Author(s): IZUMI, K., KATAYAMA, K., TANAKA, N., KANO, Y., AKIMA, H., Institution: NAGOYA UNIVERSITY, Country: JAPAN, Abstract-ID: 1575

INTRODUCTION:
Blood flow plays an important role in supplying oxygen to the exercising muscles. The impairment of oxygen supply via blood flow profoundly impacts exercise performance. Previous studies have shown a heterogeneity of the metabolic responses among the quadriceps muscle. For example, intramuscular blood flow measured by positron emission tomography is heterogeneous within the quadriceps muscle. Moreover, the kinetics of muscle deoxygenation during incremental exercise differ among muscles in the quadriceps. However, it is unknown the dynamics of intramuscular blood flow and its relationship to muscle deoxygenation within the quadriceps femoris. Therefore, the purpose of this study was to evaluate the changes in intramuscular blood flow, muscle deoxygenation, and their relationship in different muscles of the quadriceps femoris.
METHODS:
Thirteen healthy young men (19.4 ± 1.0 years) performed intermittent (5-second contraction, 5-second relaxation) and incremental isometric knee extensions. The exercise began at 30% of maximal voluntary contraction (MVC) and increased by 10% for every five contractions to 70% of MVC until task failure. Intramuscular blood flow using power Doppler ultrasonography and muscle deoxygenation using near-infrared spectroscopy (NIRS) were simultaneously measured from the vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM) in randomized order over 3 days. All variables were measured up to 5 minutes after task failure and averaged every 30 seconds. NIRS measurement provided muscle oxygen saturation (StO2) and deoxy-hemoglobin/myoglobin (deoxy-Hb/Mb).
RESULTS:
There were no significant differences in ΔIntramuscular blood flow, ΔStO2, and the ratio between intramuscular blood flow and deoxy-Hb/Mb among three muscles during exercise. However, significant regional differences were observed for all parameters after exercise. ΔIntramuscular blood flow was significantly higher in the RF (3 minutes; 1698.5 ± 1038.1 a.u., 4 minutes; 1573.9 ± 950.0 a.u.) than in the VL after 3 minutes post-exercise (824.6 ± 855.5 a.u., P = 0.009) and in the VM after 4 minutes post-exercise (713.7 ± 529.3 a.u., P = 0.037). ΔStO2 was significantly higher in the RF (3 minutes; 12.08 ± 5.36 %, 3.5 minutes; 11.78 ± 5.70 %) than in the VL after 3 minutes post-exercise (6.87 ± 3.11 %, P = 0.025) and in the VM after 3.5 minutes post-exercise (7.18 ± 5.88 %, P = 0.044). The ratio between intramuscular blood flow and deoxy-Hb/Mb was significantly higher in the RF (1.5 minutes; 15.10 ± 7.77 a.u. × 10^4, 3.5 minutes; 15.31 ± 9.74 a.u. × 10^4) than in the VL after 1.5 minutes post-exercise (9.31 ± 6.45 a.u. × 10^4, P = 0.044) and in the VM after 3.5 minutes post-exercise (4.94 ± 4.15 a.u. × 10^4, P = 0.016).
CONCLUSION:
These results suggest that the metabolic requirements in the RF are different from other quadriceps femoris during fatiguing knee extension.