The Adaptation of Oxygen Uptake, Limb Blood Flow, and Muscle Deoxygentation at the Onset of Moderate-Intensity Knee-Extension Exercise in Young and Old Adults
Bibliographic record
Abstract
The slowed pulmonary O2 uptake (VO2p) kinetics (and muscle O2 consumption) of older adults may be limited by convective O2 delivery to the exercising limb. However, the effects of age on the kinetics of femoral artery blood flow (LBF) remain unknown. PURPOSE: To determine the effect of age on VO2p, LBF and muscle deoxygenation kinetics during moderate-intensity exercise. METHODS: 5 young (Y; 25 ± 2 yrs) and 5 old (O; 70 ± 6 yrs) male subjects performed repeated (n = 4) step-transitions (6 min) from an active baseline (3 W) to moderate-intensity (80% θL), alternate-leg, knee-extension (KE) exercise. VO2p was measured breath-by-breath by mass spectrometer and volume turbine. LBF was measured via Doppler ultrasound at the femoral artery. Deoxygenated hemoglobin/myoglobin (ΔHHb) of the vastus lateralis muscle was measured continuously by near-infrared spectroscopy. The VO2p, LBF and HHb data were filtered, time-aligned and ensemble-averaged to provide a single response for each subject, and then further averaged into 10 s (VO2p, LBF) or 5 s (ΔHHb) bins. VO2p data were fit with a monoexponential function from the phase 1- phase 2 interface to the end of exercise and LBF was fit from the onset to the end of exercise. Following a delay (HHbTD), HHb data were fit with a monoexponential function to 180 s to assess the adaptation of muscle deoxygenation during the adaptation period of VO2p. RESULTS: Phase 2 τVO2p was greater in O (45 ± 12 s) compared to Y (30 ± 5 s) during the on-transient of KE exercise. The magnitude of the steady-state increase in LBF (ΔLBF/Δ VO2p; O: 5.5 ± 1.3; Y: 5.3 ± 0.3) and the rate of increase of LBF (τLBF; O: 39 ± 19 s; Y: 29 ± 12 s) were not different between O and Y. HHbTD (O: 17 ± 4 s; Y: 17 ± 3 s), τHHb (O: 15 ± 8 s; Y: 10 ± 6 s) and the effective τHHb (HHbTD + τHHb; O: 32 ± 9 s; Y: 27 ± 5 s) were not different between groups. CONCLUSIONS: These results demonstrate a slower adaptation of VO2p in older subjects during moderate-intensity KE exercise but no significant age-related differences in the adaptation of bulk limb blood flow or muscle deoxygenation. The slower adaptation of muscle O2 consumption in O compared to Y and a similar adaptation of HHb (representing a faster contribution of HHb relative to the rise in VO2p in O compared to Y) would suggest that an impairment in microvascular flow/O2 delivery but not bulk limb blood flow contributes to the slower VO2p kinetics in O compared to Y.(Supported by NSERC)
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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 | 0.001 |
| 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) | 0.001 | 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".