Is the joint-angle specificity of isometric resistance training real? And if so, does it have a neural basis?

PurposeThere are suggestions that isometric resistance training (RT) produces highly angle-specific changes in strength with the greatest changes at the training angle, but these effects remain controversial with limited rigorous evidence, and the possible underpinning physiological mechanism(s) remain opaque. This study investigated the extent of angle-specific changes in strength and neuromuscular activation after RT in comparison to a control group.MethodsA RT group (n=13) performed 14 isometric RT sessions at a knee-joint angle of 65 degrees (0 degrees is anatomical position) over a 4-week period, whilst a control group (CON, n=9) maintained their habitual activity. Pre- and post-test sessions involved voluntary and evoked isometric knee extension contractions at five knee-joint angles (35 degrees, 50 degrees, 65 degrees, 80 degrees and 95 degrees), while electromyography was recorded.ResultsRT group increased maximum voluntary torque (MVT) at the training angle (65 degrees;+12%) as well as 80 degrees (+ 7%), 50 degrees (+ 11%) and 35 degrees (+ 5%). Joint-angle specificity was demonstrated within the RT group (MVT increased more at some angles vs. others), and also by more rigorous between-group comparisons (i.e., larger improvements after RT vs. CON at some angles than others). For the RT group, normalized EMG increased at three of the same joint angles as strength, but not for CON. Importantly, however, neither within- or between-group analyses provided evidence of joint angle-specific changes in activation.ConclusionIn conclusion, this study provides robust evidence for joint angle-specific strength gains after isometric RT, with weaker evidence that changes in neuromuscular activation may contribute to these adaptations.