Neural and morphological adaptations of vastus lateralis and vastus medialis muscles to isokinetic eccentric training

Rodrigo De Azevedo Franke,Jeam Marcel Geremia,Fábio Juner Lanferdini,Rodrigo Rodrigues,Bruno Manfredini Baroni,Marco Aurélio Vaz

doi:10.1590/s1980-65742014000300011

Abstract

Vastus lateralis (VL) and vastus medialis (VM) are frequently targeted in conditioning/rehabilitation programs due to their role in patellar stabilization during knee extension. This study assessed neural and muscular adaptations in these two muscles after an isokinetic eccentric training program. Twenty healthy men underwent a four-week control period followed by a 12-week period of isokinetic eccentric training. Ultrasound evaluations of VL and VM muscle thickness at rest and electromyographic evaluations during maximal isometric tests were used to assess the morphological and neural properties, respectively. No morphological and neural changes were found throughout the control period, whereas both muscles showed significant increases in thickness (VL = 6.9%; p < .001 and VM = 15.8%; p < .001) post-training. Significant increases in muscle activity were observed in VM (47.8%; p = .003), but not in VL (19.8%; p > .05) post-training. Isokinetic eccentric training produces neural and greater morphological adaptations in VM compared to VL, which shows that synergistic muscles respond differently to an eccentric isokinetic strength training program

Highlights

The knee extensor muscle group [i.e., rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM) and vastus intermedius (VI)] is primarily responsible for the dynamic stabilization of the patellofemoral joint (Serrão, Cabral, Bérzin, Candolo, & Monteiro-Pedro, 2012)
Data obtained in baseline and pre-training evaluations presented high to very high intraclass correlation coefficient (ICC) scores for test-retest reliability for muscle thickness (VL = .91; VM = .86) and muscle activity (VL = .86; VM = .79) procedures
When comparing pre-training to post-training values, significant increases were observed in muscle thickness for VL (6.9%, p < .001; 0.548; 95% CI = 2.540 - 2.771) and VM (15.8%, p < .001; 0.570; 95% CI = 1.845 - 2.111) (Table 1)

Summary

Introduction

The knee extensor muscle group [i.e., rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM) and vastus intermedius (VI)] is primarily responsible for the dynamic stabilization of the patellofemoral joint (Serrão, Cabral, Bérzin, Candolo, & Monteiro-Pedro, 2012). Most of them have failed to show a different behavior between these two synergistic muscles during specific exercises and, to date, there is no consensus regarding a gold standard method to emphasize VM or VL muscle activity. Despite this lack of consensus, patients with patellofemoral pain syndrome have engaged in resistance training rehabilitation programs for knee extensors strengthening (American College of Sports Medicine, 2009). The conventional resistance training involves exercises with both concentric and eccentric muscle actions, eccentric training has become popular in recent decades for conditioning and rehabilitation purposes (Barstow, Bishop, & Kaminski, 2003; Lorenz & Reiman, 2011; Vikne et al, 2006; Visnes & Bahr, 2007), and the effects of eccentric training programs on knee extensor muscles have been reported for healthy adults (Rocha et al, 2011), elderly (Reeves, Maganaris, Longo, & Narici, 2009), patients with patellar tendinopathy (Jonsson & Alfredson, 2005), anterior cruciate ligament reconstruction (Gerber et al, 2009) and patellofemoral pain syndrome (Eapen, Nayak, & Pazhyaottyil Zulfeequer, 2011)

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