What Determines Mechanical Tension During Strength Training?

Introduction

• Author: Chris Beardsley
• Published: Nov 14, 2018
• Platform: Medium
• Focus: Understanding the factors that determine mechanical tension in muscles during strength training and its implications for hypertrophy.

Key Concepts

Mechanical Tension

• Defined as the type of force that stretches a material.
• During strength training, muscles experience mechanical tension when they attempt to shorten against resistance (concentric action) and when they lengthen while holding a load (eccentric action).
• The stretching force experienced by muscles is equal and opposite to the force muscles exert on the body.

Muscle Force Production

• Methods of Increasing Force:
  1. Increasing the number of active muscle fibers.
  2. Increasing the force each muscle fiber produces.
• Motor Unit Recruitment:
  • Motor units are recruited from small to large; each controls a number of muscle fibers.
  • All previously recruited motor units must remain active when a new motor unit is recruited.
• Force-Velocity Relationship: Muscle fibers exert higher forces at slower shortening speeds due to more actin-myosin crossbridges forming.

Light Loads and Force Control

• High Effort with Light Loads:
  • Maximal effort can recruit high levels of motor units even with light loads.
  • However, muscle force is not high due to rapid shortening speeds and the force-velocity relationship.
• Submaximal Effort with Light Loads:
  • Results in slow movement due to less acceleration; fewer motor units active.
  • Individual fibers can still exert high forces as they shorten slowly.

Mechanical Tension and Fatigue

• Lifting light loads can lead to fatigue, causing speed to decrease until movement stops.
• Effect of Fatigue on Motor Recruitment:
  • High motor unit recruitment can be maintained or increase with fatigue.
  • Slow bar speed increases muscle fiber tension similar to heavy weightlifting.

Implications for Hypertrophy

• Hypertrophy is linked to mechanical loading of individual muscle fibers, not just whole muscle-tendon units.
• The force-velocity relationship is crucial in determining mechanical tension that leads to muscle growth.

Key Takeaways

• Heavy loads alone do not ensure high mechanical tension; contraction velocity is crucial.
• Slow muscle shortening leads to high force exertion, contributing to muscle growth.
• Higher force and fatigue involve high motor unit recruitment and stimulate hypertrophy in responsive muscle fibers.
• Deliberate slow tempos do not always stimulate more hypertrophy compared to fast tempos due to the responsiveness of different muscle fibers (especially oxidative ones).

Conclusion

• Understanding the dynamics of force production and mechanical tension can aid in designing training programs that maximize hypertrophy by focusing on the force-velocity relationship and motor unit recruitment.

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These notes provide an overview of the critical factors affecting mechanical tension during strength training and its role in muscle hypertrophy as discussed by Chris Beardsley.