Muscular Endurance

Muscular endurance refers to the ability of a muscle or muscle groups to contract or exert force for many successive exertions or repetitions.^[1][2] It can also be thought of as a muscle’s ability to resist fatigue. While there are different theories on what exactly produces fatigue in a muscle,^[3][4] muscular endurance at least partially relies on the muscle’s ability to remove waste products^[5] and prevent a buildup of acidity in the muscle.^[6] Other models of fatigue that involve biomechanics, muscle recruitment, cellular mechanisms, and the brain have also been proposed.^[3][4]

Muscular endurance is commonly measured by assessing the number of repetitions that can be performed with a given weight or the length of time that a force can be sustained against a given load.Common tests of muscular endurance include how many repetitions a person could do of a squat or bench press at 50% of their one-repetition maximum weight, or how long a person could hold a plank or wall sit.^[6][7]

The type of training that best develops muscular endurance depends on the type of exercise. Generally, exercises can be classed as dynamic or static. Dynamic exercises can be divided into isotonic movements and isokinetic movements. Isotonic movements are where the joints and muscles move through their range of motion under a constant resistance, while isokinetic exercise requires a machine to keep the body moving at a constant speed regardless of the resistance applied. Static exercise is frequently described as isometric, meaning that the body holds the same position against a fixed resistance to perform exercises such as planks or wall sits.^[8][6] For dynamic exercises, muscular endurance is best developed by high repetitions at submaximal resistance: for example, high reps of a squat at 50% of a 1-repetition maximum (1RM) load. For static exercises, time-based training is the best way to develop endurance: for example, long-duration wall sits.

Dynamic exercise is commonly recommended due to its similarity to everyday activities, and isotonic dynamic exercise, such as weightlifting, is the most practical option for the average person. The American College of Sports Medicine recommends isotonic resistance training at a low-to-moderate intensity, or at less than 50% of a 1RM weight, for two sets of 15–25 repetitions performed 2–3 times per week to improve muscular endurance.^[9]

Caffeine can increase muscular endurance through its effects on the central nervous system as a stimulant.^[7][10]. Effects may be more consistent when consumed 60 minutes prior to exercise.^[11] Though individual variation is high for caffeine side effects and tolerance, doses of 3–6 mg/kg of body mass are typically recommended for improving muscular endurance.^[7]

Creatine monohydrate increases muscular endurance by increasing stores of creatine phosphate, which rapidly produces energy in the form of adenosine triphosphate (ATP) when it is burned. Faster ATP replenishment means an athlete is able to accomplish more repetitions or exert more effort.^[12][13] As a normal diet contains 1–2 g per day of creatine, it typically takes 5 g per day for 5–7 days to saturate muscle creatine stores. A maintenance dose is typically 3–5 g per day.^[12]

Additionally, beta-alanine can benefit muscular endurance during bouts of exercise lasting 1–10 minutes. Four weeks of 4–6 grams per day of beta-alanine can increase muscle carnosine concentrations, thereby helping to balance acidity in the cell, and may also attenuate neuromuscular fatigue. It should be known before consuming that beta-alanine may produce a strong tingling sensation on the skin that is harmless.^[14][15]

Other supplements with some promise but less overall consistency for improving muscle endurance include nitrates, sodium bicarbonate, and citrulline.^[16][17][18]

A higher carbohydrate diet (with ~60% of energy intake from carbohydrates, or around 5–8 grams of carbohydrate per kilogram of body mass per day) can help to increase overall endurance and attenuate fatigue from higher-volume training.^[19][16] When volume is high, carbohydrate mouth rinses may benefit muscular endurance as well.^[20]

Protein-wise, an intake of 1.4–2.0 g/kg of bodyweight per day is useful for building and maintaining muscle mass. Higher protein intakes (2.3–3.1 g/kg of fat-free mass per day) may help to retain muscle mass in those pursuing fat loss. In addition, recovery will likely be improved by spreading protein intake throughout the day (every 3–4 hours or so).^[16]

Sleep is an important factor for muscular endurance, especially considering the prevalence of sleep deprivation due to athletes’ traveling schedules, time zone changes, and insomnia before competition. A recent meta-analysis concluded that acute sleep loss (less than 6 hours of sleep) reduces strength endurance (i.e., ≥2 resistance reps or >5s sustained contraction) by 10%.^[21]

There is a general decline of muscular endurance with age, though this can be mediated by appropriate training regimens.^[22] There are also generally differences in muscular endurance by sex.^[23]