The speed of the initial 20 m of an all-out run from a stationary start on a flat track was continuously determined on eight medium level sprinters (3 females and 5 males) by means of a wire tachometer. The wire was attached to a belt placed approximately at the centre of mass. The running speed increased to a peak of 8.48 m s^-1 (0.33 S.D.) in females (n = 9) and to 9.31 m s^-1 (0.31) in males (n = 29) after 3.07 s (0.085) and 2.82 s (0.09) from the start, respectively. The highest forward acceleration (a_f) was observed immediately after the start (0.25 s): it was 4.75 m s^-2 (0.13) in females and 5.77 m s^-2 (0.25) in males.

In the acceleration phase, the runner leans forward by an amount that depends on a_f. The angle by which the runner leans forward can be calculated assuming that the average force (F) during the stride cycle is applied along a line joining the centre of mass and the point of contact foot-ground. If this is so, the angle α between the runner’s body (assumed to coincide with the direction of F) and the terrain is given by α = arctan g/a_f (see Fig. 1). The angle α could then be calculated, allowing us to determine the ‘equivalent slope’ (ES). This is defined as the incline of the terrain, in respect to the horizontal, which would allow the runner, if running at constant speed, to maintain a vertical body position. The equivalent slope is given by: ES (deg) = 90 – α (see Fig. 1). It was shown that ES reached a maximum of 25.9 deg (0.63) (48.6 %) in females and 30.5 deg (1.1) (58.9 %) in males, attained at the time coinciding with the highest values of a_f. Thereafter, ES decreased to a value equal to or lower than 5 % after about 3 s. It should also be pointed out that ES, as calculated, refers to the value in excess of that corresponding to running at constant speed on flat terrain, in which case the runner lies slightly forward. The maximal average vertical force during the stride cycle, as given by the product of the vectorial sum of a_f and g and the subject’s body mass (F = BM (g² + a_f²)^0.5, see Fig. 1), was also calculated: it was about 1.11 and 1.16 times the body weight in females and males, respectively. ES and F allowed us to calculate the energy cost of sprint running (C_sr) from the data recently obtained by Minetti et al. (2002) during uphill running, up to a maximum incline of 45 %. The peak C_sr, coinciding with the highest value of a_f was 20.0 and 24.9 J (kg m)^-1, in females and males; the average, integrated over the 20 m corresponding to the acceleration phase, was 10.1 and 13.3 J (kg m)^-1, to be compared with 3.8 J (kg m)^-1 for running at constant speed on flat terrain.

It is concluded that the present approach yields a fruitful estimate of the energy cost of sprint running.

All procedures accord with current UK legislation.