As part of my day job, I've been consulting the endlessly entertaining Compendium of Physical Activities, which puts all human activity on a scale to measure physical effort and the number of calories burnt. The lowest things on the scale are, reasonably enough, sleep (0.9 mets), and listening to music (1 met). The highest is "Forestry, Ax Chopping, Fast" (17 mets). To save you looking it up, 'sexual activity' ranges from 'passive, light effort, kissing, hugging' (1 met) to 'active, vigorous effort' (1.5 mets). I wouldn't want question the accuracy of the study, but 1.5 mets is the same as 'typing: electric, manual or computer'. Anyway, here are the records for musical instrument playing. To put it in context, 4.0 mets is the same as playing ping-pong. Unfortunately there's no entry for 'light mouse clicking'
2.0 Flute (sitting)
2.0 Guitar, classical, folk (sitting)
2.5 Piano or organ
3.0 Guitar, rock and roll band (standing)
3.5 Marching band, drum major (walking)
4.0 Marching band, playing an instrument, baton twirling (walking)