Ho. Hisaeda et al., Effect of local blood circulation and absolute torque on muscle endurance at two different knee-joint angles in humans, EUR J A PHY, 86(1), 2001, pp. 17-23
The effects of the local blood circulation and absolute torque on muscle en
durance at different knee-joint angles were determined. The rate of muscle
deoxygenation (using near-infrared spectroscopy), and the rate of muscle fa
tigue (using the slope of integrated electromyography. iEMG) were evaluated
concurrently. Nine healthy subjects performed submaximal (50% maximal volu
ntary contraction. MVC) static knee extension at 50 degrees (extended posit
ion, EXT) and 90 degrees (flexed position, FLEX) joint angles until the tar
get torque could no longer be maintained: that time was measured as the end
urance time. They exercised with the circulation occluded (OCCL), and witho
ut (FREE) to study the possible effects of the local circulation. Although
MVC torque was independent of joint angle [mean (SID) FLEX 250.6 (51.7) N(.
)m and EXT 246.5 (46.6) N(.)m], significantly shorter (P < 0.01) endurance
time in FLEX [FREE 71.1 (10) s and OCCL 63.1 (8.8) s] than at EXT [FREE 115
.3 (30) s and OCCL 106.7 (29.1) s] were obtained in both circulatory condit
ions. The iEMG-time slope was significantly greater in FLEX at the proximal
and distal portion (P < 0.05) in both circulatory conditions. Muscle deoxy
genation rate in OCCL was significantly greater (P < 0.05) at FLEX [20.8 (8
.0)%] than EXT [10.9 (4.0)%]. The results would suggest that different knee
-joint angle affects muscle endurance even if the local circulation is cont
rolled. Circulatory disturbance would further reduce muscle endurance in EX
T, but not in FLEX. Because of the greater muscle internal force in FLEX. l
ocal blood flow might be already limited even with a free circulation. The
greater muscle deoxygenation and muscle fatigability would be related to th
e shorter muscle endurance in FLEX.