Joint range of motion and muscle flexibility are foundations of functional performance. It is important that an adequate level of motion is available to allow for optimal movement efficiency during both activities of daily living and sports-related tasks. As a result, there is considerable interest in understanding how to best optimize joint range of motion and muscle flexibility. This is especially important in an older population as joint range of motion and flexibility often decrease as we age. In this week’s EXSS Impact post, Dr. Eric Ryan and his research team investigate the effects of stretching on the viscoelastic stretch response following a static stretching protocol.
Sobolewski EJ, Ryan ED, Thompson BJ, McHugh MP, Conchola EC. The influence of age on the viscoelastic stretch response. J Strength Cond Res. 2014 Apr;28(4):1106-1
Why did you do this study?
Many previous studies have indicated that older adults (≥ 65 years) have stiffer muscles. Stretching is an intervention that is commonly recommended to help improve maximum joint range of motion and decrease passive stiffness. Despite these recommendations, there are no studies that have specifically examined the acute viscoelastic responses of commonly used stretching routines in older populations.
Viscoelasticity refers to the time-dependent nature of skeletal muscle. For example, stretching a muscle at a constant length will result in a gradual reduction in force or stress relaxation. When stretching a muscle at a constant force, there will be an increase in tissue length or creep. Thus, the purpose of this study was to examine the influence of age on the acute viscoelastic responses to a practical stretching intervention.
What did you do and what did you find in this study?
We measured passive stiffness and the amount of stress relaxation (reduction in torque) and creep (increase in joint range of motion) over four consecutive 30-second stretches in 22 young (24±3 years) and 14 older (67±3 years) men. Our results demonstrated that younger men displayed a greater initial relative stress relaxation response that diminished across the four stretches; whereas the older men experienced a smaller initial relative response that remained constant across the four stretches. There were no differences in viscoelastic creep between age groups despite the older adults being stiffer.
How do these findings impact the public?
These findings may suggest that practical stretching protocols (four 30-second stretches) are equally effective in increasing passive range of motion in both young and older men, despite differences in the relaxation responses across stretches. Future studies are needed to determine the muscle-tendon unit behavior that accounts for these age-related changes.