Anatomy of a Class: What REALLY Happens to Your Body

Workouts leave us feeling more energized, boost our moods and help with our mental focus. While these are all the tangible physical characteristics that we recognize – you would be so amazed by what’s going on inside your body. 

From start to hours after you cool down, here’s what’s happening in that powerful, awesome bod of yours:












As you start to gear up for high intensity exercise, your heart starts pumping faster, muscles start contracting and you start reaching for cellular energy stored in your body to fuel you.

Hormones are also released to start those chain-reactions, specifically adrenaline. Adrenaline, or epinephrine, increases your metabolism quickly to allow for sudden increase in activity levels (which evolutionary would come in handy if you’re trying to out run something that is trying to eat you!) But for us, running happily and safely, the adrenaline just helps us get “up to speed” more quickly and to focus on the task at hand.












As you ramp up in intensity, your heart rate increases, too; working harder to pump oxygenated blood to your muscles. In an effort to supply as much blood as possible to your working muscles, blood flow to other non-essential systems will be reduced.  Think of it like this: when you start repping some curls, your arteries start pumping more blood to your biceps (to lift the weight) and your core (to keep you stable) – and lays off pumping blood to your digestive system, which has been bumped to the back of the priority line.

Your heart is also a critical team player here, maybe even the critical team player. During exercise the heart is responsible for pumping the blood, and it adapts to exercise over time. So, its ability to pump blood develops, allowing for increased levels of oxygen to enter the muscles you’re working. 












As you work out longer, your body needs to fuel your effort, so your body begins to release what is called “ATP” or adenosine triphosphate (better known as the energy your body creates from eating food). We have limited ability to store ATP, and so we continue to make it while working out. There are two pathways that allow for this, one using oxygen (aerobic metabolism) and one without (anaerobic metabolism). The anaerobic energy pathway is the creation of ATP from carbohydrates, resulting in a byproduct of lactic acid – something us athletes commonly recognize by the burning sensation it causes in our legs. Aerobic metabolism is what kicks in on those marathon training runs (or any long-duration activity), allowing to use our stores slower, and thus last longer.

It is possible, however, to run out ATP  – you know, like the feeling you get when you hit a wall? This just means you have fully depleted both your liver and muscle glycogen stores. You can overcome depletion by replenishing energy with a carbohydrate with a sports drink or gel.    












As you start to calm down from the stress of sport, a lot of hormonal changes begin to happen in your body. Your breathing will start to regulate and your heart rate will come down.

While some of us sweat more than others, leaving a class with soaked tank-tops or more, the literal process is one to embrace. The body is smart, and sweat glands are in place to release moisture from the body and prevent overheating.

Your body is also starting to signal its need to refuel. Insulin, the hormone responsible for regulating your blood sugar levels, can help shuttle sugar back into your muscle immediately following a workout. This is a necessary process that must happen before any muscle repair can take place. Take advantage of high insulin levels by consuming a 4:1 carb: protein ratio 15 – 30 minutes after activity.












Tiny tears occur in the muscle during exercise. As these tears are repaired (ideally through good dietary choices!) muscles grow bigger and stronger. If you feel sore the day or 2 after a workout don’t fear, this means muscles are changing and rebuilding.












Exercise is a complicated endeavor.  Though it might seem like it’s as easy as putting one foot in front of the other and then repeating, on the anatomical and molecular level, it takes a lot of steps (literal and figurative) to get your body from point A to point B. The good news is that the more you work out, the easier it becomes, both for your body and for your mind. Fuel right, push hard, and remember to give your body and little R& R after a long day and a hard workout, so that you can repair, rebuild and get back out there!

Spurred by her love of running and devotion to clean, healthy eating, Kim McDevitt is a Registered Dietitian, specializing in the female athlete, and is the National Educator for a plant-based nutrition company, Vega. Get personalized nutrition support from Kim at

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