走運動および自転車運動における最大酸素摂取量の差を決定する要因<br>～ MRI 画像からみた筋活動レベルに着目して ～

Abstract

The purpose of this study was to determine the difference in the attainment rate of maximal oxygen uptake in cycling and running (%cycVO2max). Seven healthy male subjects (22.9±1.3 yrs, 171.9±4.7 cm, 61.0±5.2 kg) participated in a maximal incremental exercise test for running and cycling. During the exercise testing, oxygen uptake, carbon dioxide output, respiratory exchange rate, minute ventilation, tidal volume, respiratory rate, and heart rate were measured. Attainment rates of each physiological measurement for cycling and running were shown as %cycVO2max, %cycVCO2max, %cycRERmax, %cycVEmax, %cycVt, %cycRR and %cycHRmax. Transverse relaxation time (T2)-weighted spin echo images were acquired before and after the exercise periods. Exercise-induced T2 values of each muscle and muscle-group are indices of muscular activity level, so the difference between the T2 value of cycling and running in each muscle or muscle group was shown as ΔT2%. VO2max in cycling was 92.2% of VO2max in running. Significant correlations were observed between %cycVO2max and %cycVCO2max, %cycVO2max and %cycRR. Furthermore, significant correlations were recognized between %cycVO2max and ΔT2% of the m. quadriceps femoris, %cycVCO2max and ΔT2% of the m. quadriceps femoris, %cycVCO2max and the m. triceps surae, as well. These results show that the higher muscular activity level of the thigh in cycling increases the uptake of oxygen in the muscle. The T2 value shows that the uptake or redistribution of fluid within muscle is driven by the accumulation of lactate and inorganic phosphate. Therefore, the T2 value of maximal incremental exercise would reflect the anaerobic capacity of the muscle. Judging from the significant correlations between %cycVO2max and %cycVCO2max or %cycRR, the anaerobic capacity of each subject would also affect the difference between the maximal oxygen uptake of cycling and running.