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Lookup NU author(s): Dr Marika Noorkoiv
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Purpose: Neuromuscular adaptations to joint angle-specific force increases after isometric training have not yet been fully elucidated. This study examined angle-specific neuromuscular adaptations in response to isometric knee extension training at short (SL; joint angle 38.1 +/- 3.7[degrees]) versus long (LL; 87.5 +/- 6.0[degrees]) muscle lengths. Methods: Sixteen men trained three times a week for six weeks either at SL (n = 8) or LL (n = 8). Voluntary maximal isometric knee extensor (MVC) force, doublet twitch force, electromyogram amplitudes (EMG:Mmax) and voluntary activation during MVC force (VA%) were measured at eight knee joint angles (30-100[degrees]) at weeks 0, 3 and 6. Muscle volume and cross-sectional area (CSA) were measured from magnetic resonance imaging scans, and fascicle length (Lf) was assessed using ultrasonography before and after training. Results: Clear joint angle specificity of force increase was seen in SL but not in LL. The 13.4 +/- 9.7% (P=0.01) force increase around the training angle in SL was related to changes in VL and VM EMG:Mmax around the training angle (r=0.84-0.88, P<0.05), without changes in the doublet twitch force-angle relationship or muscle size. In LL, muscle volume and CSA increased and the changes in CSA at specific muscle regions were correlated with changes in MVC force. A 5.4 +/- 4.9% (P = 0.001) increase in Lf found in both groups was not associated with angle-specific force changes. There were no angle-specific changes in VA%. Conclusion: The EMG:Mmax, although not VA%, results suggest that neural adaptations underpinned training-related changes at short quadriceps lengths but hypertrophic changes predominated after training at long lengths. The findings of this study should contribute to the development of more effective and evidence based rehabilitation and strength training protocols.
Author(s): Noorkoiv M, Nosaka K, Blazevich AJ
Publication type: Article
Publication status: Published
Journal: Medicine and Science in Sports and Exercise
Print publication date: 01/08/2014
Online publication date: 05/02/2014
ISSN (print): 0195-9131
ISSN (electronic): 1530-0315
Publisher: Lippincott Williams & Wilkins
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