The time course of in vivo recovery of transverse strain in high-stress tendons following exercise

Exploring the role of intratendinous pressure in the pathogenesis of tendon pathology: a narrative review and conceptual framework

Despite the high prevalence of tendon pathology in athletes, the underlying pathogenesis is still poorly understood. Various aetiological theories have been presented and rejected in the past, but the tendon cell response model still holds true. This model describes how the tendon cell is the key regulator of the extracellular matrix and how pathology is induced by a failed adaptation to a disturbance of tissue homeostasis. Such failure has been attributed to various kinds of stressors (eg, mechanical, thermal and ischaemic), but crucial elements seem to be missing to fully understand the pathogenesis. Importantly, a disturbance of tissue pressure homeostasis has not yet been considered a possible factor, despite it being associated with numerous pathologies. Therefore, we conducted an extensive narrative literature review on the possible role of intratendinous pressure in the pathogenesis of tendon pathology. This review explores the current understanding of pressure dynamics and the role of tissue pressure in the pathogenesis of other disorders with structural similarities to tendons. By bridging these insights with known structural changes that occur in tendon pathology, a conceptual model was constituted. This model provides an overview of the possible mechanism of how an increase in intratendinous pressure might be involved in the development and progression of tendon pathology and contribute to tendon pain. In addition, some therapies that could reduce intratendinous pressure and accelerate tendon healing are proposed. Further experimental research is encouraged to investigate our hypotheses and to initiate debate on the relevance of intratendinous pressure in tendon pathology.

Achilles tendon thickness reduces immediately after a marathon

BACKGROUND

The purpose of the present investigation was to evaluate the immediate effect of running a marathon on Achilles tendon anteroposterior thickness.

METHODS

In 25 runners who took part in the London marathon, ultrasonography was used to measure the Achilles tendon thickness pre- and immediately post-marathon and to identify any structural abnormalities indicating tendinopathy. Pain was recorded using a numerical rating scale at baseline and post-marathon. Twenty-one participants were included in the final analysis.

RESULTS

Running a marathon resulted in a significant decrease (- 13%, p < 0.01) in anteroposterior diameter of the Achilles tendon immediately following the marathon. There was no change in the proportion of Achilles tendons with structural abnormalities (34%) or pain (12%) following the marathon (p > 0.05).

CONCLUSION

Running a marathon resulted in an immediate reduction in anteroposterior diameter of the Achilles tendon. This finding may have implications for injury prevention and recovery following a marathon.

The acute effects of higher versus lower load duration and intensity on morphological and mechanical properties of the healthy Achilles tendon: a randomized crossover trial

The Achilles tendon (AT) exhibits volume changes related to fluid flow under acute load which may be linked to changes in stiffness. Fluid flow provides a mechanical signal for cellular activity and may be one mechanism that facilitates tendon adaptation. This study aimed to investigate whether isometric intervention involving a high level of load duration and intensity could maximize the immediate reduction in AT volume and stiffness compared with interventions involving a lower level of load duration and intensity. Sixteen healthy participants (12 males, 4 females; age 24.4±9.4 years, body mass 70.9±16.1 kg, height 1.7±0.1 m) performed three isometric interventions of varying levels of load duration (2 s and 8 s) and intensity (35% and 75% maximal voluntary isometric contraction) over a 3 week period. Freehand 3D ultrasound was used to measure free AT volume (at rest) and length (at 35%, 55% and 75% of maximum plantarflexion force) pre- and post-interventions. The slope of the force–elongation curve over these force levels represented individual stiffness (N mm⁻¹). Large reductions in free AT volume and stiffness resulted in response to long-duration high-intensity loading whilst less reduction was produced with a lower load intensity. In contrast, no change in free AT volume and a small increase in AT stiffness occurred with lower load duration. These findings suggest that the applied load on the AT must be heavy and sustained for a long duration to maximize immediate volume reduction, which might be an acute response that enables optimal long-term tendon adaptation via mechanotransduction pathways.

Summary: High levels of load duration and intensity have the greatest acute effect on the free Achilles tendon volume and stiffness.

Acute Effects of Resistance Training with Blood Flow Restriction on Achilles Tendon Thickness

The Achilles tendon is one of the strongest and thickest tendons of the human body. Several studies have reported an immediate decrease in Achilles tendon thickness after a single bout of resistance training. However, the effects of blood flow restriction training on Achilles tendon thickness have not been investigated. The purpose of this study was to investigate the acute effects of different regimens of resistance training on Achilles tendon thickness. Fiftytwo participants (27.3 ± 7 years; 177.6 ± 11 cm; 72.2 ± 13.7 kg) were randomly allocated into one of the three groups: low-intensity exercise without (LI, n = 13) and with blood flow restriction (LI-BFR, n = 24), and high-intensity exercise (HI, n = 15). Participants from LI and LI-BFR groups performed four sets (1 x 30 + 3 x 15 reps) at 30% 1RM, while the HI group performed four sets (1 x 30 with 30% 1RM + 3 x 10 reps with 75% 1RM). All groups performed a plantar flexion exercise. For the LI-BFR group, a blood pressure cuff was placed on the dominant calf and inflated at 30% of the individual´s occlusion pressure (47.6 ± 19.8 mmHg). Sonographic images of Achilles tendon thickness were taken at pre, immediately after, 60 min and 24 h following acute bouts of exercise. Achilles tendon thickness was significantly reduced immediately after, 60 min and 24 h post-LI-BFR exercise (pre: 4.4 ± 0.4 mm vs. IA: 3.8 ± 0.4 mm vs. 60 min: 3.7 ± 0.3 mm vs. 24 h: 4.1 ± 0.3 mm; p < 0.001), whereas Achilles tendon thickness was unchanged for HI and LI groups (p > 0.05). These results suggest that blood flow restriction training may be an effective strategy to stimulate a positive response in Achilles tendon thickness.

Quantitative Analysis of Patellar Tendon After Total Knee Arthroplasty Using Echo Intensity: A Nonrandomized Controlled Trial of Alpine Skiing

BACKGROUND

Despite the knee extensor weakness, less attention has been paid to the evaluation of patellar tendon after total knee arthroplasty (TKA). We previously observed patellar tendon hypertrophy after TKA. The purpose of this study is to reanalyze these ultrasound data to detect whether brightness mode ultrasound imaging reflects pathological changes of the patellar tendon after TKA.

METHODS

Twenty-eight participants with post unilateral TKA were assigned to an intervention group or control group. The intervention group underwent a 12-week skiing program. Patellar tendon mechanical properties were obtained by combining isometric dynamometry, ultrasound imaging, and electromyography in operated knee and nonoperated knee. Luminosity ratio (LR) was measured using echo intensity in a relaxed and maximally loaded phase.

RESULTS

Baseline comparisons revealed significant effects of the surgical side (P < .001) and loading phase (P = .017), but no interaction between leg and phase (P < .149). LR of the operated knee was significantly lower than LR of the nonoperated knee in relaxed (P < .001) and maximally loaded phases (P = .003). In addition, there was a significant correlation between LR of maximum phase and isometric knee extension torque (r² = 0.156, P = .038). However, LR was not related to patellar tendon stiffness, Young's modulus, or strain. There was a significant time effect in knee extension torque, but no time effects on LR and tendon force.

CONCLUSION

Patellar tendon LR is decreased along with degenerative change after TKA. Ultrasound imaging provides a promising metric to acquire in vivo patellar tendon pathological assessment after TKA.

Different Time Course of Recovery in Achilles Tendon Thickness After Low-Load Resistance Training With and Without Blood Flow Restriction

CONTEXT

Blood flow restriction research has focused on muscular strength and hypertrophy. Limited data have been reported about the blood flow restriction effect on the tendon.

OBJECTIVE

To analyze and compare the time course of recovery in Achilles tendon thickness after a single bout of low-intensity resistance training (LI-RT) and low-intensity blood flow restriction training (LI-BFRT).

METHODS

A total of 56 healthy participants (24.60 [4.0] y; 23.65 [3.4] body mass index) were included. The dominant leg was assigned for LI-BFRT using low load (30% 1-repetition maximum) and 30% of the total occlusion pressure (52.21 [17.89] mm Hg) in plantar-flexion exercise (1 × 30 + 3 × 15 repetitions). The nondominant leg was assumed as a control condition.

MAIN OUTCOME MEASURE

Sonography images were taken before the intervention, immediately posttraining, and 24 hours after exercise (post-24) for the Achilles tendon thickness.

RESULTS

Changes in Achilles tendon thickness for LI-BFRT group were significant post- (-14.5%; P < .05) and post-24 (-9.2%; P < .05). In contrast, LI-RT group showed a transient decrease after exercise (-9.67%; P < .05) followed by a recovery of thickness post-24 (-1.06%; P < .05). Thickness post-24 was different between LI-BFRT versus LI-RT (P < .01). Hedge effect size analysis showed a large effect (g = 0.90) in LI-BFRT pre-post condition and a medium effect (g = 0.57) in post- to post-24. The LI-RT obtained a medium effect (g = 0.53) in pre-post condition and a small effect (g = 0.49) in post- to post-24.

CONCLUSIONS

This study showed a different time course of the acute response in Achilles tendon thickness between LI-BFRT and LI-RT. This may be associated with intratendinous fluid movement in response to LI-BFRT.

Does Magnetic Resonance Imaging Provide Superior Reliability for Achilles and Patellar Tendon Cross-Sectional Area Measurements Compared with Ultrasound Imaging?

This study investigated the reliability of Achilles and patellar tendon cross-sectional area (CSA) measurement using ultrasound imaging (USI) and magnetic resonance imaging (MRI). Fifteen healthy adults were imaged twice on two occasions, interrupted by a tendon loading protocol. Tendon CSA segmentations were conducted by an experienced and an inexperienced rater blinded to information regarding subject, session and loading status. USI provided good test-retest reliability (intra-class correlation coefficient [ICC] 2,1 > 0.85, standard error of measurement [SEM] 5%-6%), while with MRI it was excellent (ICC 2,1 > 0.92, SEM 4%) for the experienced rater. This study suggests that MRI provides superior reliability for tendon CSA measurements compared with USI. However, the difference in reliability between the methods was small, and the results were inconclusive regarding objectivity and sensitivity to change when assessed based on the effect of loading. We concluded that both methods can be used for reliable CSA measurements of the Achilles and patellar tendons when using a highly standardized measurement protocol and when conducted by an experienced rater.

Ankle Joint Position and the Reliability of Ultrasound Tissue Characterization of the Achilles Tendon: A Pilot Study

Background

Imaging of the Achilles tendon using ultrasound tissue characterization (UTC) involves taking up the slack of the tendon by including dorsiflexion of the ankle. This pilot study aimed to determine whether different longitudinal tension applied to the Achilles tendon during imaging affected the reliability of UTC.

Material/Methods

Nine asymptomatic active volunteers, aged between 23–49 years underwent imaging of 17 Achilles tendons. Three positions of tension included plantar grade, 50%, and 100% of maximal dorsiflexion, with a range of 18–32°. Ranges were established and standardized using an isokinetic dynamometer. A test and re-test process was conducted at each position to determine the intraclass correlation coefficients (ICCs) and minimum detectable change (MDC) per echotype. Images were analyzed using UTC software.

Results

Plantar grade positioning images could not be obtained. ICCs for each echotype I–IV between test 1 and test 2 were 0.965, 0.962, 0.858, 0.739 at 100% dorsiflexion (95% CI, 0.86–0.99, 0.84–0.99, 0.51–0.97, and 0.2–0.94), and 0.771, 0.551, 0.569, 0.429 at 50% dorsiflexion (95% CI, 0.29–0.94, −0.09–0.88, −0.01–0.88, and −0.15–0.82). The MDC per echotype I–IV ranged between 4.1–1.0% of echotype data at 100% dorsiflexion, and 17.2–6.3% at 50% dorsiflexion.

Conclusions

Testing at maximum dorsiflexion provided improved reliability when using UTC in healthy individuals. The ICC at 100% dorsiflexion was increased, and the MDC was reduced for all echotypes. Therefore, standardizing test positions when using UTC is advisable for reliable comparison of results between studies.

Increased supraspinatus tendon thickness following fatigue loading in rotator cuff tendinopathy: potential implications for exercise therapy

Background/aim

Exercise imparts a load on tendon tissue that leads to changes in tendon properties. Studies suggest that loading immediately reduces tendon thickness, with a loss of this response in symptomatic tendinopathy. No studies investigating the response of tendon dimensions to load for the rotator cuff tendons exist. This study aimed to examine the short-term effect of loading on the thickness of the supraspinatus tendon and acromiohumeral distance those with and without rotator cuff tendinopathy.

Methods

Participants were 20 painfree controls, and 23 people with painful rotator cuff tendinopathy. Supraspinatus tendon thickness and acromiohumeral distance were measured using ultrasound scans before, and at three time points after loading (1, 6 and 24 hours). Loading involved isokinetic eccentric and concentric external rotation and abduction.

Results

There was a significant increase in supraspinatus tendon thickness in the pain group at 1 (7%, ∆=0.38, 95% CI 0.19 to 0.57) and 6 hours (11%, ∆=0.53, 95% CI 0.34 to 0.71), although only the 6 hours difference exceeded minimal detectable difference. In contrast, there was a small non-significant reduction in thickness in controls. The acromiohumeral distance reduced significantly in both groups at 1 hour (controls: ∆=0.64, 95% CI 0.38 to 0.90; pain: ∆=1.1, 95% CI 0.85 to 1.33), with a larger change from baseline in the pain group.

Conclusion

Those diagnosed with painful supraspinatus tendinopathy demonstrated increased thickening with delayed return to baseline following loading. Rehabilitation professionals may need to take into account the impact of loading to fatigue when planning rehabilitation programmes.

Quantitative phase measurements of tendon collagen fibres

Collagen is the main component of structural mammalian tissues. In tendons, collagen is arranged into fibrils with diameters ranging from 30 nm to 500 nm. These fibrils are further assembled into fibres several micrometers in diameter. Upon excessive thermal or mechanical stress, damage may occur in tendons at all levels of the structural hierarchy. At the fibril level, reported damage includes swelling and the appearance of discrete sites of plastic deformation that are best observed at the nanometer-scale using, for example, scanning electron microscopy. In this paper, digital in-line holographic microscopy is used for quantitative phase imaging to measure both the refractive index and diameter of collagen fibres in a water suspension in the native state, after thermal treatments, and after mechanical overload. Fibres extracted from tendons and subsequently exposed to 70 °C for 5, 15, or 30 minutes show a significant decrease in refractive index and an increase in diameter. A significant increase in refractive index is also observed for fibres extracted from tendons that were subjected to five tensile overload cycles.

Mechanotransduction: Relevance to Physical Therapist Practice-Understanding Our Ability to Affect Genetic Expression Through Mechanical Forces

Mechanotransduction, the mechanism by which mechanical perturbation influences genetic expression and cellular behavior, is an area of molecular biology undergoing rapid exploration and discovery. Cells are sensitive to forces such as shear, tension, and compression, and they respond accordingly through cellular proliferation, migration, tissue repair, altered metabolism, and even stem cell differentiation and maturation. The study of how cells sense and respond to mechanical stimulation is under robust expansion, with new scientific methods and technologies at our disposal. The application of these technologies to physical therapist practice may hold answers to some of our age-old questions while creating new avenues for our profession to optimize movement for societal health. Embracing this science as foundational to our profession will allow us to be valuable scientific collaborators with distinctive knowledge of the effects of loading. These partnerships will be key to augmenting the clinical utility of emerging therapies such as regenerative medicine, tissue engineering, and gene therapy. Collaboration with other scientific disciplines in these endeavors, along with the inclusion and application of these discoveries in our academic programs, will enhance the understanding of the impact of our practice on biologic and genetic processes. A basic understanding of mechanotransduction and its relevance to physical therapist practice is warranted to begin the conversation.

Does the adolescent patellar tendon respond to 5 days of cumulative load during a volleyball tournament?

Patellar tendinopathy (jumper's knee) has a high prevalence in jumping athletes. Excessive load on the patellar tendon through high volumes of training and competition is an important risk factor. Structural changes in the tendon are related to a higher risk of developing patellar tendinopathy. The critical tendon load that affects tendon structure is unknown. The aim of this study was to investigate patellar tendon structure on each day of a 5-day volleyball tournament in an adolescent population (16-18 years). The right patellar tendon of 41 players in the Australian Volleyball Schools Cup was scanned with ultrasound tissue characterization (UTC) on every day of the tournament (Monday to Friday). UTC can quantify structure of a tendon into four echo types based on the stability of the echo pattern. Generalized estimating equations (GEE) were used to test for change of echo type I and II over the tournament days. Participants played between eight and nine matches during the tournament. GEE analysis showed no significant change of echo type percentages of echo type I (Wald chi-square = 4.603, d.f. = 4, P = 0.331) and echo type II (Wald chi-square = 6.070, d.f. = 4, P = 0.194) over time. This study shows that patellar tendon structure of 16-18-year-old volleyball players is not affected during 5 days of cumulative loading during a volleyball tournament.