Key result
Maximal LBNP reduces arterial-cardiac baroreflex gain in endurance athletes but increases it in sedentary men.
Why the study?
Does physical fitness level alter cardiac autonomic activity and arterial-cardiac baroreflex function after severe orthostatic stress induced by maximal lower body negative pressure in healthy men?
Observational (n=22)
Does physical fitness level alter cardiac autonomic activity and arterial-cardiac baroreflex function after severe orthostatic stress induced by maximal lower body negative pressure in healthy men?
Severe orthostatic stress via maximal LBNP divergently affects baroreflex function based on fitness level, enhancing arterial-cardiac baroreflex gain in sedentary men while reducing it in endurance athletes.
Answers are grounded in this paper and cite their sources.
Fitness-specific baroreflex responses to orthostatic stress should not yet change practice; leaves open training effects on autonomic adaptation.
INTRODUCTION: This study evaluated cardiac autonomic activity and arterial-cardiac baroreflex function before and after severe orthostatic stress induced by lower body negative pressure (LBNP) in healthy sedentary men and endurance athletes. METHODS: Thirteen healthy sedentary men (Sed) and nine age-matched highly trained male endurance athletes (Fit) were recruited. Participants underwent a single maximal LBNP protocol, with negative pressure increased to -15, -30, and -40 mmHg every 5 min, followed by additional -10 mmHg increments every 3 min until presyncope. RR interval and systolic blood pressure were recorded for 5 min during controlled breathing at 0.2 Hz before and after recovery from maximal LBNP. RESULTS: Heart rate was lower in Fit than in Sed, with no significant pre-to-post change after LBNP. Low-frequency transfer function gain between systolic blood pressure and RR interval showed a significant group-by-time interaction, increasing in Sed (5.9 ± 1.8 to 8.0 ± 1.4 ms/mmHg) but decreasing in Fit (12.2 ± 7.5 to 9.7 ± 5.2 ms/mmHg). Low-frequency RR interval variability also showed a significant interaction, increasing in Sed and decreasing in Fit, whereas high-frequency RR interval variability showed a similar but non-significant pattern. DISCUSSION: Severe orthostatic stress induced by maximal LBNP enhanced arterial-cardiac baroreflex gain in sedentary men but decreased it in endurance athletes. This response may be associated with enhanced vagally mediated cardiac modulation in sedentary individuals.
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Suzuki et al. (2026) conducted an observational in Healthy sedentary men and male endurance athletes undergoing severe orthostatic stress (n=22). High physical fitness (endurance athletes) undergoing maximal lower body negative pressure vs. Healthy sedentary men undergoing maximal lower body negative pressure was evaluated on Low-frequency transfer function gain between systolic blood pressure and RR interval (arterial-cardiac baroreflex gain). Maximal lower body negative pressure decreased arterial-cardiac baroreflex gain in endurance athletes (12.2 to 9.7 ms/mmHg) but increased it in sedentary men (5.9 to 8.0 ms/mmHg).
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