I’ve been working out for about 4 months now (HIIT on a spin bike and a bit of weightlifting ~20 mins.) three times a week. I’m seeing good improvement in health and physique despite having no idea what I’m doing.
My motivator was calories, but now when I work out I burn way less calories because my body is getting used to the stress, I think. What’s happening? Is my workout less useful than before? Can I not eat as much or is my body burning more fuel now?
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The Fitbit makes an assumption of calories burned by factoring heart rate over time. It doesn’t actually know, it just runs an equation that gets you into the ballpark.
Honestly, don’t worry about how many calories you burn, but do keep an eye on how many you consume. If you’ve already hit your goal weight, then maintain it through diet. Exercise for the fitness and muscle development aspects. If you notice (over the course of a few weeks) that your losing weight, up your calories a bit. If you’re gaining, drop them a bit.
Fitness trackers are a great tool, but you shouldn’t live or die by them. Once you get accustomed to how your body is working, you won’t need to rely on a watch to tell you how you’re doing.
You are plateauing. This happens, *always* with physical activity.
When you start, it is a new activity. Your muscles and brain need to adapt and grow to accommodate this new activity, but after a few months, they do, that have adapted. You got to think of your body as innately lazy. It will do the least work possible to get the largest results to accommodate a new stress. Once the stress is accommodated for, the body say fuck it, we got here, now we can cruise.
You got to keep your body adapting to something new.
20 minutes? Nope, you need to move to 40 minutes now OR up the resistance/weight more. Replace old exercises with comparable exercises. Bench press with bar before, now bench press with 2 dumbbells. Squats now become walking lunges. Sit-ups become leg lifts and so on. Make your body adapt to a new level of time, resistance, effort, etc.
Come up with a food plan. Diet is like 75% of weight control. Simple diet adjustments can mean you losing pounds a month or not. You should calorie count a few days. Read the label, measure shit out to your normal portions and see what you eat normally. See what the calories are for those portions and then see what you can cut back on or substitute for a lower call option. If you can cut 350 cals a day out of your diet, you will be dropping a pound of fat ***every 10 days***. I just switched from eating normal pasta to that zero pasta stuff. Not really zero calories, but its 90% less. I love pastas, ramen, spaghetti, you name it. Just by swapping that, I have dropped around 15 lbs from this summer *changing nothing else*.
You burn 4.5-5 less calories per pound lost, so if you’ve lost 20 lbs, you’re burning 90-100 less calories per day. Those numbers are what you’ll find if you aceess any TDEE calculator on the web and get a TDEE estimate for someone at different weights, all other variables like height and age held constant. I actually tested this myself in a 80 lb weight loss 3 years ago and it was right in the nose at 4.5 cals per pound lost.
**Calories**: When you workout you don’t actually burn calories. The number of calories burned that your workout app or site tells you is an approximation using a mathematical formula. What you produce during a workout is watts and watts over time is energy measured in kilojoules. Those kilojoules can be approximated into calories.
**Movement efficiency**: When you start working out more frequently over time your body becomes more efficient at whatever movement you are performing. It could be running or cycling or pretty much any movement. As efficiency increases your body expends fewer calories in order to perform the same work.
**So the fitter you become and the more efficient your body becomes the more kilojoules you need use up during a workout to burn the same amount of calories.**
There are a lot of variables in calorie output for the body.
A basic explanation is that your body is becoming more efficient at the same activity and uses less energy to perform the same task (the “it doesn’t get easier, you’re just getting better” attitude).
Weight lifting as a prime example, your maximum squat is now probably larger than before, the movement is more familiar/dynamic and supporting muscles are engaged. So doing the same weight as you started will feel like a dodle, even though the same amount of “work” (in a physics sense) is done, you (the machine) are better at doing it.
Also for cardio a strong heart and reduced overall mass is easier to move, and an improved adipose/muscle mass ratio will effect caloric output as your moving less dead weight
Okay think of it this way, a calorie is just a unit of energy. The amount of energy it takes to cycle for 30 mins (assuming you keep the resistance the same) doesn’t change person to person (besides some variables like body weight) regardless of fitness
If you’re doing the same exercise you’ll burn the same amount of calories*. If your fitness tracker is reporting fewer calories burnt, that may be just be an error. Most methods of estimating calories are inaccurate to some degree, and some activities are harder to get good estimates for than others. If your fitness tracker uses heart rate to calculate calories, that’s a likely source of error. If you’re in better aerobic condition then your lungs, heart and vascular system are now better at delivering the oxygen you need to your muscles, which means your heart doesn’t have to beat as fast as before, but that doesn’t mean the exercise magically requires less energy now. The basic physics don’t change.
*There is a caveat to this statement, which is that some types of exercise involve moving your own body weight around, and so these require less energy if you lose weight. For instance, a 200-lbs person walking 10 miles will burn more calories than someone walking beside them who weighs 150 lbs. However, calories burnt on a stationary bike do not depend on weight since you’re pushing against a fixed external resistance (unless you’re doing spin class-type exercises where you get up out of the saddle and engage in a lot of vertical motion, but that’s not something the bike can track). Weightlifting *can* depend on your weight, e.g. when doing squats, but your weightlifting likely only accounts for a small portion of your calorie burn anyway, and also 20 lbs of weight loss isn’t that much relative to the combined weight of your body and the weights you’re using so it shouldn’t cause a big difference.
Also, there may be slight improvements in your body’s efficiency at doing certain things, which mean that you waste less energy doing the same exercise, but again that should be minor and definitely not something a fitness tracker can account for.
Calories are not a good measure of anything. Why? Because whatever calorie level you are at, your body will adjust to it. The body in general adapts to what you do often. Just aim for better health in general (quality of food, variety of exercises, etc). Switch it up every week and month. Have cheat days and etc just to stop your body from adapting too much. It’s all about getting your body’s regulator on it’s toes. Some people just go extra hard all the time, others just play around with it and « distract it ».
As some others already replied, your fitbit just makes and estimate based on some measured parameters, mainly heart rate, movement registered through its accelerometers and your body measurements, that you had to input into the device initially. You mention you lost ~20 pounds of weight. Have you updated this in the fitbit? Unless you have smart scale connected to the app, it doesn’t know that. As you get fitter, you probably have generally lower heart rate during the day and your workouts. So your device goes OK, this person has lower heart rate, means lower activity = less calories burned. Probably most reliable way to track is to measure all you eat and compare to your weight (maintaining, loosing, gaining) and calculating from there. But even that is just an estimate, you would use some metabolic rate equation that is based on average over many people.
Two things could be going on. If weight loss is your goal, you need to eat less calories than you burn, that’s it. There are no tricks that will make weight loss easier (outside of finding what works for you and makes it easier to stick to the formula of calories in – calories out < 0). If getting stronger is your goal then you need to constantly be increasing your workload to get further adaptation.
1: the human body is incredible at adapting to changes and starting a workout regimen will cause you to lose weight as long as you don’t wind up eating more than you burn, but over time (a few months to about a year depending on the person) your body will figure out how to burn less calories throughout the day. Simple example, person a burns about 1500 calories a day just existing and 500 doing whatever they do day to day. They eat let’s say an average of 2100 calories per day. That surplus intake cause weight gain. They start a workout regimen that adds about 500 calories per day and maybe eat an extra 100-200 calories. At the start they are now burning 2500 per day and eating only 2200-2300. That cause weight loss. As this continues the body figures out how to make existing easier and maybe day to day outside of the workout gets easier so you eventually go back to burning about 2000 calories per day (1100 existing + 400 day to day + 500 working out). So you either need to increase workout intensity or cut back on calories. At some point increasing workout load hits a limit and all you can do is cut back on calories.
2: when working out, the goal is to push your muscles to the point where they just start to break down a bit, a good workout will leave your muscles full of small tears that the body will then repair and put back together stronger than before they were broken. When you start out there is less muscle to break and it takes less work to break it. As you get stronger you need to break more muscle fibers, and they take more load and/or reps to break them. Without increasing the weight and/or number of reps/sets you do when lifting (with a HIIT workout you have to increase intensity, interval duration, or number of intervals) then you will eventually reach a point where you aren’t making your muscles do enough work to break, thus there is nothing for your body to make stronger while repairing it.
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