Blood pressure responses to static and dynamic knee extensor exercise between sexes: Role of absolute contraction intensity

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Males have larger blood pressure (BP) responses to relative intensity static handgrip exercise compared to females. Controlling for maximal voluntary contraction (MVC) absolute strength abolishes these differences. Whether similar observations exist during large muscle mass exercise or dynamic contractions remain unknown. BP, heart rate, muscle oxygenation (near-infrared spectroscopy), and rectus femoris electromyography (EMG) were recorded in 28 males and 17 females during 10% and 30% MVC static (120s) and isokinetic dynamic (180s; 1:2 work-to-rest ratio; angular velocity: 60º/s) knee extensor exercise. At baseline and during exercise, continuous BP and heart rate were measured using finger photoplethysmography and single-lead electrocardiography, respectively. MVC, as well as all submaximal exercise testing, was measured and performed on a dynamometer at 80⁰ of knee flexion, and voluntary activation was assessed using the interpolated twitch technique, with ≥90% voluntary activation of the knee extensors set as the acceptable activation threshold. Static and dynamic exercises were completed on separate visits, in a randomized order. The change from baseline of each variable was calculated for every 30 s during each submaximal test. Sex differences were then examined with and without statistical adjustment of MVC using analyses of covariance (ANCOVA). The males were taller and heavier than the females and had higher resting systolic BP (all P<0.05), while BMI, resting diastolic and mean arterial BP, and heart rate were similar between sexes (all P>0.05). Knee extensor MVC was higher in males than females (165 ± 40 vs. 94 ± 22 Nm, P<0.0001). Males had larger systolic BP responses (interaction, P<0.001) and muscle deoxygenation (interaction, P<0.01) than females during 10% static exercise, with no difference in EMG (interaction, P=0.73). Peak systolic BP was correlated to MVC (r=0.53, P=0.0002), and adjustment for MVC abolished sex differences in systolic BP (interaction, P=0.5). BP, heart rate, muscle oxygenation/deoxygenation, and EMG responses did not differ between sexes during 30% static exercise (interaction, All P>0.2), including following adjustment for MVC (All P>0.1). Males had larger systolic BP responses during dynamic exercise at 10% and 30% (interaction, Both P=0.01), which were abolished after adjustment for MVC (interaction, Both P>0.08). Systolic BP responses at 180s were correlated with MVC and stroke volume responses during 10% (r=0.31, P=0.04; r=0.61, P<0.0001, respectively) and 30% (r=0.4, P=0.007; r=0.59, P<0.0001, respectively). In conclusion, MVC can influence systolic BP responses to 10% but not 30% MVC static, as well as 10% and 30% MVC dynamic knee extensor exercise. MVC should be considered when comparing BP responses between males and females. Finally, the mechanisms mediating the larger pressor responses in stronger individuals across different exercise modalities warrant further investigation.