In a study by Jensen and colleagues examining changes in motor cortex excitability, 24 healthy adults were randomly assigned to strength training or motor skill training 3x/week for 4 weeks or to a control group.1 Measurements of biceps motor evoked potentials (MEPs) on EMG elicited by transcranial magnetic stimulation (TMS) at the site of activation of the biceps in the primary motor cortex were taken at rest and during contraction pre- and post-training.
The strength training group performed 5 sets of biceps curls. For motor skill training, a goniometer, positioned to measure a subject’s elbow motion, was configured with a computer to reflect degrees of flexion on a screen in front of the subject. Subjects controlled the position of a cursor displayed on the screen by flexing and extending the elbow. A series of 6 varying lines were shown on the screen, each suggesting different degrees of flexion. Subjects were instructed to make the cursor closely track each displayed line.
Post-training, the strength training group increased in average maximal dynamic muscle strength and isometric muscle strength by 31% and 12.5%, respectively. No changes in muscle strength were observed in the skills training or control group.
Skill performance was quantified by measuring the mean deviation from the optimal track. The skills training group improved skill performance significantly, reducing mean deviation from 162.8 mm during the first training session to 27.3 mm during the last training session.
In the skill training group, the minimal TMS required to elicit MEPs in the biceps significantly decreased and the maximal MEPs elicited by TMS increased. In the strength training group, the minimal TMS required to elicit MEPs in the biceps was unchanged and the maximum MEPs elicited by TMS decreased. No significant changes were observed in the control group.
These results demonstrate that acquisition of a visuomotor skill requiring body awareness over 4 weeks is associated with increased corticospinal excitability. Strength training, in contrast, is not accompanied by similar corticospinal changes. These results are consistent with other research that suggests awareness and learning may be important factors in promoting cortical excitability related to motor experience and that strength training alone does not result in these changes.2,3
Increased corticospinal excitability and expansion of the hand and finger muscles with motor skill acquisition is well documented.4,5 This study suggests similar changes take place for proximal arm muscles with a visuomotor tracking task requiring awareness and control of elbow flexor muscles.
1Lundbye Jensen J, Marstrand PC, Nielsen JB. Motor skill and strength training are associated with different plastic changes in the central nervous system. J Appl Physiol. 2005;99(4):1558-68.
2Perez MA, Lungholt BK, Nyborg K, Nielsen JB. Motor skill training induces in excitability of leg cortical area in healthy humans. Exp Brain Res. 2004;159(2):197-205.
3Remple MS, Bruneau RM, VanderBerg PM, et al. Sensitivity of cortical movement representations to motor experience: evidence that skill learning but not strength training induces cortical reorganization.2001;123(2):133-141.
4Pascual-Leone A, Cammarota A, Wasserman EM, et al. Modulation of muscle responses evoked by transcranial magnetic stimulation during the aquisition of new fine motor skills. J Neurophysiol. 1995;74(3):1037-45.
5Pascual-Leone A, Wasserman EM, Sadato N and Hallett M. The role of reading activity on the modulation of motor cortical outputs to the reading hand in Braille readers. Ann Neurol. 1995 Dec;38(6):910-5.