Reduction in corticospinal inhibition in the trained and untrained limb following unilateral leg strength training

Abstract

This study used transcranial magnetic stimulation to measure the corticospinal responses following 8 weeks of unilateral leg strength training. Eighteen healthy, non-strength trained participants (14 male, 4 female; 18-35 years of age) were matched for age, gender, and pre-training strength; and assigned to a training or control group. The trained group participated in unilateral horizontal leg press strength training, progressively overloaded and wave periodised, thrice per week for 8 weeks. Testing occurred prior to the intervention, at the end of 4 weeks and at the completion of training at 8 weeks. Participants were tested in both legs for one repetition maximum strength, muscle thickness, maximal electromyography (EMG) activity, and corticospinal excitability and inhibition. No changes were observed in muscle thickness in either leg. The trained leg showed an increase in strength of 21.2% (P = 0.001) and 29.0% (P = 0.007, compared to pre-testing) whilst the untrained contralateral leg showed 17.4% (P = 0.01) and 20.4% (P = 0.004, compared to pre-testing) increases in strength at 4 and 8 weeks, respectively. EMG and corticospinal excitability did not change; however, corticospinal inhibition was significantly reduced by 17.7 ms (P = 0.003) and 17.3 ms (P = 0.001) at 4 and 8 weeks, respectively, in the trained leg, and 25.1 ms (P = 0.001) and 20.8 ms (P = 0.001) at 4 and 8 weeks, respectively, in the contralateral untrained leg. This data support the theory of corticospinal adaptations underpinning cross-education gains in the lower limbs following unilateral strength training.

Ipsilateral corticomotor responses are confined to the homologous muscle following cross-education of muscular strength

“…Also consistent with previous cross-education of strength studies, was the 23% increase in strength for the untrained bicep brachii (Goodwill et al 2012;Latella et al, 2012, Kidgell et al 2011Coombs et al 2016, Farthing et al 2005. Although current systematic reviews report lower magnitudes of cross-education (Carroll et al 2006;Munn et al 2004), these training paradigms typically employ only moderate intensity and untimed contractions, which seems to lessen the cross-education effect (Kidgell et al 2011;Goodwill et al 2012, Coombs et al 2016).…”

Revisiting the continuum model of tendon pathology: what is its merit in clinical practice and research?

“…Intervening with a loading programme also has the advantage of benefiting the tendon,76 the muscle,77 as well as the cortical control of that muscle, which may lead to improvements in function and a positive clinical outcome. An incremental load-based rehabilitation programme is capable of modifying the balance of excitability and inhibition in muscle control,78 thus altering the loads transmitted by the tendon.…”

The Cross-Education Phenomenon: Brain and Beyond

“…A myriad of studies describing cross-education in both upper and lower limbs following various types of resistance training interventions have been conducted, including heavy load voluntary contractions (Munn et al, 2005; Goodwill and Kidgell, 2012; Latella et al, 2012), ballistic motor tasks (Lee et al, 2010; Hinder et al, 2013), electrically stimulated contractions (Hortobágyi et al, 1999) and motor imagery (Yue and Cole, 1992). The magnitude of strength transfer differs between studies, which may primarily be due to differences in training variables such as exercise complexity, contraction type, volume, intensity, and duration.…”