Spice up your cardio and target belly fat with intervals!  This 30-minute treadmill workout plays with speed and changes minute to minute.  And switching speeds like this not only improves your overall running stamina, but it also increases the calories you burn when the workout is over.

As always, feel free to adjust the speed up or down as necessary;  just make sure you're challenging yourself.  If you're looking to try running intervals but want to start a little slower, try this beginner's interval plan.

Lack of a gym membership is no longer an excuse for skipping workouts.  Instead of relying on equipment, let your body be the gym.  These 13 bodyweight workouts are effective, easy to follow, and plenty of fun! You can do these in the comfort of your living room!

1. Do-Anywhere Bikini Circuit

Tone all over with this printable strength-training plan that's a great option all year long and offers the element of some heart-pumping cardio.  If one of the moves is new to you, don't skip it;  you can learn the details of each move here.

2. 5-10-15 Workout

This 5-10-15 workout is the perfect starter workout for bodyweight beginners — and once you start repeating the circuit, you'll see just how effective and challenging it can be!

3. Long and Lean

Full of lengthening moves, this quick workout will strengthen your muscles while providing a good stretch.  The Long and Lean Workout is great the day after a long training run — it feels that good.

4. Just HIIT It

Seven minutes for a workout — who doesn't have time for that?  That's why we've been loving this quick circuit workout!

5. Full-Body Plyo Workout

Jump, hop, and skip your way to a stronger body with this full-body plyometric workout.

6. The "Anywhere" Workout

In need of a time-saving bodyweight workout plan?  Let this week-long plan take the guesswork out of the equation.  These short workouts can be performed on their own for a quick strength-training session or combined with your cardio routine.

7. Flat-Abs Bodyweight Workout

You can flatten your abs without crunches!  This workout tones your entire body but with an emphasis on strengthening your abs.

8. Superset Tabata Time

Tabata is all the rage for good reason, so get set to burn major calories:  print out this workout, and get your timer ready (we like the free programmable app SIT — simple interval timer).

9. The Busy-Woman's Workout

Every exercise in this quick sweat session works multiple muscles for an efficient and effective workout.  Now, get at it!

10. No-Excuses Workout

Torch calories and build some metabolism-boosting muscle with this straightforward plan.  Simply warm up, work out, and train your core, and you're done.

11. Total-Body Tabata

This 20-minute Tabata workout is quick and effective.  We even added some core exercises for your cooldown so no muscle goes unworked.

12. Fire Up Your Core Circuit Workout

While your core is certainly targeted, your whole body will be feeling the burn with this dynamic core circuit workout that combines strength-training moves with light cardio.

13. High-Intensity Tabata Training

This calorie-blasting 40-minute Tabata session moves so quickly that it's hard to get bored.  And with no equipment needed, you have no excuse not to give this effective full-body workout a try.

You know you've had an intense and effective sweat session when you have to peel your soaking-wet clothes off at the end of your workout.  If you love a good sweat, you'll appreciate these quotes.

Preparations are underway for this year's Victoria's Secret Fashion Show, which means you might very well spot an Angel sitting next to you in SoulCycle.  If Instagram is any indication, the 50+ women who are walking down the runway this December are spending some serious time in the gym.

Take Martha Hunt and Karlie Kloss, who have been working out at the Dogpound, a favourite haunt among Victoria's Secret Angels.  Known for his intense training sessions, co-founder Kirk Myers had the two women turning up their side skaters and mountain climbers on a slide board.  The momentum from the board not only ups the intensity and speed of the move, but challenges your core to work even harder as you fight to stay balanced.  If the two models can handle the slide board this easily, we suspect that the catwalk will be a walk in the park.

You know plank works your core like no other bodyweight move, so try this variation to make it more challenging.  This exercise will strengthen your core while also toning your arms and upper back.

• In a plank position, reach your left arm back and then circle it overhead, bringing your palm back to the floor; repeat on the other side.  This counts as one rep.
• Complete five to eight reps, keeping the core stable and the belly button pulled up toward the spine.
• The wider your feet are, the more stable you will be.  Do not let your pelvis drift toward the ceiling.