A randomized-controlled single-blind trial was conducted to investigate the clinical, structural and functional effects of peritendinous corticosteroid injections (CORT), eccentric decline squat training (ECC) and heavy slow resistance training (HSR) in patellar tendinopathy. Thirty-nine male patients were randomized to CORT, ECC or HSR for 12 weeks. We assessed function and symptoms (VISA-p questionnaire), tendon pain during activity (VAS), treatment satisfaction, tendon swelling, tendon vascularization, tendon mechanical properties and collagen crosslink properties. Assessments were made at 0 weeks, 12 weeks and at follow-up (half-year). All groups improved in VISA-p and VAS from 0 to 12 weeks (Po0.05). VISA-p and VAS improvements were maintained at follow-up in ECC and HSR but deteriorated in CORT (Po0.05). In CORT and HSR, tendon swelling decreased ( À 13 AE 9% and À 12 AE 13%, Po0.05) and so did vascularization ( À 52 AE 49% and À 45 AE 23%, Po0.01) at 12 weeks. Tendon mechanical properties were similar in healthy and injured tendons and were unaffected by treatment. HSR yielded an elevated collagen network turnover. At the half-year follow-up, treatment satisfaction differed between groups, with HSR being most satisfied. Conclusively, CORT has good short-term but poor long-term clinical effects, in patellar tendinopathy. HSR has good short-and long-term clinical effects accompanied by pathology improvement and increased collagen turnover.

The purpose of this study was to examine patellar tendon (PT) size and mechanical properties in subjects with a side-to-side strength difference of > or =15% due to sport-induced loading. Seven elite fencers and badminton players were included. Cross-sectional area (CSA) of the PT obtained from MRI and ultrasonography-based measurement of tibial and patellar movement together with PT force during isometric contractions were used to estimate mechanical properties of the PT bilaterally. We found that distal tendon and PT, but not mid-tendon, CSA were greater on the lead extremity compared with the nonlead extremity (distal: 139 +/- 11 vs. 116 +/- 7 mm(2); mid-tendon: 85 +/- 5 vs. 77 +/- 3 mm(2); proximal: 106 +/- 7 vs. 83 +/- 4 mm(2); P < 0.05). Distal tendon CSA was greater than proximal and mid-tendon CSA on both the lead and nonlead extremity (P < 0.05). For a given common force, stress was lower on the lead extremity (52.9 +/- 4.8 MPa) compared with the nonlead extremity (66.0 +/- 8.0 MPa; P < 0.05). PT stiffness was also higher in the lead extremity (4,766 +/- 716 N/mm) compared with the nonlead extremity (3,494 +/- 446 N/mm) (P < 0.05), whereas the modulus did not differ (lead 2.27 +/- 0.27 GPa vs. nonlead 2.16 +/- 0.28 GPa) at a common force. These data show that a habitual loading is associated with a significant increase in PT size and mechanical properties.

The free Achilles tendon demonstrates greater strain compared with that of the distal (deep) aponeurosis during voluntary isometric contraction, which suggests that separate functional roles may exist during in vivo force transmission.

Age-related loss in muscle mass and strength impairs daily life function in the elderly. However, it remains unknown whether tendon properties also deteriorate with age. Cross-linking of collagen molecules provides structural integrity to the tendon fibrils and has been shown to change with age in animals but has never been examined in humans in vivo. In this study, we examined the mechanical properties and pyridinoline and pentosidine cross-link and collagen concentrations of the patellar tendon in vivo in old (OM) and young men (YM). Seven OM (67 +/- 3 years, 86 +/- 10 kg) and 10 YM (27 +/- 2 years, 81 +/- 8 kg) with a similar physical activity level (OM 5 +/- 6 h/wk, YM 5 +/- 2 h/wk) were examined. MRI was used to assess whole tendon dimensions. Tendon mechanical properties were assessed with the use of simultaneous force and ultrasonographic measurements during ramped isometric contractions. Percutaneous tendon biopsies were taken and analyzed for hydroxylysyl pyridinoline (HP), lysyl pyridinoline (LP), pentosidine, and collagen concentrations. We found no significant differences in the dimensions or mechanical properties of the tendon between OM and YM. Collagen concentrations were lower in OM than in YM (0.49 +/- 0.27 vs. 0.73 +/- 0.14 mg/mg dry wt; P < 0.05). HP concentrations were higher in OM than in YM (898 +/- 172 vs. 645 +/- 183 mmol/mol; P < 0.05). LP concentrations were higher in OM than in YM (49 +/- 38 vs. 16 +/- 8 mmol/mol; P < 0.01), and pentosidine concentrations were higher in OM than in YM (73 +/- 13 vs. 11 +/- 2 mmol/mol; P < 0.01). These cross-sectional data raise the possibility that age may not appreciably influence the dimensions or mechanical properties of the human patellar tendon in vivo. Collagen concentration was reduced, whereas both enzymatic and nonenzymatic cross-linking of concentration was elevated in OM vs. in YM, which may be a mechanism to maintain the mechanical properties of tendon with aging.

No abstract

. Differential displacement of the human soleus and medial gastrocnemius aponeuroses during isometric plantar flexor contractions in vivo. J Appl Physiol 97: 1908 -1914, 2004. First published June 25, 2004 doi:10.1152/ japplphysiol.00084.2004.-The human triceps surae muscle-tendon complex is a unique structure with three separate muscle compartments that merge via their aponeuroses into the Achilles tendon. The mechanical function and properties of these structures during muscular contraction are not well understood. The purpose of the study was to investigate the extent to which differential displacement occurs between the aponeuroses of the medial gastrocnemius (MG) and soleus (Sol) muscles during plantar flexion. Eight subjects (mean Ϯ SD; age 30 Ϯ 7 yr, body mass 76.8 Ϯ 5.5 kg, height 1.83 Ϯ 0.06 m) performed maximal isometric ramp contractions with the plantar flexor muscles. The experiment was performed in two positions: position 1, in which the knee joint was maximally extended, and position 2, in which the knee joint was maximally flexed (125°). Plantarflexion moment was assessed with a strain gauge load cell, and the corresponding displacement of the MG and Sol aponeuroses was measured by ultrasonography. Differential shear displacement of the aponeurosis was quantified by subtracting displacement of Sol from that of MG. Maximal plantar flexion moment was 36% greater in position 1 than in position 2 (132 Ϯ 20 vs. 97 Ϯ 11 N ⅐ m). In position 1, the displacement of the MG aponeurosis at maximal force exceeded that of the Sol (12.6 Ϯ 1.7 vs. 8.9 Ϯ 1.5 mm), whereas in position 2 displacement of the Sol was greater than displacement of the MG (9.6 Ϯ 1.0 vs. 7.9 Ϯ 1.2 mm). The amount and "direction" of shear between the aponeuroses differed significantly between the two positions across the entire range of contraction, indicating that the Achilles tendon may be exposed to intratendinous shear and stress gradients during human locomotion. triceps surae; Achilles tendon; ultrasound; connective tissue mechanical properties; tendon shear strain; intratendinous stress THE HUMAN TRICEPS SURAE muscle-tendon structure is intricate in constitution and function, with three separate muscle compartments that merge via their aponeuroses into a common tendon to ultimately insert on the calcaneus. The combined forces generated by the triceps surae muscles during locomotion are transmitted to the Achilles tendon and may reach 1,400 -2,600 N during walking and 3, 100 -5,330 N during running (13, 15, 34). It has been suggested that these large forces imposed on the tendon contribute to various loading-related pathologies such as tendinopathy (19), although the exact etiology remains largely intangible. Consequently, a more detailed understanding of the intrinsic contraction properties of the multipart triceps surae structure may contribute to the development of future treatment paradigms and/or prophylactic intervention models.Information on the mechanical properties and function of the aponeurosis and tendon have tradition...

Whether the cross-sectional area (CSA) and mechanical properties of the human Achilles tendon change in response to habitual exercise remains largely unexplored. The present study evaluated the CSA and contraction-induced displacement of the aponeurosis-tendon complex of the triceps surae in 11 untrained subjects before (tests 1 and 2) and after (test 3) approximately 9 mo of regular running ( approximately 78 training sessions). Displacement of the tendon-aponeurosis complex obtained by ultrasonography; electromyography of the gastrocnemius, soleus, and dorsiflexor muscles; and joint angular rotation were recorded during graded isometric plantarflexion ramps. Tendon CSA and moment arm were measured by using MRI, and tendon force was calculated from joint moments and tendon moment arm. A treadmill test was used to determine submaximal oxygen consumption (Vo2) at a given speed and maximal Vo2. The total running duration was approximately 43 h, distributed over 34 wk. Maximal Vo2 increased 8.6% (P < 0.01), and submaximal Vo2 decreased 6.2% (P < 0.05). Tendon-aponeurosis displacement during maximal voluntary contraction was unchanged (tests 1-3, 5.2 +/- 0.6, 5.2 +/- 0.5, and 5.3 +/- 0.4 mm, respectively) and yielded a structural stiffness of 365 +/- 50, 358 +/- 40, and 384 +/- 52 N/mm for tests 1-3, respectively (P > 0.05). Tendon CSA also remained unchanged (tests 1-3, 34.2 +/- 2.2, 33.9 +/- 2.2, and 33.8 +/- 2.1 mm2, respectively). In conclusion, a total training stimulus of approximately 9 mo of running in previously untrained subjects was adequate to induce significant cardiovascular improvements, although it did not result in any changes in the mechanical properties of the triceps surea tendon-aponeurosis complex or in the dimensions of Achilles tendon.

Movement is caused by force transmission from contracting muscles to bone via tendon. The collagen structure of tendon is organized in a very hierarchical manner. The collagen fibril is considered the basic force-transmitting unit of tendon, and it is embedded in a hydrophilic extracellular matrix of proteoglycans, glycoproteins and glycosaminoglycans. It has recently been shown in human peritendinous tissue is more metabolically active in response to activity than previously thought, although it remains to be established, if the level of activity influences affects fibril diameter and/or total tendon cross-sectional area. Moreover, it cannot be unequivocally concluded that tendon adaptation to physical activity is one of a quantitative and/or qualitative nature. The currently available information is almost exclusively obtained from animal data, however, techniques such as microdialysis for tendon metabolism and ultrasound combined with MRI for tendon mechanical properties has already provided information on human tendon behavior, and is likely to further add to our understanding of how tendon adapt to physical activity. This review will address the structure and function of tendon, and the current knowledge of how tendons respond to activity with respect to biomechanical properties.