Browsing by Author "Vaz, Marco Aurélio"
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- ItemOpen AccessA clinically relevant BTX-A injection protocol leads to persistent weakness, contractile material loss, and an altered mRNA expression phenotype in rabbit quadriceps muscles(Journal of Biomechanics, 2015-07-16) Fortuna, Rafael; Sawatsky, Andrew; Herzog, Walter; Vaz, Marco Aurélio; Hart, David A.Botulinum toxin type-A (BTX-A) injections have become a common treatment modality for patients suffering from muscle spasticity. Despite its benefits, BTX-A treatments have been associated with adverse effects on target muscles. Currently, application of BTX-A is largely based on clinical experience, and research quantifying muscle structure following BTX-A treatment has not been performed systematically. The purpose of this study was to evaluate strength, muscle mass, and contractile material six months following a single or repeated (2 and 3) BTX-A injections into the quadriceps femoris of New Zealand white rabbits. Twenty three skeletally mature rabbits were divided into four groups: experimental group rabbits received 1, 2, or 3 injections at intervals of 3 months (1-BTX-A, 2-BTX-A, 3-BTX-A, respectively) while control group rabbits received volume-matched saline injections. Knee extensor strength, quadriceps muscle mass, and quadriceps contractile material of the experimental group rabbits were expressed as a percentage change relative to the control group rabbits. One-way ANOVA was used to determine group differences in outcome measures (α=0.05). Muscle strength and contractile material were significantly reduced in experimental compared to control group rabbits but did not differ between experimental groups. Muscle mass was the same in experimental BTX-A and control group rabbits. We concluded from these results that muscle strength and contractile material do not fully recover within six months of BTX-A treatment.
- ItemOpen AccessEccentric resistance training of the knee extensor muscle: Training programs and neuromuscular adaptations(IOS Press, 2015-01-01) Manfredini Baroni, Bruno; Silveira Pinto, Ronei; Herzog, Walter; Vaz, Marco AurélioPURPOSE: This review is aimed at describing the methods used in knee extensor eccentric resistance training in healthy subjects and at evaluating the adaptations in strength, activation and structure of this muscle group. METHODS: Seventy-five studies were carefully analyzed and 30 are considered in this review. RESULTS: Training programs comprised of 1-4 sessions per week for a period ranging from four to 20 weeks with isokinetic dynamometers or conventional strength training machines were considered. Isokinetic eccentric training programs included 1-6 sets of 6-12 repetitions, while isotonic eccentric training programs consisted of 3-7 sets of 5-10 repetitions. Eccentric strength gains per training session (0.45-3.42%) were typically found to be greater compared to isometric (0.08-1.30%) and concentric (0.23-1.44%) strength gains. Quadriceps activation was improved in tests performed eccentrically and isometrically, but there is poor evidence of increased concentric activation and reduced co-activation of antagonistic muscles. Regarding muscle structure, significant hypertrophic responses have been demonstrated through increases in anatomical/physiological cross-sectional area, muscle thickness and fiber diameter. Most studies measuring muscle architectural changes reported increased fascicle lengths without changes in pennation angle. Adaptations in fiber type distribution were inconsistent. CONCLUSIONS: Strength gains following knee extensor eccentric training are caused by neural and structural adaptations, and may contribute to physical fitness in healthy populations and health improvement in patients.