The combined effects of obesity and ageing on skeletal muscle function and tendon properties in vivo in men

Purpose We investigated the combined impact of ageing and obesity on Achilles tendon (AT) properties in vivo in men, utilizing three classification methods of obesity. Method Forty healthy, untrained men were categorised by age (young (18–49 years); older (50–80 years)), body mass index (BMI; normal weight (≥18.5–<25); overweight (≥25–<30); obese (≥30)), body fat% (normal adipose (<28%); high adiposity (≥28%)) and fat mass index (FMI; normal (3–6); excess fat (>6–9); high fat (>9). Assessment of body composition used dual-energy X-ray absorptiometry, gastrocnemius medialis (GM)/AT properties used dynamometry and ultrasonography and endocrine profiling used multiplex luminometry. Results Older men had lower total range of motion (ROM; −11%; P = 0.020), GM AT force (−29%; P < 0.001), stiffness (−18%; P = 0.041), Young’s modulus (−22%; P = 0.011) and AT stress (−28%; P < 0.001). All three methods of classifying obesity revealed obesity to be associated with lower total ROM (P = 0.014–0.039). AT cross sectional area (CSA) was larger with higher BMI (P = 0.030). However, after controlling for age, higher BMI only tended to be associated with greater tendon stiffness (P = 0.074). Interestingly, both AT CSA and stiffness were positively correlated with body mass (r = 0.644 and r = 0.520) and BMI (r = 0.541 and r = 0.493) in the young but not older adults. Finally, negative relationships were observed between AT CSA and pro-inflammatory cytokines TNF-α, IL-6 and IL-1β. Conclusions This is the first study to provide evidence of positive adaptations in tendon stiffness and size in vivo resulting from increased mass and BMI in young but not older men, irrespective of obesity classification.