Can Chronic Stretching Change the Muscle-Tendon Mechanical Properties?

Frietas SR et al. Can chronic stretching change the muscle-tendon mechanical properties? A review. Scan J Med Sci Sports: 2018

  • Chronic stretching induces a change is joint maximal ROM, but the reasons are not fully clear.
  • Two theories have emerged: the sensory theory proposes that ROM increase is due to increased tolerance to stretch. The second theory is the mechanical theory which argues for a change in the physical properties of the muscle-tendon unit (MTU), ie, decreased stiffness or increased fascicle length
  • This study is a systematic review of the literature regarding the effects of chronic stretching (> 2 weeks) on the MTU structure, including fascicle length and volume, muscle and tendon cross-sectional area, passive muscle stiffness, and tendon stiffness).
  • 26 studies were included in systematic review and 24 in the meta-analysis.
  • On average, intervention duration was 5 weeks (range 3-8 weeks) and time of stretch per week was 1165 seconds (270-3150)
  • Main findings: chronic stretching (3-8 weeks) has a small effect on maximal tolerated passive torque. No statistical changes were observed for the MTU properties after chronic stretching. Moderate to high heterogeneity was found for most of the variables
  • The results of the present data support the sensory theory, however, the authors acknowledge that the amount of load applied during stretching in present studies may not be sufficient for mechanical or structural adaptation.
  • Similar to strength training, the adaptations within the first few weeks are neural, not structural. Only three studies analyzed had protocols of at least 8 weeks. Little attention has also been given to stretch intensity, which includes presence or absence of rest breaks between sets.
  • To achieve structural adaptations, the authors argue that a greater duration (> 8-12 weeks) may be necessary or a greater stretching intensity per session or greater time under stretch per week. We also have to consider non-muscular factors such as fascia and neural tissues that have an effect on joint range of motion