Inter‐individual Variability in Muscle Sympathetic Nerve Activity during Static Handgrip in Healthy Young Men
Bibliographic record
Abstract
Cardiovascular responses at the onset of static handgrip are thought to be governed primarily by activation of higher brain regions (central command) and stretch‐sensitive group III/IV skeletal muscle afferents (muscle mechanoreflex), whereas responses during more prolonged contractions also involve activation of chemically‐sensitive group III/IV afferents (muscle metaboreflex). However, the contribution of central command to the muscle sympathetic nerve activity (MSNA) response at exercise onset is unclear. Existing evidence suggests that central stressors (e.g. mental stress) can either increase or decrease MSNA, identifying two populations of responders. We hypothesized that considerable inter‐individual variability may exist also at the onset of static handgrip, when the net contribution of central command is greatest. Continuous supine measurements of multi‐unit MSNA (microneurography) and blood pressure (Finometer) were recorded in 28 healthy men (24±5 years) during 2 minutes of static handgrip (30% maximal voluntary contraction) and 3 minutes of post‐exercise circulatory occlusion (PECO). Participants were divided into high (n=14) and low (n=14) MSNA responders based on the median MSNA burst frequency response during the first minute of static handgrip. High responders demonstrated greater MSNA responses during the first (Δ6±5 vs. −3±3 bursts/min, p<0.001) and second (Δ13±5 vs. 5±6 bursts/min, p<0.001) minute of handgrip and during the last minute of PECO (Δ9±7 vs. 4±6 bursts/min, p<0.05) compared to low responders. However, the change in MSNA between the first and second minute of handgrip was similar between high and low responders (Δ6±7 vs. 7±4 bursts/min, p>0.05). The increases in mean arterial pressure during handgrip (minute one: Δ9±6 vs. 7±4 mmHg; minute two: Δ20±9 vs. 16±9 mmHg) and PECO (Δ15±9 vs. 12±8 mmHg) were similar between high and low responders (All p>0.05), as were changes in heart rate, stroke volume, cardiac output, and total vascular conductance (All p>0.05). Examining the individual data as a continuous variable, the changes in MSNA and mean arterial pressure were unrelated during the first minute of handgrip (r=0.04, p>0.05), but related positively during the second minute of handgrip (r=0.50, p<0.01) and last minute of PECO (r=0.50, p<0.01). In summary, MSNA responses at the onset of static handgrip in young healthy men are highly variable and exhibit a dissociation with the pressor response. Support or Funding Information This research was supported by a Natural Science and Engineering Research Council (NSERC) of Canada Discovery Grant (P.J.M), the Canada Foundation for Innovation (P.J.M.), University of Guelph‐Humber Research Grant (P.J.M), and a Canadian Institutes of Health Research Fredrick Banting and Charles Best Canada Graduate Scholarship (A.V.I.).
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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".