Individualized Muscle-Tendon Assessment and Training

Abstract

The interaction of muscle and tendon is of major importance for movement performance and a balanced development of muscle strength and tendon stiffness could protect athletes from overuse injury. However, muscle and tendon do not necessarily adapt in a uniform manner during a training process. The development of a diagnostic routine to assess both the strength capacity of muscle and the mechanical properties of tendons would enable the detection of muscle-tendon imbalances, indicate if the training should target muscle strength or tendon stiffness development and allow for the precise prescription of training loads to optimize tendon adaptation. This perspective article discusses a framework of individualized muscle-tendon assessment and training and outlines a methodological approach for the patellar tendon.

Keywords: diagnostic; individualization; mechanical properties; performance; ultrasound.

FIGURE 1

Association between in vivo Achilles (A) and patellar (B) tendon force and tendon stiffness (normalized to tendon rest length) in 172 and 215 athletes from different sports (endurance running, sprinting, ball sports, diverse) and untrained individuals, including data from adolescents and adults. The Pearson correlation coefficients and 95% confidence intervals [lower limit, upper limit] were 0.670 [0.578, 0.745] and 0.648 [0.563, 0.719] for the Achilles and patellar tendon, respectively. The presented data is from earlier studies of our group (A: Arampatzis et al., 2007a, , ; Stafilidis and Arampatzis, 2007; Albracht and Arampatzis, 2013; B: Charcharis et al., 2019; Mersmann et al., 2019) as well as yet unpublished work (A: n = 26; B: n = 118).

FIGURE 2

In vivo Achilles (A) and patellar (B) tendon strain during maximum voluntary isometric contractions in 172 and 215 athletes from different sports (endurance running, sprinting, ball sports, diverse) and untrained individuals from child- to adulthood (white: early adolescent [12–15 years], gray: late-adolescent [16–19 years], black: adults [≥20 years]). While low levels of tendon strain suggest that the athlete may focus on muscle strength development, high levels of strain indicate the need for specific tendon training for increasing its stiffness. (C) Illustrates the individual relationship of tendon force (in percent of maximum tendon force) and strain in two athletes. The green area indicates the range of strain where an optimal mechanical stimulation for training is expected and the horizontal lines show that the respective relative training intensity in terms of force exertion may differ substantially between individuals. The presented data is from earlier studies of our group (A: Arampatzis et al., 2007a, , ; Stafilidis and Arampatzis, 2007; Albracht and Arampatzis, 2013; B: Charcharis et al., 2019; Mersmann et al., 2019) as well as yet unpublished work (A: n = 26; B: n = 118). Strain was extrapolated based on stiffness for the tendon forces during maximum voluntary isometric contractions in the respective optimum joint angle. For details on the respective methods see Arampatzis et al. (2007a) and Mersmann et al. (2016).