Psychologists from the UK have discovered swearing (either muttering or yelling) can improve muscle strength and exercise stamina. It is hypothesized that swearing activates the nervous system and boosts adrenaline production.
In the study people undertook a cycling test and were given instructions to repeatedly vocalise a neutral word or a profanity. Those who swore were able to pedal harder for longer.
If you’re thinking this is exactly what I need to do to lift my game, it’s worth noting that it’s not the words themselves, but the emotional intensity of how you present them. A powerful "c’mon" is probably just as useful and more respectful to those around you.
There is nothing wrong with showing how squash makes you feel after all!