Lecture Notes: How Exercise Impacts Motor Unit Recruitment
Main Point: Exercise, particularly strength training, significantly impacts how our nervous system recruits motor units for muscle contraction, leading to increased strength.
Key Points:
- Short-term effects (immediate to 3 weeks):
- Increased recruitment of fast-fatigable motor units: Strength training prioritizes recruiting these powerful but fatigue-prone units, compared to an untrained state.
- Enhanced firing patterns: Motor units switch from single action potentials to doublets (two rapid signals), leading to greater force generation.
- Long-term effects (after 3 weeks):
- Muscle growth: Muscle fibers themselves increase in size, allowing them to produce more force. This becomes the primary driver of strength gains.
- Improved muscle contractility: The muscle’s ability to contract more forcefully is enhanced.
Overall: Exercise triggers a two-phase adaptation in motor unit recruitment. Initially, neural adaptations optimize firing patterns and recruit more fast-twitch fibers. Over time, muscle growth takes over as the main contributor to strength increases.