What happens in the body during a weighted workout?

Updated: Aug 23, 2021


If you’ve been training for a while, you know that physical activity leads to visual and functional changes in the body.


But what exactly happens in the body during a workout that leads to those changes and how can you take control over your body’s looks and performance? In this video, we’re going to talk about the processes that happen in the body during an intense workout.


Without further ado, let’s start by first talking about muscle unit activation.


Muscle Unit Activation


Each and every movement our body can do, is possible thanks to the multiple “muscle units” of each muscle group, also known as “muscle fibers”.


Our bodies have two types of muscle fibers - Slow twitch & fast twitch fibers.


Slow twitch fibers are engaged during low-intensity activities that are long in duration.


These fibers cannot produce much force but can easily work for prolonged periods of time under low exertion.


On the other hand, we have the fast twitch muscle fibers, which are engaged during high-intensity activities.


These fibers produce the greatest amount of force, but get quickly fatigued under high exertion.


During a weighted workout and more specifically, during the challenging working sets, you activate the fast-twitch muscle fibers of your musculature, in order to endure the heavy loads.


The heavier the load, the more fast-twitch fibers are recruited.


At around 75% of your maximum strength capabilities, all the fast-twitch muscle fibers are activated.


Once you go above 75% of your maximum strength capabilities, the body relies on a higher frequency of the brain to muscle signals.


Generally, for the goal of bulk muscle gains, you should be working with up to ~80% of your maximum strength capabilities, while strength gains are better achieved at 85-100%.


ATP, Creatine and glycogen

Needless to say, the activation and contraction of any type of muscle fiber, requires an energy source.


Adenosine triphosphate, also known as “ATP” is the body’s main source of energy.


During intense workouts however, ATP gets quickly depleted in about 5 seconds.


After the 5 second mark, the body needs to regenerate ATP, in order to sustain muscular activity.


To do so, the body uses its secondary energy reserves, namely creatine.


Creatine grants energy for another 10 seconds of activity, after which, intensity naturally drops.


After your ATP & Creatine stores are depleted, the body starts relying on muscle glycogen to sustain the activity.


Muscle glycogen is essentially the stored form of blood glucose, which in turn is the end product of carbohydrate digestion.


Muscle Protein Breakdown


When your muscles are contracting repeatedly under a heavy load, there is micro damage that occurs in the muscles.


That is namely referred to as “muscle protein breakdown” and is an essential component of the muscle-building process.


So to put it simply, during an intense workout, your muscle fibers get activated, your nervous system works more intensely and you use up your muscles’ energy resources.


The heavy loads then lead to muscle-damage, which, after the workout, sets off a flurry of recovery processes that recover the damage and the energy resources, as well as the nervous system.


So here’s your take home message - Give your body energy from carbohydrates to take you through the heavy workouts and consume plenty of protein every day to sustain your muscle protein synthesis.


THIS is how you grow muscle! Got questions? Ask us in the comments below!