Influence of Motor Unit Activity on Sex Differences in Force Steadiness
Bibliographic record
Abstract
Influence of Motor Unit Activity on Sex Differences in Force Steadiness Ruth E. Brown, Nikki Karn and Jennifer M. Jakobi., University of British Columbia Okanagan, Kelowna, BC Force steadiness is the ability to maintain an isometric contraction around a given force level. Men are steadier than women, in part due to strength differences. Motor unit activity, in particular discharge rate variability might also contribute to differences in force steadiness. PURPOSE: to determine if sex differences in forces steadiness are due to differences in motor unit activity (discharge rate and discharge rate variability). METHODS: Eight young men (24 ± 3 years) and ten young women (22 ± 3 years) participated. Subjects were seated in an adjustable chair with the left (non-dominant) elbow flexed to 90° and the wrist placed in a neutral position. Fine wires were inserted into the short (SBB) and long heads of the biceps brachii (LBB) to record single motor unit activity at 5, 10 and 25% MVC. Subjects ramped up to the target line and were instructed to hold steady forces for 7.5 seconds. Three contractions were performed at each force level. Force steadiness was determined as the co-efficient of variation (CV = standard deviation/mean force). Sex comparisons were made using t-tests. RESULTS: Men (266 ± 43 N) were stronger than women (143 ± 17 N) (p < 0.01) and more steady (p < 0.05) at all force levels. Men (10.8 ± 2) had a lower motor unit discharge rate (MUDR) than women (12. 0 ± 2) in the SBB at 5% MVC (p < 0.1) but there was no sex difference in the LBB (11.3 ± 2 men; 11.8 ± 2 women) (p > 0.05). At 10% MVC, men (12.0 ± 2; 13.7 ± 2.0) had a lower MUDR compared to women (14. 6 ± 1.7; 14.1 ± 0.1) in the SBB and LBB, respectively (p < 0.05). At 25% MVC there was no sex-related difference in MUDR for either the SBB (15.7 ± 2.8 men; 15.8 ± 2.9 women) or LBB (16.6 ± 3.4 men; 16.8 ± 3 women) (p > 0.05). MUDR variability was similar between men and women at all force levels (p > 0.05). CONCLUSIONS: differences in force steadiness between men and women might relate to higher discharge rates at low relative force levels in women compared to men. 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 | 0.003 |
| 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) | 0.005 | 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".