Strength increases without detectable muscle hypertrophy and this is particularly evident in the early phases of a training programme. It takes ~12 weeks for true muscle hypertrophy to take place so we are taking about the first few weeks of training.
Strength gains were thought to happen because of changes to the nervous system allowing more contraction of the muscle a person already has. This has been collective belief for some time and this hypothesis was derived from surface electromyography (SEMG). The limitations SEMG means we can’t use this technique to differentiate which parts of the neuromuscular system were adapting to increase the efferent motor output or how much adaptation was taking place.
Recent development in tech means that our understanding has evolved and there is debate about whether or not muscle hypertrophy takes place earlier than thought and if the strength increase comes from reduced inhibition in the descending motor pathways. It’s definitely not clear what is exactly causing what and this is why a new systematic review has been completed to help clarify the current evidence.
Clinical Significance
The meta-analysis suggests that resistance training causes changes in the excitation and inhibition of descending motor pathways, which results in an increase in muscle unit firing and motor unit recruitment. It is important that this is explained to patients to emphasise the importance of continuing to muscle hypertrophy in a training plan.
It is important to also think about those who have altered motor pathways due to stroke or SCI and how this early phase of training affects them differently.
Currently it isn’t clear if different types of strength training affects these changes in different ways.