Effect of body tilt on calf muscle performance and blood flow in humans

Abstract

To explore the effect of posture on muscle performance, we tested the effects of body tilt angle on the strength, endurance, and fatigue of, and blood flow into, the plantar flexors. Human subjects were fixed to a tilt table that could tilt them from the horizontal (0 degrees ) to upright (90 degrees ) position and enabled force to be applied to a footplate through isometric action of the right calf muscle. In experiment 1, six subjects performed a strength test and graded test (intermittent contractions) to the point of failure at three tilt angles (0, 47, and 90 degrees ). In Experiment 2, seven subjects performed a strength test and constant-force test [70% maximum force (F(max)); intermittent contractions] to the point of failure in the horizontal and three inclined positions (32, 47, and 67 degrees ). In experiment 3, leg blood flow was assessed during constant-force exercise at two intensities (30 and 70% F(max)) and two tilt angles (0 and 67 degrees ) in six subjects. Strength was not affected (P > 0.05) by tilt angle. Time to failure during the graded test was significantly higher at 47 degrees (25.9 +/- 2.0 min) and 90 degrees (25.1 +/- 3.0 min) than 0 degrees (22.2 +/- 2.6 min). Time to failure during the constant-force test was also significantly higher at 32 degrees (7.1 +/- 3.6 min), 47 degrees (8.0 +/- 5.2 min), and 67 degrees (8.6 +/- 5.6 min) compared with 0 degrees (4.0 +/- 2.6 min). When graded or constant-force exercise was performed with arterial flow to the leg eliminated, there were no differences in exercise time between the horizontal and an inclined position. During nonischemic exercise, leg blood flow was significantly higher during exercise in the inclined position. These results demonstrate that head-up tilt improves endurance of the plantar flexors, that this effect occurs in the absence of an effect on strength, and that it depends on an intact peripheral circulation. Moreover, the postural effect on muscle endurance appears to be due to a greater blood flow into the leg, an effect that is established during the initial contractions.

Effect of type 2 diabetes on the dynamic response characteristics of leg vascular conductance during exercise

“…In contrast, neither the end-exercise value or phasic amplitudes of LVC were significantly affected by type 2 diabetes ( Table 2), suggesting that the capacity to vasodilate under exercise conditions that evoke near-maximal blood flows 18 remains intact. However, the phase 1 amplitude and endexercise value for LVC was 15-20% lower in the diabetic group and, although this difference was not significant, the large between-subject variation in responses might have obscured an important physiological difference which warrants further investigation.…”

“…Then, on a following day, the subject rested for 20 min in the supine position during which resting cardiovascular measurements were made (see the 'Leg vascular conductance' section), before being tilted upright to the inclined position and commencing calf exercise soon after. 18 Calf exercise consisted of intermittent and static contractions of the calf muscle (6 s duty cycle: 2 s contraction, 4 s relaxation) at a target force of 70% MVC. Each subject performed three calf exercise trials, separated by 20-30 min of rest in the supine position, and the duration of each exercise trial was 6 minutes.…”

“…18 For each of the three exercise trials this yielded 60 measurements of these three variables. Leg blood flow was measured during calf exercise using venous occlusion strain-gauge plethysmography, 18 a technique which provides similar estimates of limb blood flow during exercise when compared with Doppler ultrasound. 22 Briefly, a thigh cuff was inflated before exercise and maintained throughout exercise at a pressure of 55 mmHg.…”

Hemodynamic responses during graded and constant-load plantar flexion exercise in middle-aged men and women with type 2 diabetes

“…All participants visited the cardiovascular performance laboratory at Trinity College Dublin on two or three separate occasions separated by at least 48 h. Of the female subjects, six were premenopausal (1 with T2D and 5 nondiabetics), and their testing dates were scheduled to occur during the midfollicular phase of their menstrual cycle (days [5][6][7][8][9][10][11][12]. Before each visit subjects were asked to refrain from consuming caffeine and alcohol in the 24 h prior to testing, in addition to limiting exercise to activities of daily living.…”

Perfusion pressure and movement-induced hyperemia: evidence of limited vascular function and vasodilatory reserve with age

“…In contrast, an upright posture produces a hydrostatic column, shifting blood to the lower limbs and differentially increasing both leg arterial and venous pressure, such that femoral perfusion pressure (FPP) is increased. Therefore, as a consequence of this posture-induced increase in FPP, resting LBF may be elevated (12). Furthermore, young males exhibit a significant vasodilatory reserve (difference in ⌬LVC peak between uprightseated and supine posture) that facilitates a LBF response to passive movement in the upright-seated posture that is more than double that of the supine posture (47).…”