Running velocity at blood lactate threshold of boys aged 6-15 years compared with untrained and trained young males.

Running velocities at the blood lactate threshold, which was estimated by the velocity just below 2 mmol X l-1 of blood lactate, were measured in sixty-six 6- to 15-year-old boys during a graded exercise stress test on the track and compared with those of twenty-three 16- to 18-year-old young males and eighteen 18- to 23-year-old untrained young males. The boys were divided into five age groups: 6-7, 8-9, 10-11, 12-13, and 14-15. The mean velocity at the lactate threshold of all age groups was significantly higher than that of untrained young males and not different from that of trained young males. There was no significant difference between boys of all age groups, but a significant negative correlation between the velocity at the lactate threshold and bone maturity score (RUS score) of more than 200 was found in boys. Heart rates and percent maximal heart rate at the lactate threshold were dependent on age. These were significantly inversely related to the chronological age and RUS score. These results suggest that maturation is one of the factors influencing lactate threshold.