High intensity work is undoubtedly the best thing that can happen on a treadmill. Not only do these machines provide a great opportunity to work really really hard at running, but they also offer a unique advantage in terms of actually approaching your limits. The downside is of course that there is perhaps a slight bit more of a risk associated with actually reachingthat limit--unlike on the bike or elliptical machines, the physics of the whole operation is such that the machine is actually trying to eject you off of it. While this possibility might not even enter into your mind during more moderate intensity work, it certainly will when you're attempting that 8th 20 second sprint at a 10% incline and a 6 minute per mile pace, already red-lining after your first few steps on the belt. I've yet to fall off myself, but the imminent threat of being shot with significant speed into the back wall of the gym is always in my mind. I try to use this very real possibility to generate the primal fight or flight response (and corresponding adrenaline boost) which can help me make it through those last few seconds when they seem as within the realm of my abilities as the idea of running straight through a brick wall.

Here are a few of my favorite workouts on the 'mill sure to get those adrenal glands working:

• TM1: Treadmill Tabata. Bring on the vomit! This is a short and extraordinarily effective workout. Warm up as needed, then set the incline to 10% with your feet on the side-boards. Now get the belt going at your target pace (I recommend no faster than 10 mph--a 6:00 mile--as it is hard, at least for me, to quickly get my legs moving more quickly than this). When you're ready to go, and as the timer ticks over to a whole minute, use strong arms to support your weight and quickly match your running speed to that of the belt below you before letting go with your hands and running up the incline for 20 seconds. Hop to the side-boards using hands on the rails to facilitate the movement. Watch as 10 seconds pass in the blink of an eye. 7 more 20 second 'runs' followed by an equal number of 10 second rests on the side-boards. The first one should feel easy. The last one should feel impossible (and often is). Warm down as needed. This is a bit of an advanced workout, especially when done at near max effort--make sure you are comfortable getting on and off the always spinning belt quickly and safely.
• TM2: Double Bump. Start with 1 minute at 0% incline, using roughly the pace you'd use if racing a flat 10 miles or so (you'll use this pace throughout). After this warm-up, you'll bump up the incline for 1 minute, bump it up again for the next minute, then back to the previous incline for one minute. Then it's two minutes flat before the next bump (1 min at incline, 1 minute greater incline, 1 minute original incline). finish with 1 minute flat. Start out with both bumps having the same incline values, and with the middle (hardest) incline being approx. double the incline of the easier sections. For example your 10 minutes might be structured with the following inclines (1 min at each): 0, 4, 8, 4, 0. 0, 4, 8, 4, 0. For an added challenge, key up the speed a mph or so when you hit the very last flat--sprint it in to the finish. BASELINE WORKOUT [10 minutes]
• TM3: The Hill Program. Many of the same manufacturers make both treadmills and stationary bikes and many of the common brands out there have adopted a similar 'hill' program that offers a warm up followed by a short 'tempo' section, then four intervals of increasing difficulty, and finishing with a 2 minute 'warm down'. Choose a base pace as you would in TM2. The Hill Program set to (as done on Life-fitness machines) 10 minutes is pretty ideal--the work intervals last 30 seconds a piece, with equal length RI. You'll be running the same pace the entire workout--the intervals involve an increased incline. All you'll need to do is choose the pace (9 mph for me) and level (which will determine what inclines are used). Subsequent sessions of the same workout can either increase the pace or the level. BASELINE WORKOUT. [10 minutes]
• TM4: Progressive Hill. 2 minutes flat at a then seven successive minutes of increasing incline before a final minute of flat. Ideally you will increase the incline only 1% each minute but your first minute of incline may need to be at greater than 1% to ensure you're really tuckered out by the end. The base pace will be the same as in the previous two workouts. If you're keen, bump up the last flat section for the sprint finish again. BASELINE WORKOUT. [10 minutes]
• TM5: No Slo Random Pro. Most treadmills have a 'random' program. Choose it! Once you get a good look at the hill (incline) profile, choose a starting pace somewhat conservatively. The rules of the game are simple--1) be bold, 2) be cocky, 3) never slow down. What this means is that you need to get into your racing head space! After those first few minutes when your muscles are warm and you're feeling good make some decisions about what a bad ass you are and bump up the speed a bit. Once you're at a speed, you're committed--no slowing down! But don't shy away from this fact, instead, let your early workout bravado put you in the hurt bag by the end. This workout is best done over a longer duration than the others--I love half an hour sessions myself. [15+ minutes]

Notes:

1. TM1-3 involve intervals while TM 4 and 5 involve more steady state, race pace efforts. An ideal workout cycle will involve one workout from each group to focus on.
2. There are many ways to increase the intensity of these workouts but I favor using incline. Essentially I choose a 'base pace' that I want to feel easy, and use this for most of the workouts (except TM 1 where my pace is faster). For me, running 9 miles in an hour has always been a good benchmark--when I'm fit enough to feel like a 6:40 pace is sustainable for this duration, I'm pretty happy with where I'm at. So for me, I choose 6:40 as my base pace. As I go through cycles, I keep the base pace the same and increase the incline when repeating baseline workouts. Your paces may vary.