Abstract
Imbalances of muscle strength and tendon stiffness may increase the risk for patellar tendinopathy in growing athletes. The present study investigated if a functional high-load exercise intervention, designed to facilitate tendon adaptation and reduce muscle-tendon imbalances, may prevent patellar tendon pain in adolescent male handball players (12–14 years). Tendon pain prevalence (using VISA-P scores), knee extensor strength, vastus lateralis (VL) architecture and patellar tendon mechanical properties were measured at four measurement time points (M1–M4) over a season. The control group (CON; n = 18; age 13.1 ± 0.7 yrs, height 170 ± 8 cm, mass 58 ± 10 kg) followed the usual strength training plan, including muscular endurance and explosive strength components. In the experimental group (EXP; n = 16; 13.1 ± 0.6 yrs, 169 ± 11 cm, 58 ± 16 kg), two sessions per week with functional high-load exercises for the patellar tendon were integrated in the strength training schedule, aiming to provide repetitive high-intensity loading of at least 3 s loading duration per repetition. While in the control group 30% of the athletes reported a clinically significant aggravation of symptoms, all players in the experimental group remained or became pain-free at M2 until the end of the season. There was a similar increase of strength (normalized to body mass; CON: 3.1%, d = 0.22; EXP: 6.8%, d = 0.47; p = 0.04) and VL thickness (CON: 4.8%, d = 0.28; EXP: 5.7%, d = 0.32; p < 0.001) in both groups, but no significant changes of tendon stiffness or maximum tendon strain. Further, both groups demonstrated similar fluctuations of tendon strain over time. We conclude that functional high-load exercises can reduce the prevalence of patellar tendon pain in adolescent athletes even without a reduction of tendon strain.
Highlights
In the production of movement, muscles and tendons work as a unit
The present study investigated the effects of a functional highload exercise intervention for the patellar tendon on pain prevalence, knee extensor muscle strength and vastus lateralis architecture as well as patellar tendon mechanical properties in adolescent handball players, assessed at four measurement time points over a competitive season
The data did not substantiate the expected benefits considering imbalances of muscle strength and tendon stiffness, as tendon strain and strain fluctuations over the whole year were similar between groups
Summary
In the production of movement, muscles and tendons work as a unit. Tendons have a lower rate of tissue turnover and adapt slower to increased loading compared to muscles (Kubo et al, 2010; Heinemeier et al, 2013). An imbalanced adaptation of muscle strength and tendon stiffness during a training process reduces the tendon safety factor (i.e., ratio of ultimate to operating strain). This may lead to an increased risk of overuse injury considering the high prevalence of tendinopathy in sports featuring a high volume of plyometric loading due to jumps and change-of-direction movements (Lian et al, 2005; Mersmann et al, 2017a)
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