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I'm going to gym and i want to improve muscular endurance . My trainer (actually he's not a professional trainer, and i'm not trusting him) told me you have to do high reps with low weights .

For example, i'm doing Bench Press 3 set 15 reps . Because of 15 reps, i working with low weights. For example, i can do 10 reps with 35 KGS , but i can't do 15 reps with 35 KGS . So, i'm working with 20 KGS (yes, there are big difference) so i can do 15 reps.

I'm not sure 15 reps is good, or too much. I read a few articles about increasing endurance, all of them saying "8-10 reps", or i misunderstood them. What do you think about my training system ? I'm working with this, for a few weeks. But i want to see my muscles' improvement, i mean my biceps are still small (for example) . I want grow them.

In shortly, I'm doing 15 reps with low weights (but i'm always trying to increase weight). I want to increase muscular endurance and gain more muscle. Should i decrease reps number and increase weight?

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  • P.S. I'm taking L-Carnitine before cardio, and then doing about 45 minutes cardio. After cardio, i'm starting weight training. After all workouts, taking protein powder. Protein powder and L-carnitine working very good . I lose a lots of belly fat and gain muscle.
    – Eray
    Nov 21, 2012 at 1:32
  • Worth noting in addition to these answers, to promote growth in muscle volume, you should emphasize the eccentric phase of every movement. This is the phase when the muscles are lengthening, and you should really emphasize form and control (taking it slow & steady). I am not recommending "Eccentric Training" but many athletes find this focus beneficial for muscle size.
    – jros
    Feb 4, 2022 at 12:58

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Your trainer is correct. When training for muscular endurance you want to be in the 12-20 rep range, so 15 is a perfectly reasonable rep count. In contrast, 1-3 reps trains for strength, 3-5 trains better for power, and 6-10 trains better for mass. See below image for a reference chart on where you should focus your reps / weight depending on your desired result (endurance, strength, power, mass, etc.).

Knowing your ORM (one-rep max) is important because it allows you to set appropriate goals for different rep ranges. Since we don't know your ORM, we can only guess based off your doing 10 reps of 35kg comfortably; using the chart below, the 10 rep range should be approximately 70% ORM, so that puts you at a 35/0.7 = 50kg ORM. Using 50kg ORM, we can determine that an appropriate weight for endurance at your current level would be approximately 40-60% ORM, which in your case will be 20-30kg.

rep range chart

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    Also, while I didn't explicitly say so in my answer, you should consider increasing weights and dropping reps if you want to see notable increases in muscle mass; but that depends on what you prioritize more (mass vs endurance).
    – Moses
    Nov 21, 2012 at 16:32
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    @Eray 1) Strength is the amount of force you can apply, power is the ability to use strength quickly (quick, deliberate, applied strength). 2) Muscular Endurance (M.E.) is trained by building Type 1 muscle fibers (slow-twitch). Slow-twitch muscles have dense capillarity and high lactate generation, thus those best reflect M.E. in the chart. 3) ORM is the maximum weight you can lift once and only once; and it must include both the concentric and eccentric portion of the lift (i.e. the full movement). E.g. 50kg ORM bench means you can lower the barbell to chest and push it up once, but no more.
    – Moses
    Nov 21, 2012 at 20:36
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    @Eray Not necessarily. The sweet spot here depends entirely on your exercise; but for most weighted lifts 15 is a good round number, as it gives you a decent balance between muscle mass and endurance.
    – Moses
    Nov 21, 2012 at 20:49
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    @Eray not a problem. Just remember, even though the effects appear to scale up after 20, make sure to note the rep counts (Silliness, Madness, Death) were chosen for a reason. Going over 20 on most lifts is just plain silly, excepting the few exercises like body weight push ups / squats which often require a much higher rep count than weighted exercises.
    – Moses
    Nov 21, 2012 at 21:03
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    @Alexus - Yes it does.
    – JohnP ♦
    Feb 4, 2022 at 15:22
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Your trainer, and common wisdom, is incorrect. It is commonly thought that muscular endurance is achieved after a certain rep range. This is not true based on how substrate level respiration. Here's how it works

when you perform a repetition of an exercise, regardless of the weight, your muscles use the most available energy source, i.e. ATP. as you perform more reps, the supply of ATP runs out. this takes ~15-60 seconds, depending on the muscle type, speed of activity, and your general conditioning. But in general, any muscle that contains a high proportion of type 2 muscles will rely mostly on ATP and partial glucose metabolism.

High rep ranges (e.g. 12-20) are fine for hypertrophy, in fact, more and more research is emerging that supports high volume training for hypertrophy, as hypertrophy is a product of tension, not just a super heavy lift.

Muscular endurance is a product of training the muscles for prolonged periods of time such that they require oxygen to complete respiration. This occurs mainly in type 1 muscle, which is rich in mitochondria, where glucose is metabolized into co2 via oxygen. The complete metabolism of glucose into co2 and h2o takes a while, like a minute. So when you're running, your muscles are using ATP, but they're also using glucose, becuase it is far more plentiful and provides way more ATP and nadh for contraction. This is because running or cardio don't generate the same force during contraction.

Conversely, muscle contraction during a bench press requires the generation of force, which needs ATP. Unless you're doing a 45 seconds or more of a bench press, you're not promoting endurance. You shouldn't do more than 20 reps while lifting if bigger muscles is the goal as you need to apply a specific amount of tension.

Also, we need to define 'endurance'. I fancy myself a runner, so endurance to me is more of a cardiovascular thing. But I see what you're getting at. In that case, if you want more muscular endurance, you should be doing less pure lifting, and more conditioning and body weight exercises. You'll promote hypertrophy, but also endurance, or fatigue resistance.

Finally, here's another reason why the 15-20 reps isn't gonna prevent gains - certain muscles simply cannot handle heavy weight and low reps. Like the biceps and deltoids. These muscles are designed to move a bone or joint a certain way, and very little force is required to do that. In fact, the ideal rep range for promoting hypertrophy (and reducing injury risk) of the biceps and deltoids is 12-18.

I have a MS in nutritional immunology and am an active CPT.

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  • This goes contrary to many published studies on muscular endurance in lifting. Also, your times are a bit off on the ATP depletion and mechanisms for replenishing.
    – JohnP ♦
    Feb 4, 2022 at 15:37

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