Scientists have an amazing tool called electromyography (EMG) that shows how much muscles work during specific exercises, such as benches, squats, curls and sit-ups.

EMG measures the electrical activity of muscles. Scientists place electrodes over a muscle belly. The harder the muscle works, the more electricity is measured on the EMG. By placing the EMG electrodes (pads that pick up the electrical signal in the muscles) on key muscle groups, scientists can tell which exercises are best for building size and definition.

How EMG Works

Muscles are divided into groups of muscle fibers and nerves called motor units. A motor unit is made up of a nerve cell and between three and 100 muscle fibers. All the fibers in the motor unit contract when your nervous system (brain and spinal cord) turns on the unit.

You have fast and slow motor units. The fast motor units (Type II) are powerful but they fatigue very fast. The slower units can go all day, but they aren't very strong. Your body turns on the large fast units when it wants to pick up large weights or move very fast. Also, it calls on slower, smaller units when it doesn't need to produce much force. You use mainly slow motor units to stand in line at the grocery store. Your body uses small motor units first and only calls on the big guns when it needs to lift a very heavy load.

When you want to exert more force, your nervous system turns on more motor units. Let's say that you want to military press three weights- one weighing 135 pounds, the second weighing 155 pounds, and the third weighing 175 pounds. You turn on more motor units to lift the larger weights. Your muscles also generate more electricity, which scientists can measure using EMG.

EMG has been around for more than 60 years. However, it wasn't until recently that we had portable units that allow us to study individual weight lifting exercises. The research has given bodybuilders important information for optimal training.

When a muscle contracts, its origin and insertion- the places where it attaches to the skeleton and causes movements- move toward each other. This means that the entire muscle contracts. It is difficult or impossible to work specific parts of most muscles.

You can activate and isolate parts of some muscles because of the way individual fibers are arranged within them- arrangements that scientists call pinnation.

In a muscle such as the deltoid (round shoulder muscle), the fibers run in many directions, so it is possible to isolate parts of it. This is more difficult in the rectus abdominis (top ab muscle) because the fibers run lengthwise. However, even in the abs, EMG studies show regional muscle activation. What we don't know is whether it does any good to try to isolate parts of the muscle.

The bigger and stronger your muscles become, the more difficult it is to train them further. The EMG studies show that only higher intensities will make them grow more. The stronger and bigger you get, the harder you have to train to make gains.

Many exercises can work muscles equally well if you push hard enough. For example, you can develop the biceps equally well doing standing and preacher curls- if you push to max on each of the lifts. However, preacher curls isolate the biceps better because you can't use body sway to help you get the reps.

EMG has many problems, but it is good for telling us whether an exercise uses a muscle. In other words, we can tell whether a muscle is turned on or off. Based on EMG studies and measurements, we present 25 proven exercises that isolate and build the most important muscle groups in your body.

Now onto the lifts ...

ABS

The most important ab muscles are the rectus abdominis (six-pack muscle) and the internal and external obliques (love handle muscles). Other abdominal muscles important for spine stabilization include the transversalis and quadratus lumborum.

No single exercise works all the ab muscles optimally. The best exercises for the front abs (rectus) are the bicycle crunch exercise, hanging leg raises, and crunches on an exercise ball.

The best oblique (and quadratus) exercise was the side-bridge.

Bicycle Crunch Exercise

The technique: Lie flat on the floor on your lower back with your hands beside your head. Bring knees toward your chest to about a 45-degree angle and make a bicycle pedaling motion with your legs, touching your left elbow to your right knee, then your right elbow to your left knee.

Hanging Leg Raises

The technique: While hanging from a chin-up bar, or supporting your weight on your arms on a dip bar, bring your knees up to your chest.

Crunches on Exercise Ball

EMG shows that this exercise works the abs best on an exercise ball.

The technique: Lie on your back on the ball until your thighs and torso are parallel with the floor. Cross your arms over your chest and contract your abdominals, raising your torso to no more than 45 degrees. Increase the stress on your oblique muscles by moving your feet closer together.

OBLIQUES

Side-Bridges This is not a well-known exercise. However, EMG studies show that it strengthens the obliques and helps stabilize the spine.

The technique: Lie on your side and support your body between your forearm and knee. As you increase fitness, move the support from your knees to your feet. Repeat on the other side. Hold position for 2 X 10 seconds. Build up to at least 60 seconds on each side of your body.

CHEST

EMG studies confirmed the obvious, but also showed a few surprises. First, the bench press proved to be an excellent chest exercise. However, the incline press did not work the upper part of the chest as much as commonly believed. Inclines were very effective for working the chest and front part of the deltoid (shoulder) muscle.

The best exercises for chest development are the bench press, incline press, and dumbbell flyes. Specialized chest exercises, fly machine exercises are excellent, if you train intensely enough.

Bench Press

The technique: Lying on an incline or bench on your back with your feet on the floor grasp the bar with palms upward and hands shoulder-width apart. Lower the bar to your chest. Then return it to the starting position. Using a wider grip will slightly increase the load on the pecs. Dumbell bench press is also an excellent chest exercise.


Incline Dumbbell Bench Press

The technique: Lying on an incline bench on your back with your feet on the floor, grasp the dumbbells with palms upward and hands shoulder-width apart. Lower the dumbell to your chest. Then return it to the starting position. A steeper bench incline increases the load on the shoulders and decreases the load on the chest.

Dumbbell Flyes

The technique: Lying on a flat or incline bench on your back with your feet on the floor, grasp the dumbbells with palms facing each other and arms extended above your chest. Lower the dumbbells in a wide arc to the side until the dumbbells reach the chest and shoulder level and you feel a stretch in your pecs. Keep the dumbbells in line with your elbows and shoulders. Pull the dumbbells toward each other in a wide arc back to the starting position.

SHOULDERS

The shoulder is a complex joint that can move in many planes. The deltoid is the principal and most visible muscle. EMG studies suggest that shoulder presses and dumbbell raises are the best exercises for shoulder muscles.

Shoulder Press (Military Press)

This exercise can be done standing or seated. Standing presses load the muscles in the legs, hips, and trunk to stabilize the body. Seated presses better isolate the shoulder muscles. You can use barbells or dumbbells. As discussed, incline presses also work the front part of the shoulders.

The technique: Seated or standing, grasp the weight with your palms facing away from you. Push the weight overhead until your arms are extended. Then return to the starting position.

Shoulder Dumbbell Raises

The shape of the deltoid (shoulder) muscle makes it important that you work the front, side and back of the muscle.

The technique: Stand with feet shoulder-width apart and a dumbbell in each hand. With elbows slightly bent, slowly lift both weights until they are parallel with the ground. Do these exercises to the front, side, and back. Bend at the waist when you are working the rear deltoids.

BACK AND LATS

No EMG studies directly examined the best lat and back exercises. However, there have been studies on how joint positions activate lat and upper back muscles.

Based on these studies, the best exercises for the lats and upper back are pull-ups, wide grip lat pulldowns, and bent-over rowing.

Wide Grip Lat Pulldowns

This exercise works mainly the lats and biceps. However, it also activates the deltoids, traps, and shoulder rotator cuff muscles.

Some experts warn athletes not to pull the weight behind the neck because it may cause shoulder injury (impingement).

The technique: Begin in a seated or kneeling position, depending on the type of lat machine. Grasp the bar of the machine with arms fully extended. Slowly pull the weight down until it reaches your chest. Return slowly to the starting position.

Bent-Over Rows

This exercise builds the biceps as well as the muscles in the upper back (such as the rhomboids, lats, and traps).

The technique: Hold a barbell in front of you, bend at the waist, and bend your knees slightly. Lift the bar to your chest (without jerking), then return the bar under control to the starting position.

Pull-Ups

This exercise is one of the best predictors of the strength of major muscle groups. This is a great exercise for working the lats and biceps. Many muscles in the arms, shoulders, neck, and back help stabilize and move the body during this exercise.

The technique: Hang from a bar with palms facing away and hands placed shoulder width apart. Pull yourself up until your chin goes over the bar; then, return to the starting position. Have a spotter help you with this exercise or use a pull-up assist machine if you can't do any reps. Use weight suspended from your weight belt to increase the intensity of this exercise. You can also do lat pulls to help you develop better strength to do pull-ups.

ARMS - BICEPS

Curls are the best biceps exercises. Curls work biceps best when you stabilize the upper arm and use a supine (palms up) grip.

EMG shows that preacher curls (particularly using one-arm preacher curls) and seated alternate incline dumbbell curls are the best biceps exercises. No studies determined the best triceps exercise. However, many studies showed that triceps are loaded significantly during presses, such as bench presses, inclines, and military presses.

You work the triceps most during presses when you use a narrow grip. Based on the concept that muscles are developed best when isolated and loaded, we selected skull crushers and triceps pushdowns as a good exercises to work this muscle.

One-Arm Preacher Curls

The technique: Place your upper arm on the pad of the preacher stand. Lower your forearm slowly to near full extension. Curl the dumbbell to the starting position. Two-arm preacher curls are also highly effective.

Seated Alternate Incline Dumbbell Curls

The technique: Sit on incline bench with arms extended, holding a dumbbell in each arm. Curl dumbbell, then lower it slowly to starting position.

ARMS - TRICEPS

Triceps Pushdowns aka Pressdowns

The technique: Grasp the bar using a narrow grip, palms down, and elbows close to the body. Push the bar downward, keeping your elbows close to the body. Return to the starting position slowly.

Skull Crushers

The technique: Lie on your back on a bench and place an E-Z Bar above your head and lower the bar to your forehead with your elbows up. Keeping your upper arm fixed, extend your elbows

QUADS AND GLUTES

EMG studies show that knee extensions stress the quads more than squats and leg presses.However, as discussed, there was no difference when muscles were stressed to their max during each exercise. These data show many exercises are effective, as long as you turn on the target muscles and work them intensely.

Keep in mind that these results are most applicable to those who are interested in enlarging or defining the quads. Power athletes should do exercises- such as squats, deadlifts, cleans, and snatches- that stress the thighs and glutes as a unit. The purposes of the sports are different, so it is not surprising that the most beneficial exercises will not necessarily be the same.

Knee Extensions aka Leg Extensions

This exercise is the best for isolating the quads. Doing lockouts (last 20 percent of the range of motion) is very effective for developing the vastus medialis muscle, the quad muscle on the inside of the knee. This exercise may cause kneecap pain, so increase the volume and intensity very gradually.

The technique: Using a knee extension machine, sit on the seat with your shins under the knee extension pads. Extend your knees until they are straight. Return to the starting position.

Squats

The squat is an important exercise because it works the thighs and glutes and trunk stabilizing muscles.

The technique: Stand with feet shoulder-width apart and toes pointed slightly outward. Rest the bar on the back of your shoulders, holding it there with hands facing forward. Keeping your head up and lower back straight, squat down until your thighs are almost parallel with the floor. Drive upward toward the starting position, keeping your back fixed throughout the exercise.

Lunges

The lunge is a great exercise because it works the quads, hamstrings, and glutes.

The technique: Stand with the bar on your back, with your feet parallel to each other. Take a large step forward with your right leg, keeping your torso erect. Go into a lunge position by bending the right and left knees, and keeping the left leg stationary. Return to the starting position and repeat the movement with the other leg.

HAMSTRINGS

Hamstring development is critical for lower body muscle balance. Also, for normal knee function and stability. Many standard lower body exercises aimed at the quads and glutes- such as lunges, squats, and leg presses- also work the hamstrings.

However, you must isolate and load this muscle group if you really want to build and define it.

Hamstring Curls

EMG data demonstrate that this exercise is very effective for isolating the hamstrings and is the most important exercise for working these muscles.

The technique: Lie on your front side on the hamstring machine with hips and torso pressed firmly to the bench. Place the back of your feet on the roller pad. Flex (bend) your knees so that your heels get close to your butt. Return the weight slowly to the starting position.

Straight-Leg Deadlifts

This exercise works the glutes and spinal muscles, besides the hamstrings. Be very careful not to use too much weight during this exercise and do each rep strictly. This exercise can cause a back injury if not done correctly.

The technique: Grasp the bar shoulder-width apart, using either a deadlift (right palm one way, left palm the other) or pronated (palms toward body) grip. Start with weight at thigh level. Bend at the waist, keeping the knees slightly bent. Lower the bar until the weight plates touch the floor. Lift the weight back to the starting position, keeping the spine locked.

Deadlifts

This is one of the best overall weightlifting exercises for bodybuilders and power athletes. It loads the quads, hamstrings, glutes, and spinal muscles. It also loads the shoulder and upper back muscles. There are two deadlift styles- traditional and sumo.

While most powerlifters use the sumo style, bodybuilders/fitness enthuisiasts should use the traditional style because it works the quads and glutes better.

The technique: Stand with feet flat on the floor, shoulder-width apart and toes pointed slightly outward. Squat down and grasp the bar using either a deadlift (right palm one way, left palm the other) or pronated (palms toward body) grip. Keep back flat, chest up and out, arms straight, and eyes focused ahead. Lift the bar by extending the knees and hips. During the lift, maintain a flat back and straight arms, and keep the weight close to the body. Pull up the weight to a standing position.

CALVES

The calves are composed of the gastrocnemius, soleus, and plantaris muscles. The calf assists movements in the knee and ankle. The gastroc is mainly a fast muscle, while the soleus is a slow muscle.

Surprisingly, there are no EMG studies that have looked at the best calf exercise. However, studies on the ankle show that the best exercise works the ankle joint through a large range of motion and stresses the knee and ankle simultaneously.

Based on these criteria, the best calf exercise would be standing calf raises on a calf machine.


Standing Calf Raises (Toe Raises)

The technique: This exercise requires a standing calf machine. Stand with your head between the pads and the balls of your feet on the base of the calf machine with your heels hanging over the edge. Lower your heels until you feel a stretch in your calves and Achilles tendons. Rise up on your toes as high as you can. The calves are difficult to overload, so try to use as much weight as you can for 10 reps.