We investigated age-related changes in the mechanical properties of rabbit Achilles tendon. The animals used were immature (age 3 weeks, body mass 380 g), young adult (age 8-10 months, body mass 4.1 kg) and old (age 4-5 years, body mass 5.1 kg) rabbits. The cross-sectional area of the tendon increased with growth and the tensile strength of the young adult [67.3 (SEM 4.2) MPa] and old [66.7 (SEM 3.8) MPa] tendon was significantly higher than that of the immature tendon [23.9 (SEM 3.8) MPa]. However, there was no statistically significant difference in tensile strength between mature and old tendons. These differences may be attributable to the change in body mass. The gradient of the stress-strain curves, that is, the tangent modulus of the mature tendon [618.0 (SEM 87.0) MPa], was higher than that of the immature [281.0 (SEM 104.6) MPa] and old [530.5 (SEM 91.0) MPa] tendon, although the difference was not significant. The elongation at failure was approximately 16 percent for all age groups. These results would suggest that rabbit Achilles tendon is highly compliant during growth.

Background: It is considered that the increasing intramyocellular lipid (IMCL) affects health risks and muscle attenuation. Though body fat increases significantly with age in lean humans, it is not known whether IMCL increases or not. In this study, we investigated the changes with age in IMCL concentrations in skeletal muscles using ¹H-MR spectroscopy and studied them in relation to body fat percentage, waist-hip ratio, and blood components. Methods: Twenty-four lean young (age 21.2 ± 1.9, BMI 21.5 ± 1.8) and 23 lean old (age 70.9 ± 2.4, BMI 21.7 ± 1.3) subjects took part in the study. Subjects were grouped by gender into age- and BMI-matched young and old groups. The ¹H-MRS was obtained from the tibialis anterior (TA), medial gastrocnemius (MG) and soleus (SOL) muscles. Results: The IMCL content in SOL and MG in the old was found to be higher (p < 0.01) than that in the young. No age difference in IMCL content in TA was found. IMCL concentrations in SOL were higher than those in MG and TA in the order of SOL > MG > TA (p < 0.01). IMCL content correlated significantly with waist-hip ratio in all skeletal muscles. A significant relationship was observed between percent body fat and IMCL in TA and MG (p < 0.05). However, no correlation was found between IMCL content in each muscle and BMI. The IMCL content in all skeletal muscles significantly correlated with HbA1c, triglyceride, total cholesterol and LDL cholesterol concentrations. Conclusion: These results suggest that increased IMCL in both lean older men and women might be related to body composition, blood lipids and lipoprotein profiles, and that this might affect muscle attenuation.

We examined the influence exerted, through disuse of the hindlimb, on the collagen fibres of the achilles tendon in rats. With disuse the body mass decreased by 28%, and the mass of soleus muscle decreased by 20%. A decrease in the surface area and diameter was observed in the experimental group when compared to the control group. A histogram of the collagen fibres showed a decrease of the thick fibres in the experimental group. The maximum surface area of collagen fibres in the experimental group was seen to be only 43% of that of the control group. These results showed a decrease in the thickness of the collagen fibres of the achilles tendon through disuse. This seemed to suggest that resistance to tension is decreased by disuse.

This reports presents the changing morphological characteristics of collagen and fibroblasts in the soleus and gastrocnemius muscle tendon of female Japanese white rabbits with ageing. The fibroblasts decreased in number per 37 microns 2 with ageing in each group, and their morphology became longer and more slender through ageing. The mean fibril area and diameter of the collagen fibrils of soleus muscle tendon (SMT) and lateral gastrocnemius muscle tendon (GMT) in 8- to 10-month old rabbits were significantly higher than those of 3-wk-old rabbits during growth (P < 0.01). The mean area and diameter of collagen fibrils of SMT and GMT decreased during senescence: the values for 4- to 5-yr-old rabbits were lower than those for 8- to 10-month-old rabbits, but the difference was not significant. Statistically significant differences in fibril area and diameter between the SMT and GMT were not found during ageing. The number of thick fibrils increased during growth, but decreased in senescence. There were more thin fibrils (30-60 nm) in the 3-wk-old rabbits than in the 8- to 10-month old and 4 to 5-yr-old groups, and the large-diameter collagen (300-360 nm) was more abundant in the 8- to 10-month-old group than in the 3-wk-old and 4- to 5-yr-old groups. Differences in fibril size between slow and fast muscle tendons were not observed during ageing.

Lower aerobic capacity is a strong and independent predictor of cardiovascular morbidity and mortality in patients with metabolic syndrome (MetS). However, the mechanisms are not fully elucidated. We tested the hypothesis that skeletal muscle dysfunction could contribute to the lower aerobic capacity in MetS patients. The incremental exercise tests with cycle ergometer were performed in 12 male patients with MetS with no habitual exercise and 11 age-, sex-and activity-matched control subjects to assess the aerobic capacity. We performed 31 phosphorus-magnetic resonance spectroscopy (MRS) to assess the high-energy phosphate metabolism in skeletal muscle during aerobic exercise. Proton-MRS was also performed to measure intramyocellular lipid (IMCL) content. Peak oxygen uptake (peak VO 2 ; 34.1±6.2 vs. 41.4±8.4 ml kg À1 min À1 , Po0.05) and anaerobic threshold (AT; 18.0±2.4 vs. 23.1±3.7 ml kg À1 min À1 , Po0.01) adjusted by lean body mass were lower in MetS patients than control subjects. Phosphocreatine (PCr) loss during exercise was 1.5-fold greater in MetS, suggesting reduced intramuscular oxidative capacity. PCr loss was inversely correlated with peak VO 2 (r¼À0.64) and AT (r¼À0.60), respectively. IMCL content was threefold higher in MetS and was inversely correlated with peak VO 2 (r¼À0.47) and AT (r¼À0.52), respectively. Moreover, there was a positive correlation between IMCL content and PCr loss (r¼0.64). These results suggested that lean-body aerobic capacity in MetS patients was lower compared with activity-matched healthy subjects, which might be due to the reduced intramuscular fatty acid oxidative metabolism.