Effects of chronic stretching on soleus muscle of Wistar female rats / Efectos del estiramiento crónico en el músculo sóleo de ratas hembras Wistar

The purpose of this study was to evaluate the chronic effects of stretching exercise on soleus muscle histomorphology and histomorphometry of young and aged rats. Thirty-eight female rats were divided into young control group (YCG, n=10;274±50 g); young stretching group (YSG, n=8;274±12 g); aged control group (ACG, n=10;335±39 g); and aged stretching group (ASG, n=10;321±32g). A mechanical apparatus was used to stretch muscle in 4 repetitions, 60 s each, 30 s interval between repetitions in each session, 3 times a week for 3 weeks. Twenty-four hours after the last stretching session, soleus muscle was removed for micromorphology and immunostaining analysis. Data analyses were performed with one-way ANOVA, post-hoc Tukey, or Kruskal-Wallis tests for parametric and nonparametric, respectively (p≤0.05). Muscle fiber cross-sectional area (MFCSA) of ACG was lower (18 %) compared to the YCG. Stretching increased MFCSA comparing YSG to YCG (5,681.15± 1,943.61 µm2 vs 5,119.84±1,857.73 µm2, p=0.00), but decreased comparing ASG to ACG (3,919.54± 1,694.65 µm2 vs 4,172.82±1,446.08 µm2, p=0.00). More serial sarcomere numbers were found in the YSG than YCG (12,062.91±1,564.68 vs 10,070.39±1,072.38, p=0.03). Collagen I and collagen III were higher in YSG than ASG (7.44±7.18 % vs 0.07±0.09 %, p=0.04) and (14.37 %± 9.54 % vs 5.51 %±5.52 %, p=0.00), respectively. TNF-a was greater in ASG than YSG (43.42 %±40.19 % vs 1.72 ± 2.02 %, p=0.00). Epimysium was larger in the YSG compared to YCG (201.83±132.07 % vs 181.09±147.04 %, p=0.00). After 3-week stretching the soleus muscles from aged rats were smaller than their younger counter-parts. Interestingly, while stretching appeared to positively affect young soleus muscle, the opposite was detected in the muscle of the aged rats.

El propósito de este estudio fue evaluar los efectos crónicos del ejercicio de estiramiento sobre la histomorfología e histomorfometría del músculo sóleo de ratas jóvenes y envejecidas. Se dividieron 38 ratas hembras en un grupo control joven (YCG, n = 10; 274 ± 50 g); grupo de estiramiento joven (YSG, n = 8; 274 ± 12 g); grupo control de edad (ACG, n = 10; 335 ± 39 g); y grupo estiramiento envejecido (ASG, n = 10; 321 ± 32 g). Se usó un aparato mecánico para estirar el músculo en 4 repeticiones, 60 s cada una, intervalo de 30 s entre repeticiones en cada sesión, 3 veces por semana, durante 3 semanas. Veinticuatro horas después de la última sesión de estiramiento, se extrajo el músculo sóleo para análisis de micromorfología e inmunotinción. Los análisis de datos se realizaron con pruebas ANOVA de una vía, Tukey post-hoc o Kruskal-Wallis para pruebas paramétricas y no paramétricas, respectivamente (p≤0,05). El área de la sección transversal de fibra muscular (MFCSA) de GCE fue menor (18 %) en comparación con el GCJ. El estiramiento aumentó ASTFM comparando GEJ con GCJ (5.681,15 ± 1.943,61 µm2 vs 5.119,84 ± 1.857,73 µm2, p = 0,00), pero disminuyó comparando GEE con GCE (3.919,54 ± 1.694,65 µm2 vs 4.172,82 ± 1.446,08 µm2, p = 0,00). Se encontraron más sarcómeros en serie en el GEJ que en el GCJ (12.062,91 ± 1.564,68 vs 10.070,39 ± 1,072.38, p = 0,03). El colágeno I y el colágeno III fueron más numerosos en GEJ que en GEE (7,44 ± 7.18 % vs 0,07 ± 0,09 %, p = 0,04) y (14,37 % ± 9,54 % vs 5,51 % ± 5,52 %, p = 0,00), respectivamente. TNF-α fue mayor en GEE que GEJ (43,42 % ± 40,19 % vs 1,72 ± 2,02 %, p = 0,00). El epimisio fue mayor en el GEJ en comparación con el GCJ (201,83 ± 132,07 % vs 181,09 ± 147,04 %, p = 0,00). Después de 3 semanas de estiramiento, los músculos sóleo de las ratas envejecidas eran más pequeños que sus contrapartes más jóvenes. Curiosamente, si bien el estiramiento pareció afectar positivamente el músculo sóleo joven, se detectó lo contrario en el músculo de las ratas envejecidas.

Morphometric and molecular muscle remodeling after passive stretching in elderly female rats

OBJECTIVES: To determine the effects of three sessions of a passive stretching exercise protocol on the muscles of elderly female rats. METHODS: The effects of the stretching exercises on the soleus muscle were analyzed using immunohistochemistry [tissue inhibitors of matrix metalloproteinases (TIMP), the tumor necrosis factor-alpha (TNF-α), and the gene expression levels using real-time PCR of the transforming growth factor-beta 1 (TGF-β1), collagen type 1 (COL1), and collagen type 3 (COL3)]. Fifteen 26-month-old female Wistar rats were randomly divided into two groups, namely, Stretching (SG, n=8) and Control (CG, n=7). The passive mechanical stretching protocol consisted of a set of 4 1-minute repetitions, with 30 seconds between each repetition (total treatment of 4 minutes), three times a week for 1 week. RESULTS: Immunohistochemical analysis revealed an increase of 71.4% in the TNF-α (p=0.04) gene expression levels for the SG and a 58% decrease in the TGF-β1 gene expression levels (p=0.005) in the SG compared to that in the CG. No significant differences were observed between the groups for the immunostaining of TIMP-1 or the gene expression levels of COL1 and COL3. CONCLUSION: Three sessions of static stretching reduced the gene expression level of TGF-β1, which, owing to its anti-fibrotic role, might contribute to the remodeling of the intramuscular connective tissue of the aging muscle. In addition, immunostaining revealed that TNF-α levels increased in the aging muscle tissue in response to stretching, indicating its effect on stimulating extracellular matrix degradation. These outcomes have important clinical implications in reinforcing the use of stretching exercises in the elderly, considering that the aging muscle presents an infiltration of connective tissue.