COACTIVATION PATTERNS IN THE QUADRICEPS BY MUSCLE FUNCTIONAL MAGNETIC RESONANCE IMAGING
Hiroshi Akima, Ryuta Kinugasa, T Kizuka, S. Kuno · Medicine & Science in Sports & Exercise · 2003
It is well known that a small number of synergies is engaged in the production of movement, however, a limited information has been demonstrated on the functional interaction among the muscle synergies in humans. PURPOSE The purpose of this study is to determine coactivation patterns of the individual muscles in the quadriceps femoris (QF) using muscle functional magnetic resonance imaging (mfMRI) and electromyostimulation (EMS). METHODS Seven healthy men performed isotonic knee-extension exercises at 50% of 4 set of 10 repetition maximum (4 × 10 RM) with 1 min rest between the sets with and without EMS. First, the subjects performed the knee-extension exercise without EMS (KE), secondly, we applied to the EMS over the vastus lateralis (VL), that was induced to 80% of estimated maximal torque of the VL, during the KE with 50% of the 4 × 10 RM (KE with EMS). Before and after each protocol of the KE exercises, mfMRI of the thigh was taken, and spin-spin relaxation times (T2) of the individual muscles of the QF was calculated as an index of muscle activation. RESULTS After the KE exercise, T2 of the individual muscles in the QF significantly increased by 11 to 16% (P < 0.05). Exercised T2 in the vastus intermedius (VI) correlated with those in the VL (r=0.77, P < 0.05), rectus femoris (r=0.84, P < 0.05), and vastus medialis (r=0.89, P < 0.01), respectively, suggesting that these muscles coactivated during the KE exercise. While, after the KE with EMS exercise, a significant correlation was observed only between the VL and VI, implying that the EMS to the VL elicited coactivation of the VI. CONCLUSION These results suggested that there would be neural interactions between the VL and VI in human quadriceps. Supported by MECSST Grant#13780015 and Uehara Memorial Foundation.