It's OK to admit it: We've all used the excuse of traveling and/or not having accessible equipment to skip a workout.

And while it's not the end of the world if you skip a training session on a rare occasion, being unable to find a weight room shouldn't ever be a reason because your bodyweight can be the only resistance you need to build some muscle -- even for advanced lifters.

Bodyweight exercises sometimes can have the rap of being too easy to perform, but not everyone can do a basic pushup or squat properly. And the great thing about them is that bodyweight exercises are easily modified.

"There are four ways to modify bodyweight exercises to make them harder or easier depending on your (training) level," strength coach Nick Tumminello says. "Number one is to change the range of motion. If you want to make it harder, increase the range, if you want to make it easier, you shorten the range."

So, for example, if you are having trouble with the depth of your squats, you can start to squat deeper as you progress to make them more difficult.

"Change the lever arm ... by shortening the lever arm it makes it easier. How would you shorten the lever arm (for pushups)? You would put your hands up on the side of your couch or side of your bed or something like that," Tumminello says.

"The other one I would say is to change the base of support. So instead of doing two legged squats, you would do one legged squats. You add a balance challenge, but you've also indirectly increased the load."

You can also change the speed of your exercises if you're looking for an increased challenge too. If you're someone who can crank out sets of 15 or more pushups fairly easily, next workout, perform them as fast as possible while staying under control. By doing that, you'll increase your training stimulus and recruit more fast-twitch muscle fibers.

So here's a couple great workouts to perform if you're stuck at home or in a hotel room. And remember, you can apply the four principles mentioned above to adapt your workout if necessary.

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In this workout, Tumminello says to go for time -- anywhere from between 20 to 45 seconds per set, and perform them circuit style with as little time as you need between circuits. Perform as many circuits as you can. There is one challenge with bodyweight training -- rowing and upper body pulling movements aren't very easy to do without any equipment. However, unless you have focused on the exercises recently, you may find the posterior shoulder exercises more challenging than you think.

Beginner/Intermediate Workout

1. Incline pushups: You can perform these on the side of a couch or the seat of a chair like Tumminello mentions above.

2. Split Squats: To perform these, take a comfortable step out in front like a lunge, and touch your rear knee to the floor and stand back up and switch legs.

3. Shoulder Ts: With your knees comfortably bent, bend at the waist until your upper body is parallel to the floor. With your elbows extended, raise your arms out to your sides, forming a T.

4. Skip in Place: Remember skipping in gym class? Skipping in place is a great way to get your heart rate up to perform some conditioning work.

5. Planks: Hold your body in a straight line like a pushup position with your forearms on the floor.

Advanced Workout

1. Squat jumps: With your hands behind your head or extended in front of you, squat down as far as possible (with good form) and jump as fast as you can.

2. Pushups with your feet elevated: Instead of placing your hands on the edge of your couch or bed, put your feet on them. That increases the range of motion and thus, the difficulty.

3. Shoulder Ys and Ts: Just like the setup for the Ts in the workout above, but with Ys included on every other rep. To perform the Y, pretend that you're rocking out to the Village People's "YMCA" at the roller rink -- only parallel to the floor.

4. Jumping Jacks or Burpees: Just like skipping, jumping jacks should bring back some great P.E. flashbacks. Watch the video below to see how to perform a burpee.

5. Ab Snails: Watch this.

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