Resistance training: cortical, spinal, and motor unit adaptations

Area of Science:

• Exercise Physiology
• Neuroscience
• Biomechanics

Background:

• Maximal muscle force increases early in isometric resistance training without significant muscle hypertrophy.
• Neural adaptations were initially inferred from surface electromyography (EMG).
• Recent research suggests potential cortical level excitation changes post-short-term resistance training.

Purpose of the Study:

• To explore neural factors contributing to maximal force generation during early-stage resistance training.
• To investigate changes in synergistic and antagonist muscle activation.
• To examine neural adaptations during the ramp-up phase of isometric contractions.

Main Methods:

• Analysis of surface electromyographic (EMG) recordings.
• Investigation of motor unit recruitment thresholds and discharge rates.
• Assessment of double discharges and maximal rate of force development.

Main Results:

• Identified alterations in synergistic muscle activation and reductions in antagonist activation.
• Observed decreases in motor unit recruitment thresholds during isometric ramp-up.
• Noted increased motor unit discharge rates and double discharges.

Conclusions:

• Neural adaptations, including altered muscle activation and improved motor unit function, contribute significantly to early gains in maximal force during isometric resistance training.
• Further research is needed to understand the integration of cortical and spinal excitability with motor unit firing patterns.
• The neural mechanisms underlying the increased rate of force development require further elucidation in relation to maximal force gains.