Can something as old-fashioned as push-ups and sit-ups really make that much of a difference in your physique? The answer is a resounding yes -- with certain qualifications.
Are these two exercises alone enough to bestow you with washboard abs, erect posture and sculpted biceps, if you do enough of them? The answer here is a resounding “probably not.” Although doing a ton of sit-ups and push-ups could bring about striking improvements in physique, sticking to those two exercises alone isn’t the best idea.
So how many sit-ups and push-ups should you a day?
The Short Answer
If you’re a beginner, start with eight to 12 repetitions and do three sets of each exercise — if even that, says Los Angeles-based personal trainer and yoga instructor David Knox, author of Body School: A New Guide for Improved Movement in Daily Life. Knox advises following what he calls “80 percent rule." That means stopping at 80 percent of what you think you can do comfortably. Whatever you think is a comfortable goal, do 80 percent of that; for example, if you think your max is 15, aim for 12.
The proof of an adequate workout is that the last few repetitions are a bit of a struggle, according to the American Council on Exercise, which says that "10 to 25 repetitions for one to three sets of abdominal exercises provide a more than adequate training stimulus." If you can do more than 25 reps, you're probably not activating the muscles adequately to build strength.
The Long Answer
Pros and Cons
Push-ups are a classic calisthenic that have never fallen out of favor. Push-ups require the chest, shoulders, triceps and abdominal muscles to work as a unit to move the body toward and away from the ground. It works the core and the upper body, too, and builds a practical strength that will carry you through daily life.
Sit-ups, however, are another story. There’s a large body of thought that argues against doing sit-ups altogether because they’re notoriously prone to causing back injuries. Research indicates that the hip flexors take over from the abdominals just past the point where your shoulders are off the ground. So going farther up doesn't actually work the abdominals. Although bent-knee sit-ups with feet supported are often presented as a safe alternative, these can also pressurize the lumbar area, making disc injury a risk. In his Superb Abs Resource Manual, Dr. Len Kravitz, a researcher and exercise scientist at the University of New Mexico, concludes that "sit-ups cannot be recommended." Crunches, in which you lift your head, neck and shoulders about 45 degrees off the ground are superior.
Reps: It's Quality, Not Quantity
Understanding more about how muscles work and how they respond to “reps” in general could help you make better choices for your fitness regimen. And, of course, help you determine the right number of push-up and sit-up reps to do in a given day.
A rep — short for repetition — is a single stroke of action by the muscles that power movement at a joint or a series of joints. There are three phases of muscle action in every rep: lengthening, a momentary pause and shortening. Whatever your goals, the number of reps isn’t really the measure of progress. What matters is that you’ve worked all the fibers in a muscle.
Doing dozens of sit-ups and crunches without proper form that works all the fibers won't do you any good in terms of muscle building. Think about the quality of each move when you do it, rather than how many you achieve.
Definition vs. Bulking Up
For bulking up — that is, adding muscle mass — you should do as many reps as it takes to bring you to muscle fatigue. That’s the point where the muscle starts to give out and you just can’t complete any more reps.
For definition, what counts is how long the muscle stays under tension. A muscle acquires definition by remaining in a state of semi-contraction. The longer it’s kept in that state, the faster it acquires definition. More reps done at a slower pace generates the tension you need to boost definition. And to get it, you still need to work yourself to the point of temporary muscle fatigue.
So start out slow and through cautious trial and error, you're sure to arrive at the number of reps for each exercise that is right for you, your goals and your schedule. It will, of course, change over time. Now assume the position!