CAFFEINE INCREASES ENDURANCE WITHOUT ALTERING AVERAGE MOTOR UNIT FIRING RATE DURING SUBMAXIMAL FATIGUING CONTRACTIONS
Bibliographic record
Abstract
We have recently demonstrated the ergogenic effects of caffeine during submaximal isometric contractions. However, changes in contractile properties, motor unit activation, surface EMG, and M-wave do not account for the prolonged endurance. Caffeine has excitatory actions on the nervous system and we hypothesized that during fatigue caffeine may alter average motor unit firing rate (AMUFR) at the limit of endurance (Tlim) through some central mechanism. PURPOSE: To determine if the improved endurance performance following caffeine ingestion is the result of altered AMUFR during a fatigue protocol. METHODS: In this randomized, double-blind, repeated-measures experiment, 6 male subjects reported to the laboratory on 2 separate days. Following pre-test measures, each received either caffeine (6mg/kg) or placebo (flour) capsule and then waited 1h before completing the fatigue protocol. This protocol consisted of repeated isometric contractions of the quadriceps (50% MVC) held for 15s, with 2s of rest between contractions. Tlim was defined as the point at which force fell below 45% MVC for longer than 2s during the contractions. Tungsten intramuscular microelectrodes were used to determine the firing rates of single motor units. RESULTS: Tlim occurred at (mean ± SE) 137.7 ± 21.1s and 109.8 ± 16.4s in the caffeine and placebo treatments respectively (p < 0.05). This represented a 27.1 ± 9.4% (p < 0.05) increase in Tlim after caffeine ingestion. The AMUFRs of 95 motor units were compared at 3 time points (onset, 50 and 100% of Tlim) and were not different between the caffeine or placebo conditions at any time. During the fatigue protocol, there was no change in AMUFR from onset to Tlim in either condition. During the first contraction, AMUFR was 13.0 ± 0.9Hz in caffeine and 13.4 ± 1.4Hz in placebo conditions. At Tlim, AMUFR was 13.0 ± 0.9Hz in caffeine and 13.4 ± 1.4Hz in placebo conditions. CONCLUSION: These data suggest that the ergogenic effects of caffeine do not involve alterations in AMUFR during repeated submaximal isometric contractions. 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) | 0.001 | 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".