Tendinous tissue properties after short- and long-term functional overload: Differences between controls, 12weeks and 4years of resistance training

AimThe potential for tendinous tissues to adapt to functional overload, especially after several years of exposure to heavy-resistance training, is largely unexplored. This study compared the morphological and mechanical characteristics of the patellar tendon and knee extensor tendon-aponeurosis complex between young men exposed to long-term (4years; n=16), short-term (12weeks; n=15) and no (untrained controls; n=39) functional overload in the form of heavy-resistance training. MethodsPatellar tendon cross-sectional area, vastus lateralis aponeurosis area and quadriceps femoris volume, plus patellar tendon stiffness and Young's modulus, and tendon-aponeurosis complex stiffness, were quantified with MRI, dynamometry and ultrasonography. ResultsAs expected, long-term trained had greater muscle strength and volume (+58% and +56% vs untrained, both P<.001), as well as a greater aponeurosis area (+17% vs untrained, P<.01), but tendon cross-sectional area (mean and regional) was not different between groups. Only long-term trained had reduced patellar tendon elongation/strain over the whole force/stress range, whilst both short-term and long-term overload groups had similarly greater stiffness/Young's modulus at high force/stress (short-term +25/22%, and long-term +17/23% vs untrained; all P<.05). Tendon-aponeurosis complex stiffness was not different between groups (ANOVA, P=.149). ConclusionDespite large differences in muscle strength and size, years of resistance training did not induce tendon hypertrophy. Both short-term and long-term overload demonstrated similar increases in high-force mechanical and material stiffness, but reduced elongation/strain over the whole force/stress range occurred only after years of overload, indicating a force/strain specific time-course to these adaptations.