Cardiac Responses to Isometric Exercise

Abstract

The time course of cardiocirculatory responses to different levels of isometric handgrip (IHG) in sitting position were studied noninvasively in normal males and compared to supine IHG results in the same subjects. Control Comparisons. Resting postural differences were as expected: sitting heart rates (HR), pre-ejection phase (PEP) and PEP/LVET were higher while left ventricular ejection time (LVET) and ejection time index (ETI) were lower than those supine (P < 0.05 to P < 0.001). The following trends, while not statistically significant, were also noted: systolic and diastolic blood pressure were lower while pressure-rate product (PRP), the interval from appearance of the Q wave to the first major "mitral" component of the first heart sound (Q-I M ), and isovolumic contraction time (IVCT) tended to be higher than those supine. Isometric Exercise. The supine IHG results are consistent with data reported in the literature. During sitting IHG at 15% maximum voluntary contraction (MVC) there was no statistical change in any parameter measured. At 30%, 50%, and 100% MVC there were increases in HR, systolic and diastolic pressures, and PRP. At 30% MVC, Q-I M and pulse transmission time (PTT) decreased, ETI increased and IVCT, PEP, LVET, and PEP/LVET did not change significantly. At 50% MCV, Q-I M , IVCT, PEP, LVET, PEP/LVET and PTT shortened while ETI increased. At 100% MCV, Q-I M , IVCT, PEP, and LVET shortened but no significant changes occurred in PEP/LVET or ETI. When sitting IHG was compared to supine IHG the end points of exercise yielded statistically similar values for systolic and diastolic pressures, PRP, Q-I M , IVCT, PEP, and PTT. LVET and ETI were consistently lower ( P < 0.02) while HR and PEP/LVET were higher for sitting vs supine IHG. Standard errors were smaller supine, a finding that indicates greater homogeneity of response in this posture and probably explains why some changes in cardiac parameters at lower levels of IHG reached statistical significance in the supine but not the sitting position. The changes in systolic intervals are consistent with the increased contractility resulting from IHG. Lack of uniform decreases in PEP/LVET with higher levels of IHG, however, were believed to reflect decreased myocardial adaptability to higher pressure (vs volume) loads. Decreases in pulse transmission time appeared to be influenced by diastolic pressure increases which were directly related to the levels of IHG. Once resting postural differences are accounted for, however, the effect of posture on IHG is not very great and certainly does not present the disparity which exists between sitting and supine rhythmic exercise. Most responses were directly related to the level of exertion, with greater changes occurring at the higher levels of IHG. For noninvasive studies, 50% or 100% MVC are the recommended levels of exertion since significant cardiocirculatory responses are greater than at 15% and 30% MVC and occur within one minute.

Cardiovascular Response of Human Subjects to Isometric Contraction of Large and Small Muscle Groups

“…The cardiovascular responses to sustained static (isometric) contraction of striated muscle have been previously described (1)(2)(3)(4)(5)(6). Tuttle and Horvath (2) reported sharp increases in both systolic (SP) and diastolic (DP) pressures and Hymphreys and Lind (3), using graded handgrip contractions, noted a progressive rise in systemic blood pressure (BP) and heart rate (HR).…”

Acute Blood Pressure Response to Different Types of Isometric Exercise: A Systematic Review with Meta-Analysis

“…However, this study performed an intensity of 100% MVC, had a small sample size and measured BP with the intra-arterial method, which affect the BP response identified. Moreover, adopting 120 mmHg as the safety value for DBP [129], some studies that showed values higher than this limit included hypertensive participants [31,81,95], high intensity exercise [44,101,124], long duration of contraction (above 120 seconds) [60,98], very small sample sizes (6 and 7 participants), and sedentary individuals performing six sets of the exercise [42] In the subgroup analyses, men showed higher increases for SBP and DBP in response to handgrip than women. It could be explained by the fact that the majority of studies included young men and women, since premenopausal women seem to present attenuation of sympathetic nervous activity, catecholamine release, mechanoreflex, and the degree of vasoconstriction during exercise compared to men of the same age [130,131].…”

“…However, this study performed an intensity of 100% MVC, had a small sample size and measured BP with the intra-arterial method, which affect the BP response identified. Moreover, adopting 120 mmHg as the safety value for DBP [ 129 ], some studies that showed values higher than this limit included hypertensive participants [ 31 , 81 , 95 ], high intensity exercise [ 44 , 101 , 124 ], long duration of contraction (above 120 seconds) [ 60 , 98 ], very small sample sizes (6 and 7 participants), and sedentary individuals performing six sets of the exercise [ 42 ]…”

Isotonic (Dynamic) and Isometric (Static) Effort in the Assessment and Evaluation of Diastolic Hypertension: Correlation and Clinical Use

“…Since activities involving isometric ef forts (lifting and supporting weights, hand grip) are used many times a day, exaggerated pressure response could be a factor in the maintenance of a high arterial pressure dur ing daily activities in hypertensive persons [34,35], As shown by other studies, systolic blood pressure increases in relation to load, both in normotensive and hypertensive persons [5,34,[36][37][38]. The response of the diastolic blood pressure to the same ergometric load ing is higher in hypertensives and borderline hypertensives than in normotensives [5,10,34,39,40], The isotonic effort was used to distinguish between hypertensives and nor motensives in the population [3][4][5][6][7].…”

“…The response of the diastolic blood pressure to the same ergometric load ing is higher in hypertensives and borderline hypertensives than in normotensives [5,10,34,39,40], The isotonic effort was used to distinguish between hypertensives and nor motensives in the population [3][4][5][6][7]. Other trials showed that gripping at 30% of MVC is enough to increase the blood pressure in all the subjects if it is maintained for several minutes [10,36]. Isometric tests, such as the handgrip test, cause a constant elevation in the diastolic blood pressure by increasing the sympathetic tone.…”