A professional athlete (or even a semi-knowledgeable amateur) warms up before sending their body out on the track, into the ring or up into the air. It's common sense; asking your body to deliver a great performance without warming it up would be foolish, right?
Well, when you're speaking in front of an audience, you're asking a special group of muscles and body parts to deliver great performances: your diaphragm, vocal chords, throat, face and tongue. Most people don't take the time to warm up these parts before a speech, however. I suspect due to a belief that, "It's just public speaking, anyone can talk."
True. And anyone can run. But marathoners still stretch before jogging.
Next time you know you're going to speak in front of a crowd, the office team or your boss, take 15 minutes to run through the following warm ups and see if it makes a difference - if you stumble less, if you're more expressive, if your voice doesn't crack. You might be impressed by the improvements a good stretch can bring.
The tongue is a muscle like any other, so it needs to stretch before doing some heavy lifting. Before and after each of the following exercises, shake all the tension out of your tongue by sticking it out of your mouth and blowing a great, big raspberry (it's the mature adult's chance to rip a really great fart).
Tip of the tongue: Stick the tip of your tongue slightly out of your mouth and then slap it one corner of your mouth to the other in a horizontal motion. Do this until the tip of your tongue feels slightly tired. Relax, then do the same thing but up and down, moving from the top lip to the bottom. (Try to do this without moving your chin, so just the tongue is doing the work. You can put a fingertip on the point of your chin to help remind you not to involve your jaw).
Middle of the tongue: Say "Yah!" Now five times in a row say, "Yah-yah-yah-yah-yah!" Now say that again, but don't breathe out, so your tongue makes the motion but you don't make any sound. Feel how the middle of your tongue is getting a work out? (Again, try to do this without moving your chin).
Back of the tongue: Say "Hung-HAY!" Now do that five times in a row, then do it again without any sound, feeling how you're drawing the back of your tongue up into the roof of your mouth. Go until your tongue feels tired, then blow the tension away.
Now let your tongue go crazy, sticking it out, rolling it back, making noise like any child knows how to make. End with a great big raspberry that can be heard out in the hallway.
The lips are also muscles and crucial to forming sound. Again, do the exercises until your lips feel tired, then blow the tension away in your best imitation of a horse.
Kiss-smile: Pout your lips out as far as they can go, then stretch your lips into the biggest smile you can make. Go rapidly back and forth until your lips get tired, then relax.
Bottom lip drop: Place the tip of your finger just under your lower lip. Now use your lower lip to push against your finger. Don't move your jaw, don't move anything except your lower lip. When you can feel the muscles that you're isolating, move your finger away and keep dropping your lower lip.
Upper lip sneers: Like the previous exercise, place your finger on your upper lip, then use only your upper lip to move it up. When you take your finger away, it'll look like you're doing mini-sneers, revealing your two front teeth. (For this exercise, try to not wrinkle your brow or involve any other face muscles - just the upper lip).
Peanut butter cleanup: Keep your lips together and send your tongue for a trip around the front of your teeth, imagining that cleaning up peanut butter. Do a couple full circles in a clockwise direction, then go counter-clockwise.
And end it all by blowing all the air in your lungs out through your lips.
The diaphram is the big gut muscle that controls the lungs and should be the main focus of your breathing. Many North Americans work their shoulders and their chests too much when they breath; you see this especially among "valley girl" speakers, who talk until they run out of air, then rapidly draw in a breath with a sharp gasp, sending their shoulders flying up.
That kind of breathing adds a lot of tension to your shoulders and neck. It also doesn't draw the deepest (and quietest) breath you can, so you'll spend your speech struggling for air, getting tenser as you fight to keep going.
Breathing from the belly: Place your thumb on your belly button. Now place the palm of your hand underneath your thumb on your belly. Take a breath by pushing your belly against your hand and feel how the air gets drawn into your lungs. Now breathe out and let your hand ride your belly down. Keep breathing this way for 30 seconds, taking deep, full breaths of air. (Your shoulders shouldn't be moving when you're breathing this way - not that you're holding them tightly in place, but they shouldn't be rising and falling like the sea)
(Note: If you doubt how much better this style of breathing is, switch to just moving your shoulders and your chest when you draw in air. See how shallow your breath is by comparison?)
The vocal chords are not muscles, but flaps of tissue that can still be warmed up to give you full access to the range of sounds you can make.
The scales: There are a slew of voice warm up videos on YouTube (with the usual range in quality) but I'll point you to this quick exercise. Sing "la" with each of the notes on this scale, starting at the lower end your scale and stopping when it goes too high for you. You don't have to sing very loudly, but do work your diaphragm enough that your throat starts to feel warm by the end of the run through.
Sighs: If your voice box is feeling tight, relax it by doing a few sighs with a nice "Ahhhhh" that starts on a high note and ends on a low note. Don't push hard with your breath - your not singing - you're just letting out a full body sigh.
The whole team needs to work together for the last few exercises, pulling all the elements together.
Give yourself a shake: Put your hands together and interlace your fingers. Now raise your hands to head height and start shaking them forwards and backwards, so the whole top of your body shakes. Let your neck go loose, shaking out the tension. Let your jaw go loose so your face, lips and tongue can shake out their tension too. (Make sure to keep your tongue in your mouth or you might give yourself a bite.)
A stream of water: Breathing from the diaphragm, start humming - just a nice, constant "Mmmmmm." Feel the buzzing on your lips. Now keep that buzzing going but open your mouth, so your humming becomes an extended "Mmaaaaaaaa." Take another deep breath and this time, as you say "Mmaaaaaa," imagine the sound coming out of your mouth like a stream of water, hitting the back of the room your standing in. (Sometimes it helps to point with your arm to imagine the jet stream.) Now do the same exercise, but choose a line from your speech. Keep the buzzing going on your lips and imagine the words streaming out of you, hitting the back wall.
Tongue twisters: There are a ton of tongue twisters that work different part of your mouth. Some will be easy for you and some will be hard depending on how your mouth is set up. Here's an online resource listing a bunch. Try saying them five times fast on the same breath. Try over enunciating - something you won't do when you say your actual speech, but this is just warming up. And have fun with them! Play around, try emphasizing different words and don't beat yourself up if you trip on a word or two; the point isn't to be perfect, it's to be fully engaged with what you're speaking.
This is only a quick warm up routine and there are many more exercises you can find online. Find the ones that work best for you and develop your own routine. A personalized warm up can be part of your mental prep too, just like an athlete listening to a favourite song before game time. Routines are proven to calm nerves and help people get comfortable in the space they're in.
As a final bit of advice that someone else once gave to me: everyone in your audience is cheering for you. No one wants to see you do poorly, they are all rooting for you to give the best speech you can. Everyone is on your side. So warm up, smile, have fun and go for it.