A former ACE-certified personal trainer, I've trained men & women of all ages for fat loss, muscle building, more strength & more fitness.
One Hour: the Magic Time Limit
So just why should strength training sessions be limited to one hour anyways? What’s so magical about that one-hour limit?
Studies tend to use a one-hour mark to measure hormonal responses to exercise in humans and rodents.
Proponents of the “one hour is the limit” for exercise point out that after one hour, levels of cortisol increase and those of testosterone decrease. This is bad because cortisol promotes abdominal fat storage, while testosterone is a natural fat burner and muscle builder.
Studies that look at hormone levels usually have subjects (human and rodents) engage in endurance-based exercise such as cycling (running wheel for rodents) rather than intense weightlifting.
But some fitness experts have extrapolated from these aerobic exercise studies that lifting weights should not exceed one hour, and that to do so would result in a catabolic (muscle breakdown) effect.
However, bodybuilders – even those who don’t use anabolic steroids – rarely quit workout sessions after 60 minutes. It’s common for ripped, muscular men and women to be working out for 90 minutes, even two hours.
But, unlike a steady-state aerobic activity such as cycling, jogging, Zumba or brisk walking, the nature of strength training includes plenty of breaks in between various exercise sets.
The one-hour rule is derived from research that has used 60 minutes as a time to measure hormone levels, and a repeat of the measuring at the two-hour mark, as well as points in between those time periods.
This is why, when the subject of how long is too long to strength train comes up, the reference point is 60 minutes rather than 50 or 70.
The One Hour Rule for Lifting Weights Fails to Consider Variables
Variable #1: Rest Time in Between Sets
People who believe that strength training for longer than an hour will sabotage muscle gains fail to consider training volume.
For instance, a person may get in more training volume in 45 minutes than does the next person whose workout spans 90 minutes – because that first individual takes very short breaks, and the second one takes long breaks.
So before you deem 90 minutes or even two hours as too long to be training with weights, you need to consider just how much time is spent actually training.
There could be several trips to the toilet, several breaks engaging in texting or chit-chat with another gym member, time spent eating an apple or time spent checking online news.
The question then becomes: If a workout takes two hours due to frequent and long breaks, does this count as a catabolic workout?
Cortisol Has a Catabolic Effect
You don’t want high levels of cortisol if you want muscle growth. The obvious solution, then, is to eat a quick-acting carbohydrate with protein about an hour into a longer strength training workout. Then continue with your session.
This will help ensure a protection against catabolism or muscle breakdown. Of course, lifting weights is supposed to “break down” your muscles anyways. But they are then built back up with proper rest, hydration and nutrition. Increased cortisol levels are not a desirable outcome, and they DO increase after one hour of exercise, according to studies – and according to variables.
Variable #2: Training Intensity
If we apply a cookie-cutter template approach to the one-hour rule, this would mean that a person who spends two hours training with light resistance, putting in minimal effort, will experience a rise in cortisol and its catabolic effect, sabotaging attempts to burn fat and/or gain muscle.
But if you’re exercising well-beyond 60 minutes but with only mild effort, your cortisol levels will not rise. They will increase only with moderate or intense effort. But only intense effort, not moderate (or light) will boost testosterone and HGH – which will oppose the cortisol.
A person who trains lackadaisically for two hours, even with short breaks, doesn’t have to worry about high levels of cortisol preventing strength or muscle gains or preventing fat loss.
What will prevent muscle or strength gains and fat loss is a lackadaisical approach to weight training. If you want to torch off body fat and gain lean muscle mass, and acquire a sturdy strong physique, you must train at a high intensity.
This can be summed up as a weight load that makes eight to 12 repetitions very difficult – too difficult to complete a 13th repetition.
Not every single set must be an 8-12 rep max, however. A 20-rep max with a compound movement such as the deadlift, back squat, deep leg press or dumbbell squat to overhead press can be brutally intense. The key is choosing a load that makes you feel pummeled and panting at the end of 20 reps.
What if you’re not getting results?
The culprit has nothing to do with working out for longer than an hour. It has to do with at least one of the following:
- Not lifting heavy or intensely enough
- Excessive rigorous aerobics, which can have a catabolic effect (e.g., training for a 10K run while also trying to build muscle)
- Inadequate nutrition, especially in the 24 hours post-workout
- Not enough sleep
- Overtraining (e.g., chest workouts four times a week)
- Inconsistency (skipping workouts or going periods without training)
- Poor technique
- Wrong exercises (e.g., believing that tons of crunches will shrink the stomach)
All in all, you should not feel driven to end your strength training workouts at the 60th minute. You should not fret when you discover you’ve been training for 75 minutes.
You should not skip routines just because doing them would make your workout session go well-beyond one hour. The focus should be on intensity, proper form and technique, hydration, nutrition, adequate rest and sleep, and choosing the right exercises.
For a scientific analysis of hormonal responses to exercise, you can check out this research paper: