How Long Should a Workout be to Build Muscle?

Jeff Baldelli
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How is muscle built?

To learn how muscle is built, first you have to understand how muscle grows.

Muscle is formed by muscle cells known as myofibers. These myofibers are incredibly tiny and consist of proteins, mainly myosin and actin, that are arranged in a coil known as a sarcomere.

Muscle growth happens when two things happen. First, skeletal muscle fibers grow in size. This is caused by the fusion of skeletal myoblasts, or muscle progenitor cells. In fact, your muscle fibers grow by 250x their original size! This may seem like a lot, but keep in mind that this process is extremely slow and happens gradually over a period of months.

The second thing that causes muscle growth is the increase in the number of muscle fibers. This is where training comes in.

While the fusion of muscle cells happens to some degree regardless of training, intense training triggers the production of more myoblasts. This leads to muscle growth by increasing the number of muscle cells in the area.

As the fibers grow, they get filled with muscle glycogen and fat, which also causes the muscle to grow slightly in size.

The end result of all this is that you gain muscle.

Time under tension

Scientifically speaking, “time under tension” is the period of time that your muscle is under stress while working out.

This period of time is on a sliding scale from three seconds for really heavy weights all the way up to 90 minutes for high-rep training. Anything in between is considered “interval training” because it’s a mix of both strength and endurance.

The period of time that you decide to work out for will largely depend on what you’re after as a goal. Someone who’s trying to lift as much as they can as quickly as possible will lift heavier weights on fewer reps and complete shorter workouts. The opposite end of the spectrum would be someone who is trying to avoid injury while building endurance to run longer distances. This person will do longer but lighter workouts.

Both types of workouts are equally effective. The main thing to keep in mind is that if you push yourself to the limit for a long period of time, it’ll take longer for your body to recover.

Length of Workouts

What we’re really talking about here is training volume, or how many sets and reps you do of each workout. The more work you do, the more muscle you’ll build.


Since we’ve talked about the dreaded interval training, there’s no better time to bring up tempo runs.

Tempo runs are a form of interval training. Whereas most interval training is based on high effort and short rest, tempo runs are a little more moderate.

The reason you may want to consider this form of training is that it allows for a much higher level of cardiovascular efficiency. This is important because every component of your body needs oxygen to function.

Whether you’re pounding the pavement or pushing against the barbell, each part of your body requires oxygen to do the work. The efficiency of your cardiovascular system is vital not only for running faster and being stronger but also for your overall health.

A good pace to aim for is one that allows you to maintain a conversation, although it may take some time to get used to feeling a little light headed while you are running. Once you have the hang of it, you’ll be training at your target heart rate, which is important for the body to convert stored fat into energy.

Running at the right pace is good for you in many ways, but of course the results will vary depending on how you train.

Anatomy of a Hypertrophy workout

Training for muscle building is the opposite of training for fat loss. Instead of focusing on keeping your heart rate within a range, you want to perform all-out, intense sets that expend all of your energy.

This is because you need to exhaust your muscles in order to force them to grow, which will happen only when you perform very intense sets. These sets are referred to as “dynamic contractions” in exercise terminology.

Hypertrophy training consists of three categories:

Neural By lifting weights of less than 80% of your maximum exertion, you will increase your neuromuscular efficiency, which is basically getting more of the motor units firing when you exert force. These types of sets are sometimes referred to as light or warm-up sets.

Muscular Contractions during neural sets serve to “teach” your muscles to recruit more motor units the next time you do an intense set. Thus, neural sets don’t pump you up to the same degree as a strong muscular contraction, which takes place when you lift a heavier weight.

Strength sets These make up the bulk of your hypertrophy training. Each set consists of ten to twenty repetitions performed at 80 to 100% of your maximum exertion.

Can you build muscle with a 45 minute workout?

Yes, you can build muscle with a 45 minute workout. Longer workouts are better for burning fat, but you can still build muscle with shorter workouts. You may not build as much muscle, but it’s certainly possible.

The reason longer workouts are better for muscle gain is that in order to build muscle, you need to break your muscles down consistently over time so that they have a reason to rebuild and get stronger.

The more you break down your muscles, the more room you create for recovery, repair, and adaptation. More importantly, you cause tiny micro-lesions in your body that need to be repaired so that you can grow bigger and stronger.

As a strength training coach, I recommend higher volume, lower frequency workouts for promoting rapid muscle gain. It’s not quite the same as bodybuilding, but if you’re training for aesthetics and strength, this is a great method to follow.

What Do You Do for a 45 Minute Workout to Build Muscle?

If you’re laying out a 45 minute workout with the goal of laying down muscle, consider a two-part workout.

Perform an aerobic exercise for 20-30 minutes and then follow it up with a weight training routine consisting of barbell lifting and dumbbell exercises.

Let’s be realistic

If you are trying to build muscle, your mindset should be that this is something that is going to take several months of hard work.

Nobody has ever said that they want to lose weight and will be willing to do it in a matter of weeks, so the mentality should be the same for building muscle. Be realistic about how it will take time to see your training efforts pay off.

Training for Hours upon Hours Will Build Muscle

Despite what fitness experts may teach you, research actually shows that you don’t have to spend hours every day in the gym to actually build muscle. In fact, most of us already have a hard enough time finding the time for 1-3 workouts per week on average.

If you can get away with spending less time in the gym, then you should feel free to do so. After all, it’s likely to be more effective to get home earlier with the end result being that you have enough energy to your family or loved ones.

How Long Should a Training Session Be?

There isn’t a definitive answer for this for everyone. Most people find that 45 minutes to an hour tends to be a sweet spot for most body parts. Training for 1.5 hours may be a bit too much to maintain optimal performance.

So, How long should a workout be to build muscle?

A workout that lasts between 30 and 40 minutes will be an excellent workout for building muscle.

Your workout should stay in this time frame because your body can only sustain muscle growth for that period of time. That is enough time to work one muscle group in addition to some light stretching to aid with recovery.

Your body will thank you for keeping your routine mercifully short and sweet. Once you get past 30 minutes you start to get to the point where your body would rather begin releasing cortisol. Cortisol is a type of stress hormone that prevents the anti-inflammatory agents from doing their job.

If you would like to have maximum muscle growth, it is important that your muscles are repaired and rebuilt. This can only happen if the muscles are not damaged from too much weight or stress during your workout.

Many people set the clock to work out for a set number of minutes at the gym, so then they are encouraged to work out for as long as possible to ensure the most fat burning or muscle building. But that is counterproductive and can have negative effects if your body is unable to put the proper strain on the muscle, which is detrimental for growth.

So, set the number of sets and complete them in the time allotted. If you feel a negative reaction to the workout, such as extreme soreness, then you may have to slow down the pace the next day.