Strength training alters the viscoelastic properties of tendons in elderly humans

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Abstract
The effect of strength training for 14 weeks on patella tendon viscoelastic properties was investigated in a group of elderly individuals. Participants were assigned to training (age [mean ± SD] 73.6 ± 3.4 years; n = 7) or control (age 66.4 ± 1.7 years; n = 7) groups. Training was performed three times per week and consisted of two series of 10 repetitions of leg‐extension and leg‐press exercises at 80% of the 5‐repetition maximum. Tendon elongation during an isometric knee‐extension contraction–relaxation was measured using ultrasonography. Tendon stiffness was calculated from the gradient of the estimated force–elongation relationship and mechanical hysteresis was calculated as the area between loading–unloading curves. Knee‐flexor coactivation, estimated from biceps femoris muscle electromyographic activity, was unaltered (P > 0.05) after the training and control periods. No changes (P > 0.05) were observed in stiffness or hysteresis after the control period. In contrast, tendon stiffness increased from 1376 ± 811 to 2256 ± 1476 N.mm−1 (P < 0.01) and hysteresis decreased from 33 ± 5 to 24 ± 4% (P < 0.05), after training. These training‐induced adaptations have implications for maximal muscle force, rate of force development, and metabolic cost of locomotion. Muscle Nerve 28: 74–81, 2003