The Role of Muscle Mass in Endurance Performance and Neuromuscular Fatigue

Introduction

• Endurance performance — measured as time-to-task failure — was not significantly affected by the size of active muscle mass.
• However, smaller muscle mass exercises caused greater declines in maximal force production and contractile function, showing a more substantial effect on neuromuscular fatigue.

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Key Findings

1. Endurance Performance Is Not Dependent on Muscle Size

• Time-to-task failure was similar across exercises involving small and large muscle groups.
• Larger active muscle mass did not enhance endurance capacity compared to smaller muscle groups.

2. Smaller Muscle Mass Exercises Increase Neuromuscular Fatigue

• Exercises targeting smaller muscle groups resulted in greater declines in maximal force-generating capacity.
• This effect was primarily due to greater impairments in muscle contractile function, contributing to higher localized fatigue.

3. Central Fatigue Is Less Affected

• Voluntary activation — an indicator of central nervous system fatigue — was only slightly lower following small muscle mass exercises.
• This suggests that differences in fatigue are driven more by peripheral mechanisms within the muscles themselves.

4. Localized Fatigue Is Driven by Metabolic Stress

• Smaller muscle mass tasks may allow less inhibitory feedback to the central nervous system.
• As a result, greater local metabolic stress accumulates before task failure, leading to increased peripheral fatigue.

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Practical Applications

1. Training Design

• Single-limb or small-muscle exercises are effective for targeted strengthening and developing fatigue resilience in specific muscle groups.

2. Endurance Programming

• Since endurance performance remains similar regardless of muscle size, combining large-muscle endurance tasks (e.g., cycling, rowing) with small-muscle exercises (e.g., unilateral leg work) may create more balanced conditioning programs.

3. Rehabilitation and Return-to-Sport

• Small-muscle-mass tasks can be used safely in rehabilitation to increase localized fatigue tolerance without negatively affecting overall endurance.

4. Monitoring Fatigue

• Coaches and practitioners should recognize that peripheral fatigue can be significantly higher in smaller muscle groups, even when performance metrics appear stable.

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Conclusion