Question at position 43 Over the lifespan, when accounting for lean body mass, resting metabolism tends to:Remain the sameDecreaseIncreaseNot enough information单项选择题
A
Remain the same
B
Decrease
C
Increase
D
Not enough information

Question

Question at position 43 Over the lifespan, when accounting for lean body mass, resting metabolism tends to:Remain the sameDecreaseIncreaseNot enough information

BlackTom AI · Accepted Answer

Resting metabolic rate (RMR) is largely determined by metabolically active lean body mass (LBM), so when LBM is held constant, RMR tends to remain the same across the lifespan.

1) Relevant concepts:
- RMR is the energy expended at rest to maintain basic physiological functions.
- Major determinants of RMR are fat‑free mass (organs, muscle), with organs (heart, liver, brain, kidneys) having particularly high specific metabolic rates.
- Age-related declines in total RMR are primarily driven by loss of LBM (sarcopenia), not by a large intrinsic slowing of tissue metabolic rate.

2) Step‑by‑step reasoning:
- Empirical observation: measured RMR falls with age in many cohorts.
- Identify cause: aging adults typically lose LBM (muscle and organ mass), which reduces total metabolically active tissue.
- Normalize RMR to LBM: researchers divide RMR by fat‑free mass (or use regression adjusting for LBM). When this adjustment is made, the age effect on RMR largely disappears.
- Conclusion from these steps: intrinsic RMR per unit of LBM remains stable; the observed decline in absolute RMR is explained by reduced LBM.

3) Intermediate logical steps (illustrative):
- Person A (young): LBM = 60 kg → total RMR = R_per_kg × 60.
- Person B (older): LBM = 54 kg (loss of 6 kg) → total RMR = R_per_kg × 54.
- If R_per_kg is unchanged, total RMR falls only because LBM fell.

4) Why the correct answer is correct:
Because RMR is proportional to LBM, adjusting for LBM shows little change in metabolic rate per unit lean tissue with aging. Scientific studies support stability in mass‑specific resting metabolism.

5) Why other options are incorrect:
- “Decrease”: true for absolute RMR but misleading when LBM is accounted for—decrease is due to LBM loss.
- “Increase”: unsupported by evidence.
- “Not enough information”: unnecessary—ample research shows RMR per unit LBM is stable.

Final confirmation: Therefore, the best choice is "Remain the same," matching the provided answer.

Question at position 43 Over the lifespan, when accounting for lean body mass, resting metabolism tends to:Remain the sameDecreaseIncreaseNot enough information单项选择题

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