The human patellar tendon is frequently affected by tendinopathy, but the etiology of the condition is not established, although differential loading of the anterior and posterior tendon may be associated with the condition. We hypothesized that changes in fibril morphology and collagen cross-linking would parallel differences in material strength between the anterior and posterior tendon. Tendon fascicles were obtained from elective ACL surgery patients and tested micromechanically. Transmission electron microscopy was used to assess fibril morphology, and collagen cross-linking was determined by HPLC and calorimetry. Anterior fascicles were markedly stronger (peak stress: 54.3 ± 21.2 vs. 39.7 ± 21.3 MPa; P < 0.05) and stiffer (624 ± 232 vs. 362 ± 170 MPa; P < 0.01) than posterior fascicles. Notably, mature pyridinium type cross-links were less abundant in anterior fascicles (hydroxylysylpyridinoline: 0.859 ± 0.197 vs. 1.416 ± 0.250 mol/mol, P = 0.001; lysylpyridinoline: 0.023 ± 0.006 vs. 0.035 ± 0.006 mol/mol, P < 0.01), whereas pentosidine and pyrrole concentrations showed no regional differences. Fibril diameters tended to be larger in anterior fascicles (7.819 ± 2.168 vs. 4.897 ± 1.434 nm²; P = 0.10). Material properties did not appear closely related to cross-linking or fibril morphology. These findings suggest region-specific differences in mechanical, structural, and biochemical properties of the human patellar tendon.

Background: Overuse tendon injuries are frequent. Corticosteroid injections are commonly used as treatment, although their direct effects on the material properties of the tendon are poorly understood. Purpose: To examine the influence of corticosteroids on the tensile strength of isolated collagen fascicles. Study Design: Controlled laboratory study. Methods: Single strands (300-500 [.mu]m) of rat-tail collagen fascicles were incubated in either high (1 mL of 40 mgmL-1 mixed with 0.5 mL saline 9%) or low (1 mL of 40 mgmL-1 mixed with 2 mL saline 9%) concentration of methylprednisolone acetate (Depomedrol) for 3 or 7 days, while the control segment from the same fascicle was kept in saline (N = 64). After the incubation period, the fascicles underwent displacement to failure in a mechanical test rig at 0.13 mm/s, and thereafter hydroxylysyl pyridinoline and lysyl pyridinoline cross-link content was evaluated in a high-performance liquid chromatography system. Data for each group were analyzed with a 2-way analysis of variance (time × incubation) for ultimate stress (mean ± standard deviation). Results: In the high-concentration groups, strength was reduced after 3 (16.6 ± 4.6 MPa) and 7 (8.6 ± 1.7 MPa) days compared to the controls (30.2 ± 5.0 MPa and 25.6 ± 4.6 MPa, respectively; P <. 05). In the low-concentration groups, strength was reduced after 3 (12.0 ± 3.1 MPa) and 7 days (10.9 ± 2.5 MPa) compared to the controls (31.5 ± 5.0 MPa and 32.4 ± 5.6 MPa, respectively; P <. 05). The amount of cross-linking was unaffected by the intervention. Conclusion: Data show that the tensile strength of isolated fascicles is markedly reduced after 3-and 7-day incubation in both high and low concentration of corticosteroids, although the observed effect on whole tendon remains unknown. Clinical Relevance: Corticosteroids may weaken specific regions of the injected tendon and leave it more prone to rupture. This weakening effect is manifested in the individual collagen fascicles that constitute the tendon.

Conclusive insight into the microscopic principles that govern the strength of tendon and related connective tissues is lacking and the importance of collagen cross-linking has not been firmly established. The combined application of whole-tissue mechanical testing and atomic force spectroscopy allowed for a detailed characterization of the effect of cross-linking in rat-tail tendon. The cross-link inducing agent glutaraldehyde augmented the tensile strength of tendon fascicles. Stress at failure increased from ∼8 MPa to ∼39 MPa. The mechanical effects of glutaraldehyde at the tendon fibril level were examined by atomic force microscopy. Peak forces increased from ∼1379 to ∼2622 pN while an extended Hertz fit of force-indentation data showed a ∼24 fold increase in Young's modulus on indentation. The effect of glutaraldehyde cross-linking on the tensile properties of a single collagen fibril was investigated by a novel methodology based on atomic force spectroscopy. The Young's modulus of a secluded fibril increased from ∼407 MPa to ∼1.1 GPa with glutaraldehyde treatment. Collectively, the findings indicate that cross-linking at the level of the collagen fibril is of key importance for the mechanical strength of tendon tissue. However, when comparing the effects at the level of the tendon fascicle and fibril, respectively, further questions are prompted regarding the pathways of force through the tendon microstructure as fibril strength seems to surpass that of the tendon fascicle.

Muscle strength assessment is fundamental to track the progress of performance and prescribe correct exercise intensity. In field settings, simple tests are preferred. This study develops equations to estimate maximal muscle strength in upper- and lower-extremity muscles based on submaximal elastic resistance tests. Healthy adults (n = 26) performed a maximal test (1 RM) to validate the ability of the subsequent submaximal tests to determine maximal muscle strength, with elastic bands. Using a within-group repeated measures design, three submaximal tests of 40%, 60%, and 80% during (1) shoulder abduction, (2) shoulder external rotation, (3) hip adduction, and (4) prone knee flexion were performed. The association between number of repetitions and relative intensity was modeled with both 1st and 2nd order polynomials to determine the best predictive validity. For both upper-extremity tests, a strong linear association between repetitions and relative intensity was found (R² = 0.97–1.00). By contrast, for the lower-extremity tests, the associations were fitted better with a 2nd order polynomial (R² = 1.00). The results from the present study provide formulas for predicting maximal muscles strength based on submaximal resistance in four different muscles groups and show a muscle-group-specific association between repetitions and intensity.

Purpose: We aimed to investigate the influence of wearing a ballistic vest on physical performance in police officers. Methods: We performed a cross-over study to investigate the influence of wearing a ballistic vest on reaction and response time, lumbar muscle endurance and police vehicle entry and exit times. Reaction and response time was based on a perturbation setup where the officers’ pelvises were fixed and EMG of lumbar and abdominal muscles was recorded. We used a modified Biering–Sørensen test to assess the lumbar muscle endurance and measured duration of entry and exit maneuvers in a variety of standard-issue police cars. Results: There was a significant difference of 24% in the lumbar muscle endurance test (no vest: 151 s vs. vest: 117 s), and the police officers experienced higher physical fatigue after the test when wearing a vest. Furthermore, officers took longer to both enter and exit police cars when wearing a vest (range: 0.24–0.56 s) depending on the model of the vehicle. There were no significant differences in reaction and response times between the test conditions (with/without vest). Discussion and Conclusion: Wearing of a ballistic vest significantly influenced the speed of movement in entry and exit of police cars and lumbar muscle endurance, although it does not seem to affect reaction or response times. The ballistic vest seems to impair performance of tasks that require maximal effort, which calls for better designs of such vests.

Background: Persistent postconcussion symptoms (PPCSs) represent a complex phenomenon following mild traumatic brain injury (mTBI), and this phenomenon is characterized by a diverse range of symptoms that greatly impact daily functioning, including the ability to engage in physical, cognitive, and social activities. Effective rehabilitation strategies and a nuanced understanding of brain function and patient perception remain insufficiently explored in adults with PPCSs. Objective: This study aims to assess the physiological and neurofunctional effects of targeted physical exercise carried out as a graded subsymptomatic aerobic exercise program. Furthermore, the project seeks to alleviate the complex symptomatology and perception of PPCSs through the planned intervention. In addition, the study aims to obtain feedback from patients and researchers involved in this interprofessional project and to conduct a comprehensive 360-degree evaluation combining subjective and objective data in order to obtain novel insights into the symptom complexity of PPCSs, ultimately paving the way for future strategic initiatives in mTBI treatment. Methods: This randomized controlled trial enrolled 70 patients with PPCSs. The patients were randomized in a 1:1 ratio to either a control group or a training group. Patients in the control group maintained their usual activities and care. Patients in the training group underwent a 12-week tailored aerobic exercise program designed to stay below symptom-provocation thresholds, using the Buffalo Concussion Bike Test (BCBT) as the assessment instrument. The study consisted of qualitative patient interviews, physical tests, exercise evaluations, neurofunctional and structural magnetic resonance imaging (MRI) scans, and process evaluations. MRI assessed neurophysiological changes, including blood-brain barrier integrity and cerebral metabolism. The primary outcome is improvement in physical performance on the BCBT. The secondary outcomes are symptom severity, neurophysiological function, and quality of life. The study will incorporate a multimodal approach, combining subjective patient reports with objective clinical and neuroimaging data, enabling the interdisciplinary research group to perform comprehensive evaluations of the complexity of PPCSs. Results: Study funding was awarded in December 2022. Enrollment and randomization of 70 patients were completed in March 2025. The 12-week postintervention assessments concluded in August 2025. Data analysis is ongoing and expected to conclude in 2026. The results will be published in separate manuscripts in 2027. Conclusions: This study is innovative in its approach to patients with PPCSs, focusing on the effect of an individualized exercise regimen and exploring the neurofunctional underpinnings of symptom improvements as well as the patient perceptions of dealing with PPCSs. The findings are anticipated to contribute greatly to the field of PPCS management, potentially transforming current rehabilitation practices.