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.[reference|url=https://pubmed.ncbi.nlm.nih.gov/3920711|title=Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research.|published=1985|authors=Caspersen CJ, Powell KE, Christenson GM|journal=Public Health Rep|][reference|url=https://pubmed.ncbi.nlm.nih.gov/11665913|title=Musculoskeletal fitness, health outcomes and quality of life.|published=2001|authors=Kell RT, Bell G, Quinney A|journal=Sports Med|] 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,[reference|url=https://pubmed.ncbi.nlm.nih.gov/15388560|title=Logical limitations to the "catastrophe" models of fatigue during exercise in humans.|published=2004-Oct|authors=Noakes TD, St Clair Gibson A|journal=Br J Sports Med|][reference|url=https://pubmed.ncbi.nlm.nih.gov/10843507|title=Physiological models to understand exercise fatigue and the adaptations that predict or enhance athletic performance.|published=2000-Jun|authors=Noakes TD|journal=Scand J Med Sci Sports|] muscular endurance at least partially relies on the muscle’s ability to remove waste products[reference|url=https://pubmed.ncbi.nlm.nih.gov/28067808|title=Effects of Beetroot Juice Supplementation on Cardiorespiratory Endurance in Athletes. A Systematic Review.|published=2017-Jan-06|authors=Domínguez R, Cuenca E, Maté-Muñoz JL, García-Fernández P, Serra-Paya N, Estevan MC, Herreros PV, Garnacho-Castaño MV|journal=Nutrients|] and prevent a buildup of acidity in the muscle.[reference|url=https://pubmed.ncbi.nlm.nih.gov/32096113|title=Effects of Sodium Bicarbonate Supplementation on Muscular Strength and Endurance: A Systematic Review and Meta-analysis.|published=2020-Jul|authors=Grgic J, Rodriguez RF, Garofolini A, Saunders B, Bishop DJ, Schoenfeld BJ, Pedisic Z|journal=Sports Med|] Other models of fatigue that involve biomechanics, muscle recruitment, cellular mechanisms, and the brain have also been proposed.[reference|url=https://pubmed.ncbi.nlm.nih.gov/15388560|title=Logical limitations to the "catastrophe" models of fatigue during exercise in humans.|published=2004-Oct|authors=Noakes TD, St Clair Gibson A|journal=Br J Sports Med|][reference|url=https://pubmed.ncbi.nlm.nih.gov/10843507|title=Physiological models to understand exercise fatigue and the adaptations that predict or enhance athletic performance.|published=2000-Jun|authors=Noakes TD|journal=Scand J Med Sci Sports|]

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.[reference|url=https://pubmed.ncbi.nlm.nih.gov/32096113|title=Effects of Sodium Bicarbonate Supplementation on Muscular Strength and Endurance: A Systematic Review and Meta-analysis.|published=2020-Jul|authors=Grgic J, Rodriguez RF, Garofolini A, Saunders B, Bishop DJ, Schoenfeld BJ, Pedisic Z|journal=Sports Med|][reference|url=https://pubmed.ncbi.nlm.nih.gov/33388079|title=International society of sports nutrition position stand: caffeine and exercise performance|published=2021 Jan 2|authors=Nanci S Guest, Trisha A VanDusseldorp, Michael T Nelson, Jozo Grgic, Brad J Schoenfeld, Nathaniel D M Jenkins, Shawn M Arent, Jose Antonio, Jeffrey R Stout, Eric T Trexler, Abbie E Smith-Ryan, Erica R Goldstein, Douglas S Kalman, Bill I Campbell|journal=J Int Soc Sports Nutr|]

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.[reference|url=https://pubmed.ncbi.nlm.nih.gov/9624661|title=American College of Sports Medicine Position Stand. The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults.|published=1998-Jun|authors=|journal=Med Sci Sports Exerc|][reference|url=https://pubmed.ncbi.nlm.nih.gov/32096113|title=Effects of Sodium Bicarbonate Supplementation on Muscular Strength and Endurance: A Systematic Review and Meta-analysis.|published=2020-Jul|authors=Grgic J, Rodriguez RF, Garofolini A, Saunders B, Bishop DJ, Schoenfeld BJ, Pedisic Z|journal=Sports Med|] 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.[reference|url=https://pubmed.ncbi.nlm.nih.gov/21694556|title=American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise|published=2011 Jul|authors=Garber CE, Blissmer B, Deschenes MR, Franklin BA, Lamonte MJ, Lee IM, Nieman DC, Swain DP, American College of Sports Medicine|journal=Med Sci Sports Exerc|]

Caffeine can increase muscular endurance through its effects on the central nervous system as a stimulant.[reference|url=https://pubmed.ncbi.nlm.nih.gov/33388079|title=International society of sports nutrition position stand: caffeine and exercise performance|published=2021 Jan 2|authors=Nanci S Guest, Trisha A VanDusseldorp, Michael T Nelson, Jozo Grgic, Brad J Schoenfeld, Nathaniel D M Jenkins, Shawn M Arent, Jose Antonio, Jeffrey R Stout, Eric T Trexler, Abbie E Smith-Ryan, Erica R Goldstein, Douglas S Kalman, Bill I Campbell|journal=J Int Soc Sports Nutr|][reference|url=https://pubmed.ncbi.nlm.nih.gov/20019636|title=Effect of caffeine ingestion on muscular strength and endurance: a meta-analysis.|published=2010-Jul|authors=Warren GL, Park ND, Maresca RD, McKibans KI, Millard-Stafford ML|journal=Med Sci Sports Exerc|]. Effects may be more consistent when consumed 60 minutes prior to exercise.[reference|url=https://www.sciencedirect.com/science/article/abs/pii/S0765159716000563|title=Acute Effect of Caffeine Consumption on Isotonic Muscle Strength and Endurance: A Systematic Review and Meta-Analysis|authors=Polito et al|journal=Science and Sports|published=June 2016] 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.[reference|url=https://pubmed.ncbi.nlm.nih.gov/33388079|title=International society of sports nutrition position stand: caffeine and exercise performance|published=2021 Jan 2|authors=Nanci S Guest, Trisha A VanDusseldorp, Michael T Nelson, Jozo Grgic, Brad J Schoenfeld, Nathaniel D M Jenkins, Shawn M Arent, Jose Antonio, Jeffrey R Stout, Eric T Trexler, Abbie E Smith-Ryan, Erica R Goldstein, Douglas S Kalman, Bill I Campbell|journal=J Int Soc Sports Nutr|]

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.[reference|url=https://pubmed.ncbi.nlm.nih.gov/28615996|title=International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine|published=2017 Jun 13|authors=Kreider RB, Kalman DS, Antonio J, Ziegenfuss TN, Wildman R, Collins R, Candow DG, Kleiner SM, Almada AL, Lopez HL|journal=J Int Soc Sports Nutr|][reference|url=https://pubmed.ncbi.nlm.nih.gov/32599716|title=Effects of Creatine Supplementation during Resistance Training Sessions in Physically Active Young Adults.|published=2020-Jun-24|authors=Mills S, Candow DG, Forbes SC, Neary JP, Ormsbee MJ, Antonio J|journal=Nutrients|] 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.[reference|url=https://pubmed.ncbi.nlm.nih.gov/28615996|title=International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine|published=2017 Jun 13|authors=Kreider RB, Kalman DS, Antonio J, Ziegenfuss TN, Wildman R, Collins R, Candow DG, Kleiner SM, Almada AL, Lopez HL|journal=J Int Soc Sports Nutr|]

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.[reference|url=https://pubmed.ncbi.nlm.nih.gov/26175657|title=International society of sports nutrition position stand: Beta-Alanine|published=2015 Jul 15|authors=Trexler ET, Smith-Ryan AE, Stout JR, Hoffman JR, Wilborn CD, Sale C, Kreider RB, Jäger R, Earnest CP, Bannock L, Campbell B, Kalman D, Ziegenfuss TN, Antonio J|journal=J Int Soc Sports Nutr|][reference|url=https://pubmed.ncbi.nlm.nih.gov/27797728|title=β-alanine supplementation to improve exercise capacity and performance: a systematic review and meta-analysis|published=2017 Apr|authors=Saunders B, Elliott-Sale K, Artioli GG, Swinton PA, Dolan E, Roschel H, Sale C, Gualano B|journal=Br J Sports Med|]

Other supplements with some promise but less overall consistency for improving muscle endurance include nitrates, sodium bicarbonate, and citrulline.[reference|url=https://pubmed.ncbi.nlm.nih.gov/30068354|title=ISSN exercise & sports nutrition review update: research & recommendations|published=2018 Aug 1|authors=Kerksick CM, Wilborn CD, Roberts MD, Smith-Ryan A, Kleiner SM, Jäger R, Collins R, Cooke M, Davis JN, Galvan E, Greenwood M, Lowery LM, Wildman R, Antonio J, Kreider RB|journal=J Int Soc Sports Nutr|][reference|url=https://pubmed.ncbi.nlm.nih.gov/14600563|title=Effect of creatine and weight training on muscle creatine and performance in vegetarians|published=2003 Nov|authors=Burke DG, Chilibeck PD, Parise G, Candow DG, Mahoney D, Tarnopolsky M|journal=Med Sci Sports Exerc|][reference|url=https://pubmed.ncbi.nlm.nih.gov/33554654|title=Effect of dietary nitrate ingestion on muscular performance: a systematic review and meta-analysis of randomized controlled trials|published=2021 Feb 8|authors=Thiago Silveira Alvares, Gustavo Vieira de Oliveira, Mônica Volino-Souza, Carlos Adam Conte-Junior, Juan Manuel Murias|journal=Crit Rev Food Sci Nutr|]

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.[reference|url=https://pubmed.ncbi.nlm.nih.gov/27766133|title=The Effect of a Moderately Low and High Carbohydrate Intake on Crossfit Performance.|published=2016|authors=Escobar KA, Morales J, Vandusseldorp TA|journal=Int J Exerc Sci|][reference|url=https://pubmed.ncbi.nlm.nih.gov/30068354|title=ISSN exercise & sports nutrition review update: research & recommendations|published=2018 Aug 1|authors=Kerksick CM, Wilborn CD, Roberts MD, Smith-Ryan A, Kleiner SM, Jäger R, Collins R, Cooke M, Davis JN, Galvan E, Greenwood M, Lowery LM, Wildman R, Antonio J, Kreider RB|journal=J Int Soc Sports Nutr|] When volume is high, carbohydrate mouth rinses may benefit muscular endurance as well.[reference|url=https://pubmed.ncbi.nlm.nih.gov/35373671|title=Effect of carbohydrate mouth rinse on muscle strength and muscular endurance: A systematic review with meta-analysis.|published=2022-Apr-04|authors=Rodrigues Oliveira-Silva IG, Dos Santos MPP, Learsi da Silva Santos Alves SK, Lima-Silva AE, Araujo GG, Ataide-Silva T|journal=Crit Rev Food Sci Nutr|]

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).[reference|url=https://pubmed.ncbi.nlm.nih.gov/30068354|title=ISSN exercise & sports nutrition review update: research & recommendations|published=2018 Aug 1|authors=Kerksick CM, Wilborn CD, Roberts MD, Smith-Ryan A, Kleiner SM, Jäger R, Collins R, Cooke M, Davis JN, Galvan E, Greenwood M, Lowery LM, Wildman R, Antonio J, Kreider RB|journal=J Int Soc Sports Nutr|]

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%.[reference|url=https://pubmed.ncbi.nlm.nih.gov/35708888|title=Effects of Acute Sleep Loss on Physical Performance: A Systematic and Meta-Analytical Review.|published=2022-Nov|authors=Craven J, McCartney D, Desbrow B, Sabapathy S, Bellinger P, Roberts L, Irwin C|journal=Sports Med|]

There is a general decline of muscular endurance with age, though this can be mediated by appropriate training regimens.[reference|url=https://pubmed.ncbi.nlm.nih.gov/9587183|title=Age-related alterations in muscular endurance.|published=1998-Apr|authors=Bemben MG|journal=Sports Med|] There are also generally differences in muscular endurance by sex.[reference|url=https://pubmed.ncbi.nlm.nih.gov/11404668|title=Effect of resistance training on women's strength/power and occupational performances.|published=2001-Jun|authors=Kraemer WJ, Mazzetti SA, Nindl BC, Gotshalk LA, Volek JS, Bush JA, Marx JO, Dohi K, Gómez AL, Miles M, Fleck SJ, Newton RU, Häkkinen K|journal=Med Sci Sports Exerc|]