Dillon Casey simply has to work out.

This is partly for job preservation. The 29-year-old Canadian-American actor has spent a fair part of the last decade playing TV and movie characters which are apparently allergic to shirts.

However, Casey also admits that he quickly gets bored with exercise programs, and their initial appeal was only to help him study better in school. Today, he places himself among those fitness enthusiasts who exercise because they must work to the point of exhaustion before they can quiet their minds and get anything else done.

Whatever the system, it appears to be working, because this former competitive squash player's star has been on a steady rise for a number of years. Currently, aside from a steady role as the spy Sean Pierce in the CW drama Nikita, he is poised to make his highest-profile film role to date, as an underground mixed martial artist in the upcoming drama Only I. Along the way, he also churned out a steady series of acclaimed comic web videos and short films in collaboration with his brothers Connor and Lyndon.

Shortly after the launch of Nikita's third season, Casey chatted with Bodybuilding.com about how his training regimen has changed and evolved with his acting career, and how being an up-and-coming actor is like being like an aspiring MMA fighter. He's worked like a bodybuilder, a competitive athlete, and a fighter, and his diverse and challenging workout program shows influences from all three. Along the way, he's both appeared on a billboard in Times Square, and done cardio classes in a 75-pound weight vest. Who else can say that?

On your Twitter page it says you are a nerd in a jock's body. Break that down for me.

Well, I always studied science growing up, and I was always good at sports, but I never had the mental game for it. But the way that I go to the gym and the way that I work out, I look like a jock. I look like I would be an ex-football player or something, but I'm actually more into school and science.

So what the two sides think of each other?

That's the thing. Whenever I played sports, especially tennis back in the day, I was so in my head, overthinking and analyzing every single thing, that I would beat the shit out of myself. It was sort of like the jocks always beating on nerds. I had all the tools to be a great athlete, but my head was never there.

A lot of my training is just to calm me down. I'm not the most relaxed person, and I have an anxiety about me, so I have to get to the gym and work out until I'm so tired I can't think anymore. I always felt like I couldn't focus and study until I got the physical stuff out of the way. I would go to the gym and work out until I was like a zombie, and then I could go to the library.

Early in your career, you appeared on a giant billboard in your underwear in Times Square. As an anxious person, that must have been an interesting experience for you. What did you learn from that?

Yeah, that was for an old Canadian television show called MVP, where I played a hockey player. Part of the plot of the show was that the character does an underwear ad, and it ends up on a billboard in the city, so it was like life imitating art. When I did it, I had this fearful look in my eyes in the picture like, What the hell am I getting myself into here? I was just doing what I was told, no questions asked. I wanted to make everybody happy.

So I guess I learned to ask more questions. But at the same time, I thought it was cool that they wanted to put that up there. You only get to have that body once in your life, what the hell, why not show it off?

I see you still have it as your Twitter avatar. Does that mean that was the best shape of your life?

Actually no, but I guess as I have gotten older I have embraced it more, like Yeah, I fucking did that!

Four or five years later, what do you know about training that you didn't know then?

Well, when I did that I was into lifting weights just for the sake of it, and I look like a bodybuilder. I've been even bigger than I was in that MVP picture. I've gone up to like 210 pounds and even more, and the thing is when you are working as an actor, that really limits what you can do. You get known for that.

Even in Nikita there are a lot of shirtless shots, but it is really worked into the plot, whereas in MVP and a lot of stuff I did after it was just gratuitous. I became the guy who gets hired to take his shirt off. As a guy who likes to do comedy, there is no fucking way I'll get to do comedy when I look like a bodybuilder—unless I'm playing the "dumb jock."

So I've learned that if I'm going to be addicted to this fitness lifestyle, I need to also try to look like more of an everyman, like I have these muscles for a reason. Like in Nikita I'm a Navy SEAL, and there is a certain look to those guys. Bodybuilders almost never make it through the training, because they're too big. It's almost like being a fat guy, but muscle instead of fat.

How is the type of fitness or training you needed in athletics different than as "the shirtless actor" or what you are doing now?

I really liked the feeling I got when I played squash. Squash is the perfect sport to combine that anaerobic and the aerobic because it is all about intervals. The pros are some of the fittest athletes on the planet, and when I was playing at University of Toronto, that really changed my way of training. We would just have to do 400-meter sprints with no break in between.

Then, when I would play, I loved that feeling of being able to do these sprints and recover. I really got addicted to that feeling. So now when I train, I like to have a really intense cardio session, or when I do weights, I guess my weights have sort of become a hybrid between weightlifting and cardio. I don't like sitting on a bench and just pushing weight. Now it's more like, "What can I do to make my heart rate go 180?"

Now that you're splitting your time between Toronto and Los Angeles, how is it different for you trying to be a fit person in those two places?

Obviously in Canada we've got winter for eight months out of the year, so that is why squash is such a great sport. You're inside, just running around in a little box. When I went to L.A., I tried to find some squash out there, but there is really only one guy who plays, and he's so much better than me that he never wanted to play with me.

So instead, I started to take advantage of Los Angeles and the outdoors. I would go to Santa Monica and run the stairs. Those were pretty killer. I always wanted to do martial arts, but for whatever reason I never did it while I was in Canada, so I found an awesome studio called White Tiger Kung Fu in Westwood.

There is this guy there named Dennis Wood who's an Iraq war vet, a Marine, black belt in kung fu. The minute that you meet him you become his bitch, which is actually kind of a nice feeling, to meet a guy who you have to listen to and you take his word for everything. He started getting me into martial arts and kung fu. I had no money at the time, so I would teach his kung fu cardio class in exchange.

Dennis is one of these guys who knows what you are capable of, and if you aren't pushing yourself, you have to answer to him. He would wake me up at seven in the morning and we would go run the Santa Monica stairs and then come back and I'd teach a cardio class or do a kung fu class or go paintballing. It was cool because all of our training was functional.

Had you ever thrown yourself into someone's tutelage like that before?

Never. I always just went to the gym and looked at what other people were doing and kind of imitated them. I remember when I first started there was this guy who was the biggest guy at the gym, and I just looked at him and imitated what he was doing.

I think a lot of people do that. So what did you get from the experience of having someone lay it all out for you for an extended period of time?

It was a pain in the ass! I'm sure you know how when you go to the gym you get into routines and you hate anyone breaking your routine. So I would have to just be open to it and I forced myself to listen to him. I thought that I was working hard, but it turned out that I was just going through the motions.

After a while this guy had me doing a cardio class—the hardest cardio class I have ever done in my life—wearing a 75-pound weight vest. But I kind of liked the feeling of everybody looking at me like I was a freak, and him still thinking that I was being a pussy. After a while I couldn't take the class without wearing the vest, or I'd feel like a pussy. I love that feeling of just setting the limit for yourself just a little bit higher every time.

Did that training prepare you to play an MMA fighter in Only I? That's a whole different type of fitness than anything we've talked about so far.

Honestly, it at least made me look like I knew how to fight technically. When we had to do those fight scenes, it was as close as you could get to having to go through a fight without getting hit. We rehearsed it before and it wasn't that tiring, but when Brendan [Fehr] and I went full out after the first take we were both wheezing—and we both thought we were fit guys! But that was just the wide shot. Then we had to do the wide shot like five more times and then come in close. That was just half a round. We looked at the clock and we had like eight or nine more hours of this.

It was the hardest thing I've ever had to do in my life. It trained us both to look like we knew what we were doing, but fitness-wise, I have never touched anything like that. I knew that I could get there, but it was just a matter of going moment to moment rather than thinking about all the shit we still had left to do.

Did you have to train outside the set to keep up, or could you just spend your time recovering?

I tried to just act like I wasn't as tired as I was. That's all I could do. Any athlete will say you have to be ready to fight or play a match or whatever a few weeks in advance. If your training isn't up to par the day the tournament starts, you can't do anything to get it.

By that point, you're screwed. I wasn't in the shape I wanted to be in for Only I cardio-wise, but at least I still looked like I was in shape.

How was being an up-and-coming fighter, as you were in this film, similar to your experience as an up-and-coming actor?

There's a great moment in the film when a character loses a huge fight he's been working toward for ages. The character is found in the showers afterward, in full fight gear, covered in blood, processing his loss. He's devastated, and everything is telling him to quit and get out—that he's a failure. He worked so hard to get here, and now has nothing to show for it. Then out of nowhere, something clicks, and he gets up—loss processed, lessons learned—and he's off to fight another day.

That's the same feeling as doing a screen test or a big audition. You can get so close to having your entire life changed from this one tiny role. You literally sign a contract that tells you, "Next year you could make a million dollars." Then you do the test, and you get a phone call that says, "Nope. Not gonna be him." That's all. And your manager says, "Sorry," and hangs up.

It's not necessarily personal. Maybe somebody didn't like the color of your hair. But you're back to your same old life. You're still broke, and tomorrow you've got an audition for a two-line role in a bad sitcom. I've been through that a few times and it's devastating. You can't help but take a moment or two to let that loss process. You cry, you punch the wall, you blame yourself, and you hate everybody.

You consider going online to buy a plane ticket home to apply to law school. But then something clicks. You realize you're in it for the long haul, and you get in there and land that two-line role and fight another day. This is where my "Living in LA" series came from.

But also like a fight, you probably feel beat up even when you win.

Oh man. The problem is you put so much into every audition you do. That's the lesson: You have to learn to not do that. In Only I, this is like the underground of the underground of fighting. The contract that they are fighting for is not to get into the UFC; it's like two steps down from where someone from the UFC might eventually see them.

So it would be the equivalent of me trying to get the role I had on Vampire Diaries. It's just a guest star, but the problem is when you are sitting there in Los Angeles, alone, you have put all your cards into being an actor. Every minute that goes by is another minute lost that you could be devoting to learning another skill that could help you in the future. That means that every audition you go into means way too much. You go to the gym and workout another eight hours, and those are eight hours that you could be spending learning to be an electrician or a plumber.

And then all of a sudden you wake up and you are 31- or 32-years-old, and it's not going to happen for you. You have this window where it is either going to happen or it's not. And every time you get rejected that adds to the pile that tells you it's not going to happen. You get a million rejections and then one huge acceptance. And then you work for four days, and you feel great, and then you are back for another million rejections and one acceptance.

Every time you get accepted and somebody says you are good at something you are moving forward in some way. Every time you get a part, it's like winning a fight.

Dillon Casey's Shirtless Actor Workout

My workouts have become all about maintaining interest. After hitting the gym for 14 years straight it starts to get old. I can't really do the same workout for more than a month now without it getting devastatingly boring. So I've learned to adapt and change it as I go. It's almost all improvised.

The one thing that has stayed pretty much standard is starting with about 30-45 minutes of cardio. Within that, I try to keep my body guessing. I'll do 30 minutes on the treadmill with an incline of 2.5 percent at around 7.0 speed, and then get on the elliptical to round it out for a quick 15 minutes and some extra calories burned. I'll also sometimes do a HIIT workout on the treadmill with some interval training.

The issue here is making sure I give myself enough time to recover. With these intense cardio workouts you have to be careful or you'll fall into overtraining without even realizing it. It's all about listening to your body, setting your ego and compulsions to hit the gym for just "one more quick workout" aside, and learning to take that extra one or two days off from the gym. It's OK! Rest is good!

After cardio I'll do a 5-minute ab circuit using Round Timer on my iPhone.

I take a couple minutes to get hydrated, and then start another five-minute circuit workout. I'll mix it up and add time here or there if I'm feeling good. I try to merge the best of all worlds. Sometimes I'll grab a heavy weight and lift it for one minute, followed by a bodyweight exercise like chin-ups. I want my body to get used to not being used to things.

It's all about functionality—not having a mirror-body but a useful body. You might not look like a bodybuilder in the end, but you'll feel good and look like a warrior! A sample workout would be: