TY - JOUR
T1 - Effect of body tilt on calf muscle performance and blood flow in humans
AU - Egaña, Mikel
AU - Green, Simon
PY - 2005/6
Y1 - 2005/6
N2 - 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°) to upright (90°) 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°). In Experiment 2, seven subjects performed a strength test and. constant-force test [70% maximum force (Fmax); intermittent contractions] to the point of failure in the horizontal and three inclined positions (32, 47, and 67°). In experiment 3, leg blood flow was assessed during constant-force exercise at two intensities (30 and 70% Fmax) and two tilt angles (0 and 67°) 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° (25.9 ± 2.0 min) and 90° (25.1 ± 3.0 min) than 0° (22.2 ± 2.6 min). Time to failure during the constant-force test was also significantly higher at 32° (7.1 ± 3.6 min), 47° (8.0 ± 5.2 min), and 67° (8.6 ± 5.6 min) compared with 0° (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.
AB - 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°) to upright (90°) 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°). In Experiment 2, seven subjects performed a strength test and. constant-force test [70% maximum force (Fmax); intermittent contractions] to the point of failure in the horizontal and three inclined positions (32, 47, and 67°). In experiment 3, leg blood flow was assessed during constant-force exercise at two intensities (30 and 70% Fmax) and two tilt angles (0 and 67°) 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° (25.9 ± 2.0 min) and 90° (25.1 ± 3.0 min) than 0° (22.2 ± 2.6 min). Time to failure during the constant-force test was also significantly higher at 32° (7.1 ± 3.6 min), 47° (8.0 ± 5.2 min), and 67° (8.6 ± 5.6 min) compared with 0° (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.
KW - Endurance
KW - Fatigue
KW - Strength
UR - http://www.scopus.com/inward/record.url?scp=19444368462&partnerID=8YFLogxK
U2 - 10.1152/japplphysiol.01235.2004
DO - 10.1152/japplphysiol.01235.2004
M3 - Article
C2 - 15661836
AN - SCOPUS:19444368462
SN - 8750-7587
VL - 98
SP - 2249
EP - 2258
JO - Journal of Applied Physiology
JF - Journal of Applied Physiology
IS - 6
ER -