This book represents a paradigm shift examining the relevance of stretching, specifically stretching intensity and its importance for the proper recovery of musculoskeletal tissue. Stretching, and it various forms, has been associated with sports (warm-up, warm-down), with delayed onset muscle soreness (DOMS) post activities, as well as a modality in rehabilitative medicine. Similar to most forms of activity (i.e., strength and cardiovascular training), stretching is defined by the parameters of training: intensity, duration, frequency, as well as body position, with numerous investigators attempting to identify whether stretching pre-, during, and post-exercise was beneficial. Based on eligible randomized controlled trials, a Cochrane Collaboration systematic review suggested that stretching did not exhibit any clinically important benefits with the reduction of DOMS, a decrease in creatine kinase values (a measure of muscle damage), and soreness. This review mentioned the duration and frequency, but not the intensity of the stretching exercises. Unlike duration and frequency which are quantitative in nature, stretching intensity is qualitative, thus difficult to measure, accounting for why it is relatively under-researched.
Stretching, defined as movement applied by an external/internal force used to increase muscle flexibly and/or joint ROM, stresses the connective and muscle tissues mechanically. It depends on the active and passive tension of the muscle, the musculo-tendinous unit, as well as the proprioceptors of the musculoskeletal system (i.e., muscle spindles and Golgi tendon organs). Although duration and frequency are important, the rate and magnitude of force (stretching intensity) is of greater significance, with too much force possibly being responsible for stimulating an inflammatory response. This is associated with both a mechanical and biochemical response, with the former characterized by a 'local reaction' at the site of stress resulting in the accumulation of leukocytes, and the latter referring to the release of pro-inflammatory cytokines signaling acute inflammation. In conjunction with stretching intensity, the influence of body position may directly or indirectly influence stretching intensity, for muscle and tendon tissue and their components (i.e., collagen) are known to respond to altered levels of activity.
