# Biomechanical, Healing and Therapeutic Effects of Stretching: A Comprehensive Review
## 2 Topics and Results
### Biomechanical and Biological (Cellular and Molecular) Mechanisms of Stretching  
The cellular and molecular mechanisms underlying the changes in joint flexibility, muscle strength, and power are not well clarified in medicine and cell biology, and thus, further investigations are needed. The additional effects of individual training status, age, sex, and different pathological states that moderate the influences of stretching exercises on the joints, muscles, tendons, and ligaments can be characterized as indirect [6; 18; 22; 24; 35]. Stretching modulates the synthesis, deposition, concentration, degradation, and distribution of collagen and glucosoaminoglycans (GAGs), affecting the remodeling of the extracellular matrix [57]. The data obtained encourage the therapeutic application of stretches and stretching physiotherapy at the cellular and molecular levels--preliminary in the treatment and management of arthitic joints [58]. The contributions of [PERSON] et al. [59] and [PERSON] et al. [7] demonstrate the importance of transforming growth factor \(\beta\)-1 (TGF \(\beta\)-1) in collagen synthesis and extracellular matrix remodeling after a brief static stretching (SS) application. Simultaneously, stretching also modulates the aggrecan concentrations in the matrix. [PERSON] et al. [60] examined the expression of TGF \(\beta\)-1 as a tissue inhibitor of metalloproteinases. TGF \(\beta\)-1 is one of the more important cytokines regulating fibroblast responses in connective tissue. In health and diseases, collagen is a major protein in the extracellular matrix, and aggrecan is the main proteoglycan in articular cartilage. Stretching can be used to enhance and engineer the connective tissue's extracellular matrix with desirable collagen/elastin concentrations, improved elastic properties, and regular mesenchymal cell (fibroblast/chondroblast) functions [61]. Moreover, the biomechanical aspects underlying the different influences of active and passive stretches on joint, tendon, ligament, and muscle flexibility at rest are yet to be identified [5; 26; 62]. The recent results in medical and sports scientific literature indicate that chronic SS exercises have the potential to improve muscle strength and power [5; 20]. Further investigations could examine the benefits of chronic SS exercises in old, healthy, and ill individuals, as compared to young, active, and well-trained persons, as well as compared to professional athletes [20; 30; 63; 64; 65; 66; 67]. Stretching Is an Integral Component of Mind-Body Exercises Such as Yoga (Mainly Hatha Yoga), Tai Chi, and Gingong  
Gothe, [PERSON] et al. [65; 67] compared the functional benefits of stretching and yoga exercises. Four standard fitness tests assessing balance, strength, flexibility, and mobility were administered [64; 65]. The experimental stretching protocols varied with combinations of the functional parameters of exercise duration, intensity, frequency, and whole-body posture [66]. [PERSON] and colleagues (2012) concluded that yoga practice and stretching exercises led to improvements in strength, flexibility, mobility, and quality of life in older adults [64]. Considering the benefits of stretching and yoga exercises, the special sports programs in functional fitness could be adapted for healthy individuals in the elderly population, as well as for people with socially important diseases (arthritis, diabetes mellitus, chronic inflammation, etc.). [PERSON] and co-authors [65; 67] recommendedthe effects of stretching and/or yoga exercises for improving functional fitness outcomes in health and diseases, as well as for improving sports performance and health-related quality of life. The potential preventive and therapeutic effects of static and yoga stretching (SS and YS) were examined in relation to different pathological states, such as chronic inflammation, wound healing, tumor growth, etc. [15; 66; 68; 69; 70].