The knowns and unknowns of neural adaptations to resistance training

Abstract

The initial increases in force production with resistance training are thought to be primarily underpinned by neural adaptations. This notion is firmly supported by evidence displaying motor unit adaptations following resistance training; however, the precise locus of neural adaptation remains elusive. The purpose of this review is to clarify and critically discuss the literature concerning the site(s) of putative neural adaptations to short-term resistance training. The proliferation of studies employing non-invasive stimulation techniques to investigate evoked responses have yielded variable results, but generally support the notion that resistance training alters intracortical inhibition. Nevertheless, methodological inconsistencies and the limitations of techniques, e.g. limited relation to behavioural outcomes and the inability to measure volitional muscle activity, preclude firm conclusions. Much of the literature has focused on the corticospinal tract; however, preliminary research in non-human primates suggests reticulospinal tract is a potential substrate for neural adaptations to resistance training, though human data is lacking due to methodological constraints. Recent advances in technology have provided substantial evidence of adaptations within a large motor unit population following resistance training. However, their activity represents the transformation of afferent and efferent inputs, making it challenging to establish the source of adaptation. Whilst much has been learned about the nature of neural adaptations to resistance training, the puzzle remains to be solved. Additional analyses of motoneuron firing during different training regimes or coupling with other methodologies (e.g., electroencephalography) may facilitate the estimation of the site(s) of neural adaptations to resistance training in the future.

Resistance Exercise After Laparoscopic Surgery Enhances Improvement in Exercise Tolerance in Geriatric Patients With Gastrointestinal Cancer

“…Previous studies reported that resistance exercise, even at low intensity, improves exercise tolerance [ 19 ]. The improvement in physical function with resistance training in the early phase is considered to be a result of neural adaptations and may be associated with an increase in motor units [ 20 , 21 ]. Resistance exercise was shown to be significantly and positively related to 6MWT at hospital discharge.…”

Neural adaptations to long-term resistance training: evidence for the confounding effect of muscle size on the interpretation of surface electromyography

“…Resistance training is known to increase maximal force generating capacity of muscle when performed regularly (27). The initial (<2-4 weeks) increases in muscle force production following resistance training are thought to be primarily underpinned by neural factors (60), followed by adaptation in muscle morphology (>5-8 weeks;…”

Corticospinal excitability and motor representation after long‐term resistance training

“…Although the specific neural loci remain opaque, the motor cortex is thought to play a fundamental role in the control of movements, from the generation of 'low-level' control signals such as muscle force production (Evarts, 1968;Cheney & Fetz, 1980; and see Omrani et al, 2017 for a review) to involvement in 'high-level' control functions such as motor skill acquisition and consolidation (Papale & Hooks, 2018). The motor cortex therefore seems a plausible site of nervous system adaptation with changes in the excitatory and/or inhibitory intracortical circuits that appear to mediate increases in force generation after RT (for reviews, see Kidgell et al, 2017;Skarabot et al, 2020) and decreases in strength after disuse (Clark et al, 2010). An enhanced understanding of the modulations in the motor cortex following RT may help to improve and refine the exercise prescription of RT, which is now part of the physical activity recommendations for the general populations as well as people with neurological disorders (Kim et al, 2019;Verschuren et al, 2016).…”