Running economy during a simulated 60-km trial

The effect of a prolonged running trial on the energy cost of running (Cr) during a 60-km ultra marathon simulation at the pace of a 100-km competition was investigated in 13 men (40.8 yy ± 5.6; 70.7 kg ± 5.5; 177.5 cm ± 4.5) and 5 women (40.4 yy ± 2.3; 53.7 kg ± 4.4; 162.4 cm ± 4.8) who participated in a 60-km trial consisting of 3 consecutive 20-km laps. VO2 at steady state was determined at constant speed before the test and at the end of each lap; stride length (SL) and frequency (SF) and contact time (CT) were measured at the same time points; Serum creatine kinase (S-CPK) was measured before and at the end of the test. Cr in J kg-1 m-1, as calculated from VO2ss and respiratory exchange ratio, did not increased with distance. SL significantly decreased with distance. The net increase in S-CPK was linearly related with the percent increase of Cr observed during the trial. It is concluded that, in spite of increased S-CPK, this effort was not able to elicit any peripheral or central fatigue leading or biomechanical adaptation leading to any modification of Cr.