Speed

Definition

“Speed” is the distance covered per unit of time. In endurance sport it is usually given in kilometres per hour (km/h); in running and swimming it is more often expressed as its reciprocal, pace (min/km or min/100 m).

It is an external load measure: it describes what happens on the course, not what the body has to do to produce it. Conversion: pace [min/km] = 60 / speed [km/h].

Why it matters

Speed is what counts in competition. Whoever covers the course faster wins, regardless of watts or heart rate. As a training control variable, however, it is only usable where external conditions are constant: flat course, little wind, track, or treadmill.

As soon as gradient, surface, or wind vary, speed loses its link to internal load. In cycling, air resistance grows with the square of speed; in running, every percent of gradient raises energy cost noticeably. That is why power is the preferred control metric in cycling and Normalized Graded Pace in running.

How obseed measures it

obseed takes speed from the session’s GPS data or, on the treadmill and indoor trainer, from the speed sensor. It is stored per second and evaluated together with heart rate and power.

Threshold speeds come from treadmill testing: obseed stores the speed at the first and second ventilatory threshold (VT1, VT2) and derives the pace zones from them. A 5 km field test gives only a rough approximation, because it shows neither fat metabolism nor the ventilatory thresholds.

Over longer periods obseed tracks the ratio of speed to heart rate on comparable courses. If speed rises at the same heart rate, aerobic efficiency has improved.

Example

A runner completes the same flat 10 km loop in January and April, each time at a heart rate target of 145 bpm (just below his VT1 of 150 bpm).

At practically the same heart rate, speed rose by 0.9 km/h, an improvement in aerobic efficiency of about 9 %. The April test confirms it: VT1 speed rose from 10.5 to 11.4 km/h. On a hilly course this comparison would not have been possible; there obseed would have used Normalized Graded Pace.