The aim of the present study was to investigate a suitable step frequency during running to the metabolic energy cost and running performance. Trained runners (n=5; age 19.6±0.6 yr, x±SD) underwent running on a treadmill (fixed speed; 200m/min, 1% grade added every1 min) with three different step frequencies, freely chosen step frequency (FP), a increased 5 % step frequency from FP (IP), a decreased 5 % step frequency from FP (DP) to voluntary exhaustion. Breath-by-breath pulmonary ventilation (VE), O_2 uptake (V^^・O_2), and CO_2 output (V^^・CO_2) were determined by computerized metabolic system and subject's gas exchange threshold (GET) could be evaluated using V-slope method. At maximum effort of exercise, there were no significant differences in peak values of metabolic variables including V^^・O_2 V^^・CO_2, and VE among three differences of step frequencies. The V^^・O_2 at gas exchange threshold (V^^・O_<2GET>) during submaximal running under IP condition (56.9±1.4 m〓/kg/min) , however, was significantly higher compared with FP conditions (FP;51.3±3.8 m〓/kg/min). Besides we found a significantly inverve correlation between 5000m running record and V^^・O_<2GET> in FP (r = 0.94, p<0.05), even if no significant difference between them were observed in either IP or DP and 5000m running record (IP, r = 0.29, DP, r = 0.49), indicating that IP could induce the augmentation of V^^・O_<2GET> in runners who had a lower performance record. These results suggest that a increased 5% step frequency from freely chosen one can take physiologically advantage effects on an oxidative metabolic response and then would remarkably improve their running performance on long distance.
