The sites of neural adaptation induced by resistance training in humans

• DOI: 10.1113/jphysiol.2002.024463
• Publication Date: 2002-10-15T16:45:17Z
• Authors: Timothy J. Carroll; Stephan Riek; Richard G. Carson
• Keywords: name=Physiology; Adult; Male; /dk/atira/pure/subjectarea/asjc/1300/1314; Weight Lifting; 610; 796; Fingers; Magnetics; 03 medical and health sciences; C1; 0302 clinical medicine; Isometric Contraction; Reaction Time; Humans; Nervous System Physiological Phenomena; Neural adaptation; Muscle, Skeletal; Physical Education and Training; Electromyography; Cognitive neuroscience; 730104 Nervous system and disorders; Evoked Potentials, Motor; Adaptation, Physiological; 321403 Motor Control; Electric Stimulation; Torque; Female; Muscle Contraction

Although it has long been supposed that resistance training causes adaptive changes in the CNS, the sites and nature of these adaptations have not previously been identified. In order to determine whether the neural adaptations to resistance training occur to a greater extent at cortical or subcortical sites in the CNS, we compared the effects of resistance training on the electromyographic (EMG) responses to transcranial magnetic (TMS) and electrical (TES) stimulation. Motor evoked potentials (MEPs) were recorded from the first dorsal interosseous muscle of 16 individuals before and after 4 weeks of resistance training for the index finger abductors (n= 8), or training involving finger abduction‐adduction without external resistance (n= 8). TMS was delivered at rest at intensities from 5 % below the passive threshold to the maximal output of the stimulator. TMS and TES were also delivered at the active threshold intensity while the participants exerted torques ranging from 5 to 60 % of their maximum voluntary contraction (MVC) torque. The average latency of MEPs elicited by TES was significantly shorter than that of TMS MEPs (TES latency = 21.5 ± 1.4 ms; TMS latency = 23.4 ± 1.4 ms; P < 0.05), which indicates that the site of activation differed between the two forms of stimulation. Training resulted in a significant increase in MVC torque for the resistance‐training group, but not the control group. There were no statistically significant changes in the corticospinal properties measured at rest for either group. For the active trials involving both TMS and TES, however, the slope of the relationship between MEP size and the torque exerted was significantly lower after training for the resistance‐training group (P < 0.05). Thus, for a specific level of muscle activity, the magnitude of the EMG responses to both forms of transcranial stimulation were smaller following resistance training. These results suggest that resistance training changes the functional properties of spinal cord circuitry in humans, but does not substantially affect the organisation of the motor cortex.