Effects of a 12-Week Chronic Stretch Training Program at Different Intensities on Joint and Muscle Mechanical Responses: A Randomized Clinical Trial

Abstract

Context: Stretching intensity is an important variable that can be manipulated with flexibility training. However, there is a lack of evidence regarding this variable and its prescription in stretching programs. Objective: To investigate the effects of 12 weeks of knee flexor static stretching at different intensities on joint and muscle mechanical properties. Design: A randomized clinical trial. Setting: Laboratory. Participants: A total of 14 untrained men were allocated into the low- or high-intensity group. Main Outcome Measures: Assessments were performed before, at 6 week, and after intervention (12 wk) for biceps femoris long head architecture (resting fascicle length and angle), knee maximal range of motion (ROM) at the beginning and maximal discomfort angle, knee maximal tolerated passive torque, joint passive stiffness, viscoelastic stress relaxation, knee passive torque at a given angle, and affective responses to training. Results: No significant differences were observed between groups for any variable. ROM at the beginning and maximal discomfort angle increased at 6 and 12 weeks, respectively. ROM significantly increased with the initial angle of discomfort (P < .001, effect size = 1.38) over the pretest measures by 13.4% and 14.6% at the 6- and 12-week assessments, respectively, and significantly improved with the maximal discomfort angle (P < .001, effect size = 1.25) by 15.6% and 18.8% from the pretest to the 6- and 12-week assessments, respectively. No significant effects were seen for muscle architecture and affective responses. Initial viscoelastic relaxation for the low-intensity group was lower than ending viscoelastic relaxation. Conclusion: These results suggest that stretching with either low or high discomfort intensities are effective in increasing joint maximal ROM, and that does not impact on ROM, stiffness, fascicle angle and length, or affective response differences.

Comparison Between High- and Low-Intensity Static Stretching Training Program on Active and Passive Properties of Plantar Flexors

“…As we did not investigate the time-course of the changes in these variables, future studies may consider exploring it to identify whether there are differences between HI-SS and LI-SS groups; i.e., whether different intensities influence stretch tolerance and muscle stiffness in different time-courses. Interestingly, our results are in opposition to those of Beltrão et al (2020) and Fukaya et al (2020b), which found no differences between low and high intensities on improving muscle passive properties. However, it is important to note that they analyzed the hamstring muscles, while we analyzed the plantar flexors.…”

“…However, in contrast to these immediate acute effects, no benefits have been shown for higher intensities following bouts of SS on chronic adaptations (Magnusson et al, 1996;Folpp et al, 2006;Beltrão et al, 2020;Fukaya et al, 2020b). Specifically, Fukaya et al (2020b) investigated two different stretching intensities for 4 weeks (100 vs. 120% of the hamstring muscles maximum tolerable ROM; 1 set of 60 s; 3×/week) and showed similar results on ROM between conditions and no change in passive stiffness in both conditions.…”

“…Specifically, Fukaya et al (2020b) investigated two different stretching intensities for 4 weeks (100 vs. 120% of the hamstring muscles maximum tolerable ROM; 1 set of 60 s; 3×/week) and showed similar results on ROM between conditions and no change in passive stiffness in both conditions. In a longer duration study, Beltrão et al (2020) compared the effects of SS performed at low (1-2 out of 10) and high intensities (9-10 out of 10; pain/discomfort intensity scale) on the hamstring muscles (3 sets of 60 s; 3×/week; 12 weeks). Results indicated adaptations of similar magnitudes on ROM and stretching tolerance for both groups, however, none showed changes in passive stiffness and muscle architecture.…”

The effects of 12 weeks of static stretch training on the functional, mechanical, and architectural characteristics of the triceps surae muscle–tendon complex

“…Moreover, regional differences seem to occur in the chronically stretched muscle, since a different remodelling was observed between its middle and distal portions (Dix and Eisenberg 1990 ). However, the architectural responses to PST in humans are not clear (Nakamura et al 2012 ; Akagi and Takahashi 2014 ; Konrad and Tilp 2014 ; Blazevich et al 2014 ; Freitas and Mil-Homens 2015 ; Simpson et al 2017 ; Sato et al 2020 ; Beltrão et al 2020 ) and more studies may be required to evaluate the impact of a long-term PST program on muscle architecture (Medeiros and Lima 2017 ).…”

Effects of Different Long-Term Exercise Modalities on Tissue Stiffness

“…All the retrieved studies applied passive stretching interventions [ 45 – 52 ], except for that of Halbertsma and Göeken who applied a contract–relax (PNF) protocol [ 53 ]. The interventions had a length of 3 [ 48 ], 4 [ 45 , 46 , 52 , 53 ], 5 [ 51 ], 6 [ 49 ] and 12 weeks [ 47 , 50 ]. Stiffness was assessed in five studies through passive resistance to a stretch [ 45 – 47 , 49 , 53 ] and in three studies using SWE [ 50 – 52 ].…”