Strength training improves body composition primarily by

Question

BlackTom AI · Accepted Answer

Increasing muscle mass is the primary mechanism by which strength training improves body composition.

Relevant knowledge points and concepts:
- Body composition describes the relative amounts of fat mass and lean mass (including skeletal muscle).
- Strength (resistance) training produces mechanical tension, metabolic stress, and microdamage to muscle fibers, which trigger muscle protein synthesis and hypertrophy.
- Hypertrophy increases lean (muscle) mass and often increases resting metabolic rate, which can reduce fat mass over time and thus improve the fat:lean ratio.

Step-by-step reasoning:
1. Mechanical overload from resistance exercise activates intracellular signaling (e.g., mTOR pathway) that increases muscle protein synthesis.
2. Satellite cell activation and increased synthesis cause muscle fibers to enlarge (hypertrophy), especially type II fibers, resulting in greater lean body mass.
3. Greater muscle mass elevates resting energy expenditure because muscle is metabolically active, so daily calorie needs increase slightly.
4. With the combined effects of increased energy expenditure and often improved insulin sensitivity, fat mass tends to decrease, improving overall body composition (higher percent lean mass, lower percent fat mass).
5. Therefore, the direct and primary change caused by strength training is an increase in muscle mass, which explains improved body composition.

Why the correct answer is correct:
- "Increasing muscle mass" directly changes the lean vs fat proportions that define body composition; it is the main adaptation to strength training.

Why other options are incorrect:
- "Decreasing body weight." Strength training often increases or maintains weight as muscle mass rises even as fat decreases; therefore body weight is not the primary or reliable effect.
- "Decreasing slow twitch muscle fibers." Strength training does not eliminate slow-twitch (type I) fibers; it may increase performance of fibers but does not reduce their number.
- "Increasing fast twitch muscle fibers." Training induces hypertrophy (larger fast-twitch fibers) and some fiber-type shifts in properties, but it does not create new fast-twitch fibers; the primary measurable effect is increased muscle mass, not an increase in fiber count or wholesale conversion.

Conclusion:
The correct answer is increasing muscle mass, which matches the provided answer.

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