Introduction: Traditional resistance training involves both concentric and eccentric contraction, even if the latter has been shown to be more effective in total strength and muscle mass increment (Roig, 2009). However, often total training volume has been not considered. In addition, less is known about improvements retention after a detraining period. Therefore, aim of the study is to evaluate if muscle strength and structure changes are contraction dependent. In addition, we want to investigate if contraction modality can influence modifications retention after detraining. Methods: Sixty healthy female sport science students were randomly allocated in eccentric only (E), concentric only (C), eccentric plus concentric training (E+C) or control group (CG). Training groups exercised isovolume unilateral isotonic leg extension for 8 weeks, while CG did not train. Isokinetic eccentric, concentric and isometric Maximal Voluntary Contraction (MVC), 1RM, vastus lateralis fascicle angle (FA), fascicle thickness (FT) and fascicle length(FL) and fat free mass (FFM) were recorded at baseline, 1 and 4 weeks after the end of training. Changes of dependent variables were detected using two- way repeated measures ANOVA. Results: Significant two way interaction resulted in concentric (p<0,001), eccentric (p<0,001) and isometric (p<0.001) MVC, 1RM (p<0.001) and FA (p<0.05). FFM showed a strong tendency in two way interaction (p=0.058), while FT and FL did not displayed it. Post hoc analysis showed different strength coupling training-testing behavior both after training and detraining. FFM increased only in E after detraining (p<0.05). PA similarly increased in all training groups; FT incremented only in E (0.01) and C (0.05); Fascicle lengthened after detraining in E (p<0.01) and C (p<0.05). Discussion: Effectiveness of resistance training depend both on volume and contraction modality. Confirming literature, high intensity resistance training showed muscle strength and improvement retention (Fatouros, 2005). Hence, even if high intensity isovolume resistance training improved total strength, contraction specific training- testing is a torque high lightening factor, with a superiority of eccentric training (Guilhem, 2012). Trainers and conditioners should keep in mind that a timeline adaptations knowledge resulted in a more effective training planning. Fatouros, I. G., et al. (2005). Strength training and detraining effects on muscular strength, anaerobic power, and mobility of inactive older men are intensity dependent. British journal of sports medicine, 39(10) Guilhem, G.,et al. (2012). Neuromuscular Adaptations to Isoload versus Isokinetic Eccentric Resistance Training. Medicine and science in sports and exercise. Roig, M., et al.(2009). The effects of eccentric versus concentric resistance training on muscle strength and mass in healthy adults: a systematic review with meta-analysis. British journal of sports medicine, 43(8), 556–68.
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