Influence of Long-Lasting Static Stretching on Maximal Strength, Muscle Thickness and Flexibility

Abstract

Background: In animal studies long-term stretching interventions up to several hours per day have shown large increases in muscle mass as well as maximal strength. The aim of this study was to investigate the effects of a long-term stretching on maximal strength, muscle cross sectional area (MCSA) and range of motion (ROM) in humans.Methods: 52 subjects were divided into an Intervention group (IG, n = 27) and a control group (CG, n = 25). IG stretched the plantar flexors for one hour per day for six weeks using an orthosis. Stretching was performed on one leg only to investigate the contralateral force transfer. Maximal isometric strength (MIS) and 1RM were both measured in extended knee joint. Furthermore, we investigated the MCSA of IG in the lateral head of the gastrocnemius (LG) using sonography. Additionally, ROM in the upper ankle was investigated via the functional “knee to wall stretch” test (KtW) and a goniometer device on the orthosis. A two-way ANOVA was performed in data analysis, using the Scheffé Test as post-hoc test.Results: There were high time-effects (p = 0.003, ƞ² = 0.090) and high interaction-effect (p < 0.001, ƞ²=0.387) for MIS and also high time-effects (p < 0.001, ƞ²=0.193) and interaction-effects (p < 0.001, ƞ²=0,362) for 1RM testing. Furthermore, we measured a significant increase of 15.2% in MCSA of LG with high time-effect (p < 0.001, ƞ²=0.545) and high interaction-effect (p=0.015, ƞ²=0.406). In ROM we found in both tests significant increases up to 27.3% with moderate time-effect (p < 0.001, ƞ²=0.129) and high interaction-effect (p < 0.001, ƞ²=0.199). Additionally, we measured significant contralateral force transfers in maximal strength tests of 11.4% (p < 0.001) in 1RM test and 1.4% (p=0.462) in MIS test. Overall, there we no significant effects in control situations for any parameter (CG and non-intervened leg of IG).Discussion: We hypothesize stretching-induced muscle damage comparable to effects of mechanical load of strength training, that led to hypertrophy and thus to an increase in maximal strength. Increases in ROM could be attributed to longitudinal hypertrophy effects, e.g., increase in serial sarcomeres. Measured cross-education effects could be explained by central neural adaptations due to stimulation of the stretched muscles.

Influence of One Hour versus Two Hours of Daily Static Stretching for Six Weeks Using a Calf-Muscle-Stretching Orthosis on Maximal Strength

“…Previous research on daily long-lasting static stretching showed significant increases in MSt measured in the extended knee joint, comparable to those in the present study. Since Warneke et al [ 31 ] showed significant hypertrophy in the plantar flexors due to long-lasting stretching intervention, which could possibly be attributed to stretch-induced mechanical tension, leading to hypertrophy and MSt increases, a general transferability of the effects observed in animal studies to humans could be hypothesized. The hypothesis of mechanical-induced structural changes are confirmed by the results of a variety of animal studies [ 40 ], showing significant increases in muscle mass, the muscle cross-sectional area and the fiber cross-sectional area due to chronic stretching interventions: “It is Stretch that causes the Hypertrophy of Muscle” ([ 41 ] p. 93).…”

“…However, the aim of this study was not to investigate gender-related differences regarding stretching-induced improvements in MSt. Since it is well accepted that stretch training could lead to increases in flexibility in general [ 48 , 49 ], and Warneke et al [ 31 ] showed significant improvements in flexibility due to a similar stretching intervention, we did not examine the influence of stretching on flexibility in this study. It was not possible to include equal sample sizes in the study as not all participants were willing to join the two-hour stretching group.…”

“…Furthermore, Caldwell et al [ 30 ] showed that stretching the quadriceps twice daily for two weeks resulted in significant increases in MSt of 7.1% (d = 0.8) in the stretched leg and of 6.6% (d = 0.45) in the contralateral leg, while stretching once per day did not lead to a contralateral force transfer. Warneke et al [ 31 ] also showed cross-educational effects in dynamic strength testing of 11.4% ( p < 0.001) after stretching the plantar flexors for one hour, while no effects were obtained in isometric strength testing (1.4%, p = 0.46). Furthermore, jumping height was also increased in the stretched as well as in the contralateral leg with 13.7%, d = 1.28 and 13%, d = 1.01, respectively.…”

“…Only one investigation has examined the long-term effects of long-lasting static stretching on MSt, showing significant improvements in MSt of about 16% in the plantar flexors by using a one-hour stretching protocol daily [ 31 ]. However, some investigations could not point out any significant changes in MCSA or maximal strength after several weeks of stretch training [ 18 , 22 , 34 ].…”

“…Furthermore, Apostolopoulos et al [ 35 ] pointed out the high relevance of high intensity in stretching interventions: at lower intensities, tension is compensated via elastic tissue instead of generating adequate muscle tension. Considering a dose–response relationship of stretching in animal experiments [ 36 , 37 ] and the results from Warneke et al [ 31 ], it can be assumed that long-lasting stretching could lead to improved MSt capacity in humans, which can be seen as highly relevant in designing rehabilitation programs: “The therapeutic application of stretch should therefore be kept in mind when designing regimes for rehabilitation” [ 38 ]. Therefore, the aim of this longitudinal study was to investigate the effects of a stretching stimuli lasting one or two hours per day, respectively, on MSt in the plantar flexors with a bended knee joint, and to investigate whether a contralateral strength transfer can be induced via long-lasting stretching interventions.…”