Does cross-education minimize the loss of muscle force and power and sEMG amplitude during short-term detraining in older women who are recreationally engaged in resistance training?

This study aimed to investigate whether 4 weeks of unilateral resistance training (RT) could attenuate the decline in muscle function in the contralateral limb of older women recreationally engaged in RT compared to control group (CTL). Twenty-four participants completed a 10-week RT before the cross-education (CR-Edu) phase and subsequent detraining. Afterward, participants were randomized into two groups: CTL (n = 8 women, n = 16 legs) who underwent 4 weeks of detraining without any training, and CR-Edu (n = 16 women, n = 16 legs) who performed 4 weeks of unilateral RT. Muscle force, power, and surface electromyography were measured unilaterally before and after the 4-week period, using five repetitions conducted at 40% and 60% of the 1RM. The results showed a reduction in muscle force at both 40% and 60% of 1RM, as well as a decrease in power at 60% of 1RM (P-time < 0.05) without significant differences between the two groups (P interaction > 0.05). There was a decline in power at 60% of 1RM (P-time < 0.05) but no significant change at 40% of 1RM (P-time > 0.05), and again, no significant differences were observed between the groups (P-interaction > 0.05). The surface electromyography of vastus lateralis decreased only in the CTL group (P-interaction < 0.05). Older women recreationally engaged in RT who perform in unilateral leg extension compared to a brief period of detraining seem not to retain muscle force and power, and sEMG amplitude of their homologous and contralateral limb.

Resistance training prevents dynamics and mitochondrial respiratory dysfunction in vastus lateralis muscle of ovariectomized rats.

To investigate whether ovariectomy affects mitochondrial respiratory function, gene expression of the biogenesis markers and mitochondrial dynamics of the vastus lateralis muscle, female Wistar rats divided into ovariectomized (OVX) and intact (INT) groups were kept sedentary (SED) or submitted to resistance training (RT) performed for thirteen weeks on a vertical ladder in which animals climbed with a workload apparatus. RT sessions were performed with four climbs with 65, 85, 95, and 100 % of the rat's previous maximum workload. Mitochondrial Respiratory Function data were obtained by High-resolution respirometry. Gene expression of FIS1, MFN1 and PGC1-α was evaluated by real-time PCR. There was a decrease on oxidative phosphorylation capacity in OVX-SED compared to other groups. Trained groups presented increase on oxidative phosphorylation capacity when compared to sedentary groups. For respiratory control ratio (RCR), OVX-SED presented lower values when compared to INT-SED and to trained groups. Trained groups presented RCR values higher compared to INT-SED. Exercise increased the values of FIS1, MFN1 and PGC1-α expression compared to OVX-SED. Our results demonstrated that in the absence of ovarian hormones, there is a great decrease in oxidative phosphorylation and electron transfer system capacities of sedentary animals. RT was able to increase the expression of genes related to mitochondrial dynamics markers, reversing the condition determined by ovariectomy.

LLLT actives MMP-2 and increases muscle mechanical resistance after nerve sciatic rat regeneration.

The purpose of this study was to analyze the low-level laser therapy (LLLT) on metalloproteinase expression and the mechanical strength of skeletal muscle regeneration after peripheral nerve injury. Rats were subjected to crush injury of the right sciatic nerve, followed by LLLT (830 nm, 35, 70, 140, and 280 J/cm2) for 21 consecutive days. Functional gait analysis was performed at weekly intervals and the animals were sacrificed after the last evaluation at day 21 for collection of the gastrocnemius muscles, which were submitted to analysis of resistance, and the tibialis anterior, for evaluation of metalloproteinase-2 (MMP-2). The results were statistically analyzed at a significance level of 5%. The irradiated groups showed a significant decrease in the sciatic functional index and a significant increase in the mechanical strength when compared to the injured group with no treatment (p < 0.05), with no significant difference among the energy densities used. While no difference among groups was observed for the activity of MMP-2 in pro-active band, at the intermediate band, the activity was significantly higher (p < 0.05) for the groups irradiated with 35, 70, and 140 J/cm2, and at the active band, the activity was significantly more intense in the group irradiated with 280 J/cm2. The present study demonstrated that injury of the sciatic nerve, with consequent muscle denervation, are benefited by the laser therapy, which restores neuromuscular function, active MMP-2 and increases the maximum breaking strength.

Resistance training improves body composition and increases matrix metalloproteinase 2 activity in biceps and gastrocnemius muscles of diet-induced obese rats

OBJECTIVE: We investigated the influence of resistance training on body composition and matrix metalloproteinase 2 activity in skeletal muscles of rats fed a high-fat diet. METHODS: Thirty-two Wistar rats were divided into four experimental groups (n = 8/each) according to diet and exercise status: Control (standard diet), Obese Control (high-fat diet), Resistance Training (standard diet) and Obese Resistance Training (high-fat diet) groups. Animals were fed a high-fat diet for 12 weeks to promote excessive weight gain. Resistance Training groups performed 12 weeks of training periods after this period in a vertical ladder three times/week. Fat percentage, fat-free mass and fat mass were assessed using dual-energy X-ray absorptiometry, and matrix metalloproteinase 2 activity in biceps and gastrocnemius muscles was analyzed using zymography. RESULTS: Resistance training significantly reduced body and fat masses and fat percentages in both trained groups (p<0.05). The maximal carrying load between trained groups was not different, but relative force was higher in the Resistance Training group (p<0.05). Of note, increased matrix metalloproteinase 2 activity was noted in the tested muscles of both trained groups (p<0.05). CONCLUSION: In conclusion, altered body composition and muscle matrix metalloproteinase 2 activity promoted by excessive weight gain were positively modified by resistance training. .

Resistance training may concomitantly benefit body composition, blood pressure and muscle MMP-2 activity on the left ventricle of high-fat fed diet rats.

OBJECTIVE: The purpose of this study was to evaluate the effect of resistance training (RT) on body composition, systolic and diastolic blood pressures (BP), and activity of muscle MMP-2 in the left ventricle of high-fat fed rats. MATERIALS/METHODS: We have evaluated 32 male Wistar rats divided into four experimental groups (n=8/each) according to diet and exercise status: sedentary (SED; standard diet), sedentary obese (SED-OB; diet: 30% of fat), RT (RT; standard diet) and RT obese (RT-OB; diet: 30% of fat). After weaning (day 21), animals were subjected to the experimental diet according to their groups during 24 weeks. A 12-week strength-training period was used, during which the rats climbed a 1.1-m vertical ladder with weights attached to their tails. Sessions were performed three times/week (Mondays, Wednesdays and Fridays), with 4-9 climbs/session and 8-12 dynamic movements/climb. RESULTS: RT induced higher muscle MMP-2 activity in the left ventricle in RT and RT-OB groups. Moreover, this study demonstrated that RT promoted lower body and fat masses, fat percentage, systolic and diastolic BPs and higher fat free mass in both trained groups. CONCLUSION: RT increased muscle MMP-2 activity in the left ventricle, induced positive changes on body composition and lowered BPs in high-fat diet fed rats, suggesting that it may be a useful tool to prevent alterations induced by high-fat diet consumption.