INFLUENCE OF RUNNING SPEED AND EXERCISE DURATION ON BLOOD GLUCOSE THRESHOLD DURING LONG-DISTANCE RUNNING / 体力科学

This study was intended to clarify 1) the difference of the exercise intensity at blood lactate threshold (LT) and blood glucose threshold (GT), 2) the effect of exercise duration on the LT and GT during two sets of incremental running test. Ten male runners (age 25.0±3.2 yr, height 171.2±5.5 cm, body mass 57.9±4.0 kg, VO_2max 64.6±3.0 ml/kg/min) completed two sets of incremental running test (each set was set to run ten stages at 60-90% VO_2max). Second set was repeated after 8 min recovery. LT and GT speed were investigated at the first set. Lactate minimum (LM) and glucose minimum (GM) speed were selected where the blood lactate and glucose concentration were at the lowest during the second set. Using the indirect calorimetry (VO₂, VCO₂), fat and carbohydrate oxidation rates were calculated. GT was observed in all runners. VO₂ and energy expenditure were similar between the two incremental running tests, however, fat oxidation was significantly higher and carbohydrate oxidation was significantly lower during the first half of the second set. This change was regarded as the influence of the exercise duration in the first set. Furthermore, GM speed was significantly lower than GT speed, but LM speed and LT speed were not different. It was considered that the shift of GT was affected by the substrate utilization change during prolonged exercise.

DETERMINING THE DIFFERENCE IN MAXIMAL OXYGEN UPTAKE OF RUNNING AND CYCLING－ MRI EVALUATION OF MUSCULAR ACTIVITY LEVEL － / 体力科学

The purpose of this study was to determine the difference in the attainment rate of maximal oxygen uptake in cycling and running (%cycVO_2max). 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 %cycVO_2max, %cycVCO_2max, %cycRER_max, %cycVE_max, %cycVt, %cycRR and %cycHR_max. 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_%. VO_2max in cycling was 92.2% of VO_2max in running. Significant correlations were observed between %cycVO_2max and %cycVCO_2max, %cycVO_2max and %cycRR. Furthermore, significant correlations were recognized between %cycVO_2max and ΔT2_% of the m. quadriceps femoris, %cycVCO_2max and ΔT2_% of the m. quadriceps femoris, %cycVCO_2max 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 %cycVO_2max and %cycVCO_2max or %cycRR, the anaerobic capacity of each subject would also affect the difference between the maximal oxygen uptake of cycling and running.

THE RELATIVE CONTRIBUTION OF ANAEROBIC AND AEROBIC ENERGY SYSTEMS DURING FLAT-WATER KAYAK PADDLING / 体力科学

The purposes of this study were to investigate the characteristics of physiological responses during flat-water kayaking events, and to quantify the contribution of aerobic and anaerobic energy systems. Eight male kayak paddlers participated in the study. The subjects performed an incremental test and five all-out tests (20, 40, 120, 240 and 600 sec) on a kayak ergometer. Peak oxygen uptake (VO₂peak ; 3790 ml · min^-1) in the incremental test was significantly lower than maximal oxygen uptake (VO₂max ; 3944 ml · min^-1) in the all-out test. In contrast, power at VO₂peak (154.0 W) was significantly higher than power at VO₂max (144.1 W). The contributions of energy systems were calculated by measurements of the accumulated oxygen uptake and accumulated oxygen deficit. The relative anaerobic energy system contributions for 200 m(40 sec), 500 m (120 sec), and1000 m (240 sec) averaged 71%, 43%, and 26%, respectively. These higher relative anaerobic energy system contributions, due to higher anaerobic capacity in kayak athletes, and the smaller muscle mass involved in kayak paddling limit oxygen uptake when exercise intensity is high. Furthermore, slower exercise cadence in kayak paddling leads to higher muscular tension, and thus may enhance the limiting of oxygen uptake.

RELATIONSHIP BETWEEN FLAT-WATER KAYAK PERFORMANCE AND ENERGY SUPPLY CAPACITY / 体力科学

The purpose of this study was to investigate the relationship between 2-min kayak ergometer performance (KEP) and energy supply capacity. Seventeen (male : 9, female : 8) kayak paddlers completed a maximal incremental test to determine aerobic capacity{maximal oxygen uptake (VO_2max) and lactate threshold (LT)}, and a 2-min all-out test to measure performance and anaerobic capacity{maximal accumulated oxygen deficit (MAOD)}. In addition, total energy supply capacity was estimated by these variables [{(T-score of VO_2max+T-score of LT)/2+T-score of MAOD}/2]. Oxygen uptake and blood lactate concentrations were continuously measured during the incremental test and at the completion of both tests. These tests were conducted on an air-braked kayak ergometer. Unlike the previous research, no significant relationships were found between KEP and VO_2max and LT in either male or female. MAOD correlated with KEP in female (r=0.75, p<0.05), but not in male. On the other hand, there was a significant correlation between KEP and total energy supply capacity (r=0.89, p<0.05, both male and female). In conclusion, total energy supply capacity accounted for a large part of KEP. These results indicate that flat-water kayak paddlers need to develop both aerobic and anaerobic capacities.