ABSTRACT
Objective To analyze the similarities and differences between four-point hand-knee position and hand-foot kneeling positions in trunk muscle activation and co-contraction, explore the possibility of hand-foot kneeling position as core stabilization exercises, so as to provide suggestions for actual training.Methods Nineteen healthy volunteers randomly performed exercises of four-point hand-knee position (4 motions) and hand-foot kneeling position (3 motions), while surface electromyography (sEMG) signals were collected from bilateral rectus abdominis, external oblique, erector spine, and multifidus muscles. The average sEMG and muscle co-contraction index (CCI) based on the sEMG signals were analyzed and compared.Results Significant differences were found in the sEMG and CCI within and between the two positions. Under four-point hand-knee position with the right hand and left leg lifting, the activation of all muscles was higher than that in the starting position. In four-point hand-knee position with the left leg lifting, the activation of ipsilateral multifidus muscle was significantly higher than that in hand-foot kneeling position. The activation degree of external oblique muscle and rectus abdominis was higher in hand-foot kneeling position with right hand lifting. A total of 28 muscle matching methods were obtained by pair-to-pair matching of 8 muscles. The starting posture in four-point hand-knee position fluctuated the least, indicating that the spine was the most stable, while the index of other exercises fluctuated in a larger range.Conclusions The possibility of hand-foot kneeling position as core stabilization exercises was proved from two aspects, namely, muscle activation and CCI. The hand-foot kneeling position and four-point hand-knee position can be used for strengthening abdominal muscles and back muscles, respectively. The four-point hand-knee position with contralateral upper and lower limbs lift is a more advanced exercise for trunk muscles, but sports injuries should be avoided.
ABSTRACT
The aim of this study was to compare co-contraction of ankle muscles between older and young adults performing a voluntary sway task, and identify any relationships between co-contraction, balance ability and muscular strength. The task involved displacement of the center of mass backwards and forwards continually during upright stance under three amplitude conditions, large, small and preferred, with sway speeds of slow, medium and fast. The participants comprised 17 older (64.1±2.9 years) and 14 young (21.3±3.3 years) women. Electromyographic recordings were obtained from the tibialis anterior and the medial gastrocnemius muscles during task performance to calculate the co-contraction index (CCI) and evaluate the relative level of co-contraction of antagonist muscle. Additional measurements were obtained from balance tests including body sway tests, functional reach, gait tests, and the EquiTest (Neurocom), and also muscular strength of plantar flexion and dorsiflexion. The CCI was highest under large sway amplitude, but did not differ among sway speeds. The CCI was higher in the older group (23%) than in the young group (15%). Multiple regression analysis revealed that the CCI correlated with body sway in the EquiTest and functional reach, and dorsiflexion strength. Therefore, this study suggested that co-contraction of ankle muscles increased with aging and related to not only static and dynamic balance abilities, but also ankle dorsiflexor strength.