Central and peripheral modulation of exercise pressor reflex sensitivity after nonfatiguing work

Abstract

Autonomic blood pressure control is fundamentally altered during a single bout of exercise, as evidenced by the downward resetting of the baroreflex following exercise (postexercise hypotension). However, it is unclear if an acute bout of exercise is also associated with a change in the sensitivity of the exercise pressor response to a controlled stimulus, such as a static contraction. This study tested the hypothesis that the blood pressure response to a controlled static contraction would be attenuated after unilateral cycling of the contralateral (opposite) leg, but preserved after cycling of the ipsilateral (same) leg. To test this, the blood pressure response to 90 s of isometric plantar flexion [50% maximal voluntary contraction (MVC)] was compared before and after 20 min of contralateral and ipsilateral single-leg cycling at 20% peak oxygen consumption and rest (control) in 10 healthy subjects (three males and seven females). The mean arterial pressure response was significantly attenuated after contralateral single-leg cycling (+9.8 ± 7.5% ∆mmHg vs. +6.7 ± 6.6% ∆mmHg pre and postexercise, respectively, P = 0.04) and rest (+9.0 ± 7.5% ∆mmHg vs. +6.6 ± 5.2% ∆mmHg pre and postexercise, respectively, P = 0.03). In contrast, the pressor response nonsignificantly increased following ipsilateral single-leg cycling (+5.5 ± 5.2% ∆mmHg vs. +8.9 ± 7.2% ∆mmHg pre and postexercise, respectively, P = 0.08). The heart rate, leg blood flow, and leg conductance responses to plantar flexion were not affected by any condition (P ≥ 0.12). These results are consistent with the notion that peripheral, but not central mechanisms promote exercise pressor reflex sensitivity after exercise.

Keywords: autonomic; blood pressure; neurovascular; pressor response.

Fig. 1.

A timeline of the experimental visits 2–4. Each visit began with a 2-min baseline, followed by 90 s of plantar flexion (PF) and 60 s of postexercise cuff occlusion (PECO) of each subject’s nondominant leg. Next, subjects performed 20 min of contralateral single-leg cycling, ipsilateral single-leg cycling, or control (rest), followed by a final PF + PECO assessment of the nondominant leg. The order of exercise stimuli was counterbalanced between conditions. The red stripe indicates active skeletal muscle, and the blue stripe indicates the location of the occlusion cuff used to elicit PECO.

Fig. 2.

Mean arterial pressure (MAP) expressed as a percent change during plantar flexion (PF) at the baseline and after control (top), ipsilateral single-leg cycling (middle), and contralateral single-leg cycling (bottom). Linear mixed models indicated that the MAP response to plantar flexion was significantly attenuated after contralateral single-leg cycling and control, but was preserved after ipsilateral single-leg cycling (MAP: F_{2,2 5} = 6.54, P = 0.005). *P ≤ 0.05. Data are presented as means ± SD and Cohen’s-D (d) is provided as an estimate of effect size for each individual comparison.

Fig. 3.

Changes in leg conductance (mL·min⁻¹·mmHg⁻¹) from rest to plantar flexion (PF) pre and postcontrol (top), ipsilateral single-leg cycling (middle), and contralateral single-leg cycling (bottom). Although leg conductance tended to increase during plantar flexion, linear mixed models analyses indicated that neither the contralateral cycling condition, the ipsilateral cycling condition, nor the control condition influenced the magnitude of this response. Data are presented as means ± SD and Cohen’s-D (d) is provided as an estimate of effect size for each individual comparison.

Fig. 4.

Mean arterial pressure (MAP) expressed as a percent change during postexercise cuff occlusion (PECO) at the baseline and after control (top), ipsilateral single-leg cycling (middle), and contralateral single-leg cycling (bottom). Despite an apparent decrease in MAP after control, linear mixed models indicated no significant interaction, or main effects of time or condition for the MAP response to PECO. Data are presented as means ± SD and Cohen’s-D (d) is provided as an estimate of effect size for each individual comparison.

Fig. 5.

Changes in leg conductance (mL·min⁻¹·mmHg⁻¹) from rest to postexercise cuff occlusion (PECO) pre- and postcontrol (top), ipsilateral single-leg cycling (middle), and contralateral single-leg cycling (bottom). Although leg conductance tended to increase during PECO, linear mixed models analyses indicated that neither the contralateral cycling condition, the ipsilateral cycling condition, nor the control condition influenced the magnitude of this response. Data are presented as means ± SD and Cohen’s-D (d) is provided as an estimate of effect size for each individual comparison.