The Best Exercises for Fat Loss

As with cardio intervals, strength intervals like these won't work if your reps aren't high-intensity. "The 'off' bout needs to be long enough that the 'on' bout is effective," Jack explained.

Continue alternating between the exercises for a set time -- 10 or 15 minutes, for example -- keeping track of how many total sets you can do. In following sessions, try to beat your score by finishing more sets in that time or by finishing the same number of sets but with tougher weights.

Density training sessions are great to add to the end of a traditional strength training workout, Jack says.

For a complete density training workout, he suggests performing multiple time blocks in the same session, using new exercise pairings for each. Other pairs he recommends include a goblet squat with a single-arm dumbbell row, a reverse lunge with pushups or pulldowns, deadlifts with dumbbell overhead presses or split squats with a rowing exercise.

Countdown to a Better Body

Countdown workouts also use exercise pairs and are a motivating way to finish a workout, says Mike Wunsch, performance director at Results Fitness in Santa Clarita, California.

"They keep you engaged in what you're doing -- you have to keep the count and pay attention," he said.

With each round of the exercise pair, the workout involves one fewer rep of each move -- moving from sets of six to five to four, and so forth, until the count reaches zero. That finish-line mentality can keep you going.

As with density training, Wunsch recommends pairing opposing exercises for countdowns, but also suggests picking moves that have a rhythm. Moves like the kettlebell swing, squat thrusts and pushups work well. Wunsch says stress-busting med ball slams and throws can add to the fun.

"I stay away from lunging and other knee-dominant moves, though," Wunsch said. Moves like these, he explains, can result in injury if your form falters while performing exercises at a fast pace. For the same reason, he also advises avoiding overhead-pressing moves like dumbbell thrusters.

To try your own countdown, choose a pair of exercises from Wunsch's following list. Start by performing six reps of the first exercise, then six of the other move. Return to the first exercise and perform five reps, then do five reps of the second exercise. Continue alternating in this way until you reach zero.

In each workout after that, add one rep to every exercise, Wunsch says. If one countdown isn't enough, choose a second pair from the list of exercises or create your own pair of opposing moves.

Mike Wunsch's suggested exercise pairs:

Kettlebell swing with squat thrust

Medicine ball side toss with medicine ball slam

Jumping jacks with pushup

Squat thrust with pushup

Put Your Body Through a Storm

"Cardiovascular training is archaic," Rooney said. "It not only takes a long time, it's boring."

To combat boredom and train faster and harder, Rooney designed a workout protocol around that's kept him lean: lifting weights and interval training. He calls this workout "the hurricane."

"The easiest way to explain a hurricane workout is that it's brief but intense," he said.

Each hurricane is broken into three groups of three exercises, called rounds.

"Each round is composed of an exercise that gets your heart rate up, and then other exercises in between," he said.

This design allows users to build muscle and keep their heart rates up throughout the workout, which usually lasts between 16 and 22 minutes.

Like the storm after which they're named, hurricane workouts are categorized into five levels, each one an increased challenge. If you're new to intense training, Rooney suggests starting with Category 1. Details on these workouts, including exercise descriptions, can be found on Rooney's website.

Individuals who are more fit can start with Category 3 hurricanes, like this sample workout:

Begin by warming up for the workout, then move to round 1. For all rounds in this workout, perform 1 set of each exercise, then move to the next exercise. Complete the entire round three times before moving to the next round.

Round 1: Run on a treadmill at 10.5 mph and a 10 percent incline for 25 seconds. Perform a kettlebell Turkish getup four times on each side of the body. and 10 chinups. Repeat this sequence three times.

Round 2: Run on a treadmill at 11 mph and a 10 percent incline for 25 seconds. Perform 10 dips and 15 reps of the barbell rollout. Repeat this sequence three times.

Round 3: Run on a treadmill at 11.5 mph and a 10 percent incline for 25 seconds. Next perform 10 reps of the G.I. row. Then perform 20 reps of the knee grab. Repeat this sequence three times.