Neuro-Physiological Adaptations Associated with Cross-Education of Strength

Abstract

Cross-education of strength is the increase in strength of the untrained contralateral limb after unilateral training of the opposite homologous limb. We investigated central and peripheral neural adaptations associated with cross-education of strength. Twenty-three right-handed females were randomized into a unilateral training group or an imagery group. A sub-sample of eight subjects (four training, four imagery) was assessed with functional magnetic resonance imaging (fMRI) for patterns of cortical activation during exercise. Strength training was 6 weeks of maximal isometric ulnar deviation of the right arm, four times per week. Peak torque, muscle thickness (ultrasound), agonist-antagonist electromyography (EMG), and fMRI were assessed before and after training. Strength training was highly effective for increasing strength in trained (45.3%; P < 0.01) and untrained (47.1%; P < 0.01) limbs. The imagery group showed no increase in strength for either arm. Muscle thickness increased only in the trained arm of the training group (8.4%; P < 0.001). After training, there was an enlarged region of activation in contralateral sensorimotor cortex and left temporal lobe during muscle contractions with the untrained left arm (P < 0.001). Training was associated with a significantly greater change in agonist muscle EMG pooled over both limbs, compared to the imagery group (P < 0.05). These results suggest that cross-education of strength may be partly controlled by adaptations within sensorimotor cortex, consistent with previous studies of motor learning. However, this research demonstrates the involvement of temporal lobe regions that subserve semantic memory for movement, which has not been previously studied in this context. We argue that temporal lobe regions might play a significant role in the cross-education of strength.

Cross-education of wrist extensor strength is not influenced by non-dominant training in right-handers

“…Given that much of the cross-education literature has only considered cross-education effects following unilateral strength training of the dominant right limb (Farthing et al 2007;Hortobagyi et al 2011;Kidgell et al 2011;Lee et al 2009), the objective of this study was to examine the directionality effects of crosseducation following unilateral strength training of either the dominant or non-dominant wrist in right-handed individuals. A secondary objective was to examine the corticospinal responses associated with unilateral strength training and cross-education.…”

Motor Imagery Training on Muscle Strength and Gait Performance in Ambulant Stroke Subjects: A Randomized Clinical Trial

“…Our results have shown that MIT training also added benefits to improve paretic muscle strength in hip flexors and extensors, knee extensors and dorsiflexors. Neural adaptation is a key factor for strength gain in voluntary skeletal muscle training [36]. Earlier studies on MIT and muscle strength had shown that mental practice with motor imagery actively changes in central programming process such as motor planning which enhances for neural adaptation for maximal voluntary contraction (MVC) [37] and also kinesthetic imagery training could alter the greater activation in motor units which may attribute for our present findings [38][39][40].…”

The Effects of Self-induced and Therapist-assisted Lower-limb PNF Pattern Training on the Activation of Contralateral Muscles

“…Many related studies have been undertaken recently, as cross-training can strengthen the muscular power of body parts that are hard to train directly 12) . These studies have shown that muscular and endurance training for limbs of one side can enhance the muscular power, function, and endurance of the limbs on the other side due to the interlateral transfer of training 13) and can enhance their performance function 14) . Muun et al (2004) conducted a meta-analysis to examine the effect of training on one side on muscular strength of the other side and reported that cross-training can be effective.…”