Influence of Phase I Duration on Phase II VO2 Kinetics in Older and Young Adults
Bibliographic record
Abstract
Older adults (O) may have a longer Phase I pulmonary O2 uptake kinetics (VO2p) compared to young adults (Y). This longer Phase I duration may affect the parameter estimates of Phase II VO2p. PURPOSE: 1) To experimentally determine the duration of Phase I VO2p in O and Y during transitions to moderate-intensity exercise; 2) to examine the effects of Phase I duration on the parameter estimates of Phase II VO2p response. METHODS: Nineteen O (68±6 yr; mean ± SD) and 19 Y (24±5 yr) participated in the study. Phase I VO2p and Phase II VO2p kinetics were examined using the average response from four step transitions from a baseline of 20 W to a work rate corresponding to 80-90% of estimated lactate threshold. VO2p was measured breath-by-breath using a volume turbine and a mass spectrometer. The experimentally determined Phase I VO2p duration was identified by visual inspection and corresponded to the point at which there was a sharp decrease from baseline values (20 W cycling) in both respiratory exchange ratio and end-tidal O2 partial pressure. For fitting purposes, the Phase I-Phase II transition was assigned durations of 15s, 25 s, 35s, or 45s. Phase II VO2p was modeled with a mono-exponential using non-linear regression starting at but not constrained to each one of these discrete times. RESULTS: Phase I VO2p was longer in O (31±4 s) than in Y (20±7 s) (p<0.05). In O, the Phase II τVO2p was larger (p<0.05) when fitting started at 15 s and thus included ~15 s of "Phase I" data (49±12 s) compared to 25 s (42±10 s), 35 s (42±12 s), and 45 s (45±15 s). In Y, τVO2p was not affected by the time at which Phase II VO2p fitting started (τVO2p = 31±7 s, 29±9 s, 30±10 s, and 32±11 s for fittings starting at 15 s, 25 s, 35 s, and 45 s, respectively). Fitting from 25 and 35 s resulted in the smallest τVO2p CI in both O and Y. CONCLUSION: Fitting Phase II VO2p from (but not constrained to) 25 s or 35 s provides consistent estimates of VO2p kinetics parameters in Y and O, despite the fact that O had a longer Phase I VO2p compared to Y. Supported by: CIHR, NSERC, Standard Life Assurance Company of Canada.
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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 | 0.001 | 0.002 |
| 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".