Author(s): HAKAMADA, N., KAMEDA, M., IIZUKA, S., Institution: JAPAN INSTITUTE OF SPORTS SCIENCES, Country: JAPAN, Abstract-ID: 1273

INTRODUCTION:
The purpose of this study was to examine the characteristics of trunk muscles morphology based on the cross-sectional areas of each muscle, focusing on Paralympic athletes who compete in a seated position.
METHODS:
Fifteen Paralympic athletes who compete in a seated position participated in this study (9 males: 36.4±11.8 yrs; 6 females: 30.6±7.0 yrs) who compete in a seated position. Magnetic resonance imaging (MRI; Magnetom Symphony, Siemens) was used to measure the cross-sectional areas of the trunk muscles just above the upper pelvis (Jacoby line). Scanning was performed using a conventional T1-weighted fast spin-echo sequence with a repetition time of 500 ms, echo time of 8.2 ms, slice thickness of 10 mm, field of view of 240 mm, and matrix size of 256 × 256 mm. Cross-sectional areas were measured from the slice adjusted to the middle of the L4/L5 disc space. The cross-sectional area of each muscle (rectus abdominis, external oblique, psoas major, quadratus lumborum, and erector spinae) was calculated by summing the pixels surrounded by the fasciae using an analysis software. The percentage of cross-sectional area of each muscle relative to the total cross-sectional area was also calculated.
RESULTS:
The cross-sectional areas of the trunk muscles were 13.5 ± 4.2 cm2 for the rectus abdominis, 45.9 ± 17.1 cm2 for the external oblique, 15.5 ± 11.5 cm2 for the psoas major, 8.5 ± 4.9 cm2 for the quadratus lumborum, and 31.7 ± 15.0 cm2 for the erectus spinalis, respectively. The percentages of each muscle were 3.2 ± 1.0 % for the rectus abdominis, 10.5 ± 3.3 % for the external oblique, 3.7 ± 2.8 % for the psoas major, 2.0 ± 1.2 % for the quadratus lumborum, and 7.5 ± 3.6 % for the erector spinae. Compared to the percentages of each muscle of Olympic athletes in similar events, the values were smaller, especially in the psoas major, quadratus lumborum, and erector spinae muscles. In the psoas major and quadratus lumborum muscles, there was a trend toward muscle atrophy, whereas intramuscular fat infiltration tended to increase in the erector spinae.
CONCLUSION:
The results of this study suggest that the characteristics of the trunk muscle cross-sectional area in athletes who compete in a seated position differ for each muscle.