Effects of a 4-week static stretch training program on passive stiffness of human gastrocnemius muscle-tendon unit in vivo

Abstract

Static stretch is commonly used to prevent contracture and to improve joint mobility. However, it is unclear whether the components of the muscle-tendon unit are affected by a static stretch training program. This study investigated the effect of a four-week static stretch training program on the viscoelastic properties of the muscle-tendon unit and muscle. The subjects comprised 18 male participants (mean age 21.4 ± 1.7 years). The range of motion (ROM), passive torque, myotendinous junction (MTJ) displacement and, muscle fascicle length of the gastrocnemius muscle were assessed using both ultrasonography and a dynamometer while the ankle was passively dorsiflexed. After the initial test, the participants were assigned either to a group that stretched for 4 weeks (N = 9) or to a control group (N = 9). The tests were repeated after the static stretch training program. The ROM and MTJ displacement significantly increased, and the passive torque at 30° significantly decreased, in the stretching group after the study period. However, there was no significant increase in muscle fascicle length. These results suggest that a 4-week static stretch training program changes the flexibility of the overall MTU without causing concomitant changes in muscle fascicle length.

Does long-term passive stretching alter muscle–tendon unit mechanics in children with spastic cerebral palsy?

“…This finding has previously been reported in healthy populations following stretching (Kubo et al, 2002;Nakamura et al, 2012). Nakamura et al (2012) reported a 13% reduction in passive joint stiffness following four weeks (120 s per day).…”

“…This finding has previously been reported in healthy populations following stretching (Kubo et al, 2002;Nakamura et al, 2012). Nakamura et al (2012) reported a 13% reduction in passive joint stiffness following four weeks (120 s per day). Similarly, in children with spastic CP, O'Dwyer et al (1994) showed a reduction in passive joint stiffness after 30 minutes of stretching, three times per week for six weeks, which is consistent with the findings from this study.…”

“…Previous research investigating stretching in human populations has demonstrated increases in joint range of motion (ROM) (McPherson et al, 1984;Miedaner and Renander, 1987), and decreased joint stiffness in response to long-term stretching (Kubo, et al, 2002;McPherson et al, 1984;Nakamura et al, 2012;O'Dwyer et al, 1994). Often, such decreases in MTU stiffness are interpreted to be reflective of changes in muscle stiffness.…”

Range of motion, neuromechanical, and architectural adaptations to plantar flexor stretch training in humans

“…Flexibility training programs are commonly employed with the aim of improving ROM (6 -8, 17, 23, 35, 42) and, sometimes, reducing the passive resistance to stretch (21,42). In contrast, an increased stretch tolerance, rather than changes in the stiffness/ viscoelastic properties of the muscle-tendon unit (MTU), has been proposed to explain the observed gain in joint ROM following stretch training (23,35).…”

Does Stretching Have Long-Term Effects on Muscle Performance? A Clinical Commentary

“…If there is an increase in ROM, but no shift (to the right) of the length/tension curve is observed, the only reasonable explanation for such enhancement in ROM is modification in the perception of stretching [30], but it remains unknown whether this is a peripheral and/or central adaptation though [30]. Even though the increase in stretching tolerance itself still needs to be better understood, several recent studies using ultrasonography images have established this as a real mechanism for increased flexibility [26,27,38,40]. A recent investigation [41] has proposed that the reason why several investigations have not found a decrease in MTU stiffness following stretching is that there might be an interference of other structures such as nerves and fascia.…”