Muscular Endurance for Athletes: Measure & Improve (How To)

 You’ve been all-in on strength training for a long time now, dedicating yourself to building a body that can lift as much weight as it possibly can. You’ve dabbled with rep ranges of anywhere from three to 10 reps for most of your sets whenever you’re lifting weights, and test your one-rep max for several lifts on a monthly basis, just to see how you’re progressing.

When someone asks you “How much weight should you lift?” when you’re doing resistance training, you’re the type of person who answers, “Yes.” To you, the objective has always been to focus solely on boosting strength above all else by maximizing your peak lifting capacity.

Still, there’s one thing that bothers you: Why is it that so many of the best athletes in your gym perform more repetitions with less weight whenever they get around to strength training? From the experienced ultramarathon runner to the elite masters swimming sprinter, they all seem to be interested in cranking out more repetitions to improve muscular endurance.

So now you’re wondering, have you been going about this all wrong? Should you be paying more attention to muscular endurance training, and less to muscle strength? Finally, even if you did want to pay more attention to muscular endurance, how can you raise your endurance level without compromising your precious strength gains?

What is Muscular Endurance?

Muscular endurance is one of those things that you recognize when you see it, but knowing its literal definition can help you to see everywhere that the concept of endurance can be applied.

 In short, muscular endurance is the ability of a muscle or group of muscles to carry out repeated contractions against a force for an extended duration. The more you enhance your muscular endurance, the greater number of repetitions you can perform.

The tradeoff being mentioned here probably sounds very straightforward if you frequent the gym and have a lot of experience with resistance training. For example, person A may be able to complete more bench press repetitions of 300 pounds than person B, but person B may be able to complete more reps at 150 pounds than person A.

In this scenario, person A has greater upper body strength than person B, but person B has superior upper body endurance to person A. However, there is another underrated component to muscular endurance that is very evident in cardio. To the extent that the pressing of your feet against the ground triggers muscle activity, the ability of your lower body muscles to perform repeated contractions is a sign of superior lower body muscular endurance.

Muscle Fibers and the Musculoskeletal System

In order to understand where a muscle’s ability comes from, it’s helpful to understand the musculoskeletal system. In essence, it’s the system comprising muscles, joints, tendons, ligaments, bones, and connective tissues that enables your body to move.

Viewed systematically, and with an emphasis on developing and maintaining movement, musculoskeletal fitness consists of muscle strength, muscle endurance, and muscle flexibility. 

Put another way, your muscles’ ability to exert force in the form of a contraction to the maximum extent, their ability to perform contracts for an extended period, and the ability to maximize joint movement.

While these are the markers of musculoskeletal fitness, the health and structure of your muscles is massively influenced by the sort of exercise program you opt to engage in. You’re about to see that if you want improved muscular endurance, it’s an attribute that you’re going to need to acquire through specific features in your training program.

Fast-Twitch Muscle Fibers

Your body builds the sort of muscle fibers that are geared toward muscular strength by engaging in explosive movements. These movements are short and quick, and usually aren’t sustainable for long periods of time. 

Outside of lifting weights, workouts like high intensity interval training, which can throw exercises like sprints, box jumps, and other quick-burst calisthenic movements into the mix, can also help you make significant gains in strength.

Slow-Twitch Muscle Fibers

Your body develops an entirely different variety of muscle fiber to boost muscular endurance. These slow-twitch muscle fibers confer several health benefits to you, chief of which is the ability to help you sustain physical performance for a long period of time, and also help you develop a support system in line with your aerobic capacity.

To put it another way, your athletic performance in most sports would be significantly handicapped if your muscular endurance was lacking, and your muscles couldn’t keep up with your heart. 

Why Does Muscular Endurance Matter?

The reason why muscular endurance matters is twofold. First of all, there are few practical situations in real life requiring the use of your muscles, including the performance of everyday tasks, where your muscles won’t have to exert force consistently, and for a prolonged period of time.

One example of this is if you’re helping a friend move. In an endeavor that might take several hours, lifting and carrying an object requires isometric contractions that might last minutes at a time and extend over several muscle groups. In this instance, muscle endurance is of foremost importance.

This is opposed to the 20 seconds or less of intense force that are applied when you train for strength using specific exercises to target isolated muscle groups. Although muscular strength will certainly come in handy in many real-life situations, there are several times when it is of minimal importance if you lack the stamina to sustain the effort.

The same principle applies to your athletic performance when it comes to most sports. While a few sports are designed to favor athletes who exert force in short bursts, with long rest periods in between efforts, most sports eventually require you to tap into a combination of your aerobic fitness, and your muscular endurance. 

In most sports, if you lack stamina across multiple muscle groups, your overall performance is going to suffer markedly when compared with that of athletes who have specifically trained to increase muscular endurance through targeted endurance exercise.

Ways to Improve Muscle Endurance During Exercise

If you’re anxious to get into the gym to get to work maximizing your muscular endurance, your heart and mind are both in the right place. There are several ways to use the tools available inside of a commercial gym, or within your own home gym, to boost the stamina of one muscle group, or all of them.

Resistance Training

One of the easiest places to see muscular endurance being improved upon is through resistance training exercises. 

Many people who lift for strength are usually focused on how many repetitions they can complete with a very heavy weight, while often only completing one-max rep lifts. Muscular endurance training is different, and a little less stressful. 

The number of repetitions you should look to complete in order to increase your muscular endurance should be in the realm of 12 to 20 reps. This is going to be true of every muscle group, so the number of reps won’t truly change whether you’re training for lower body or upper body muscular endurance.

It can take a lot of discipline for people who have been entirely strength-focused to dial it back, lower the weight, and focus on improving muscular endurance. However, in addition to making broad improvements to muscle endurance, lifting with lighter weights can also help you to relax and focus on lifting with proper form. Going forward, that can also help you to maintain good form and prevent injury when you go back to lifting heavy weights, 

Isometric Exercise

Isometric exercises are an underrated, yet very important way to improve muscular endurance in a practical sense. In most cases, an isometric exercise tests how long muscles can maintain their position while a constant force or pressure is acting against them. 

This is a challenge that shows up in many everyday tasks; the simple act of lifting and carrying a suitcase or a garbage can is both a common physical activity and an isometric exercise that tests your muscular endurance. With this in mind, it makes sense that a well-structured muscular endurance workout would include endurance training of an isometric variety.

Chances are that you’ve already engaged in exercises like planks, where you brace your body on the floor and prevent your midsection from dipping, and farmer’s carries, where you walk forward while holding heavy objects at shoulder width. These are endurance training methods that require you to sustain exercise against constant force, and usually with rest periods interspersed between attempts. 

In short, since the most common tests of muscular endurance that you encounter day to day arrive in an isometric form, a well-rounded approach to improving muscular endurance should also feature some form of isometric work. That way, your endurance training will more closely mirror the physical tests you’re most likely to face in the real world.

Cardiovascular Exercise

Depending on how you train yourself aerobically, it’s quite possible to build your cardiovascular endurance — literally the vitality and efficiency of your heart — to the point where you could complete a marathon. Even then, you might still lack the lower body muscle endurance required to complete the race, because there are multiple facets to cardiovascular conditioning.

Most cardiovascular exercises can improve your muscular endurance in one way or another. At its essence, cardiovascular training boosts the fortitude of your heart, which is also a muscle. Training to boost your aerobic capacity will train your heart to perform optimally, and teach it to use oxygen more efficiently. This will automatically upgrade the durability of your joints.

Just as important, the repeated motion of your limbs against resistance will increase your local muscular endurance with respect to your muscles’ ability to hold up under the rigors of that particular exercise. 

This means that running regularly will also improve your muscular endurance in your calf muscles, specifically in terms of their ability to propel your body weight forward and endure the impact with the ground’s surface. 

In fact, much of the improvement new runners experience during the first few months of training has more to do with enhancing physical fitness with respect to lower body muscular endurance than it does with going through all of the physiological adaptations that constitute cardiovascular endurance, like tolerating and eliminating lactic acid.

Ways to Improve Endurance Aside From Exercise

While it’s important to engage in guided muscular endurance training in order to make clear endurance gains that are visible from one muscle group to the next, many of the advancements to your overall health are likely to come as a result of what you do outside of structured exercise. 

So while it’s true that muscular endurance refers to the ability of your muscles to apply force for an extended period of time, one of the keys to building endurance is the ability to conduct yourself with discipline even when you’re not working out. With this in mind, here are some things you can do during your downtime that will also gradually increase your muscular endurance.

Eat Protein

Although you are not training with the purpose of maximizing your peak strength, muscular endurance training still involves systematically breaking down your muscle tissue so that it can be rebuilt for better performance. You should plan accordingly, and ingest plenty of protein.

During your extended rest periods away from exercise, protein will help to rebuild your muscle fibers in a stronger configuration, preparing them to be torn down and rebuilt yet again. 

Studies show that consuming protein in relatively high quantities can help to repair muscle more efficiently, even if the training involved was primarily taken for cardiovascular endurance, or was focused on improvement in an area other than strength. (1) (2)

Precise Supplementation

Aside from protein, there are also supplements you can take to assist you as you strive to build your muscular endurance. One of those supplements is creatine, which has been proven in studies to increase the number of reps you can complete, and also delay the production of lactic acid during cardiovascular exercise. (3)

Betaine is a chemical compound made in the body —  but also available in supplement form — that reduces homocysteine, which is an amino acid that correlates negatively with an athlete’s endurance. (4) Supplementing with products containing betaine has been proven to be a strategic way to suppress the production of homocysteine and improve your muscular endurance. (5)

Last but not least is beta-alanine, which fights fatigue through the creation of carnosine, a molecule that reduces the muscle acidity that builds up during exercise. By supplementing with beta-alanine, you enable your body to generate elevated levels of carnosine, which helps to delay muscle fatigue and lengthen your physical performance. (6)

Resting

While it may seem like muscular endurance is built through the diligent physical pursuit of improved performance — which is correct — the scheduling of adequate rest is a requirement to ensure that your body can recover from those efforts properly. 

Studies show that performance in endurance activities deteriorates significantly when trainees don’t receive sufficient rest. Therefore, if the full benefits of your endurance training are going to set in and have tangible results on your conditioning level, you’ll need to provide your body with sufficient time to recover from training. This included getting adequate sleep.

Building an Unbreakable Body

There may be fewer people as fixated on training for muscular endurance through high intensity exercise as there are training for strength and size, and that’s a shame. If you take the time to focus on reinforcing the ability of your muscles to endure stress and resistance for longer periods of time, you’ll find yourself occupying a body that’s more durable, injury resistant, and quite frankly, more useful.

References:

1. Saunders MJ, Luden ND, Herrick JE. Consumption of an oral carbohydrate-protein gel improves cycling endurance and prevents postexercise muscle damage. J Strength Cond Res. 2007 Aug;21(3):678-84. doi: 10.1519/R-20506.1. PMID: 17685703.

2. Berardi JM, Noreen EE, Lemon PW. Recovery from a cycling time trial is enhanced with carbohydrate-protein supplementation vs. isoenergetic carbohydrate supplementation. J Int Soc Sports Nutr. 2008 Dec 24;5:24. doi: 10.1186/1550-2783-5-24. PMID: 19108717; PMCID: PMC2626573.

3. Lee S, Hong G, Park W, Lee J, Kim N, Park H, Park J. The effect of short-term creatine intake on blood lactic acid and muscle fatigue measured by accelerometer-based tremor response to acute resistance exercise. Phys Act Nutr. 2020 Mar 31;24(1):29-36. doi: 10.20463/pan.2020.0006. PMID: 32408412; PMCID: PMC7451837.

4. Herrmann M, Schorr H, Obeid R, Scharhag J, Urhausen A, Kindermann W, Herrmann W. Homocysteine increases during endurance exercise. Clin Chem Lab Med. 2003 Nov;41(11):1518-24. doi: 10.1515/CCLM.2003.233. PMID: 14656035.

5. Dobrijević D, Pastor K, Nastić N, Özogul F, Krulj J, Kokić B, Bartkiene E, Rocha JM, Kojić J. Betaine as a Functional Ingredient: Metabolism, Health-Promoting Attributes, Food Sources, Applications and Analysis Methods. Molecules. 2023 Jun 17;28(12):4824. doi: 10.3390/molecules28124824. PMID: 37375378; PMCID: PMC10302777.

6. Ostfeld I, Hoffman JR. The Effect of β-Alanine Supplementation on Performance, Cognitive Function and Resiliency in Soldiers. Nutrients. 2023 Feb 19;15(4):1039. doi: 10.3390/nu15041039. PMID: 36839397; PMCID: PMC9961614.