UNC Healthy Heels

by Emily Wheeler

Did you know that you can build muscle strength just by trying repeatedly to lift weights that are actually too heavy for you to move? And what is the point of holding the dreaded “plank” exercise for a minute at a time? The answer lies in the difference between isotonic and isometric exercise, and you’ll want to include both in your strength training routine to receive maximum health benefits!

Many people are aware that the Center for Disease Control and Prevention (CDC) recommends that all healthy adults engage in some type of physical activity each week. These recommendations are not just important for maintaining a healthy weight and metabolism, but also for maintaining cardiovascular, muscle, and bone health that are so important for healthy aging, disease prevention, and a long life. Even if you never lose a single pound, exercising regularly in accordance with the CDC guidelines can improve overall health tremendously.

But it’s not just as simple as going for a brisk walk or a jog a few times a week; the CDC recommendation for adults is at least 150 minutes of moderate-intensity aerobic exercise each week (or 75 minutes of vigorous-intensity aerobic activity each week) AND doing muscle strengthening activities on at least two days each week.¹ These two categories can overlap if you’re doing a Pilates class that uses weights and raises your heart rate, or if you participate in the Absolution or Lower Body Conditioning group fitness classes at the SRC on campus, for example. But the point is that it’s important to include muscle strengthening exercises into your routine. These exercises help you to maintain muscle tone, which helps to prevent a decrease in metabolism over time, and also increase bone strength and reduces calcium loss and risk of osteoporosis as you age, especially in women.

Now that we know that muscle strengthening exercises are important and recommended by the CDC for all healthy adults, we can talk about the two categories of muscle strengthening exercises: isotonic and isometric exercise.

Isotonic exercise is probably the type completed most often, which is when a muscle faces a resistance that it is strong enough to overcome, so when the person uses their strength to resist the weight, the muscle contracts and shortens and there is motion in the attached joint as it does so. Isotonic exercises build muscular strength and endurance, but they aren’t too hard on the cardiovascular system, so depending on the weight, your heart rate may or may not increase. Simply lifting a bag of groceries is an example of isotonic exercise.

Isometric exercise, on the other hand, is when a muscle faces a resistance that it is not strong enough to overcome, so even when the person uses all of their strength to resist the weight, the muscle contracts but doesn’t shorten, and therefore the attached joint doesn’t move either.² Think of the feeling when you do squats with the barbell loaded close to your maximum weight, then you do a few and eventually you reach a point when you squat down, but it seems like no matter how hard you push your feet into the floor and engage your legs, you just can’t stand back up and that’s when your spotter steps in. The squats before that one were isotonic exercises, but the last squat was an isometric exercise. If you were familiar with the feeling in that example, you’ll recognize that while isotonic exercises don’t always raise the heart rate, isometric exercises definitely do raise the heart rate, and are therefore more taxing for the cardiovascular system and cannot be done for as long or as often as isotonic exercises.

Here is a 1 minute video that demonstrates the difference between isotonic and isometric muscle contraction if you’re a visual learner:

Here are some examples of isotonic exercises that you can incorporate into your workout routine:

• Push-ups
• Pull-ups
• Crunches or sit ups
• Triceps and biceps curls with dumbbells
• Squats (be sure to maintain proper form and keep the knees behind the toes)
• Russian twists
• Supermans (where you lay on your stomach and lift your hands, chest, feet, and legs off of the ground; try three sets of 10 or 15 repetitions)
• Reverse crunches (lay on your back with legs together and pointed straight up toward the ceiling, feet flexed, and use your abdominal muscles to lift the gluts off of the floor and push the feet straight up toward the ceiling)
• Burpees
• Bench presses

And here are some examples of isometric exercises that you can incorporate into your workout. Notice that many isotonic exercises engage the abdominal muscles, which is great because they are the ones supporting your spine and trunk all day, every day! This just becomes especially noticeable when you’re holding the position and can actually feel the abs working compared to when you’re just walking around or sitting. If you want to know which muscles an isometric exercise is working, just hold the position for long enough and I promise you’ll start to feel the burn.

• The humble plank (Can be a full plank, with arms straight, or a forearm plank. Just make sure to keep arms parallel instead of hands clasped together for maximum benefit to the forearm plank. And keep that butt down and in line with the rest of your body!)
• The dreaded wall-sit (Hold for 1 minute, three times and your thighs will understand the meaning of isometric exercise.)
• Squat holds (Exactly what it sounds like—squat down and hold it there for at least 30 seconds before you stand back up.)
• Side plank (Holding a proper side plank, or side forearm plank, with the top arm extended up and held pointed toward the ceiling is one of the most intense and difficult isometric exercises, in my opinion)
• Abdominal cross holds (Laying on your back, extend one leg out and keep the other knee bent toward the body. Then cross your opposite elbow to that knee, hold for 30 seconds, and switch to the other side. Repeat 5-10 times.)
• Tree pose (Stand on one leg and cross the other leg so that your food rests right above the knee on the standing leg. Bend the standing leg as much as you can so that you are sitting back with your tush, and bring upper body down with the palms pressed together so that elbows reach the knees if you wish. Hold for 30 seconds-1 minute on each leg.)
• Yoga warrior two (Feet are spread wide apart, left foot facing forward and right foot perpendicular to left. Bend the right leg until the thigh is parallel to the floor, extend arms straight out toward each side, and look toward the right middle finger as you hold for 30 seconds. Repeat on other side. Almost like a side lunge.)
• Chair pose (Stand with legs and feet pressing together, and then sit back as if there is a chair behind you. Tuck the tail bone to engage the abs, and extend the arms above the head. Sit as low as you can and hold for 30 seconds)
• Push against a sturdy wall (This one is super simple: stand with feet hip-distance apart, face a sturdy wall, and push against it as hard as you can for 30 seconds. It seems silly, but it’s a good workout! I say “sturdy” wall because it’s important to choose a wall where you’re not going to push a hole in the sheetrock if you’re strong enough.)

People with high blood pressure should be careful about doing isometric exercises because they can raise the blood pressure while you hold the position. If you have high blood pressure, ask your doctor if purposefully doing isometric exercises regularly is safe. Whether or not you have high blood pressure, don’t forget to keep breathing as you hold the position!! (And remember to include both isotonic and isometric exercises into your strength training routine, at least two days a week! 🙂

Sources:

1. Center for Disease Control and Prevention. http://www.cdc.gov/physicalactivity/everyone/guidelines/adults.html
2. Harvard Public Health Glossary of Exercise Terms. http://www.health.harvard.edu/newsletters/Harvard_Health_Letter/2008/September/Glossary-of-exercise-terms