Influence of exercise intensity on training-induced tendon mechanical properties changes in older individuals

This study compared the effects of low vs. high intensity training on tendon properties in an elderly population. Participants were pair-matched (gender, habitual physical activity, anthropometrics, and baseline knee extension strength) and then randomly assigned to low (LowR, i.e., similar to 40 % 1RM) or high (High R, i.e., similar to 80 % 1RM) intensity resistance training programmes for 12 weeks, 3x per week (LowR, n=9, age 74 +/- 5 years; HighR, n=8, age 68 +/- 6 years). Patellar tendon properties (stiffness [K], Young's modulus [YM], cross-sectional area [T-CSA], and tendon length [T-L]) were measured pre and post training using a combination of magnetic resonance imaging (MRI), B-mode ultrasonography, dynamometry, electromyography and ramped isometric knee extensions. With training K showed no significant change in the LowR group while it incremented by 57.7 % in the HighR group (p<0.05). The 51.1 % group difference was significant (p<0.05). These differences were still apparent when the data was normalized for T-CSA and T-L, i.e., significant increase in YM post-intervention in HighR (p<0.05), but no change in LowR. These findings suggest that when prescribing exercise for a mixed genders elderly population, exercise intensities of <= 40 % 1RM may not be sufficient to affect tendon properties.