The dynamics of human tendon protein synthesis in response to short-term exercise and injury is poorly understood, and whether this occurs heterogeneously in the tendon remains an enigma. This study aimed to determine whether protein synthesis is affected by short-term exercise, and whether it is altered in patellar tendinopathy. Protein synthesis was studied in humans using an 8 day intake of deuterated water (D2O), and analyses of blood and tendon biopsies. Eighteen patients with chronic uni- or bilateral patellar tendinopathy (8 females and 10 males) and 18 healthy, matched participants (8 females and 10 males) were included. Both patellar tendons investigated in all participants, and the healthy participants additionally completed three bouts of unilateral heavy resistance training prior to biopsy sampling. Tendon protein synthesis rates were markedly higher (10-20 fold) in the soluble matrix fraction compared to the insoluble collagen fraction. Protein synthesis did not differ between tendinopathic and healthy tendons in either fraction. Unilateral resistance exercise had no significant impact on protein synthesis in either tendon fraction. Protein synthesis was not influenced by biological sex. The present study demonstrates that tendon protein synthesis predominantly occurs in the soluble matrix fraction compared to the insoluble collagen fraction of human patellar tendon, and chronic tendinopathy and short-term exercise do not appear to alter synthesis rates in healthy, physically active humans. These data increase our understanding of tendon protein synthesis, and could help explain why patellar tendinopathy becomes a chronic condition. KEY POINTS: The dynamics of human tendon protein synthesis in different protein fractions are not well-understood, and the effect of short-term exercise or tendinopathy remains largely unknown. In this study, protein synthesis was significantly higher in the soluble matrix proteins compared to the insoluble collagen fraction. No apparent differences in tendon protein synthesis in either fraction were observed between healthy and tendinopathic tendons. Unilateral short-term exercise had no measurable impact on tendon protein synthesis in either protein fraction. The results increase our understanding of protein dynamics in human tendon and suggest that neither chronic tendinopathy nor short-term exercise measurably alters tendon protein synthesis over an 8 day period.

Loading intervention is the predominant treatment strategy for tendinopathy and the response may depend on restitution time between loading exposure. Therefore, the purpose of this study was to investigate if a 12-week exercise-based rehabilitation regime for patellar tendinopathy is influenced by restitution time. We hypothesized that longer restitution would yield greater improvements in clinical outcomes, tissue structure, and function compared to shorter restitution. Fifty-two participants with chronic patellar tendinopathy were randomized to a short restitution group (SR, 3 exercise days/week) or an extended restitution group (ER, 1 exercise day/week). For both groups, each session consisted of resistance exercises (Leg press and knee extension) with a load starting at ~60% of 1 RM and progressing to ~75% of 1 RM and impact activities (running and jumping), restricted in both groups. Function and symptoms (VISA-P), tendon pain during activity (NRS), tendon function (functional tests), and ultrasound (tendon vascularization and swelling) were assessed before and after the intervention. Self-reported improvement and satisfaction with function and treatment were measured at week 12. The results revealed that ER was not superior to SR for any of the outcomes. Both groups attained significant improvements in clinical outcomes and muscular strength. Conversely, there were no improvements in jumping height or tendon structure. Moreover, there were no group differences in self-reported improvement or satisfaction with function or treatment. In conclusion, there was no superior effect of 1 exercise day/week compared to 3 exercise days/week. Both groups demonstrated equal clinical and muscular strength improvement after 12 weeks without any improvement in structure or jumping performance. No group differences were found in self-reported improvement or satisfaction with function or treatment at week 12.

Elite swimming is characterized by high training volumes, which increases the risk of overuse injuries. Detailed information on whether specific disciplines or competitive distance matters for the occurrence of injuries is sparse. This study aimed to describe the injury epidemiology among elite swimmers and to identify potential explanatory factors. We employed a retrospective, self-reported design, with the known limitations of recall bias. In June 2024, a questionnaire was sent to elite swimming clubs across Denmark, Norway, and Sweden. A total of 220 swimmers completed the questionnaire describing training and injury characteristics in the 2023/2024 season and injury history from their entire swimming career. Throughout their careers, 128 out of 196 swimmers experienced at least one injury, resulting in a total of 183 injuries. We documented 113 injuries in 93 participants during the 2023/2024 season. For the 2023/2024 season, a total of 73 580 athlete exposures (AEs) were recorded, yielding an injury incidence of 1.54 injuries/1000 AEs. The shoulder was the most prevalent injury site (0.87 injuries/1000 AEs). Injury location appeared to differ across primary disciplines. When looking at overall injury incidence across disciplines, butterfly and breaststroke swimmers showed a slightly higher numerical injury incidence than other disciplines, although non-significant (1.69 and 1.58 vs. 0.98 injuries/1000 AEs). Finally, freestyle sprinters had a higher injury incidence compared to freestyle long-distance swimmers (rate ratio = 2.17, 95% CI 1.15-4.31). This indicates that both discipline and competitive distance play important roles in the risk for injury in elite swimming. However, due to the limitations of the study design, this should be interpreted with caution.

PURPOSE:Thoracic aortic disease (TAD), including type A acute aortic dissection and Marfan Syndrome, requires lifelong management. Exercise may offer benefits, but the impact of exercise on quality of life (QoL), cardiovascular outcomes, and safety remains unclear. This scoping review synthesizes evidence on exercise effects in patients with TAD. REVIEW METHODS:A comprehensive search was conducted in PubMed, Embase, and CINAHL for studies published up to June 30, 2025. Eligibility criteria included original studies evaluating exercise interventions in patients with TAD or related genetic conditions. Studies reporting outcomes on QoL and cardiovascular status or safety were included. Two reviewers independently screened titles and abstracts, followed by a full-text review; discrepancies were resolved by a third. Data extraction covered population, intervention, and outcomes related to QoL, cardiovascular health, and adverse events. SUMMARY:Nine studies were included, comprising randomized controlled trials, cohort studies, and observational designs. Exercise interventions varied from moderate-intensity aerobic training, resistance training, and personalized rehabilitation programs. Most studies reported improved physical function and capacity, particularly in post-surgical patients with type A acute aortic dissection. Mental health outcomes showed mixed results; some studies reported significant reductions in anxiety and depression, while others found no significant changes in the mental component of QoL. No serious adverse events occurred, although systolic blood pressure responses varied greatly. Despite limited evidence, exercise may enhance physical performance in patients with TAD, although the impact on mental health remains uncertain. Future research should focus on optimizing intervention protocols, incorporating psychosocial support, and establishing evidence-based safety thresholds for exercise-induced blood pressure changes.

BackgroundAchilles tendinopathy is one of the most frequent conditions affecting runners. Exercise-based interventions are the main treatment options for Achilles tendinopathy; however, the ideal exercise dosage remains unknown.ObjectiveThe objective of this study is to investigate the effects of a moderate-load exercise intervention compared to a high-load exercise intervention in runners with Achilles tendinopathy in terms of pain, symptom severity, quality of life, muscle strength, and function.MethodsSixty amateur runners will be randomly allocated to one of two groups: high-load exercise group (HLG) and moderate-load exercise group (MLG). The HLG will start the treatment with calf exercises with 55% of 1 repetition maximum (1RM) and progressively increase the exercise load in 12 weeks to 90% 1RM. The MLG will perform exercises with 55% 1RM during the 12 weeks of intervention. The RM load will be reassessed every 2 weeks, and the total training volume (total repetitions and tendon time under tension per week) will be the same in both groups. Both groups will also perform strengthening exercises for the quadriceps and gluteal muscles. The primary outcome will be symptom severity (Victorian Institute of Sport Assessment-Achilles), which will be evaluated at baseline, at week 6, at week 12 (end of intervention), and 6 months after the intervention. Pain will be evaluated using the visual analogue scale during the same time points. Secondary outcomes will include peak isometric strength of ankle, knee, and hip muscles, function of plantar flexor muscles, quality of life, and perception of improvement. Results will be analyzed under the intention-to-treat principle using generalized estimating equations (GEE) and Bonferroni-adjusted post hoc tests.DiscussionThis will be the first randomized controlled trial comparing high-load exercises versus moderate-load exercises in individuals with Achilles tendinopathy applying equal training volume.Trial registration numberRBR-4vwy5xj.

Objective: The objective of this study was to investigate subchondral bone turnover at rest and after acute loading using Fluorine-18-labeled sodium fluoride (Na[18F]F) Positron Emission Tomography (PET), in patients with unilateral PFP. Design: Twenty-seven patients with unilateral PFP were recruited from the Institute of Sports Medicine Copenhagen. Participants underwent Na[18F]F-PET imaging before and after a bout of single-leg squats. Bone turnover measures, including mean and maximal standardized uptake value (SUVmean and SUVmax), rate of bone perfusion (K1), rate of tracer uptake into bone (Ki), and extraction fraction of tracer absorbed into bone mineral were assessed for patella and trochlea. Results: At rest, the painful knees showed lower SUVmax, K1, and Ki compared to the pain-free knees in the superficial part of the patella. No significant differences were found in the profound part of the patella or trochlea at rest. Following knee loading, the acute increases in SUVmean, SUVmax, Ki and blood flow were reduced in the superficial patella of the painful knees compared to the pain-free knees. In the trochlea, painful knees showed larger increases in SUVmean and Ki in the lateral part, whereas the medial part showed greater increases in K1, Ki, and a larger decrease in extraction fraction after loading. Conclusion: Patella displayed decreased bone metabolism at rest and reduced response to loading in the painful versus pain-free knees. Trochlea in the painful knees showed significantly larger increases in subchondral bone metabolism following knee loading compared to the pain-free knees. These novel findings highlight potential differences in bone turnover between the patellar and trochlear regions.

BACKGROUND:Anabolic-androgenic steroids (AASs) are synthetic derivatives of testosterone that are abused by athletes to enhance their physical appearance and performance. AAS abusers have an increased risk of tendon ruptures compared with nonusers, and it has been proposed that AASs damage tendon tissue. Only a few human studies have investigated the effect of AASs on tendon tissue, and to our knowledge, there are no data on female sex. PURPOSE/HYPOTHESIS:The purpose was to investigate the effect of current and former abuse of AASs on the patellar tendon (PT). It was hypothesized that AASs would not affect tendon tissue. STUDY DESIGN:Cross-sectional study; Level of evidence, 3. METHODS:This study included recreational athletes with current (female: n = 4; male: n = 18; total: n = 22) or former (female: n = 5; male: n = 7; total: n = 12) AAS abuse and nonusers (female: n = 5; male: n = 9; total: n = 14). The authors investigated the proportion of tendon injuries, PT cross-sectional area by magnetic resonance imaging, mechanical properties by ultrasound, gene expression levels of connective tissue proteins, and cell density by histological staining from tendon biopsy samples. RESULTS:The combined AAS group (both current and former abusers) reported a higher proportion of upper body tendon injuries compared with nonusers (79.4% vs 28.6%, respectively; P = .002). There was no difference in PT cross-sectional area (P = .918) or cell density (fascicular matrix: P = .413; interfascicular matrix: P = .982) between current AAS abusers, former AAS abusers, and nonusers. There was a greater expression of IGF-1 mRNA in current AAS abusers compared with nonusers (P = .043), but there were no group differences in other mRNA targets. Former AAS abusers had significantly higher tendon deformation (P = .030) and strain (P = .026) at common force compared with nonusers. There were no significant differences between male and female participants in the effect of AASs on tendon tissue. CONCLUSION:These data show that the PT itself was not severely affected by AAS abuse.

Purpose: This study investigated effects of delayed initial loading in comparison to a standard regime following an Achilles tendon rupture (ATR) on tendon cross-sectional area (CSA) and fat infiltration by using 3D magnetic resonance imaging (MRI) and ultrasound (US) measurements. Methods: Secondary analysis of a randomized controlled trial. Forty-eight patients with an ATR were randomized to a Standard regime with weight-bearing after 6 weeks or a Delayed regime with weight-bearing after 12 weeks postsurgery. Achilles tendon CSA, fat fraction, and vascularization were measured on both the injured and the uninjured side using MRI and US at 12 and 52 weeks. Results: The injured tendon was significantly larger (> 300%) than the uninjured tendon for both the distal and proximal parts (p < 0.0001). The CSA of the distal part was smaller in the Delayed group at 3 months (p=0.038), but not at 12 months. Fat fraction in the tendon increased in both groups. The Delayed group had significantly less vascularization compared with the Standard group at 3 months, and the vascularization decreased in both groups from 3 to 12 months. Conclusion: In comparison to the Standard treatment, the Delayed group had reduced CSA and vascularization for the distal part of the tendon after 3 months. After a year, these differences had become insignificant. From 3 to 12 months, the distal parts of the injured tendon showed an accumulation of fat in both groups. Not only the rupture site but also the entire tendon was affected by the inflammatory repair response. Trial Registration: ClinicalTrials.gov identifier: NCT04263493.

Tendinopathy represents a major musculoskeletal health problem, yet its pathogenesis remains poorly understood. Tendinopathy development is studied in humans with early (< 3 months of symptoms, n = 14) (ET) or chronic (> 3 months, n = 16) (CT) patellar tendinopathy and in healthy subjects (n = 15) (CTRL). Pain increases, and function declines with tendinopathy duration and correlated with tendon size (3T and 7T MRI). Tendon blood flow (Doppler ultrasonography) increases gradually in ET and CT, while peritendinous blood flow only rose in CT. Microscopy-based mapping (immunofluorescence microscopy and Cell DIVE) of vasculature shows marked changes in CT only, indicating flow increases in existing vessels early in tendinopathy, whereas angiogenesis is a late phenomenon. Cell DIVE indicates perivascular cell recruitment and potential lymphatic expansion in tendinopathy. Further, proteomics reveals that most matrix regulation occurs late in tendinopathy. Data from a previous study from the lab demonstrate faster treatment effect in tendinopathy with shorter symptom duration, supporting that early tissue changes may be more receptive to treatment. It is concluded that early tendinopathy is dominated by pain correlating with tendon swelling and hyperperfusion, whereas chronic tendinopathy is characterized by neovascularization and matrisome changes. These findings suggest that targeting early tissue changes can lead to superior treatment effects in tendinopathy.

Little is known about early tendinopathy in elite athletes. This study aimed to investigate changes in clinical and ultrasonography outcomes over 1 year and assess the prognostic values of these outcomes at baseline with respect to tendinopathy progression. Sixty-two elite athletes (24 ± 5 years) with early phase (symptom duration < three months) Achilles or patellar tendinopathy (AT and PT) were examined at baseline and after one year. Pain-guided activity modification was the only intervention. Clinical outcomes were assessed using Victorian Institute of Sports Assessment questionnaires (VISA) for function and symptoms, pain scores (1-10 numerical rating scale (NRS)) and ultrasound tendon morphology (thickness, echogenicity and power Doppler (PD) flow area). A linear mixed-effects model analysed changes from baseline to 1 year. Athletes showed clinical improvements in VISA-Achilles (baseline: 66 ± 5 vs. one-year: 87 ± 2, 95% CI: 13-30, p < 0.0001 and effect size d = 3.8), VISA-Patella (baseline: 69 ± 3 vs. one-year: 86 ± 1, 95% CI: 10-26, p < 0.0001 and effect size d = 3.6) scores and most NRS pain scores (≥ 2 points). Tendinopathic Achilles tendons' peritendinous thickness was reduced (-0.79 mm, p = 0.0188 and effect size d = 0.5), whereas patellar tendons remained enlarged. For both AT and PT, lower baseline PD was associated with a greater reduction in thickness over time (p < 0.001) and higher baseline VISA scores were linked to greater increases in echo intensity over time (p = 0.0363). In conclusion, elite athletes with early phase AT and PT showed clinical improvement over 1 year, with morphological changes in tendinopathic Achilles tendons only. Lower baseline PD and better initial VISA scores represent a better prognosis for tendinopathy morphology and symptoms.

Standard rehabilitation for knee osteoarthritis (knee-OA) combines patient education and neuromuscular exercises (NEMEX). Heavy-load resistance training (HLRT) has shown positive effects on pain, functionality, and muscle mass, but can be painful with knee-OA. Low-load blood-flow restricted resistance exercise (BFR-RE) has shown comparable effects to HLRT without promoting exercise-induced pain. Therefore, the present study examined the effect of BFR-RE vs. NEMEX on self-perceived knee pain, functional performance, and pain sensitization in knee-OA individuals. Ninety-six participants (age 56.7 ± 7.6; 49 females, 47 males) with symptomatic knee-OA were randomized to 12 weeks biweekly BFR-RE or NEMEX. BFR-RE was performed at 60%-80% of total arterial occlusion pressure. Control participants completed a 12-week NEMEX program. Both groups also attended patient education. Primary outcome: Change in the Knee injury and Osteoarthritis Outcome Score (KOOS) pain subscale from baseline to 12 weeks. Secondary outcomes: Remaining KOOS subscales, Oxford Knee Score (OKS), 30-s sit-to-stand (STS), STS power, 4 × 10 m fast-paced walking (4 × 10 m-FWT), stair climb test (SCT), spreading and local pain sensitization measured as pressure pain thresholds (PPT). No significant between-group difference in the change in KOOS-Pain was observed (+6.4 points, 95% CI = -1.0-13.7, effect size (ES) = 0.35, p = 0.07) or the remaining KOOS subscales and OKS (ES = 0.05-0.20, p > 0.05). BFR-RE demonstrated greater improvements than NEMEX for all functional outcomes (STS, STS power, 4 × 10 m FWT, SCT) (ES = 0.89-1.56, p < 0.01) and spreading sensitization (ES = 0.43-0.55, p < 0.05). BFR-RE and NEMEX were equally effective in reducing knee pain, while BFR-RE achieved greater statistical gains in functional performance and improved spreading sensitization in persons with moderate knee-OA. The enhanced improvements with BFR-RE compared to NEMEX represent novel insights that should be considered in future treatments of knee-OA.

Knee osteoarthritis (knee OA) is a prevalent condition worldwide. Globally recognized rehabilitation guidelines for knee OA include patient education and neuromuscular exercises (NEMEX). While heavy-load resistance exercise (70%-90% 1RM) often induces pain with knee OA, low-load exercise (20%-40% 1RM) combined with partial blood-flow restriction (BFR-RE) has been introduced without inducing excessive knee joint pain. The present study aimed to compare the effects of NEMEX and BFR-RE on mechanical muscle function in knee OA individuals. Ninety-six participants (age 56.7 ± 7.6; 47 males, 49 females) with symptomatic, radiographic knee OA were randomized to free-flow land-based NEMEX or unilateral machine-based BFR-RE. Both groups exercised biweekly for 12 weeks while also receiving patient education. Outcomes measured from baseline to 12 weeks included maximal isometric knee extensor strength (MVIC), rate of force development (RFD), maximal leg extensor power (LEP), and cross-sectional area (mCSA) of rectus femoris (RF) and vastus lateralis (VL). Significant (p < 0.01) within-group improvements from baseline to 12 weeks were observed in both groups for MVIC (BFR-RE: +0.4 vs. NEMEX: +0.1 Nm/kg), LEP (+0.6 vs. +0.2 W/kg), mCSA for RF (+1.8 vs. +0.6 cm2), and VL (+3.7 vs. +1.0 cm2). BFR-RE led to increases in RFD (+2.11 (50-ms), +4.48 (200-ms) Nm/s/kg) (p < 0.01), whereas NEMEX did not (p > 0.05). Between-group comparisons revealed greater improvements with BFR-RE for all outcomes (p < 0.01). BFR-RE appears superior to NEMEX in enhancing mechanical muscle function and knee extensor mCSA in knee OA individuals. The enhanced physiological responses observed with BFR-RE suggest that this exercise modality should be considered as an adjunct therapeutic tool in future treatment protocols for knee OA patients.

Certain skeletal muscles are specialized for their functional roles, yet direct comparisons of cellular morphology of distinct muscles beyond fibre type distribution are limited. This study investigated myofibre morphology in predominantly slow, fast and mixed fibre muscles in humans and mice, with the aim of establishing reference values for muscle‐specific myofibre size and shape. Nine healthy young men (Age: 26 ± 1 years, BMI: 23 ± 1 kg/m 2 ) had muscle biopsies taken from soleus, triceps brachii and vastus lateralis muscles. Additionally, the soleus and gastrocnemius muscles were harvested from 7 male C57BL/6 mice. Muscle samples were analysed by ATPase (human) or immunofluorescence (mouse) stainings of fibre type specific cross‐sectional area, perimeter and Shape Factor Index (SFI; fibre perimeter 2 /4 × π × fibre cross‐sectional area). In humans, type I fibres had 30%–40% larger CSA and 4%–7% higher SFI in soleus (1.54 ± 0.06) compared to triceps brachii (1.47 ± 0.05) and vastus lateralis (1.43 ± 0.04). Type IIa fibres SFI were 10%–11% higher in soleus (1.61 ± 0.08) compared to triceps brachii (1.45 ± 0.04) and vastus lateralis (1.45 ± 0.08). Soleus type I fibres were more heterogeneous in terms of size and shape compared to other muscles. Analyses of mouse muscle showed a similar pattern, in that CSA and SFI were higher in type I and IIa fibres of the soleus compared to the gastrocnemius. These findings suggest a consistent morphological characteristic of soleus fibres across species, with potentially important implications for future biomedical research.

BACKGROUND:Mechanically measured leg extensor muscle power (LEP) predicts functional performance, patient-reported outcomes (PROMs) and mechanical muscle function in patients with knee osteoarthritis (OA). The stair climb test (SCT) have been used to assess LEP in clinical populations, but the relationship between SCT derived LEP and functional- and self-reported outcome measures in patients with knee-OA remains unknown. OBJECTIVES:To investigate the relationship between LEP derived from SCT, and patient-reported outcomes (PROMs), functional performance, knee extensor muscle strength (MVIC), rate of force development (RFD) and Nottingham LEP in individuals with knee-OA. DESIGN:Cross-sectional study. METHOD:SCT power was obtained in 96 knee-OA patients (age 56.9 ± 7.7 yr. males n = 47, females n = 49). The dependent variable was SCT power, while independent variables included 4 × 10 m fast-paced walk (4x10m-FWT), sit-to-stand (STS), STS power, KOOS, Oxford Knee Score (OKS), LEP, MVIC, and RFD. RESULTS:There were strong correlations (r = 0.72-0.80, p < 0.01) between SCT power and 4x10m-FWT and STS. There were weak-to-moderate correlations (r = 0.22-0.42, p < 0.05) between SCT power versus OKS and all KOOS subscales. Moderate correlations were observed between SCT power and Nottingham LEP, MVIC, and RFD (r = 0.53-0.64, p < 0.01). CONCLUSIONS:SCT power correlates positively with functional performance, PROMs and mechanical lower limb muscle function in male and female individuals with knee-OA.

BACKGROUND:It is necessary to better understand the structural characteristics of the supraspinatus tendon and associated muscle after rotator cuff repair and in the event of retear. PURPOSE:To study structural differences between the repaired and contralateral shoulders 1 year after rotator cuff repair in patients who received either progressive exercise therapy (PR) or usual care (UC) in a randomized controlled trial and to investigate whether there was interaction with tendon retear and limb dominance. STUDY DESIGN:Cohort study; Level of evidence, 2. METHODS:Patients with surgically repaired traumatic full-thickness rotator cuff tears involving the supraspinatus tendon were included. After surgery, they were randomized to PR or UC (active from postoperative week 2 or 6, respectively). The subacromial structures (acromiohumeral distance, supraspinatus tendon thickness, and vascularity) and the supraspinatus muscle thickness were examined with ultrasound at the 1-year follow-up. RESULTS:A total of 79 patients were included. The characteristics of the 2 intervention groups (PR and UC) were comparable, including the Western Ontario Rotator Cuff Index score and number of retears. The authors found significantly thinner supraspinatus tendon (PR, P < .001; UC, P = .003) and reduced acromiohumeral distance (PR, P = .023; UC, P = .025) in the repaired versus the contralateral shoulders in both intervention groups. For neovascularization, there was no interlimb difference in either of the groups or between groups (PR vs UC). In patients with intact tendons, there was no interlimb difference in the muscle thickness, but in patients with tendon retear the muscle was significantly thinner on the repaired side (P = .024 and P < .001, respectively). When the dominant supraspinatus tendon was repaired (both groups), it was significantly thinner than the nondominant healthy tendon, but this difference was not seen when the nondominant supraspinatus tendon was repaired (P = .006). CONCLUSION:One year after rotator cuff surgery, the repaired supraspinatus tendon was significantly thinner and the corresponding acromiohumeral distance was reduced. In patients with retear, the supraspinatus muscle was significantly thinner on the repaired side and early initiation of tendon-loading exercises did not affect these findings. REGISTRATION:NCT02969135 (ClinicalTrials.gov identifier).