You’re pacing it along the lake with Sebastian Coe as your fantasy running mate and just as you enter the “zone” some melancholy ballad comes on to meltdown your momentum.

With Yamaha’s Bodibeat strapped to your arm, runners need not fret about tempos messing with their target. This nifty device measures your heart rate and picks a tune with a tempo to match.

Bodibeat arrives preloaded with thousands of tracks but you can also add your own music.

We’ll take ''Chariots of Fire'' at the 10-mile point.

$300, www.bodibeat.com