Partial neuromuscular blockade and cardiovascular responses to static exercise in man.
Level 3 - non-randomized controlled study
Non-randomized within-subject experimental laboratory study
PubMed 3999043 · doi:10.1113/jphysiol.1985.sp015590
What was done
Human subjects performed sustained static contractions of the quadriceps femoris in one leg at identical absolute and relative intensities before and after partial neuromuscular blockade (using either decamethonium or tubocurarine to reduce strength to ~50% of control values). The metabolic component of the exercise pressor reflex was evaluated by applying an arterial occlusion cuff 30 seconds before exercise cessation and maintaining it for 3 minutes of rest. Muscle biopsies from the vastus lateralis were analyzed for fast- and slow-twitch fiber composition.
What was found
No numerical values or variance measures were provided in the abstract for cardiovascular parameters. The reported findings were: - At the same absolute force, heart rate and blood pressure responses were greater during neuromuscular blockade compared to control contractions. - At the same relative force, cardiovascular responses were almost the same with and without blockade. - These effects occurred regardless of whether decamethonium or tubocurarine was used. - Post-exercise circulatory occlusion caused higher post-exercise heart rate and blood pressure values both with and without blockade. - Muscle fiber composition ranged from 27% to 66% slow-twitch fibers and showed no correlation with cardiovascular responses.
Why it matters
This study shows that central command and reflex neural mechanisms operate redundantly to set cardiovascular responses during static exercise, with central command predominating when effort becomes disproportionate to muscle tension.
Limits
The abstract does not state sample size, subject characteristics (e.g., sex, age), or quantitative cardiovascular measurements. It evaluates an acute pharmacological blockade in healthy volunteers, which may not fully represent chronic neuromuscular conditions.
Cited by
- supports Experiments by Jere Mitchell and Niels Secher using curare nerve blocks demonstrated that attempt to contract paralyzed muscle causes heart rate to rise through Central Command independent of actual muscle contraction.