Keepingpressed locks and unlocks buttons.
You can change the button lock behavior in the watch settings under General » Tones/display » Button lock.
Your Suunto Ambit3 Sport has two button lock settings: one for general use, Time mode lock, and one for when you are exercising, Sport mode lock:
Time mode lock:
Sport mode lock
Select the Actions only button lock setting for sport modes to avoid accidentally starting or stopping your log. When the and buttons are locked, you can still change displays by pressing and views by pressing .