Four‐week cold acclimation in adult humans shifts uncoupling thermogenesis from skeletal muscles to brown adipose tissue
Bibliographic record
Abstract
Key points Muscle‐derived thermogenesis during acute cold exposure in humans consists of a combination of cold‐induced increases in skeletal muscle proton leak and shivering. Daily cold exposure results in an increase in brown adipose tissue oxidative capacity coupled with a decrease in the cold‐induced skeletal muscle proton leak and shivering intensity. Improved coupling between electromyography‐determined muscle activity and whole‐body heat production following cold acclimation suggests a maintenance of ATPase‐dependent thermogenesis and decrease in skeletal muscle ATPase independent thermogenesis. Although daily cold exposure did not change the fibre composition of the vastus lateralis, the fibre composition was a strong predictor of the shivering pattern evoked during acute cold exposure. Abstract We previously showed that 4 weeks of daily cold exposure in humans can increase brown adipose tissue (BAT) volume by 45% and oxidative metabolism by 182%. Surprisingly, we did not find a reciprocal reduction in shivering intensity when exposed to a mild cold (18°C). The present study aimed to determine whether changes in skeletal muscle oxidative metabolism or shivering activity could account for these unexpected findings. Nine men participated in a 4 week cold acclimation intervention (10°C water circulating in liquid‐conditioned suit, 2 h day –1 , 5 days week –1 ). Shivering intensity and pattern were measured continuously during controlled cold exposure (150 min at 4 °C) before and after the acclimation. Muscle biopsies from the m. vastus lateralis were obtained to measure oxygen consumption rate and proton leak of permeabilized muscle fibres. Cold acclimation elicited a modest 21% ( P < 0.05) decrease in whole‐body and m. vastus lateralis shivering intensity. Furthermore, cold acclimation abolished the acute cold‐induced increase in proton leak. Although daily cold exposure did not change the fibre composition of the m. vastus lateralis , fibre composition was a strong predictor of the shivering pattern evoked during acute cold. We conclude that muscle‐derived thermogenesis during acute cold exposure in humans is not only limited to shivering, but also includes cold‐induced increases in proton leak. The efficiency of muscle oxidative phosphorylation improves with cold acclimation, suggesting that reduced muscle thermogenesis occurs through decreased proton leak, in addition to decreased shivering intensity as BAT capacity and activity increase. These changes occur with no net difference in whole‐body thermogenesis.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".