Co-existence of peripheral fatigue of the knee extensors and jump potentiation after an incremental running test to exhaustion in endurance trained male runners.

The aim of the present study was to investigate the effect of an incremental running exercise until exhaustion on twitch responses and jump capacity in endurance trained runners. For this purpose, 8 experienced endurance male runners were required to perform neuromuscular function tests before and after a submaximal running bout (control condition -CTR-) or an incremental running test to volitional exhaustion (experimental conditions -EXP-). The twitch interpolation technique was used to assess voluntary activation and muscle contractile properties before and after each condition (CTR and EXP). Countermovement jump was also used to assess the stretch-shortening cycle function before and after both conditions. In addition, rating of perceived exertion, heart rate, blood lactate and skin temperature were also recorded. Only EXP improved jump performance, however, it was also accompanied by a reduction in maximal voluntary contraction and the peak twitch force of the knee extensors evoked by electrical stimulation at 10 Hz (Db10). It is likely that reductions in maximal voluntary contraction may be related to an excitation-contraction coupling failure (i.e. low-frequency fatigue) as suggest the reduction in the Db10. The current results confirm that acute changes in jump performance may not be appropriate to evaluate acute fatigue in endurance trained runners.

INFLUENCE OF LOW GLYCOGEN STORAGE ON BLOOD GLUCOSE AND BLOOD LACTATE KINETICS DURING INCREMENTAL RUNNING TEST / 体力科学

Blood lactate kinetics is an important physiological determinant of endurance exercise performance. Recently, some studies reported that the blood glucose transition point can also be observed (blood glucose threshold; GT) and the GT is consistent with the lactate threshold (LT). However, we have recently reported that blood glucose kinetics and blood lactate kinetics were different during two sets of incremental running tests in the same day. This result suggested that influence of low glycogen storage on GT and LT are different. This study was intended to clarify the effect of low glycogen storage on the blood glucose and the blood lactate kinetics during incremental running test performed two successive days. Eight male endurance runners participated in incremental running test performed two successive days. The main finding was that the blood glucose was significantly lower in the second day than the first day during incremental test, although blood glucose was not different at rest in both days. However, blood lactate was not different form rest to fifth stages in both days, significantly lower only at the final stage in the second day than the first day. Respiratory exchange ration were lower in the second day compared to the first day. GT was significantly higher in the second day than the first day, but LT was not different in both days. We concluded that low glycogen storage effected blood glucose kinetics more than blood lactate kinetics, and resulted in only the change of GT.

Difference in physiological responses to an incremental running test between middle- and long-distance runners / 体力科学

To obtain a viewpoint concerning evaluation of endurance type of athletes, we investigated the difference in physiological responses between middle- and long-distance runners in an incremental running test. Measurements were VO<SUB>2</SUB>max and time of its appearance, change of VO<SUB>2</SUB> from 1.5 min before exhaustion to exhaustion (ΔVO<SUB>2</SUB>), heart rate (HR), and blood lactate after exhaustion.<BR>Results were as follows.<BR>(1) The time of VO<SUB>2</SUB> max appearance in the middle distance runners was earlier than in the long distance runners.<BR>(2) VO<SUB>2</SUB>max was significantly higher in the long distance runners than in the middle distance runners.<BR>(3) Blood lactate after exhaustion and HRmax were significantly higher in the middle distance runners than in the long distance runners.<BR>(4) Blood lactate after exhaustion was significantly related to ΔVO<SUB>2</SUB> (r =-0.660, P<0.05) .<BR>These findings suggest that the endurance type of athletes could be evaluated from the time of VO<SUB>2</SUB>max appearance, blood lactate after exhaustion and HRmax in incremental running, and that VO<SUB>2</SUB>max appearance may be effected by high blood lactate accumulation.