Sometimes the easiest way to get in an efficient workout is to let someone else do the planning. Here are three classes and three DVDs, clocking in at 45 minutes or less, that may make it easier.
Speed Racer (class): I thought I'd seen every possible piece of exercise equipment. Then I met the SmartBells. It's an oval weight with cutout grips that resembles nothing so much as a heavy steering wheel (hence the name of this class at Equinox Fitness, a trendsetting chain of gyms operating in seven states and the District of Columbia). We spent a good chunk of the 45-minute Speed Racer workout swinging the strange object around, passing it between our legs, and using it to make calisthenics and abdominal exercises even more challenging. The instructor gave us three different levels of difficulty, too. The easier option was helpful toward the end, when I was so tired I was about to crash my imaginary car.
30/60/90 (class): The name of this Equinox Fitness class refers to the length of the strength and aerobics intervals it features. After a warm-up, we alternated among bursts of high-intensity calisthenics, moves on the step bench, and bouts of strength training using dumbbells and a weighted body bar. Each burst of an activity lasted 30 seconds at the beginning and hit 90 seconds by the end. It got my heart racing so much that I welcomed the breaks for strength work, even when they required doing push-ups using a body bar placed perpendicularly on the step bench. My muscles got such a workout that when I put on mascara after my post-class shower, my hand was shaking.
BodyWeb With TRX (class): The only weight used in this class at Crunch Fitness, another chain known for its innovative classes, is your own body but with a twist: You work with the TRX system, a simple strap with handles anchored to the wall above you. One minute you're leaning back, holding the handles, and pulling yourself up to work your biceps. The next, your feet are in the straps and you're doing push-ups on the ground. It sounds mellow, but the squats, push-ups, and leg exercises got my heart going as much as a moderate aerobics class. Plus, I felt like a gymnast when we put our feet in the straps and did a pike up into a semihandstand.
The Firm Total Body Time-Crunch (DVD): The Firm series of videos was an early adopter of combining weights and aerobics, a practice that's now standard for timesaving workouts. The main workout, lasting 45 minutes, cycles through aerobic and sculpting segments. I loved the strength segments, which mixed upper- and lower-body movements to work out both at the same time; the "power press," for example, combines a squat with a bicep curl and an outer side leg lift. The aerobics segments are fairly intricately choreographed, so if you have two left feet, this probably isn't for you. And the moves themselves are straight out of that class you might have taken in the 1980s and 1990s—not that there's anything wrong with that.
Total Body Cardio With Tanja Djelevic (DVD): The Utah mountains in the background and house-style music give this video a New Age-y, relaxing vibe—even as it delivers a good workout. A 30-minute express workout incorporates yoga, Pilates, and balance-improving exercises. Unlike the others, it doesn't require hand weights, but you could use them for an extra challenge with most of the moves. Also included in the DVD: a longer, 50-minute workout and a bonus core and ab segment.
30-Day Shred With Jillian Michaels (DVD): Jillian Michaels was a trainer on The Biggest Loser, and I wondered if her workout video would be challenging enough for people who start out in better shape than the reality show's contestants. It was. Each of three progressively harder 20-minute workouts cycles among segments: three minutes of strength training, two minutes of aerobics, and one minute of abs. (During one aerobics segment, Michaels says she wants you to work so hard that you're "gargling your heart.") Within each workout, there are three levels of difficulty for most moves, which means almost all those working out will be able to gargle their hearts, if they so desire. The only thing I disliked: Some of the ab exercises strained my back.