Tendinopathy alters ultrasound transmission in the patellar tendon during squatting

The Biomechanics of Musculoskeletal Tissues during Activities of Daily Living: Dynamic Assessment Using Quantitative Transmission-Mode Ultrasound Techniques

The measurement of musculoskeletal tissue properties and loading patterns during physical activity is important for understanding the adaptation mechanisms of tissues such as bone, tendon, and muscle tissues, particularly with injury and repair. Although the properties and loading of these connective tissues have been quantified using direct measurement techniques, these methods are highly invasive and often prevent or interfere with normal activity patterns. Indirect biomechanical methods, such as estimates based on electromyography, ultrasound, and inverse dynamics, are used more widely but are known to yield different parameter values than direct measurements. Through a series of literature searches of electronic databases, including Pubmed, Embase, Web of Science, and IEEE Explore, this paper reviews current methods used for the in vivo measurement of human musculoskeletal tissue and describes the operating principals, application, and emerging research findings gained from the use of quantitative transmission-mode ultrasound measurement techniques to non-invasively characterize human bone, tendon, and muscle properties at rest and during activities of daily living. In contrast to standard ultrasound imaging approaches, these techniques assess the interaction between ultrasound compression waves and connective tissues to provide quantifiable parameters associated with the structure, instantaneous elastic modulus, and density of tissues. By taking advantage of the physical relationship between the axial velocity of ultrasound compression waves and the instantaneous modulus of the propagation material, these techniques can also be used to estimate the in vivo loading environment of relatively superficial soft connective tissues during sports and activities of daily living. This paper highlights key findings from clinical studies in which quantitative transmission-mode ultrasound has been used to measure the properties and loading of bone, tendon, and muscle tissue during common physical activities in healthy and pathological populations.

Transmission-Mode Ultrasound for Monitoring the Instantaneous Elastic Modulus of the Achilles Tendon During Unilateral Submaximal Vertical Hopping

Submaximal vertical hopping capitalizes on the strain energy storage-recovery mechanism associated with the stretch-shortening cycle and is emerging as an important component of progressive rehabilitation protocols in Achilles tendon injury and a determinant of readiness to return to sport. This study explored the reliability of transmission mode ultrasound in quantifying the instantaneous modulus of elasticity of human Achilles tendon during repetitive submaximal hopping. A custom-built ultrasound transmission device, consisting of a 1 MHz broadband emitter and four regularly spaced receivers, was used to measure the axial velocity of ultrasound in the Achilles tendon of six healthy young adults (mean ± SD; age 26 ± 5 years; height 1.78 ± 0.11 m; weight 79.8 ± 13.6 kg) during steady-state unilateral hopping (2.5 Hz) on a piezoelectric force plate. Vertical ground reaction force and lower limb joint kinematics were simultaneously recorded. The potential sensitivity of the technique was further explored in subset of healthy participants (n = 3) that hopped at a slower rate (1.8 Hz) and a patient who had undergone Achilles tendon rupture-repair (2.5 Hz). Reliability was estimated using the mean-within subject coefficient of variation calculated at each point during the ground-contact phase of hopping, while cross-correlations were used to explore the coordination between lower limb kinematics ground reaction forces and ultrasound velocity in the Achilles tendon. Axial velocity of ultrasound in the Achilles tendon was highly reproducible during hopping, with the mean within-subject coefficient of variation ranging between 0.1 and 2.0% across participants. Ultrasound velocity decreased immediately following touch down (−19 ± 13 ms^–1), before increasing by 197 ± 81 ms^–1, on average, to peak at 2230 ± 87 ms^–1 at 67 ± 3% of ground contact phase in healthy participants. Cross-correlation analysis revealed that ultrasound velocity in the Achilles tendon during hopping was strongly associated with knee (mean r = 0.98, range 0.95–1.00) rather than ankle (mean r = 0.67, range 0.35–0.79) joint motion. Ultrasound velocity was sensitive to changes in hopping frequency in healthy adults and in the surgically repaired Achilles tendon was characterized by a similar peak velocity (2283 ± 13 ms^–1) but the change in ultrasound velocity (447 ± 21 ms^–1) was approximately two fold that of healthy participants (197 ± 81 ms^–1). Although further research is required, the technique can be used to reliably monitor ultrasound velocity in the Achilles tendon during hopping, can detect changes in the instantaneous elastic modulus of tendon with variation in hopping frequency and tendon pathology and ultimately may provide further insights into the stretch-shortening cycle and aid clinical decision concerning tendon rehabilitation protocols and readiness to return to sport.

Structural and Functional Changes in the Coupling of Fascial Tissue, Skeletal Muscle, and Nerves During Aging

Aging is a one-way process associated with profound structural and functional changes in the organism. Indeed, the neuromuscular system undergoes a wide remodeling, which involves muscles, fascia, and the central and peripheral nervous systems. As a result, intrinsic features of tissues, as well as their functional and structural coupling, are affected and a decline in overall physical performance occurs. Evidence from the scientific literature demonstrates that senescence is associated with increased stiffness and reduced elasticity of fascia, as well as loss of skeletal muscle mass, strength, and regenerative potential. The interaction between muscular and fascial structures is also weakened. As for the nervous system, aging leads to motor cortex atrophy, reduced motor cortical excitability, and plasticity, thus leading to accumulation of denervated muscle fibers. As a result, the magnitude of force generated by the neuromuscular apparatus, its transmission along the myofascial chain, joint mobility, and movement coordination are impaired. In this review, we summarize the evidence about the deleterious effect of aging on skeletal muscle, fascial tissue, and the nervous system. In particular, we address the structural and functional changes occurring within and between these tissues and discuss the effect of inflammation in aging. From the clinical perspective, this article outlines promising approaches for analyzing the composition and the viscoelastic properties of skeletal muscle, such as ultrasonography and elastography, which could be applied for a better understanding of musculoskeletal modifications occurring with aging. Moreover, we describe the use of tissue manipulation techniques, such as massage, traction, mobilization as well as acupuncture, dry needling, and nerve block, to enhance fascial repair.

Do habitual foot-strike patterns in running influence functional Achilles tendon properties during gait?

The capacity of foot-strike running patterns to influence the functional properties of the Achilles tendon is controversial. This study used transmission-mode ultrasound to investigate the influence of habitual running foot-strike pattern on Achilles tendon properties during barefoot walking and running. Fifteen runners with rearfoot (RFS) and 10 with a forefoot (FFS) foot-strike running pattern had ultrasound transmission velocity measured in the right Achilles tendon during barefoot walking (≈1.1 ms^-1) and running (≈2.0 ms^-1). Temporospatial gait parameters, ankle kinematics and vertical ground reaction force were simultaneously recorded. Statistical comparisons between foot-strike patterns were made using repeated measure ANOVAs. FFS was characterised by a significantly shorter stance duration (-4%), greater ankle dorsiflexion (+2°), and higher peak vertical ground reaction force (+20% bodyweight) than RFS running (P < .05). Both groups adopted a RFS pattern during walking, with only the relative timing of peak dorsiflexion (3%), ground reaction force (1-2%) and peak vertical force loading rates (22-23%) differing between groups (P < .05). Peak ultrasound transmission velocity in the Achilles tendon was significantly higher in FFS during walking (≈100 ms^-1) and running (≈130 ms^-1) than RFS (P < .05). Functional Achilles tendon properties differ with habitual footfall patterns in recreational runners.

Fascial tissue research in sports medicine: from molecules to tissue adaptation, injury and diagnostics: consensus statement

The fascial system builds a three-dimensional continuum of soft, collagen-containing, loose and dense fibrous connective tissue that permeates the body and enables all body systems to operate in an integrated manner. Injuries to the fascial system cause a significant loss of performance in recreational exercise as well as high-performance sports, and could have a potential role in the development and perpetuation of musculoskeletal disorders, including lower back pain. Fascial tissues deserve more detailed attention in the field of sports medicine. A better understanding of their adaptation dynamics to mechanical loading as well as to biochemical conditions promises valuable improvements in terms of injury prevention, athletic performance and sports-related rehabilitation. This consensus statement reflects the state of knowledge regarding the role of fascial tissues in the discipline of sports medicine. It aims to (1) provide an overview of the contemporary state of knowledge regarding the fascial system from the microlevel (molecular and cellular responses) to the macrolevel (mechanical properties), (2) summarise the responses of the fascial system to altered loading (physical exercise), to injury and other physiological challenges including ageing, (3) outline the methods available to study the fascial system, and (4) highlight the contemporary view of interventions that target fascial tissue in sport and exercise medicine. Advancing this field will require a coordinated effort of researchers and clinicians combining mechanobiology, exercise physiology and improved assessment technologies.

Frontiers in fascia research

Basic sciences are the backbone of every clear understanding of how the body is composed and how different structures and functions are connected with each other. It is obvious that there is a huge variability in human beings - not only in terms of the outer appearance such as measurements of height, weight, muscle mass and other physical properties, but also with respect to metabolic and functional parameters. This article highlights recent developments of research activities in the field of fascia sciences with a special emphasis on assessment strategies as the basis of further studies. Anatomical and histological studies show that fascial tissue is highly variable in terms of density, stiffness, and other parameters such as metabolic and humoral activity. Moreover, it encompasses nerves and harbours a system of micro-channels, also known as the primo vascular system. As ultrasound is a widely available method, its use is appealing not only for imaging of fascial structures, but also for thorough scientific analysis. Unlike most other imaging technologies, US has the advantage of real-time analysis of active or passive movements. In addition, other assessment methods for fascial tissue are discussed. In conclusion, fascial tissue plays an important role not only in functional anatomy, but also in evolutionary and molecular biology, sport, and exercise science as well as in numerous therapeutic approaches. A high density of nerves is found in fascial tissue. Knowledge of individual characteristics, especially by visualizing with ultrasound, leads to personalized therapeutic approaches, such as in pain therapy.

Lower material stiffness in rupture-repaired Achilles tendon during walking: transmission-mode ultrasound for post-surgical tendon evaluation

PURPOSE

This cross-sectional study used transmission-mode ultrasound to evaluate dynamic tendon properties during walking in surgically repaired and contralateral Achilles tendon (AT), with a median (range) post-operative period of 22 (4-58) months. It was hypothesised that the axial transmission speed of ultrasound (TSOU) during walking would be slower, indicating lower material stiffness in repaired compared with contralateral AT.

METHODS

Ten patients [median (range) age 47 (37-69) years; height 180 (170-189) cm; weight 93 (62-119) kg], who had undergone open surgical repair of the AT and were clinically recovered according to their treating clinicians, walked barefoot on a treadmill at self-selected speed (1.0 ± 0.2 m/s). Synchronous measures of TSOU, sagittal ankle motion, vertical ground reaction force (GRF), and spatiotemporal gait parameters were recorded during 20 s of steady-state walking. Paired t tests were used to evaluate potential between-limb differences in TSOU, GRF, ankle motion, and spatiotemporal gait parameters.

RESULTS

TSOU was significantly lower (≈175 m/s) in the repaired than in the contralateral AT over the entire gait cycle (P < 0.05). Sagittal ankle motion was significantly greater (≈3°) in the repaired than in the contralateral limb (P = 0.036). There were no significant differences in GRF or spatiotemporal parameters between limbs.

CONCLUSIONS

Repaired AT was characterised by a lower TSOU, reflecting a lower material stiffness in the repaired tendon than in the contralateral tendon. A lower material stiffness may underpin greater ankle joint motion of the repaired limb during walking and long-term deficits in the muscle-tendon unit reported with AT repair. Treatment and rehabilitation approaches that focus on increasing the material stiffness of the repaired AT may be clinically beneficial. Transmission-mode ultrasound would seem useful for quantifying tendon properties post AT rupture repair and may have the potential to individually guide rehabilitation programmes, thereby aiding safer return to physical activity.

LEVEL OF EVIDENCE

II.

Achilles Tendon Load is Progressively Increased with Reductions in Walking Speed

INTRODUCTION

Achilles tendon rehabilitation protocols commonly recommend a gradual increase in walking speed to progressively intensify tendon loading. This study used transmission-mode ultrasound to evaluate the influence of walking speed on loading of the human Achilles tendon in vivo.

METHODS

Axial transmission speed of ultrasound was measured in the right Achilles tendon of 33 adults (mean ± SD: age, 29 ± 3 yr; height, 1.725 ± 0.069 m; weight, 71.4 ± 19.9 kg) during unshod, steady-state treadmill walking at three speeds (slow, 0.85 ± 0.12 ms; preferred, 1.10 ± 0.13 m·s; fast, 1.35 ± 0.20 m·s). Ankle kinematics, spatiotemporal gait parameters and vertical ground reaction force were simultaneously recorded. Statistical comparisons were made using repeated-measures ANOVA models.

RESULTS

Increasing walking speed was associated with higher cadence, longer step length, shorter stance duration, greater ankle plantarflexion, higher vertical ground reaction force peaks, and a greater loading rate (P < 0.05). Maximum (F1,38 = 7.38, P < 0.05) and minimum (F1,46 = 8.95, P < 0.05) ultrasound transmission velocities in the Achilles tendon were significantly lower (16-23 m·s) during the stance but not swing phase of gait, with each increase in walking speed.

CONCLUSIONS

Despite higher vertical ground reaction forces and greater ankle plantarflexion, increasing walking speed resulted in a reduction in the axial transmission velocity of ultrasound in the Achilles tendon; indicating a speed-dependent reduction in tensile load within the triceps surae muscle-tendon unit during walking. These findings question the rationale for current progressive loading protocols involving the Achilles tendon, in which reduced walking speeds are advocated early in the course of treatment to lower Achilles tendon loads.