Velocity-dependent Power Loss In The Knee Extensors Of Young And Old Men
Bibliographic record
Abstract
Neuromuscular fatigue, defined as any exercise induced reduction in the ability to generate force or power can be influenced by age, muscle group and contraction type. During isometric tasks old adults incur less muscle fatigue than young, but whether this advantage for fatigue-resistance is found for velocity-dependent dynamic tasks has not been well explored. With dynamic fatiguing contractions both torque and velocity of the contraction can contribute to changes in power. PURPOSE: To investigate the contributions of fatigue-related declines in shortening velocity in 10 young (∼25 y) and 10 old (∼75 y) healthy men. METHODS: Neuromuscular measures were collected from the knee extensors at baseline and during a bout of 30 maximal velocity-dependent shortening contractions at 20% maximal voluntary isometric contraction (MVC), using a Biodex System 3 dynamometer. Measures included: electrically evoked twitch properties, MVCs, voluntary activation, maximal velocity-dependent power and ratings of perceived exertion (RPE). RESULTS: At baseline MVC and twitch torques were 32% and 37% less, respectively, contraction duration (time to peak twitch + half relaxation time) of the twitch was 12% longer, and velocity-dependent power was 46% lower than the young. Both groups were capable of high voluntary activations (>95%). At fatigue in both groups MVC and twitch torque were reduced to ∼70% and ∼85% of baseline. Contraction duration of the twitch was lengthened to ∼120% in the old men, with no change in the young. The young decreased to ∼80% of baseline power by task termination (30 contractions), while the old decreased to ∼80% of baseline power by the 20th contraction, with a further reduction to ∼63% of baseline at task termination. During fatigue, RPE increased similarly in both groups from 5 to 8. CONCLUSIONS: Despite similar reductions in MVC the old men fatigued to a greater extent and at a faster rate than the young during the velocity-dependent contractions. The results suggest fatigue-related declines in shortening velocity contributed to power reduction, especially in the older group. Such loss of the capacity to generate muscle power in a fatigued state could potentially impair tasks of daily living. Supported by NLCAHR and 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 | 0.001 | 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".