Aquatic Training after Joint Immobilization in Rats Promotes Adaptations in Myotendinous Junctions

Abstract

The myotendinous junction (MTJ) is the muscle-tendon interface and constitutes an integrated mechanical unit to force transmission. Joint immobilization promotes muscle atrophy via disuse, while physical exercise can be used as an adaptative stimulus. In this study, we aimed to investigate the components of the MTJ and their adaptations and the associated elements triggered with aquatic training after joint immobilization. Forty-four male Wistar rats were divided into sedentary (SD), aquatic training (AT), immobilization (IM), and immobilization/aquatic training (IMAT) groups. The samples were processed to measure fiber area, nuclear fractal dimension, MTJ nuclear density, identification of telocytes, sarcomeres, and MTJ perimeter length. In the AT group, the maintenance of ultrastructure and elements in the MTJ region were observed; the IM group presented muscle atrophy effects with reduced MTJ perimeter; the IMAT group demonstrated that aquatic training after joint immobilization promotes benefits in the muscle fiber area and fractal dimension, in the MTJ region shows longer sarcomeres and MTJ perimeter. We identified the presence of telocytes in the MTJ region in all experimental groups. We concluded that aquatic training is an effective rehabilitation method after joint immobilization due to reduced muscle atrophy and regeneration effects on MTJ in rats.

Myotendinous Junction: Exercise Protocols Can Positively Influence Their Development in Rats

“…The telocytes have already been identified in protocols of immobilization and aquatic remobilization [ 44 ], but their network and possible proliferation in the face of physical exercise was only demonstrated in exercise on a treadmill [ 45 ], albeit in a moderate way, compared to the vertical ladder exercises where we could observe their organization and diversification in relation to the protocols proposed.…”

Ultrastructural and Molecular Development of the Myotendinous Junction Triggered by Stretching Prior to Resistance Exercise

“…Static stretching demonstrated shorter sarcoplasmic invaginations compared to all experimental groups. The MTJ invagination length after 10 days of joint immobilization was also shortened (Rocha et al, 2021), as a consequence, the muscle–tendon interaction area decreases in size and has a predisposition for stress concentrations and failure (De Palma et al, 2011). The reduction of the interface area can theoretically weaken the MTJ, and thereby, become it more susceptible to injuries (Bengtsson et al, 2019).…”

“…Considering that the sarcoplasmic evaginations are formed from muscle tissue (Ciena et al, 2010), the morphological adaptations of expanding this tissue guarantee new spaces for the distal sarcomeres’ insertion. Furthermore, the MTJ sarcomeres exhibited different adaptations in their lengths like the growth with the menopause model (Jacob et al, 2019) and with immobilization (Rocha et al, 2021).…”

“…The MTJ is a specialized region between striated skeletal muscle and tendon that presented plasticity in animals exposed to exercise (Jakobsen & Krogsgaard, 2021), aging (Ciena et al, 2011), obesity (Grillo et al, 2021), menopause (Sierra et al, 2018), joint immobilization (Rocha et al, 2021), and in mdx mice (Martinez et al, 2021). Furthermore, the MTJ adapts to different exercise programs such as running (Curzi, 2016) and swimming (Jacob et al, 2019).…”

Molecular Morphology and Function of Stromal Cells

“…The in vivo study by Rocha and colleagues [4] reports the effectiveness of aquatic training as a rehabilitation method after joint immobilization to reduce skeletal muscle atrophy and promote regenerative processes in the myotendinous junction microenvironment, possibly involving tissue-resident telocytes/CD34 + stromal cells.…”