Determinants of maximal oxygen uptake in highly trained females and males: a mechanistic study of sex differences using advanced invasive methods
Bibliographic record
Abstract
Abstract Females typically have lower body mass‐normalised maximal oxygen uptake () than males. However, whether this difference is solely due to body composition or also reflects sex‐based differences in cardiovascular and muscular capacities for O2 delivery and O2 extraction remains unclear. This study examined sex differences in the O2 transport chain when normalised to lean body mass (LBM). Twenty‐three highly trained cyclists and triathletes (10 females; 29 ± 6 years) performed incremental cycling to exhaustion on an ergometer with simultaneous assessment of cardiac output, leg blood flow (thermodilution), O2 delivery, and leg O2 extraction (arterial and femoral venous catheters). Mitochondrial (TEM) and capillary (immunohistochemistry) densities were assessed in the vastus lateralis. Maximal cardiac output was 26% lower in females than males (22 ± 3 vs. 30 ± 3 l min−1; P < 0.001). However, this difference disappeared when normalised to LBM (P = 0.375). Two‐leg blood flow was similar after normalisation to leg lean mass (LLM; P = 0.327). However, females had 10% lower haemoglobin concentration and arterial O2 content (177 ± 10 vs. 194 ± 15 ml l−1; P = 0.004), resulting in 11%–14% lower lean mass‐normalised systemic and leg O2 delivery. Leg O2 extraction (91 ± 3 vs. 92 ± 3%; P = 0.204) and mitochondria, cristae, and capillary densities were similar between sexes. Therefore, proportional to sex differences in O2 delivery, females had lower lean mass‐normalised pulmonary (63 ± 8 vs. 73 ± 4 ml min−1 kgLBM−1; P = 0.003) and leg (135 ± 14 vs. 160 ± 14 ml min−1 kgLLM−1; P = 0.002) . These findings demonstrate that highly trained females and males have similar muscle O2 extraction and perfusion per kg LBM. However, females’ 10% lower haemoglobin concentration results in lower LBM‐normalised O2 delivery and . image Key points Females and males differ substantially in body size and composition, with males having greater skeletal muscle mass and females a higher body fat percentage. During maximal exercise, the active skeletal muscles consume most of the body's oxygen uptake. Consequently, males exhibit higher absolute and body‐mass‐normalised maximal oxygen uptakes. Here, we show that the heart's capacity to pump blood and perfuse the exercising muscles is similar between sexes when scaled to muscle mass. Despite similar perfusion, oxygen delivery per exercising muscle mass is approximately 10% lower in females than males, caused by a 10% lower blood haemoglobin concentration and oxygen‐carrying capacity. Conversely, the fractional oxygen extraction by the skeletal muscles, along with their mitochondria and capillary densities, are similar between sexes. These findings demonstrate that sex differences in body composition and haemoglobin concentration are the primary mechanisms underpinning the lower body‐mass normalised maximal oxygen uptake in females compared to males.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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) | 0.002 | 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 source (direct Gemma or distilled Codex), 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".