Metabolite Accumulation And Power Output During And After Fatiguing Exercise In Young And Older Adults
Bibliographic record
Abstract
Fatigability of limb muscles during high-intensity dynamic exercise is postulated to be determined by the accumulation of metabolites, namely hydrogen ions (H+) and inorganic phosphate (Pi). We previously showed that the increased fatigability of older adults during dynamic exercise was accompanied by a greater accumulation of metabolites compared with young adults. However, the time course of metabolite accumulation in relation to power output during and after dynamic fatiguing exercise is unknown. PURPOSE: Determine the time course of metabolite accumulation and changes in power during lower limb fatiguing exercise and recovery in young and older adults. METHODS: 9 young (20-36 yrs; 5 women) and 8 older adults (69-77 yrs; 4 women) performed a 4-min fatiguing knee extension exercise (1 maximal velocity contraction every 2 s) lifting a load equivalent to 20% of their maximal voluntary isometric contraction while prone in the bore of an MRI scanner. Recovery was measured with sets of 5 maximal dynamic contractions (1 every 2 s) at 30, 60, 150, 300, and 600 s after exercise. Intramuscular [Pi] and [H+] were measured with 31P-MRS, and statistical parametric mapping was used to evaluate the time course differences between the metabolite accumulation and power during exercise and recovery. RESULTS: Fatigability was ~1.6-fold greater in older than young adults (P < 0.001), which was accompanied by a greater decrease in pH (6.71 ± 0.07 vs. 6.62 ± 0.10, P = 0.043) and increase in Pi (24.7 ± 2.4 mM vs. 32.2 ± 5.6 mM, P = 0.002) by the end of exercise. Except for the first 32 s of exercise where pH increased while power decreased, the time course of H+ accumulation and power loss was similar. However, after exercise H+ continued to increase for 60s as power was recovering. In contrast, Pi accumulated more rapidly than the loss in power for the first 152 s of exercise, after which Pi no longer accumulated but power continued to decrease. After exercise, the recovery of power and Pi followed a similar time course. There were no age effects on the relationship between power output and metabolites at any time point during or after exercise. CONCLUSIONS: These data suggest that both H+ and Pi are essential metabolites disrupting power during and in recovery from fatiguing exercise and that the effects of these metabolites are similar in young and older adults. Supported by NIA R01 grant (AG048262) to Christopher Sundberg, Robert Fitts and Sandra Hunter.
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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".