# Biomechanical, Healing and Therapeutic Effects of Stretching: A Comprehensive Review
## 2 Topics and Results
### Biomechanical and Biological (Cellular and Molecular) Mechanisms of Stretching
The biological, cellular, and molecular mechanisms underlying the anti-inflammatory and anti-cancer properties of stretching, yoga, and TCC were very well summarized and presented in the review of [PERSON] et al. [16]. These physical exercises could enhance the immune state, change the IL-6 and IL-10 levels, and improve the health-related quality of life in older individuals [71; 72; 73]. On the other hand, chronic inflammation could contribute to the initiation, progression, and development of tumorigenesis [74]. In these and other pathological states, stretching exercises are recommended and included in programs for diabetes mellitus type 2 (DM-2) patients and in stroke and malignant disease rehabilitation and treatment [75; 76]. Stretching may serve as a method of connective tissue healing [15; 77]. [PERSON] and colleagues (2006) [77] examined mechanical signals as having strong anti-inflammatory effects and recommended the use of mechanical forces of an appropriate intensity in the rehabilitation of knee meniscus cartilage. Further studies are required to understand the role of collagen and aggrecan in the remodeling and destruction of the articular cartilage's extracellular matrix (e.g., in osteoarthritis of various etiologies). Collagen and the impaired synthesis of proteoglycan/aggecan is related to diseases such as local and systemic (disseminated) scleros [16]. The same authors pointed out that daily stretching may be a part of therapy in patients with systemic sclerosis (SSC). Similar conclusions could be valid for a local Dupuytren contracture (Morbus Dupuytren) [25]. [PERSON] and [PERSON] studied the effects of static stretching training on the characteristics of the plantar-flexor muscles in 12 subjects. An improved muscle flexibility was associated (\(r^{2}=0.88\); \(p<0.001\)) with a decrease in passive muscle stiffness. Although the changes in the flexibility and passive stiffness were partially maintained 1 month after the end of the training program, the reflex activities had already returned to control levels. It was concluded that the increased flexibility resulted mainly from the reduced passive stiffness of the muscle-tendon unit and the tonic reflex activity [25]. In only one study [78], a mouse breast cancer model was presented, and the results showed slower tumor growth (from 2-4 weeks) under the influence of stretching. By comparing various stretching techniques to study their short- and long-term effects on different parameters (knee joint ROM, hamstring flexibility, muscle electromyographic activity, etc. ), the researchers registered significant preliminary results for both the joint ROM and hamstring flexibility parameters [79]. The same authors applied static stretching (SS) as a variant of proprioceptive neuromuscular facilitation-contact-relax (PNF-CR) techniques. The knee range of motion (ROM), hamstring flexibility, and knee flexor muscle electromyographic (EMG) activity were also investigated [3; 79]. The results obtained demonstrated an immediate, as well as a long-term, effect on the knee ROM and only a long-term effect on flexibility in the elderly. The aging human population exhibited an increase in muscle stiffness, as well as disturbances in the syntheses of types I-III collagens and an alteration in ROMs and EMG activities, due to the cellular and molecular processes in the elderly [3; 25; 30; 31; 63]. On the other hand, the PNF-CR and SS techniques were described as effective for increasing hamstring flexibility in young individuals [31; 63; 79]. [PERSON] et al. [3] applied three PNF stretching techniques: static stretching (SS), contact relaxation (CR), and agonist contact relaxation (ACR). The purposes of these studies were to characterize the effects of stretching on the ROM of joints and the EMG activity of muscles. The authors concluded that the PNF stretching technique increased the ROM in older adults.