Exercise makes us stronger. This we know. But how exactly does exercise make us stronger? It turns out to be a interesting story and not all of it involving dense cellular biology. I’d like to share with you a few of my favorite fun facts about what goes on in your muscles after you exercise. Keep them in mind the next time you’re in the midst of a tough workout, and you may find they give you a deeper understanding and appreciation of the experience.

Star Wars action figures smallFirst, I want to tell you about “dark muscle” and “white muscle” fibers. People have both types of these fibers in their muscles in varying proportions according to each individual.

“Dark muscle” fibers are dedicated to keeping us moving indefinitely. They’re called “slow twitch” fiber. You use this endurance-oriented-type fiber when you walk and run long distances. Our neck muscles have a lot of slow twitch fibers so that we can easily hold our head erect all day. Our deep calf muscles also have a lot of them so that we can run around from dawn to dusk if we want to. Look at “slow twitch” fibers through a microscope and they will appear dark. That’s because slow twitch fibers are filled with capillaries, giving them a rich blood flow that is a source of continuing energy (Muscle cells also produce their own energy.)

White and dark muscle fibers smallerBy doing lots of aerobic exercise, and you’ll infuse your slow twitch fibers with even more capillaries. Slow twitch fibers burn lots of calories, but no matter how long you work them, these fibers stay pretty much the same size, so they don’t contribute significantly to sculpting you. Finally, as their name implies, slow twitch fibers have a relatively slow reaction time.

Studies have shown that elite marathoners tend to be genetically endowed with a higher-than-average percentage of slow twitch fibers, while Olympic sprinters have more fibers that give them strength and quickness.

tiffany in thigh 2013 edit lighter text crop small1…Which brings us to the other major type of fiber in your muscles, “fast twitch” or “white muscle.” “Fast twitch” fibers are designed for power and speed. They have has less blood flow, which makes them lighter in color. Fast twitch fibers are what most reshapes your muscles. Do strength training, and these fibers get firmer. Keep training and these fibers will undergo “hypertrophy,” that is, they will get larger. Women’s muscles (fortunately) don’t increase size easily, so women can use heavy weights and still not see a lot of hypertrophy. Whatever sex you are, the manner in which you work out will determine the body shape you achieve. If you use heavy weights with few reps for several months, your “fast twitch” muscle fibers will increase in size. If your routine employs light weights with lots of reps, the result will be muscles that are firm and shapely but not significantly larger. The Bar Method’s practice of performing many reps with light weights produces just enough hypertrophy to sculpt muscles but not bulk them up.

One last note on dark and white fibers: Each of our muscles has a different proportion of “slow twitch” and “fast twitch” cells according to what that muscle does. For example, your hamstrings and arm muscles have a high percentage of fast twitch fibers for power and speed. Your glutes have a lot of both types (one reason they’re so large!)

hypertrophy text edited smallerHere’s how both types of fibers get stronger from exercise: First, working out causes “micro-tears” in your muscle fiber. The torn muscle fibers then heal themselves, building new fiber that is stronger than the old. The more intensely you exercise and the heavier the weights you use, the more micro-tears you’ll create, and the larger your healed “fast twitch” fibers will become (see “hypertrophy” above).

You know you’ve had a good workout when you get “delayed-onset soreness” (DOMS) 24 to 48 hours afterwards. This soreness is caused by your fibers’ healing process, not from lactic acid as has previously been believed.

Cindy ChuThere is a second type of strengthening that happens after exercise. It is less well known but has been found to give women most of the results they get from working out. Exercise physiologists called it “synchronous activation.” What this means is, in effect, improved mind/body coordination. Here’s how it works: An untrained muscle is weak in part because the message it gets from the brain and nerves is disorganized. A student literally does not have the neural connection between her brain and her muscle to perform the action she wants to. She may intend to fire a muscle to move a part of her body, but she can’t recruit enough of that muscle to make it behave. Mark A. W. Andrews, an associate professor of physiology, explains it this way: Exercise, especially when it focuses on form and precision, gives you “the ability to recruit more muscle cells – and thus more power strokes – in a simultaneous manner.” Andrews adds, “This neural adaptation generates significant strength gains with minimal hypertrophy and is responsible for much of the strength gains seen in women and adolescents who exercise.”

The Bar Method workout is especially focused on this fitness component. So the next time you’re doing a Bar Method workout and struggling with your form, take satisfaction in knowing that improving your form is increasing your strength and fitness as well.

best back exercise chartFinal fun fact: Most of your largest and most powerful muscles are on your back side. When you’re working out, pay attention to your back! That side of you houses most of the largest muscles in your body. They include the latissimus dorsi, the largest muscle in your torso; the triceps, the largest muscle in your arm; and the gluteus maximus, the largest muscle that moves your legs and the most massive muscle in your entire body.

So don’t assume your back has to be “out of sight out of mind.” During exercise try imaging your back in your mind’s eye and feel what’s happening back there. By doing so you’ll use more muscle and burn more calories, not to mention benefit your posture awareness as well.



One of the most commonly asked questions I get at the Bar Method is how many calories you burn during a workout. No scientific assessments of caloric burn-rate in Bar Method classes have yet been done, but here’s what I can tell you based on burn rates of comparable exercise techniques. A 125-pound woman in good shape burns about 350 calories with the Bar Method DVD workouts (and closer to 400 calories in a beginning/intermediate studio class due to the faster pace). In addition, Bar Method workouts give an approximately 100-calorie additional post-workout burn-off from the build-up of lactic acid.

Advanced classes burn more, as a Bar Method student named Kristen reported a few years ago. “I wore my heart rate monitor for a couple of level two classes, and burned almost 500 calories [per class];” she said. “I burn about 600 on an hour long run.” Another student, a guy who took his first class wearing a heart rate monitor, told me he burned 800 calories. Students in other bar fitness classes who wore calorie counting devices reported burn-offs of between 136 and 701 calories.

Heart Rate MonitorThe variation in these numbers is due to differences in these students’ body size, gender, age, muscle mass, level of fitness, when they last ate, the level of the class, their familiarity with the workout, etc. Another reason for the variation in results is the heart rate monitors themselves. As one researcher wrote, “All caloric expenditure information that you read off of a heart monitor or an exercise machine like a treadmill or indoor bike, are estimates of calories spent and usually not very accurate.”

Nevertheless people are fascinated by the idea that we can make a zero-sum game of calories in/calories out, but in practice, this approach may not live up to all the interest it generates. If we could actually tweak our caloric intake and outtake by measuring it – even if heart rate monitors were 100% accurate — it wouldn’t matter how many extra calories we burned in a particular workout. As long as we burn at least some additional calories, they’d add up, and we’d lose weight sooner or later. The truth is, weight loss doesn’t routinely result from exercise, not because of our inability to measure calories “out,” but because of our inability to control calories “in.” The real culprit is, in a word, food. Our deep attachment to this substance has ways of tricking us into refueling after we work out in spite of our intentions. Consider two of food’s lesser strategies for getting us to eat:

Your Moment Dove commercialFood as pleasure: Many people grow to expect a certain amount of pleasure from food, apart from their need to satisfy their hunger, so that it becomes an entitlement. We ate dessert as children and through sheer habit feel we warrant it indefinitely. TV commercials play to this mindset by showing us beautiful young women eating candy as if it contained the secret of happiness.

StarbucksFood as comfort: The comforting feeling food gives us can serve an emotional sedative. In the new movie “No Strings Attached” Natalie Portman, when upset with her love life, wolfs down three boxes of donut holes. Donut holes are 220 calories each, and let’s say there are six of them per box. That would mean that she’d be consuming almost 4,000 calories, two days worth of fuel, to make herself feel better (great movie by the way – except that it was hard to believe that Natalie Portland’s size zero character ever ate an excess calorie in her life).

If these emotional addictions to food don’t do the trick of seducing us into replacing our calories just burned off, food pulls out its big guns, namely hunger pangs. After an intense workout, hunger will scream at you to replace those calories. Even if you succeed in resisting the Starbucks Venti White Chocolate Mocha (630 calories), you might distractedly go for a second helping at dinner or an extra piece of the birthday cake served at the office, all devoured before you put much thought into doing so.

The good news in this state of affairs is that exercise absolutely will change your body dramatically if you commit to it for the long term. Numerous studies made of people over decades have found that those who lead sedentary lives tend to gain weight from age 30 – 60 while those who exercise stay lean and youthful. Other research found that exercise performed regularly has appetite-suppressing qualities.

I’d like to add that Bar Method workout in particular includes a few additional features that help you lose weight and keep it off.

  • It builds dense muscle mass in our large muscle groups. Dense muscles increase metabolic rate, plus make us feel more energetic and less in need of sweet pick-me-ups throughout the day.
  • It boosts confidence and mental toughness, strengthening our ability to make resolutions and follow through on them.
  • It rewards us for leaning down because the exercises are more doable the lighter you get. Over time, students learn on a visceral level that fewer pounds translate into more ability to get through the workout.
  • It gives us beautiful bodies that become a source of continual positive feedback for staying lean.

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None of these weight-control techniques involve calculating calories but there is plenty of evidence that they work. Thousands of Bar Method students have transformed their bodies, and hundreds have written in to tell us about it.


interval trainingThe Bar Method delivers on intensity. It calls on multiple muscle groups to perform each exercise and prevents these muscles from releasing between reps, workout them all the harder.  And it keeps our legs, the top calorie burning parts of our bodies, working hard for most of the class.

Best of all, the Bar Method takes advantage of interval training’s tough, “go for broke” format to maximize caloric burn. Students generate more lactic acid in its hour-long workout than they would in a week of typical jogging.  These students thus enjoy lengthy post-exercise calorie burn-offs and heightened metabolic rates.

interval trainingWhile harnessing interval training’s power, the Bar has also corrected a flaw in its standard format.  Conventional internal training routines alternate their strength sets with slowed-down versions of the activity at hand — running becomes walking; spinning becomes pedaling.  Yes, students do get to process their built up lactic acid, but their muscles are also losing elasticity.  But with less range of motion, muscle strength is compromised.

stretchingThe Bar Method fixed this problem by alternating its strength sets with stretches.  As “down” intervals go, these stretches are ideal for processing any built-up lactic acid.  At the same time, these stretches perform the added task of pulling apart the still clenching “muscle filaments” (the parts of our muscles that overlap to contract and separate to release).  The result is increased elasticity, which enables muscles to more easily contract and expand, thus becoming functionally stronger.  What’s more, the placement of these stretches to follow immediately on the heels of the strength sets gives them added potency.  This added stretching, need I mention, also allows our muscles to drape themselves more gracefully across their underlying bones, giving Bar Method bodies their signature long, lean look.


Wait a second!  Why would anyone want to produce lactic acid?

Isn’t that the waste product that you need to flush out of your system or it will make you sore?  Here’s where I want to set the records straight.  Lactic acid production in exercise is a good thing, in fact a great thing, for your overall state of health and fitness.

So what, actually, is lactic acid?  For one, it is not a waste product, and it does not make you sore. Soreness is caused by tiny breaks in your muscles. The truth is, lactic acid is a pure, condensed form of fuel – a kind of power bar — that your body isn’t able to process quickly enough to use for the task at hand.  As soon as your body catches a break, so to speak, it goes to work feeding this high-octane fuel to your organs and muscles, which gain from its rich ingredients.

No doubt about it, the health benefits of lactic acid are huge.  First, your body uses extra calories for as long as six hours after you stop exercising, just to process the stuff.  Once absorbed, lactic acid acts to firm up your muscles and increase your aerobic capacity.  In subsequent workout sessions, your body gets better and better at processing this excess fuel, and you gain athletic stamina and a higher metabolic rate.  Also, your heart and lungs are now able to send more oxygen through your veins to get rid of fat (which needs a good supply of oxygen to be burned as fuel).  Last but not least, the more you “feel the burn” during exercise, the more growth hormone (HGH) – an almost magical substance that helps keep us youthful – your body will make.  So: cook up some nice, fresh lactic acid during your workout and you’re on your way to becoming your dream “lean, mean, fat burning machine!”

Let’s take one more look at lactic acid’s many body-slimming benefits: 

1. Your body uses extra calories to absorb lactic acid.

2. Every workout session triggers a lengthy post-exercise calorie burn-off, melting away extra calories for hours after you stopped exercising.

3. Once lactic acid is absorbed into your muscles, they become firmer and stronger, increasing your metabolic rate.

4.  Your body develops “lactic-acid tolerance”, or the ability to work longer before your muscles give out.  This added stamina enables you to work harder during exercise, burning more and more calories along the way.

5. Your body gains aerobic capacity, making it both more efficient at burning fat during exercise (Remember, your body needs oxygen to burn fat).

6. Lactic acid stimulates your endocrine system to produce our bodies’ own natural anti-aging serum, human growth hormone, staving off the withering effects of aging and keeping your metabolic rate high.

Interval training helps us produce this totally natural weight loss product. With interval training, you can work above your “lactic acid threshold,” the point at which your muscles become so fatigued they give out, for brief intervals!  After each “full-out-effort” set, you work at a slower pace to give the lactic acid a chance to work its way though your system.  Then onto another intense, “feel-the-burn until-you-drop” interval.  Your body virtually explodes with energy in the heat of these intense, go-for-broke moments.  Your muscles draw energy from every source available, namely the fat and carb stores under your skin and in your belly, and also from within your muscles themselves.

This incredibly intense way of working out generates a huge quantity of lactic acid.  In contrast, on a run you have no choice but to stay at or slightly below your “lactic acid threshold.”  Pit interval training against long distance running in a lactic acid making contest, and minute for minute, interval training wins hands down. Read more about new findings on interval training here.

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