 codes. NFL data were obtained from publicly available sites according to previously validated studies.

RESULTS

A total of 588 patients who sustained AATRs and underwent primary surgical repair were identified, primarily men (75.7%, n = 445), with an average age of 43.22 ± 14.4 years. The number and corresponding incidence of AATR repairs per year was: 2017: n = 124 (21.1%), 2018: n = 110 (18.7%), 2019: n = 130 (22.1%), 2020: n = 86 (14.6%), 2021: n = 138 (23.5%), indicating a 7.5% decrease in rate of AATRs from 2019 to 2020, followed by an 8.9% increase in incidence from 2020 to 2021. Within the NFL, the number of AATRs resulting in an injured reserve stint increased every regular season from 2019 to 2020: n = 11 (21.2%), to 2020-2021: n = 17 (32.7%), to this past 2021-2022 season: n = 24 (46.2%).

CONCLUSION

AATR surgeries seem to have increased in 2021 following a 2020 COVID pandemic-induced quarantine for recreational athletes at a single academic institution and for professional athletes in the NFL, although these results are of questionable clinical significance. This provides prognostic information when counseling patients and athletes on return to activity or sport.

LEVEL OF EVIDENCE

Level IV.

Measuring Mechanical Properties of Spastic Muscles After Stroke. Does Muscle Position During Assessment Really Matter?

OBJECTIVE

To investigate the influence of muscle position (relaxed vs stretched) on muscle mechanical properties and the ability of myotonometry to detect differences between sides, groups, and sites of testing in patients with stroke. We also analyzed the association between myotonometry and clinical measures of spasticity.

DESIGN

Cross-sectional study.

SETTING

Outpatient rehabilitation units including private and public centers.

PARTICIPANTS

Seventy-one participants (20 subacute stroke, 20 chronic stroke, 31 controls) were recruited (N=71).

INTERVENTION

Muscle mechanical properties were measured bilaterally with a MyotonPRO at muscle belly and musculotendinous sites during 2 protocols (muscle relaxed or in maximal bearable stretched position).

MAIN OUTCOME MEASURES

Muscle tone and stiffness of the biceps brachii and gastrocnemius. Poststroke spasticity was evaluated with the Modified Tardieu Scale (MTS). A mixed-model analysis of variance was used to detect differences in the outcome measures.

RESULTS

The analysis of variance showed a significant effect of muscle position on muscle mechanical properties (higher tone and stiffness with the muscle assessed in stretched position). Measurements with the stretched muscle could help discriminate between spastic and nonspastic sides, but only at the biceps brachii. Overall, there was a significant increase in tone and stiffness in the chronic stroke group and in myotendinous sites compared with muscle belly sites (all, P<.05). No correlations were found between myotonometry and the MTS.

CONCLUSIONS

Myotonometry assessment of mechanical properties with the muscle stretched improves the ability of myotonometry to discriminate between sides in patients after stroke and between people with and without stroke.

Age- and muscle-specific reliability of muscle architecture measurements assessed by two-dimensional panoramic ultrasound

Background

Age-related changes in muscle properties affect daily functioning, therefore a reliable assessment of such properties is required. We examined the effects of age on reliability, muscle quality and interrelation among muscle architecture (MA) parameters of the gastrocnemius medialis (GM), tibialis anterior (TA), and vastus lateralis (VL) muscles.

Methods

Three raters scored ultrasound (US) scans of 12 healthy younger and older adults, on fascicle length (FL), pennation angle (PA) and muscle thickness (MT). Intra- and inter-rater reliability of MA measures in rest and contraction was assessed by intraclass correlation coefficients (ICC) and standard error of measurements (SEM, SEM%). The relationship between MA parameters was examined using Pearson correlation coefficients. Muscle quality (MQ) was examined using mean pixel intensity.

Results

Reliability was moderate to excellent for TA in both groups (ICCs: 0.64–0.99, SEM% = 1.6–14.8%), and for VL in the younger group (ICCs: 0.67–0.98, SEM% = 2.0–18.3%). VL reliability was poor to excellent in older adults (ICCs: 0.22–0.99, SEM% = 2.7–36.0%). For GM, ICCs were good to excellent (ICCs: 0.76–0.99) in both groups, but GM SEM% were higher in older adults (SEM%Younger = 1.5–10.7%, SEM%Older = 1.6–28.1%). Muscle quality was on average 19.0% lower in older vs. younger adults. In both groups, moderate to strong correlations were found for VL FL and MT (r ≥ 0.54), and TA PA and MT (r ≥ 0.72), while TA FL correlated with MT (r ≥ 0.67) in younger adults only.

Conclusions

In conclusion, age- and muscle-specificities were present in the relationships between MT and PA, and MT and FL at rest. Furthermore, the reliability of MA parameters assessed with 2D panoramic US is acceptable. However, the level of reliability varies with age, muscle and MA measure. In older adults notably, the lowest reliability was observed in the VL muscle. Among the MA parameters, MT appears to be the simplest and most easily reproducible parameter in all muscles and age groups.

Age-related alterations in muscle architecture are a signature of sarcopenia: the ultrasound sarcopenia index

BACKGROUND

The assessment of muscle mass is a key determinant of the diagnosis of sarcopenia. We introduce for the first time an ultrasound imaging method for diagnosing sarcopenia based on changes in muscle geometric proportions.

METHODS

Vastus lateralis muscle fascicle length (Lf) and thickness (Tm) were measured at 35% distal femur length by ultrasonography in a population of 279 individuals classified as moderately active elderly (MAE), sedentary elderly (SE) (n = 109), mobility impaired elderly (MIE) (n = 43), and in adult young controls (YC) (n = 60). The ratio of Lf/Tm was calculated to obtain an ultrasound index of the loss of muscle mass associated with sarcopenia (USI). In a subsample of elderly male individuals (n = 76) in which corresponding DXA measurements were available (MAE, n = 52 and SE, n = 24), DXA-derived skeletal muscle index (SMI, appendicular limb mass/height2 ) was compared with corresponding USI values.

RESULTS

For both young and older participants, USI values were found to be independent of sex, height and body mass. USI values were 3.70 ± 0.52 for YC, 4.50 ± 0.72 for the MAE, 5.05 ± 1.11 for the SE and 6.31 ± 1.38 for the MIE, all significantly different between each other (P < 0.0001). Based on the USI Z-scores, with reference to the YC population, the 219 elderly participants were stratified according to their muscle sarcopenic status. Individuals with USI values within a range of 3.70 < USI ≥ 4.23 were classified as non-sarcopenic (prevalence 23.7%), those with USI values within 4.23 < USI ≥ 4.76 were classified as pre-sarcopenic (prevalence 23.7%), those with USI values within 4.76 < USI ≥ 5.29 were classified as moderately sarcopenic (prevalence 15.1%), those with USI values within range 5.29 < USI ≥ 5.82 were classified as sarcopenic (prevalence 27.9%), and those with USI values >5.82 were classified as severely sarcopenic (prevalence 9.6%). The DXA-derived SMI was found to be significantly correlated with USI (r = 0.61, P < 0.0001). Notably, the USI cut-off value for moderate sarcopenia (4.76 a.u.) was found to coincide with the DXA cut-off value of sarcopenia (7.26 kg/m2 ).

CONCLUSIONS

We propose a novel, practical, and inexpensive imaging marker of the loss of muscle mass associated with sarcopenia, called the ultrasound sarcopenic index (USI), based on changes in muscle geometric proportions. These changes provide a useful 'signature of sarcopenia' and allow the stratification of individuals according to the presence and severity of muscle sarcopenia. We are convinced that the USI will be a useful clinical tool for confirming the diagnosis of sarcopenia, of which the assessment of muscle mass is a key-component.

Age-related reductions in the number of serial sarcomeres contribute to shorter fascicle lengths but not elevated passive tension

We investigated age-related changes to fascicle length, sarcomere length and serial sarcomere number (SSN), and how this affects passive force. Following mechanical testing to determine passive force, the medial gastrocnemius muscle of young (n=9) and old (n=8) Fisher 344BN hybrid rats was chemically fixed at the optimal muscle length for force production; individual fascicles were dissected for length measurement, and laser diffraction was used to assess sarcomere length. Old rats had ∼14% shorter fascicle lengths than young rats, which was driven by a ∼10% reduction in SSN, with no difference in sarcomere length (∼4%). Passive force was greater in the old than in the young rats at long muscle lengths. Shorter fascicle lengths and reduced SSN in the old rats could not entirely explain increased passive forces for absolute length changes, owing to a slight reduction in sarcomere length in old rats, resulting in similar sarcomere length at long muscle lengths.

Translational research on Myology and Mobility Medicine: 2021 semi-virtual PDM3 from Thermae of Euganean Hills, May 26 - 29, 2021

On 19-21 November 2020, the meeting of the 30 years of the Padova Muscle Days was virtually held while the SARS-CoV-2 epidemic was hitting the world after a seemingly quiet summer. During the 2020-2021 winter, the epidemic is still active, despite the start of vaccinations. The organizers hope to hold the 2021 Padua Days on Myology and Mobility Medicine in a semi-virtual form (2021 S-V PDM3) from May 26 to May 29 at the Thermae of Euganean Hills, Padova, Italy. Here the program and the Collection of Abstracts are presented. Despite numerous world problems, the number of submitted/selected presentations (lectures and oral presentations) has increased, prompting the organizers to extend the program to four dense days.

Measurement of excitation-contraction coupling time in lower extremities

OBJECTIVE

The aim of this study was to apply a novel method to measure excitation-contraction coupling time (ECCT) in normal soleus muscles.

METHODS

We performed simultaneous recordings of soleus compound muscle action potential (CMAP) and foot movement-related potential (MRP), and measured ankle plantar flexion torque in 36 healthy subjects. We calculated ECCT and examined the relations between CMAP, MRP, ECCT and ankle plantar flexion torque.

RESULTS

Statistical analyses established reference ranges (mean ± SE) for CMAP (13.4 ± 0.9 mV), MRP (5.3 ± 0.4 m/s²), ECCT (5.2 ± 0.1 ms), torque (85.9 ± 6.4 Nm) and torque/body weight (1.4 ± 0.1 Nm/kg). The torque showed a positive linear correlation with CMAP (p = 0.041) and a negative linear correlation with ECCT (p = 0.045).

CONCLUSION

Soleus ECCT can be recorded easily, and is useful to assess the impairment of E-C coupling in muscles of the lower extremities.

Theaflavin Promotes Myogenic Differentiation by Regulating the Cell Cycle and Surface Mechanical Properties of C2C12 Cells

Aging and muscle diseases often lead to a decline in the differentiation capacity of myoblasts, which in turn results in the deterioration of skeletal muscle (SkM) function and impairment of regeneration ability after injury. Theaflavins, the "gold molecules" found in black tea, have been reported to possess various biological activities and have a positive effect on maintaining human health. In this study, we found that among the four theaflavins (theaflavin (TF1), theaflavin-3-gallate (TF2A), theaflavin-3'-gallate (TF2B), and theaflavin-3,3'-digallate (TF3) monomers), TF1 (20 μM) significantly promoted the fusion index of myoblasts, number of mature myotubes, and degree of myotube development. By combining transcriptomics, bioinformatics, and molecular biology experiments, we showed that TF1 may promote myoblast differentiation by (1) regulating the withdrawal of myoblasts from the cell cycle, inducing the release of myogenic factors (MyoD, MyoG, and MyHC) and accelerating myogenic differentiation and (2) regulating the adhesion force of myoblasts and mechanical properties of mature myotubes and promoting the migration, fusion, and development of myoblasts. In conclusion, our study outcomes show that TF1 can promote myoblast differentiation and regulate myotube mechanical properties. It is a potential dietary supplement for the elderly. Our findings provide a new scientific basis for the relationship between tea drinking and aging.

Age-related differences in vastus lateralis fascicle behavior during fast accelerative leg-extension movements

Leg-extensor rate of power development (RPD) decreases during aging. This study aimed to identify the underlying mechanism of the age-related decline in RPD during a fast acceleration in terms of in vivo vastus lateralis (VL) fascicle shortening behavior. Thirty-nine men aged between 25 and 69 years performed three maximal isokinetic leg-extensor tests with a fixed initial acceleration of 45° knee extension in 150 ms until 340°/s knee angular velocity. RPD, VL activity, and ultrasound images were recorded to assess (relative) fascicle shortening and mean shortening velocity for the phases of electromechanical delay, pretension, and acceleration. Our findings show that fascicle shortening and mean shortening velocity during a fast action increase with aging (0.002 per year, P = .035 and 0.005 s^-1 per year, P = .097, respectively), mainly due to a higher amount of shortening in the phase of electromechanical delay. The ratio of VL fascicle length over upper leg length at rest showed a negative correlation (r = -.46, P = .004) with RPD/body mass, while pennation angle at rest showed a trend toward a positive correlation (r = .28, P = .089). To conclude, our findings indicate that the ability to reach high VL fascicle shortening velocities in vivo is not reduced in older men while performing preprogrammed fast accelerations. The greater amount of fascicle shortening in old age is probably the result of age-related differences in the tendinous properties of the muscle-tendon complex, forcing the fascicles to shorten more in order to transmit the muscle force to the segment.

Tendon Extracellular Matrix Remodeling and Defective Cell Polarization in the Presence of Collagen VI Mutations

Mutations in collagen VI genes cause two major clinical myopathies, Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD), and the rarer myosclerosis myopathy. In addition to congenital muscle weakness, patients affected by collagen VI-related myopathies show axial and proximal joint contractures, and distal joint hypermobility, which suggest the involvement of tendon function. To gain further insight into the role of collagen VI in human tendon structure and function, we performed ultrastructural, biochemical, and RT-PCR analysis on tendon biopsies and on cell cultures derived from two patients affected with BM and UCMD. In vitro studies revealed striking alterations in the collagen VI network, associated with disruption of the collagen VI-NG2 (Collagen VI-neural/glial antigen 2) axis and defects in cell polarization and migration. The organization of extracellular matrix (ECM) components, as regards collagens I and XII, was also affected, along with an increase in the active form of metalloproteinase 2 (MMP2). In agreement with the in vitro alterations, tendon biopsies from collagen VI-related myopathy patients displayed striking changes in collagen fibril morphology and cell death. These data point to a critical role of collagen VI in tendon matrix organization and cell behavior. The remodeling of the tendon matrix may contribute to the muscle dysfunction observed in BM and UCMD patients.

Changes in human skeletal muscle architecture and function induced by extended spaceflight

The aim of this study was to quantitatively describe the relationships between joint angles and muscle architecture (lengths (L_f) and angles (Θ_f) of fascicles) of human triceps surae [medial (MG) and lateral (LG) gastrocnemius and soleus (SOL) muscles] invivo for three men-cosmonaut after long-duration spaceflight. Sagittal sonographs of MG, LG, SOL were taken at ankle was positioned at 15° (dorsiflexion), 0° (neutral position), +15°, and +30° (plantarflexion), with the knee at 90° at rest and after a long-duration spaceflight. At each position, longitudinal ultrasonic images of the MG and LG and SOL were obtained while the cosmonauts was relaxed from which fascicle lengths and angles with respect to the aponeuroses were determined. After space flight plantarflexor force declined significantly (26%; p < 0.001). The internal architecture of the GM, and LG, and SOL muscle was significantly altered. In the passive condition, L_f changed from 45, 53, and 39 mm (knee, 0°, ankle, -15°) to 26, 33, and 28 mm (knee, 90° ankle, 30°) for MG, LG, and SOL, respectively. Different lengths and angles of fascicles, and their changes by contraction, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses. The three heads of the triceps surae muscle substantially differ in architecture, which probably reflects their functional roles. Differences in fiber length and pennation angle that were observed among the muscles and could be associated with differences in force production and in elastic properties of musculo-tendinous complex and aponeuroses.

Low-load blood flow restriction training induces similar morphological and mechanical Achilles tendon adaptations compared with high-load resistance training

Low-load blood flow restriction (LL-BFR) training has gained increasing interest in the scientific community by demonstrating that increases in muscle mass and strength are comparable to conventional high-load (HL) resistance training. Although adaptations on the muscular level are well documented, there is little evidence on how LL-BFR training affects human myotendinous properties. Therefore, the aim of the present study was to investigate morphological and mechanical Achilles tendon adaptations after 14 wk of strength training. Fifty-five male volunteers (27.9 ± 5.1 yr) were randomly allocated into the following three groups: LL-BFR [20-35% of one-repetition maximum (1RM)], HL (70-85% 1RM), or a nonexercising control (CON) group. The LL-BFR and HL groups completed a resistance training program for 14 wk, and tendon morphology, mechanical as well as material properties, and muscle cross-sectional area (CSA) and isometric strength were assessed before and after the intervention. Both HL (+40.7%) and LL-BFR (+36.1%) training induced significant increases in tendon stiffness (P < 0.05) as well as tendon CSA (HL: +4.6%, LL-BFR: +7.8%, P < 0.001). These changes were comparable between groups without significant changes in Young's modulus. Furthermore, gastrocnemius medialis muscle CSA and plantar flexor strength significantly increased in both training groups (P < 0.05), whereas the CON group did not show significant changes in any of the evaluated parameters. In conclusion, the adaptive change in Achilles tendon properties following low-load resistance training with partial vascular occlusion appears comparable to that evoked by high-load resistance training.NEW & NOTEWORTHY Low-load blood flow restriction (LL-BFR) training has been shown to induce beneficial adaptations at the muscular level. However, studies examining the effects on human tendon properties are rare. The findings provide first evidence that LL-BFR can increase Achilles tendon mechanical and morphological properties to a similar extent as conventional high-load resistance training. This is of particular importance for individuals who may not tolerate heavy training loads but still aim for improvements in myotendinous function.

Architectural and functional specifics of the human triceps surae muscle in vivo and its adaptation to microgravity

Long-term exposure to microgravity (μG) is known to reduce the strength of a skeletal muscle contraction and the level of general physical performance in humans, while little is known about its effect on muscle architecture. Architectural and contractile properties of the triceps surae (TS) muscle were determined in vivo for male cosmonauts in response ( n = 8) to a spaceflight (213.0 ± 30.5 days). The maximal voluntary contraction (MVC), tetanic tension ( Ро), and voluntary and electrically evoked contraction times and force deficiency (Pd) were determined. The ankle was positioned at 15° dorsiflexion (−15°) and 0, 15, and 30° plantar flexion, with the knee set at 90°. At each position, longitudinal ultrasonic images of the medial (MG) and lateral (LG) gastrocnemius and soleus (SOL) muscles were obtained while the subject was relaxed. After a spaceflight, MVC and Pо decreased by 42 and 26%, respectively, and Pd increased by 50%. The rate of tension of a voluntary contraction substantially reduced but evoked contractions remained unchanged. In the passive condition, fiber length ( Lf) changed from 43, 57, and 35 mm (knee, 0°; ankle, −15°) to 34, 38, and 25 mm (knee, 0°; ankle, 30°) for MG, LG, and SOL, respectively, and Θf changed from 27, 21, and 23° (knee, 0°; ankle, −15°) to 43, 29, and 34° (knee, 0°; ankle, 30°) for MG, LG, and SOL, respectively. Different Lf and Θf, and their changes after spaceflight, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses.

NEW & NOTEWORTHY The present work was the first to combine measuring the fiber length and pennation angle (ultrasound imaging) as main determinants of mechanical force production and evaluating the muscle function after a long-duration spaceflight. The results demonstrate that muscles with different functional roles may differently respond to unloading, and this circumstance is important to consider when planning rehabilitation after unloading of any kind, paying particular attention to postural muscles.

Bouncing Back! Counteracting Muscle Aging With Plyometric Muscle Loading

The preservation of muscle power is crucial in aging for maintaining mobility and performing daily tasks. Resistance training involving high movement velocities represents a valid strategy to slow down the rate of sarcopenia, counteracting the loss of muscle mass and muscle power. Plyometric exercise may represent an effective training modality for increasing muscle power; however, its application in older populations has been sparingly investigated, as the high impact actions involved may reduce its feasibility for older individuals. By adopting a safer modality of plyometric training, we investigated if a 6-week plyometric training intervention could increase knee extensor muscle size, architecture, force and power in 14 young (YM, age = 25.4 ± 3.5 y; means ± SD) and nine older males (OM, age = 69.7 ± 3.4 y). Volunteers trained 3 times/week using a device similar to a leg press machine where the user was required to bounce against his body mass on a trampoline. Pre-to-post training changes in isometric maximum voluntary torque (MVT), leg extension power and vastus lateralis (VL) architecture were assessed. Muscle power increased in both groups (+27% OM -P < 0.001, 20% YM -P < 0.001), although the total external work performed during the training period was significantly lower for OM (i.e., ~-47%). Both groups showed significant increases in muscle thickness (MT) (+5.8 OM -P < 0.01 vs. +3.8% YM -P < 0.01), fascicle length (Lf) (+8% OM -P < 0.001 vs. +6% YM -P < 0.001), and pennation angle (PA) (+7.5% OM -P < 0.001 vs. +4.1% YM -P < 0.001). The current study shows that trampoline-based plyometric training is an effective intervention producing a rapid increase in muscle mass and power in both young and older individuals. The training modality used in this study seems to particularly benefit the older population, targeting the morphological and functional effects of sarcopenia in human muscle.

Effect of aging on muscle and tendon properties in highly functioning elderly people

This study analyzes long-term changes in muscle strength, muscle architecture, and patellar tendon mechanical properties in a specific sample of physically active elderly people. Twenty-two participants were re-examined from a former 12-week-long skiing intervention study: 11 from the intervention group (IG: 7 ♀, 4 ♂; 67 ± 3 years) and 11 from the control group (CG: 6 ♀, 5 ♂; 66 ± 4 years). Muscle architecture, strength endurance, maximum torque, and tendon properties were analyzed three times within 6 months, and again 6 years later in a follow-up test. No changes in either group could be observed between June 2009 and April 2015 in any parameter. This can be interpreted positively because no age-related decreases were found. Although our participants were physically active from the very beginning (>150 min/wk), it must be noted that the intensity of the physical activity was too low to provoke physiological improvements in leg strength or muscle/tendon morphology.

Hip muscle weakness and reduced joint range of motion in patients with femoroacetabular impingement syndrome: a case-control study

BACKGROUND

Femoroacetabular impingement (FAI) syndrome is a hip joint motion-related clinical disorder characterized by abnormal contact between the hip joint structures. Abnormal hip morphology and joint pain may impair the hip joint range of motion (ROM) and muscle function. However, FAI effects on hip joint ROM and muscle strength remain controversial.

OBJECTIVES

The purpose of this study was to compare hip joint ROM and muscle strength between FAI syndrome patients and healthy controls.

METHODS

Twenty FAI syndrome male patients and 20 healthy male controls (CG) matched for age (FAI=28±6 years; CG=27±5 years), body mass (FAI=81±12kg; CG=80±13kg) and height (FAI=177±6cm; CG=178±6cm), participated in the study. Hip joint ROM for flexion, internal rotation and external rotation were assessed through goniometry. Maximal isometric strength for hip flexion, extension, abduction and adduction were evaluated through hand-held dynamometry.

RESULTS

Hip joint ROM was significantly lower in FAI syndrome patients compared with CG for passive flexion (-4%; effect size - ES=0.65), active internal rotation (-42%; ES=1.60), active external rotation (-28%; ES=1.46) and passive external rotation (-23%; ES=1.63). FAI patients' hip extensors (-34%; ES=1.46), hip adductors (-33%; ES=1.32), and hip flexors (-25%; ES=1.17) were weaker compared to the CG subjects.

CONCLUSIONS

FAI syndrome patients presented both hip muscle weakness and reduced joint ROM compared to match CG.

Muscle and Tendon Contributions to Reduced Rate of Torque Development in Healthy Older Males

Background

The ability to rapidly generate and transfer muscle force is essential for effective corrective movements in order to prevent a fall. The aim of this study was to establish the muscle and tendon contributions to differences in rate of torque development (RTD) between younger (YM) and older males (OM).

Method

Twenty-eight young males (23.9 years ± 1.1) and 22 old males (68.5 years ± 0.5) were recruited for assessment of Quadriceps Anatomical CSA (ACSA), maximal voluntary contraction (MVC), rate of torque development (RTD), and tendon biomechanical properties. Activation capacity (AC), maximal muscle twitch df/dt) and time to peak EMG amplitude (TTPE) were also assessed.

Results

Absolute RTD (aRTD) was lower in OM (577.5 ± 34.6 Nm/s vs 881.7 ± 45.6 Nm/s, p < .0001). RTD remained lower in OM following normalization (nRTD) for muscle ACSA (9.93 ± 0.7 Nm/s/cm2 vs 11.9 ± 0.6 Nm/s/cm2, p < .05). Maximal muscle twitch df/dt (1,086 Nm∙s-1 vs 2,209 Nm∙s-1, p < .0001), TTPE (109.2 ± 8.6ms vs 154.6 ± 16.6 ms, p < .05), and AC (75.8 ± 1.5% vs 80.1 ± 0.9%, p < .01) were all affected in OM. Tendon stiffness was found to be lower in OM (1,222 ± 78.4 N/mm vs 1,771 ± 154.1 N/mm, p < .004). nRTD was significantly correlated with tendon stiffness (R2 = .15).

Conclusion

These observations provide evidence that in absolute terms, a lower RTD in the elderly adults is caused by slower muscle contraction speeds, slower TTPE, reduced ACSA, reduced MVC, and a decrease in tendon stiffness. Once the RTD is normalized to quadriceps ACSA, only MVC and tendon stiffness remain influential. This strongly reinforces the importance of both muscle and tendon characteristics when considering RTD.

Effect of Knee Joint Angle and Contraction Intensity on Hamstrings Coactivation

PURPOSE

This study investigated the effect of knee joint angle and contraction intensity on the coactivation of the hamstring muscles (when acting as antagonists to the quadriceps) in young and older individuals of both sexes.

METHODS

A total of 25 young (24 ± 2.6 yr) and 26 older (70 ± 2.5 yr) healthy men and women participated. Maximal voluntary isometric contraction of the knee extensors and flexors was assessed at two knee joint angles (90° and 60°, 0° = full extension). At each angle, participants performed submaximal contractions of the knee extensors (20%, 50%, and 80% maximal voluntary isometric contraction), whereas surface EMG was simultaneously acquired from the vastus lateralis and biceps femoris muscles to assess the level (EMG root-mean-square) of agonist activation and antagonist coactivation. Subcutaneous adipose tissue in the areas corresponding to surface EMG electrode placements was measured via ultrasonography.

RESULTS

The contractions performed at 90° knee flexion demonstrated higher levels of antagonist coactivation (all P < 0.01) and agonist activation (all P < 0.01) as a function of contraction intensity compared with the 60° knee flexion. Furthermore, after controlling for subcutaneous adipose tissue, older participants exhibited a higher level of antagonist coactivation at 60° knee flexion compared with young participants (P < 0.05).

CONCLUSIONS

The results of the present study suggest that 1) the antagonist coactivation is dependent on knee joint angle and contraction intensity and 2) subcutaneous adipose tissue may affect the measured coactivation level likely because of a cross-talk effect. Antagonist coactivation may play a protective role in stabilizing the knee joint and maintaining constant motor output.

Skeletal muscle performance and ageing

The world population is ageing rapidly. As society ages, the incidence of physical limitations is dramatically increasing, which reduces the quality of life and increases healthcare expenditures. In western society, ~30% of the population over 55 years is confronted with moderate or severe physical limitations. These physical limitations increase the risk of falls, institutionalization, co-morbidity, and premature death. An important cause of physical limitations is the age-related loss of skeletal muscle mass, also referred to as sarcopenia. Emerging evidence, however, clearly shows that the decline in skeletal muscle mass is not the sole contributor to the decline in physical performance. For instance, the loss of muscle strength is also a strong contributor to reduced physical performance in the elderly. In addition, there is ample data to suggest that motor coordination, excitation-contraction coupling, skeletal integrity, and other factors related to the nervous, muscular, and skeletal systems are critically important for physical performance in the elderly. To better understand the loss of skeletal muscle performance with ageing, we aim to provide a broad overview on the underlying mechanisms associated with elderly skeletal muscle performance. We start with a system level discussion and continue with a discussion on the influence of lifestyle, biological, and psychosocial factors on elderly skeletal muscle performance. Developing a broad understanding of the many factors affecting elderly skeletal muscle performance has major implications for scientists, clinicians, and health professionals who are developing therapeutic interventions aiming to enhance muscle function and/or prevent mobility and physical limitations and, as such, support healthy ageing.

Role of Dietary Protein and Muscular Fitness on Longevity and Aging

Muscle atrophy is an unfortunate effect of aging and many diseases and can compromise physical function and impair vital metabolic processes. Low levels of muscular fitness together with insufficient dietary intake are major risk factors for illness and mortality from all causes. Ultimately, muscle wasting contributes significantly to weakness, disability, increased hospitalization, immobility, and loss of independence. However, the extent of muscle wasting differs greatly between individuals due to differences in the aging process per se as well as physical activity levels. Interventions for sarcopenia include exercise and nutrition because both have a positive impact on protein anabolism but also enhance other aspects that contribute to well-being in sarcopenic older adults, such as physical function, quality of life, and anti-inflammatory state. The process of aging is accompanied by chronic immune activation, and sarcopenia may represent a consequence of a counter-regulatory strategy of the immune system. Thereby, the kynurenine pathway is induced, and elevation in the ratio of kynurenine to tryptophan concentrations, which estimates the tryptophan breakdown rate, is often linked with inflammatory conditions and neuropsychiatric symptoms. A combined exercise program consisting of both resistance-type and endurance-type exercise may best help to ameliorate the loss of skeletal muscle mass and function, to prevent muscle aging comorbidities, and to improve physical performance and quality of life. In addition, the use of dietary protein supplementation can further augment protein anabolism but can also contribute to a more active lifestyle, thereby supporting well-being and active aging in the older population.

Loss of maximal explosive power of lower limbs after 2 weeks of disuse and incomplete recovery after retraining in older adults

KEY POINTS

Disuse in older adults can critically decrease lower limb muscle power, leading to compromised mobility and overall quality of life. We studied how muscle power and its determinants (muscle mass, single muscle fibre properties and motor control) adapted to 2 weeks of disuse and subsequent 2 weeks of physical training in young and older people. Disuse decreased lower limb muscle power in both groups; however, different adaptations in single muscle fibre properties and co-contraction of leg muscles were observed between young and older individuals. Six physical training sessions performed after disuse promoted the recovery of muscle mass and power. However, they were not sufficient to restore muscle power to pre-disuse values in older individuals, suggesting that further countermeasures are required to counteract the disuse-induced loss of muscle power in older adults.

ABSTRACT

Disuse-induced loss of muscle power can be detrimental in older individuals, seriously impairing functional capacity. In this study, we examined the changes in maximal explosive power (MEP) of lower limbs induced by a 14-day disuse (bed-rest, BR) and a subsequent 14-day retraining, to assess whether the impact of disuse was greater in older than in young men, and to analyse the causes of such adaptations. Sixteen older adults (Old: 55-65 years) and seven Young (18-30 years) individuals participated in this study. In a subgroup of eight Old subjects, countermeasures based on cognitive training and protein supplementation were applied. MEP was measured with an explosive ergometer, muscle mass was determined by magnetic resonance, motor control was studied by EMG, and single muscle fibres were analysed in vastus lateralis biopsy samples. MEP was ∼33% lower in Old than in Young individuals, and remained significantly lower (-19%) when normalized by muscle volume. BR significantly affected MEP in Old (-15%) but not in Young. Retraining tended to increase MEP; however, this intervention was not sufficient to restore pre-BR values in Old. Ankle co-contraction increased after BR in Old only, and remained elevated after retraining (+30%). Significant atrophy occurred in slow fibres in Old, and in fast fibres in Young. After retraining, the recovery of muscle fibre thickness was partial. The proposed countermeasures were not sufficient to affect muscle mass and power. The greater impact of disuse and smaller retraining-induced recovery observed in Old highlight the importance of designing suitable rehabilitation protocols for older individuals.

EFEITO AGUDO DO VOLUME DE ALONGAMENTO ESTÁTICO NO DESEMPENHO NEUROMUSCULAR DE JOVENS E IDOSAS

RESUMO Introdução: Os exercícios prévios de alongamento estático (AE) podem promover decréscimo transitório da força muscular. Características dos protocolos de AE e da amostra estudada podem interferir no desempenho neuromuscular subsequente às rotinas de alongamento. Objetivo: Investigar o efeito agudo de dois diferentes volumes de AE sobre o sistema neuromuscular de mulheres jovens e idosas durante a execução do leg press horizontal. Métodos: Vinte e quatro mulheres (12 jovens e 12 idosas), aparentemente saudáveis, compareceram ao local de realização do experimento em seis ocasiões distintas. Nas três primeiras visitas realizaram-se coleta dos dados pessoais, de dados antropométricos, familiarização com o protocolo de AE e registro de esforço isométrico no leg press horizontal. Nas três últimas visitas, foram realizados registros da curva força-tempo isométrica e atividade eletromiográfica (EMG) dos músculos vasto medial e vasto lateral após realização de uma de três condições experimentais: controle (sem alongamento), alongamento com volume total de 60 segundos e 120 segundos. A ordem das condições experimentais foi aleatorizada. O protocolo de AE envolveu três exercícios executados em duas séries de 30 segundos (AE60) ou em quatro séries de 30 segundos (AE120). O teste ANOVA two-way foi utilizado para análises dos dados. Resultados: Nenhuma das rotinas de AE acarretou alteração de taxa de desenvolvimento de força (TDF), contração voluntária máxima e atividade EMG nas mulheres jovens e idosas. Conclusões: Diferentes volumes de AE, em conformidade com recomendações atuais, não influenciaram o desempenho neuromuscular de mulheres jovens e idosas no exercício leg press horizontal.

Hip mechanics underlie lower extremity power training-induced increase in old adults' fast gait velocity: The Potsdam Gait Study (POGS)

BACKGROUND

Aging is associated with slowed gait and old compared with young adults generally walk with greater positive hip work (H1) and reduced positive ankle work (A2). The role of exercise interventions on old adults' gait mechanics that underlie training-induced improvements in gait velocity is unclear. We examined the effects of lower extremity power training and detraining on old adults' gait kinetics.

METHODS

As part of the Potsdam Gait Study (POGS), healthy old adults completed a no-intervention control period (69.1±4.4yrs, n=14) or a power training program followed by detraining (72.9±5.4yrs, n=15). We measured isokinetic knee extensor and plantarflexor power and measured hip, knee and ankle kinetics at habitual, fast and standardized walking speeds.

RESULTS

Power training significantly increased isokinetic knee extensor power (25%), plantarflexor power (43%), and fast gait velocity (5.9%). Gait mechanics underlying the improved fast gait velocity included increases in hip angular impulse (29%) and H1 work (37%) and no changes in positive knee (K2) and A2 work. Detraining further improved fast gait velocity (4.7%) with reductions in H1 (-35%), and increases in K2 (36%) and A2 (7%).

CONCLUSION

Power training increased fast gait velocity in healthy old adults by increasing the reliance on hip muscle function and thus further strengthened the age-related distal-to-proximal shift in muscle function.

Tendon Extracellular Matrix Alterations in Ullrich Congenital Muscular Dystrophy

Collagen VI (COLVI) is a non-fibrillar collagen expressed in skeletal muscle and most connective tissues. Mutations in COLVI genes cause two major clinical forms, Bethlem myopathy and Ullrich congenital muscular dystrophy (UCMD). In addition to congenital muscle weakness, patients affected by COLVI myopathies show axial and proximal joint contractures and distal joint hypermobility, which suggest the involvement of the tendon function. We examined a peroneal tendon biopsy and tenocyte culture of a 15-year-old patient affected by UCMD with compound heterozygous COL6A2 mutations. In patient’s tendon biopsy, we found striking morphological alterations of tendon fibrils, consisting in irregular profiles and reduced mean diameter. The organization of the pericellular matrix of tenocytes, the primary site of collagen fibril assembly, was severely affected, as determined by immunoelectron microscopy, which showed an abnormal accumulation of COLVI and altered distribution of collagen I (COLI) and fibronectin (FBN). In patient’s tenocyte culture, COLVI web formation and cell surface association were severely impaired; large aggregates of COLVI, which matched with COLI labeling, were frequently detected in the extracellular matrix. In addition, metalloproteinase MMP-2, an extracellular matrix-regulating enzyme, was increased in the conditioned medium of patient’s tenocytes, as determined by gelatin zymography and western blot. Altogether, these data indicate that COLVI deficiency may influence the organization of UCMD tendon matrix, resulting in dysfunctional fibrillogenesis. The alterations of tendon matrix may contribute to the complex pathogenesis of COLVI related myopathies.

Angle-torque relationship of the subtalar pronators and supinators in younger and elderly males and females

BACKGROUND

The angle-dependent torque capacity of the subtalar pronators and supinators is important to maintain dynamic ankle stabilisation. Based on the peak torques during maximum voluntary isometric pronation and supination across the subtalar range of motion, the strength curves of younger and elderly males and females were investigated.

METHODS

Maximum voluntary isometric subtalar pronator and supinator strength tests were administered to 30 younger and 30 elderly volunteers (each 15 male and 15 female subjects). Total active subtalar range of motion and peak pronator and supinator torques were measured in five anatomical subtalar joint angles using a custom-built apparatus with two force transducers. Furthermore, relative torques (normalised to the individual peak torque) and pronator-to-supinator strength-ratios were also calculated.

RESULTS

Pronator-to-supinator strength ratio, and peak pronator and supinator torques are affected by age and by joint angle x age interactions. All supinator strength curves show a steadily descending characteristic from the pronated to the supinated positions. The pronator strength curve had an inverted U-shaped characteristic, except for younger women of whom 47 % exert highest peak values in the end-range pronation angle. Both relative pronator and supinator strength are dependent on sex (P < 0.05). Relative pronator strength is also affected by joint angle x sex (P < 0.0001) and joint angle x sex x age (P < 0.05) interactions. Beside age effects on all range of motion parameters, pronation range of motion is influenced by a sex x age interaction (P < 0.05).

CONCLUSIONS

Age- and sex-related differences in both subtalar strength profile and range of motion have to be considered when testing strength across subtalar range of motion. Younger females have higher pronator strength capacity in the most pronated joint angle, which may be due in part to their greater subtalar joint range of motion compared to the other groups. In the most supinated position both pronator and supinator strength capacity is reduced in younger females compared to younger males.

Early structural remodeling and deuterium oxide-derived protein metabolic responses to eccentric and concentric loading in human skeletal muscle

We recently reported that the greatest distinguishing feature between eccentric (ECC) and concentric (CON) muscle loading lays in architectural adaptations: ECC favors increases in fascicle length (Lf), associated with distal vastus lateralis muscle (VL) hypertrophy, and CON increases in pennation angle (PA). Here, we explored the interactions between structural and morphological remodeling, assessed by ultrasound and dual x-ray absorptiometry (DXA), and long-term muscle protein synthesis (MPS), evaluated by deuterium oxide (D₂O) tracing technique. Ten young males (23 ± 4 years) performed unilateral resistance exercise training (RET) three times/week for 4 weeks; thus, one-leg trained concentrically while the contralateral performed ECC exercise only at 80% of either CON or ECC one repetition maximum (1RM). Subjects consumed an initial bolus of D₂O (150 mL), while a 25-mL dose was thereafter provided every 8 days. Muscle biopsies from VL midbelly (MID) and distal myotendinous junction (MTJ) were collected at 0 and 4-weeks. MPS was then quantified via GC–pyrolysis–IRMS over the 4-week training period. Expectedly, ECC and CON RET resulted in similar increases in VL muscle thickness (MT) (7.5% vs. 8.4%, respectively) and thigh lean mass (DXA) (2.3% vs. 3%, respectively), albeit through distinct remodeling: Lf increasing more after ECC (5%) versus CON (2%) and PA increasing after CON (7% vs. 3%). MPS did not differ between contractile modes or biopsy sites (MID-ECC: 1.42 vs. MID-CON: 1.4% day⁻¹; MTJ-ECC: 1.38 vs. MTJ-CON: 1.39% day⁻¹). Muscle thickness at MID site increased similarly following ECC and CON RET, reflecting a tendency for a contractile mode-independent correlation between MPS and MT (P = 0.07; R² = 0.18). We conclude that, unlike MT, distinct structural remodeling responses to ECC or CON are not reflected in MPS; the molecular mechanisms of distinct protein deposition, and/or the role of protein breakdown in mediating these responses remain to be defined.

Gastrocnemius muscle architecture and achilles tendon properties influence walking distance in claudicants with peripheral arterial disease

INTRODUCTION

The extent to which gastrocnemius muscle and Achilles tendon properties contribute to the impaired walking endurance of claudicants is not known.

METHODS

Ultrasound images quantified muscle architecture of the lateral and medial gastrocnemius (GL and GM) and were combined with dynamometry during plantarflexor contractions to calculate tendon stress, strain, stiffness, the Young modulus, and hysteresis. Key parameters were entered into multiple regression models to explain walking endurance.

RESULTS

Worse disease severity was significantly associated with longer fascicle: tendon length ratios (GL R = -0.789 and GM R = -0.828) and increased tendon hysteresis (R = -0.740). Walking endurance could be explained by GL and GM pennation angle, maximum tendon force, tendon hysteresis, and disease severity (R(2)  = ∼0.6).

CONCLUSIONS

Peripheral arterial disease was associated with functionally important changes in muscle and tendon properties, including the usage of stored elastic energy. Interventions known to target these characteristics should be adopted as a means to improve walking endurance.

Effects of resistance training with moderate vs heavy loads on muscle mass and strength in the elderly: A meta-analysis

The purpose of the present study was to perform a meta-analysis to compare the efficacy of heavy (∼80% of one repetition maximum, 1RM) vs light-moderate load (∼45% 1RM) resistance training (RT) programs in inducing strength gains and skeletal muscle hypertrophy in elderly people. To assess the role of training volumes, studies in which training protocols were matched for mechanical work were independently analyzed. In all 15 studies included (448 subjects, age 67.8 years), when comparing heavy with light-moderate loads, strength gains tended to be larger following RT with higher intensities of load, with the resulting total population effect being μ = 0.430 (P = 0.060). Effect sizes were substantially smaller in "work-matched" studies (μ = 0.297, P = 0.003). Training with higher loads also provoked marginally larger gains in muscle size, although the degree of training-induced muscle hypertrophy was generally small (0.056 < μ < 0.136). To conclude, provided a sufficient number of repetitions is performed, RT at lower than traditionally recommended intensities of load may suffice to induce substantial gains in muscle strength in elderly cohorts.

Sex differences with aging in the fatigability of dynamic contractions

This study determined the sex difference with aging in fatigability of the elbow flexor muscles during a dynamic fatiguing task, and explored the associated mechanisms. We compared fatigability of the elbow flexor muscles in 18 young (20.2 ± 1 years: 9 men) and 36 old adults (73.5 ± 1 years: 16 men) during and in recovery from repeated dynamic contractions (~60°/s) with a load equivalent to 20% of maximal voluntary isometric contraction (MVIC) torque until failure. Transcranial magnetic stimulation (TMS) was used to assess supraspinal fatigue (an increase in the superimposed twitch, SIT) and the peak rate of muscle relaxation. Time to failure was briefer for the men than the women (6.1 ± 2.1 vs. 9.7 ± 5.5 min, respectively; P=0.02) with no difference between young and old adults (7.2 ± 2.9 vs. 8.4 ± 5.2 min, respectively, P=0.45) and no interaction (P>0.05). The relative decline in peak relaxation rate with fatigability was similar for young and old adults (P=0.11), but greater for men than women (P=0.046). Supraspinal fatigue increased for all groups and was associated with the time to failure (P<0.05). Regression analysis however, indicated that the time to failure was best predicted by the peak relaxation rate (baseline values and slowing with fatigability) (r(2)=0.55). Rate-limiting contractile mechanisms (e.g. excitation-contraction coupling) were responsible for the increased fatigability of the elbow flexors of men compared with women for a dynamic fatiguing task of slow angular velocity, and this sex difference was maintained with aging. The age difference in fatigability for the dynamic task was diminished for both sexes relative to what is typically observed with isometric fatiguing contractions.

A fibre-reinforced poroviscoelastic model accurately describes the biomechanical behaviour of the rat Achilles tendon

Background

Computational models of Achilles tendons can help understanding how healthy tendons are affected by repetitive loading and how the different tissue constituents contribute to the tendon’s biomechanical response. However, available models of Achilles tendon are limited in their description of the hierarchical multi-structural composition of the tissue. This study hypothesised that a poroviscoelastic fibre-reinforced model, previously successful in capturing cartilage biomechanical behaviour, can depict the biomechanical behaviour of the rat Achilles tendon found experimentally.

Materials and Methods

We developed a new material model of the Achilles tendon, which considers the tendon’s main constituents namely: water, proteoglycan matrix and collagen fibres. A hyperelastic formulation of the proteoglycan matrix enabled computations of large deformations of the tendon, and collagen fibres were modelled as viscoelastic. Specimen-specific finite element models were created of 9 rat Achilles tendons from an animal experiment and simulations were carried out following a repetitive tensile loading protocol. The material model parameters were calibrated against data from the rats by minimising the root mean squared error (RMS) between experimental force data and model output.

Results and Conclusions

All specimen models were successfully fitted to experimental data with high accuracy (RMS 0.42-1.02). Additional simulations predicted more compliant and soft tendon behaviour at reduced strain-rates compared to higher strain-rates that produce a stiff and brittle tendon response. Stress-relaxation simulations exhibited strain-dependent stress-relaxation behaviour where larger strains produced slower relaxation rates compared to smaller strain levels. Our simulations showed that the collagen fibres in the Achilles tendon are the main load-bearing component during tensile loading, where the orientation of the collagen fibres plays an important role for the tendon’s viscoelastic response. In conclusion, this model can capture the repetitive loading and unloading behaviour of intact and healthy Achilles tendons, which is a critical first step towards understanding tendon homeostasis and function as this biomechanical response changes in diseased tendons.

Assessment of muscle architecture of the biceps femoris and vastus lateralis by ultrasound after a chronic stretching program

OBJECTIVE

To evaluate the chronic effects of a static stretching program on the muscle architecture of biceps femoris (BF) and vastus lateralis (VL) muscles in ultrasound (US) images.

DESIGN

Randomized controlled longitudinal trial.

SETTING

Biomechanics Laboratory of Physical Education School of the Army, Rio de Janeiro, Brazil.

PARTICIPANTS

The study included 24 healthy and physically active male volunteers (19.05 ± 1.40 years, 1.73 ± 0.07 m, and 73.15 ± 8.33 kg), randomly allocated to 1 of 2 groups: stretching group (SG, n = 12) and control group (n = 12).

INTERVENTIONS

The SG was submitted to 3 sets of 30 seconds of static stretching 3 times a week during 8 weeks.

MAIN OUTCOME MEASURES

Ultrasound equipment (7.5 MHz) was used for the evaluation of BF and VL muscle architecture variables (pennation angle, fiber length, muscle thickness, and fascicle displacement) before and after training. Knee range of motion (ROM) and isometric flexion and extension torque (TQ) were also measured.

RESULTS

There were no significant changes in muscle architecture, TQ, and maximum knee flexion angle (P > 0.05). However, maximum knee extension angle (MEA) increased significantly in the SG (pretraining: 159.37 ± 7.27 degrees and posttraining: 168.9 ± 3.7 degrees; P < 0.05).

CONCLUSIONS

Volume or intensity (or both) of the stretching protocol was insufficient to cause structural changes in the VL and BF muscles. The increase in MEA could not be explained by muscle architecture changes.

CLINICAL RELEVANCE

To describe changes in the VL and BF muscle tendon unit using US after a long-term stretching program to identify which structures are responsible for ROM increase.