People with down syndrome exhibit a blunted hemodynamic response to isometric handgrip but not cycling exercise

People with Down syndrome (DS) have a depressed heart rate (HR) and blood pressure (BP) response to exercise. We tested the hypothesis that people with DS, compared to controls (CON), would have more blunted HR and BP responses to isometric rather than dynamic cycling exercise. Twenty-eight individuals with DS and 14 controls (16-40 years) completed a 6-min cycling exercise at 50% body weight and 2-min handgrip isometric exercise at 30% maximum voluntary contraction (MVC). HR and BP were sampled via a single-lead system and finger photoplethysmography, respectively. Hemodynamic responses to both exercises were tested with linear mixed models. Individuals with DS showed a blunted HR increase to handgrip (DS: difference (d)_60s-rest= 3, 95% CI: -10 to 4 bpm, p = 0.989; CON: d_60s-rest = 16, 95%CI: 6 to 26 bpm, p < 0.001) but not cycling exercise (DS: d_60-rest = 21, 95%CI: 6 to 26 bpm, p < 0.001). Exercise-induced increases in mean arterial pressure were smaller in people with DS during handgrip (DS: d_60s-rest = 7, 95% CI: 3-12 mmHg, p < 0.001; CON: d_60s-rest = 15, 95% CI: 12 to 22 mmHg, p < 0.001) but not during cycling exercise (DS: d_60s-rest = 13, 95% CI: 7 to 18 mmHg, p < 0.001; CON: d_60s-rest= 8, 95% CI:1 to 16 mmHg). Controlling for group differences in resting BP, fitness, %peak HR and MVC did not change results. People with DS exhibited a blunted hemodynamic response to isometric, but not dynamic cycling exercise, suggesting that HR and BP control differ between these two exercise modes in this population.